COVID Vaccine Side Effects (Pfizer, Moderna & Updated Boosters — VAERS at Scale)
This page answers “covid vaccine side effects” with sourced pharmacovigilance data — largest U.S. VAERS dataset with lot-level drill-down and DAEN/EU mirrors. Counts are database reports, not proven vaccine-caused injury rates.
How to read database counts: Pharmacovigilance systems (VAERS, EudraVigilance, Yellow Card, VigiBase, Lareb, DAEN) collect spontaneous, unverified reports. A report is not a confirmed adverse event and does not prove the vaccine caused the outcome. Under-reporting, stimulated reporting, and missing denominators limit rate interpretation. Compare with trials and epidemiological studies on each page before drawing conclusions.
Gold Standard EO (Aug 10, 2026)Federal recommendation status: Based on shared clinical decision-making
The August 10, 2026 Executive Order on Gold Standard Childhood Vaccine Recommendations places COVID-19 in the Based on shared clinical decision-making category — not a universal recommendation for all children. The EO also expresses a preference, to the maximum extent feasible, for administering all childhood immunizations at separate medical visits, and directs the HHS Task Force on Safer Childhood Vaccines to evaluate timing, sequencing, and alternative adjuvants.
Last updated: July 2026 · Status: Current U.S. authorized/licensed products reviewed
ⓘ Methodology Note
This page summarizes published pre-licensure clinical trial data, post-licensure surveillance findings, and peer-reviewed epidemiological studies for COVID-19 vaccines recommended for children and adolescents in the United States. Products include mRNA vaccines (Pfizer-BioNTech Comirnaty® and Moderna Spikevax®) and the protein subunit vaccine (Novavax). The Johnson & Johnson (Janssen) adenoviral vector vaccine is no longer available in the U.S. but is included where safety data are informative. Safety and efficacy data are presented without interpretive language that implies the vaccine is "safe" or "unsafe." The COVID-19 vaccine evidence base is the largest and most intensively studied in global public health, but the relative recency of licensure (2020–2022) means long-term follow-up data are limited.
1. Basic Information
Disease Protected Against
Coronavirus Disease 2019 (COVID-19), caused by SARS-CoV-2, ranges from asymptomatic infection to severe respiratory failure, multiorgan dysfunction, and death. Children generally experience milder acute disease than adults, but severe outcomes — including MIS-C (Multisystem Inflammatory Syndrome in Children), hospitalization, and death — occur. As of 2024, COVID-19 remains a leading cause of pediatric respiratory hospitalization during seasonal waves. Post-acute sequelae ("Long COVID") are reported in children at lower rates than adults but are not negligible (~1–5% prevalence estimates vary by case definition and study design).
CDC Schedule (U.S., 2025)
Population
Recommendation
All persons ≥6 months
Universal recommendation for COVID-19 vaccination; updated formulations matched to circulating variants
Children 6 months–4 years (unvaccinated)
2–3 dose primary series (depending on product and age)
Children 6 months–4 years (previously vaccinated)
1 dose of updated vaccine
Children ≥5 years (unvaccinated)
1 dose of updated mRNA vaccine, or 2-dose Novavax primary series
Children ≥5 years (previously vaccinated)
1 dose of updated vaccine
Immunocompromised
Additional doses per ACIP guidance
Source: CDC ACIP, 2025 schedule. As of the 2024–25 season, updated vaccine formulations target circulating variants (transitioning from the bivalent BA.4/5 formulation to monovalent formulations matched to Omicron sublineages such as JN.1, KP.2, etc.).
Licensed/Authorized Products (U.S., Pediatric)
Comirnaty® (Pfizer-BioNTech, BNT162b2) — mRNA vaccine. Licensed for ages ≥12 (August 2021); EUA for ages 6 months–11 years. Encodes the SARS-CoV-2 spike protein. Lipid nanoparticle (LNP) formulation.
Spikevax® (Moderna, mRNA-1273) — mRNA vaccine. Licensed for ages ≥18; EUA for ages 6 months–17 years. Also spike-protein-encoding mRNA in LNP.
Novavax COVID-19 Vaccine (NVX-CoV2373) — Recombinant spike protein subunit vaccine with Matrix-M adjuvant. Authorized for ages ≥12. Represents a non-mRNA option using more traditional protein-based technology.
Janssen COVID-19 Vaccine (Johnson & Johnson, Ad26.COV2.S) — Adenoviral vector vaccine. No longer available in the U.S. (EUA revoked June 2023). Noted here for completeness because safety signals identified with this product (TTS/VITT — thrombosis with thrombocytopenia syndrome) are important to the overall COVID-19 vaccine safety narrative.
2. Temporal Distribution: When Adverse Events Are Reported
Understanding when adverse events cluster post-vaccination helps distinguish vaccine-related reactions from coincidental illness. Two independent surveillance systems — VAERS (passive reports) and V-SAFE (active surveillance app) — show similar temporal patterns, validating the timing windows.
VAERS vs V-SAFE: Side-by-Side Comparison
VAERS Data (Passive Reporting)
Total Reports: 2,478 (10 key conditions)
Peak Day: Day 4 (203 reports, 15.3%)
Within 7 days: 917 reports (73%)
Within 14 days: 1,145 reports (92%)
Spontaneous reports from healthcare providers and public. Likely underreporting.
✓ Key Finding: Both independent systems show 84-92% of reports cluster within 0-14 days post-vaccination. Similar temporal patterns across different collection methods validates that adverse events peak early and taper rapidly, consistent with direct vaccine-reaction mechanisms rather than coincidental illness.
Temporal Distribution Histogram
Side-by-side comparison: VAERS (red) and V-SAFE (blue) showing percentage of adverse event reports by days post-vaccination. Source: CDC VAERS (2021-2024) and V-SAFE FOIA 12th Final Release (2021-2026).
Clinical Interpretation
Day 0-3 (Acute Phase): Immediate and early reactions (anaphylaxis, myocarditis). V-SAFE peak at day 3 reflects maximal reporting of acute systemic symptoms.
Day 4-7 (Immune Response Window): Peak window for delayed immune-mediated reactions (Guillain-Barré syndrome, Bell's palsy, thrombocytopenia). VAERS peak at day 4 captures this window.
Day 8-14 (Tail-off): Reports decline rapidly. 84-92% threshold indicates most vaccine-related reactions manifest within 2 weeks.
Day 15-30 (Late Phase): Remaining reports likely represent either late manifestations (myocarditis complications, thrombosis) or coincidental illness.
After Day 30: Reports become increasingly rare, suggesting minimal temporal association with vaccination.
Data Quality & Limitations
VAERS: Spontaneous passive system; underreporting is documented. No denominator (total doses) limits rate calculations. Reports span 2021-2024.
V-SAFE: Active CDC-sponsored surveillance from smartphone app. Higher completeness but selection bias (participants must download app). 518,511 responses analyzed; 32.4% have explicit timing data.
Temporal Window Assignment: Based on clustering patterns: early-onset AEs (anaphylaxis, myocarditis) 0-7 days; delayed neurological 7-42 days. Outliers beyond day 30 likely unrelated.
Causality vs. Temporal Association: Clustering does NOT prove causation. Confounding, reporting bias, and coincidental illness all affect interpretation. See individual adverse event pages for causality assessment.
Ingredients (Package Insert)
Structured composition for 3 branded products covered on this page,
taken from FDA-approved package inserts (DailyMed / manufacturer prescribing information).
Lists are per product — formulations differ by manufacturer and presentation.
Click an ingredient name to open its safety-context page when available.
Ingredient lists are sourced from official package inserts for the specific brands named above.
Formulations can change between lots and over time — verify against the current label before any clinical decision.
Presence of a substance does not by itself indicate harm; toxicology is dose-, route-, and context-dependent.
Browse the full ingredient database:
Vaccine Ingredients index.
Causality assessment & potential mechanisms
Conditions below combine WHO-style causality levels with potential biological mechanisms
from the site mechanism catalog
(ae_mechanisms_catalog.json).
HRSA VICP table listing (where shown) indicates a compensable temporal association under U.S. program rules —
not automatic proof of causation for every case. Mechanisms are hypothesis-level pathways with graded evidence.
Pre-existing or newly formed IgE against vaccine antigens or excipients (e.g., gelatin, egg proteins, PEG, polysorbate) triggers mast-cell and basophil degranulation with systemic mediator release.
Innate inflammatory response and possible molecular mimicry between spike protein and cardiac proteins can injure myocardium/pericardium, especially after mRNA COVID-19 vaccines in young males.
Vaccine- or infection-triggered immune responses cross-react with peripheral-nerve gangliosides or myelin components, producing demyelinating or axonal polyneuropathy.
SIRVA
0–2 days
Very likely / Probable
Evidence: High
SIRVA — incorrect injection into shoulder structures (primary · procedural)
Needle placement into the subdeltoid/subacromial bursa or joint rather than deltoid muscle causes prolonged local inflammation and restricted range of motion (procedural, not antigen-specific).
Syncope
0–1 days
Possible
Evidence: Moderate
Vasovagal (needle) syncope (primary · vasovagal)
Pain, anxiety, or orthostatic stress from injection triggers parasympathetic surge with bradycardia and hypotension, producing transient loss of consciousness—common in adolescents.
Framework: WHO causality + HRSA VICP (where applicable) + AE mechanism catalog.
Last updated: 2026-07-18.
Schema: schemas/vaccine_injury_table.schema.json
· Mechanisms: schemas/ae_mechanism.schema.json.
Not medical or legal advice.
2. Pre-Licensure Clinical Trial Data
Licensure trial design (ICAN / OpenVAERS)
The table below reproduces ICAN’s No Placebo Table rows for U.S. childhood-schedule products relevant to this page — including the control/comparator used in FDA licensing trials (not always saline placebo). OSMF presents this for transparency; it is not an endorsement of ICAN interpretations.
Vaccine
Brand
Manufacturer
Doses (schedule)
Ages injected
Control / comparator
Placebo
Safety review window
Covid19
Comirnaty
Pfizer
3
6M 7M 10M
Placebo
Yes
6 months
Source: OpenVAERS — No Placebo Table · ICAN original PDF
· Attribution: Informed Consent Action Network (ICAN) via OpenVAERS
· Last fetched: 2026-07-16.
For many trials listing '6 months' safety review, ICAN notes review was typically ~30 days post-injection with a phone call at 6 months.
COVID-19 vaccines underwent the largest and most rapidly conducted pre-licensure clinical trial programs in history, under Emergency Use Authorization (EUA) frameworks that required demonstration of safety and efficacy but allowed for accelerated review timelines.
100% efficacy (95% CI 75–100) against symptomatic COVID-19; short follow-up period
Pfizer (ages 5–11)
~3,100 (2:1 randomization); immunobridging design
90.7% efficacy (95% CI 67.7–98.3)
Pfizer (ages 6 months–4 years)
~4,500 (3-dose series); immunobridging
Immunobridging to young adults met; limited clinical efficacy data due to low case counts
Moderna (ages 12–17)
~3,700
~93% efficacy (against original strains); immunobridging met
Moderna (ages 6–11)
~4,000; immunobridging
Immunobridging met
Moderna (ages 6 months–5 years)
~6,400 (2-dose series); immunobridging
Immunobridging met; efficacy against symptomatic infection ~37–51% during Omicron
Note: Efficacy estimates were generated during periods of specific variant predominance (e.g., original strain, Alpha, Delta). Effectiveness against Omicron sublineages and more recent variants is lower, particularly against infection, though protection against severe disease is better preserved.
Most Common Adverse Reactions (mRNA Vaccines, Children)
Reaction
Adolescents (12–17)
Children (5–11)
Young Children (6m–4y)
Injection site pain
~80–90%
~70–80%
~30–50%
Fatigue
~50–65%
~35–45%
~25–35%
Headache
~45–60%
~25–35%
~10–15%
Myalgia
~35–50%
~15–25%
~8–12%
Fever
~10–20%
~8–15%
~8–15%
Chills
~25–35%
~8–12%
~3–5%
Sources: Pfizer and Moderna pivotal trial data; FDA VRBPAC briefing documents. Reactogenicity is generally dose-dependent (higher with the second dose of a primary series; data on updated formulations are more limited). Adverse reactions in children are less frequent and less severe than in adults.
Key Limitations of Pre-Licensure Trial Data
Short follow-up duration: The median safety follow-up in the pediatric EUA submissions was ~2–3 months post-dose 2. This was adequate to detect common acute adverse events but inherently limited for evaluating long-term outcomes or rare events with longer latency.
Small sample sizes relative to adult trials: Pediatric trials were substantially smaller than the adult pivotal trials (Pfizer adult: ~44,000; Pfizer 12–15: ~2,260). Rare adverse events — especially myocarditis, which occurs at ~1–10 per 100,000 in adolescent males — were not expected to be detected in pre-licensure pediatric trials.
Evolving variant landscape: Efficacy estimates from the pre-Omicron era are not directly applicable to current circulating variants. Effectiveness is now assessed primarily through post-licensure observational studies.
Immunobridging endpoints: Pediatric licensure was based primarily on immunobridging (demonstrating non-inferior neutralizing antibody titers compared to young adults in whom clinical efficacy was demonstrated), not direct clinical efficacy, with the exception of the 12–15-year Pfizer trial.
3. Post-Licensure Safety Data
Myocarditis / Pericarditis — Confirmed Safety Signal (mRNA Vaccines)
An elevated risk of myocarditis and pericarditis following mRNA COVID-19 vaccination (particularly the second dose) was identified in post-licensure surveillance beginning in mid-2021. This is the most significant confirmed pediatric safety signal for COVID-19 vaccines.
Highest-risk group: Adolescent and young adult males aged 12–29. Risk is highest after the second dose of a primary series.
Rate estimates (VSD and international data): Pfizer: ~2–10 cases per 100,000 doses in males aged 12–17; ~5–15 per 100,000 in males aged 18–29. Moderna: some data suggest a slightly higher rate than Pfizer (possibly ~2–3x higher in young adult males), though data in children are less extensive.
Risk after booster doses: Lower than after the second primary dose, though data are more limited.
Clinical course: The majority of cases are mild and self-limited, with symptom resolution within days to weeks and normal cardiac MRI findings at follow-up. However, a small proportion require ICU admission, and long-term cardiac outcomes are still being studied.
Comparison to COVID-19-associated myocarditis: Myocarditis risk following SARS-CoV-2 infection is substantially higher (~10–40x) than the risk following mRNA vaccination across most age/sex strata. COVID-19 infection itself is a well-established cause of myocarditis.
IOM / NASEM have not yet issued a comprehensive causality assessment for COVID-19 vaccines (as of the 2012 report which predates these products). The CDC and FDA have acknowledged the association and incorporated it into product labeling and clinical guidance.
Other VSD / Active Surveillance Findings (Pediatric)
Anaphylaxis: Estimated at ~2–5 per million doses for mRNA vaccines. Comparable to or slightly higher than rates for other vaccines.
Febrile seizures: A VSD study (Goddard et al., 2023) found a small increased risk of febrile seizures in children aged 2–5 following concomitant administration of mRNA COVID-19 vaccine and IIV (influenza). Rate was ~1 excess seizure per 2,500–4,000 concomitant administrations. The signal was not observed with COVID-19 vaccine alone or IIV alone.
Multisystem Inflammatory Syndrome in Children (MIS-C): No evidence that COVID-19 vaccination causes MIS-C. Multiple studies suggest vaccination reduces MIS-C risk, consistent with MIS-C being a post-infectious complication prevented by vaccination.
No increased risk for GBS, VTE, stroke, or other thromboembolic events identified with mRNA vaccines in children (unlike the Janssen TTS/VITT signal in adults, which is product-specific).
Janssen (J&J) Specific Safety Signals (Not a Pediatric Product; Noted for Context)
Thrombosis with Thrombocytopenia Syndrome (TTS/VITT): ~3–4 cases per million doses in adults (highest in females aged 30–49). Causal mechanism involves anti-PF4 antibodies. The J&J EUA was restricted (May 2022) and revoked (June 2023) in the U.S., in part due to this safety signal and the availability of safer alternatives (mRNA vaccines). TTS/VITT is not associated with mRNA vaccines.
GBS: A small increased risk of GBS (~3–5 per million doses) was observed with Janssen. Not associated with mRNA vaccines after extensive surveillance.
VAERS
VAERS Metric (COVID-19, cumulative U.S. data)
Approximate Figures
Total COVID-19 vaccine doses administered (U.S., through 2024)
>675 million doses
Total VAERS reports received for COVID-19 vaccines
>1.5 million (largest VAERS reporting volume for any vaccine in history, reflecting unprecedented scale and stimulated reporting)
Reports classified as "serious"
~6–8% of total reports
⚠ Critical Caveat
VAERS data represent unverified reports temporally associated with vaccination. A report to VAERS does not mean the vaccine caused the event. The COVID-19 vaccine VAERS database is the largest in history and has been extensively affected by stimulated/heightened reporting due to unprecedented public and media attention. Raw VAERS report counts for COVID-19 vaccines are particularly unsuitable for causal inference, and analyses using VAERS data to claim causality are scientifically invalid.
VAERS Reporting Data — Halma & Varon (2025), DARE-SAFE
The DARE-SAFE paper (Halma & Varon, Pharmacoepidemiology 2025, CC BY 4.0) analyzed VAERS reports for vaccines administered in the United States from 2006–2022. The following data are extracted from Table 1 of that paper for this vaccine (COVID-19 (all mRNA + adenoviral vector products combined). *Dose count from Our World in Data (2021–2022), not the CDC series — different source & time span than other rows (2006–2022 for all other vaccines). See full paper for manufacturer-level breakdowns (Pfizer, Moderna, J&J, Novavax).):
Metric
Value
U.S. doses administered (2006–2022)
663,000,000*
Total VAERS AE reports
781,075
AE reporting rate (per 100,000 doses)
117.7
Total death reports
11,288
Death reporting rate (per 100,000 doses)
1.70
AE-to-Death ratio
69:1
Source: Halma, M.; Varon, J. DARE-SAFE. Pharmacoepidemiology. 2025. DOI: 10.3390/pharma4020007. CC BY 4.0. Data from Table 1.
📚 Important Interpretive Caveats (from the paper itself)
Reporting rate ≠ incidence rate. VAERS is a passive, unverified system. A report means someone submitted a claim of temporal association, not a confirmed causal event. The paper is explicit that causality cannot be inferred from these numbers alone.
Reporting behavior is not uniform. More serious, unusual, or media-salient events are reported at much higher rates than mild ones. Products receiving more public, media, legal, and clinical attention (particularly COVID-19 vaccines, which also benefited from V-safe active-surveillance prompts and CICP compensation pathways) generate more reports per dose regardless of true risk.
Age and comorbidity confounding is not adjusted. COVID-19 vaccines were disproportionately administered to elderly and comorbid populations (nursing homes, 65+, high-risk groups in early 2021) with much higher background all-cause mortality than the general child/working-age population. Some fraction of temporally-associated deaths would occur regardless of vaccination, and the paper does not perform a background-rate comparison.
Stimulated reporting is a known, documented phenomenon. Media coverage, plaintiff attorney solicitation, and advocacy campaigns — all independently inflate VAERS reporting propensity. The paper cites this literature but does not correct for it.
Small-denominator rows are unreliable. Rates computed from small denominators (e.g., monovalent measles, DT, mumps, rubella) have enormous statistical uncertainty and should not be compared to vaccines with hundreds of millions of administered doses without noting the wide confidence intervals.
Source: Halma, M.; Varon, J. DARE-SAFE: Denominator-Adjusted Rate Estimates of Substance Adverse Events Frequency Evaluation in Pharmaceuticals and Vaccines. Pharmacoepidemiology. 2025, 4, 7. DOI: 10.3390/pharma4020007. CC BY 4.0.
Passive Surveillance: AE Type Breakdown (Multi-System)
Side-by-side view of U.S. VAERS, Health Canada Canada Vigilance, Japan JADER (PMDA), EU EudraVigilance, and live-scraped international systems via SurVigilance (VigiAccess, Lareb, DAEN, DMA, Medsafe). SurVigilance panels show MedDRA PT mention totals (not individual-case counts). Category assignment uses keyword matching — approximate, not official SOC coding. VAERS ZIP CAPTCHA downloads use this site’s vaers_pipeline.py; FAERS is bulk quarterly ZIP via SurVigilance (not product search).
VAERS (United States)
Canada Vigilance (Canada)
JADER (PMDA, Japan)
EudraVigilance (EU)
No matching vaccine cases in the current EudraVigilance DAP export.
Denmark DMA interactive ADR search is currently offline (Danish Medicines Agency IT transition; public overviews frozen at 12 Mar 2024). Live product PT tables cannot be retrieved until DKMA restores the search. See DKMA notice. Denmark continues to report into EU EudraVigilance (panel above).
Medsafe (New Zealand)
VAERS (U.S., 2006–2024): 4,923,243 symptom mentions (371.29/100k doses). Largest share: Other / Unclassified (22%), General / Systemic (non-local) (18%), Neurological (12%). Canada Vigilance (CV Online extract): 60,469 reaction mentions in 12,929 unique reports (85.6% serious (11,070 of 12,929 reports)). Largest share: Cardiac / Cardiovascular (14%), Neurological (13%), General / Systemic (non-local) (12%). JADER (PMDA public CSV extract): 125,347 reaction mentions in 31,435 unique reports (10.9% serious (3,431 of 31,435 reports)). Largest share: Other / Unclassified (33%), Neurological (13%), General / Systemic (non-local) (12%). VigiAccess (WHO): 18,107,554 reaction-term mentions · search: COVID-19. Largest share: General / Systemic (non-local) (23%), Neurological (17%), Other / Unclassified (13%). Lareb (Netherlands): 119,155 reaction-term mentions · search: COVID-19 vaccine. Largest share: Other / Unclassified (33%), Musculoskeletal (13%), Neurological (13%). DAEN (Australia): 470,194 reaction-term mentions · search: COVID-19 vaccine. Largest share: Neurological (21%), General / Systemic (non-local) (15%), Cardiac / Cardiovascular (11%). Medsafe (New Zealand): 360 reaction-term mentions · search: COVID-19. Largest share: General / Systemic (non-local) (34%), Injection-site / Local reaction (15%), Gastrointestinal (13%). Cross-database note: All systems are passive and unverified; reporting rates are not directly comparable across countries (different populations, reporting incentives, and lack of dose denominators for Canada/Japan/EU). top VAERS: Other / Unclassified; top Canada Vigilance: Cardiac / Cardiovascular; top JADER: Other / Unclassified. SurVigilance note: VigiAccess, Lareb, DAEN, DMA, and Medsafe counts are live-scraped MedDRA PT mention totals (not deduplicated individual cases). Data via SurVigilance (GPL-3.0; pip install SurVigilance). Category assignment uses keyword matching on reported reaction terms — approximate and exploratory. Neither database establishes causality.
Pharmacovigilance Lot Signal Detection — Hypothesis-Generating Only
Multi-system context below. VAERS (U.S.) supports lot-level volume z-scores and seriousness flags by product and lot (2006–2024). Each lot links to a summary with report count, seriousness %, adverse-event pie chart, U.S. state map, and timeline. A signal flag means a statistical threshold was exceeded — not that a lot is unsafe. Full dashboard →
VAERS flags:VOL high report volume (z ≥ 3) ·
BURST clustered in <90 days ·
SER serious reports >50%.
Lot numbers are voluntary/incomplete in VAERS. Location data is U.S. state only (no postal codes in the public extract).
VAERS (United States) — all lots by product
714,061 reports with usable lot across 6,145 lots · 629 flagged
Loading lot tables…
Other Pharmacovigilance Systems
Lot-level analysis is only possible where reporters supply batch/lot numbers in the public extract. Canada Vigilance, JADER (PMDA, Japan), and most other national systems publish product-level spontaneous reports without lot fields.
Canada Vigilance (Health Canada)
12,929 unique reports · 60,469 reaction mentions · 85.6% serious (11,070 of 12,929 reports). Top categories: Cardiac / Cardiovascular (14%), Neurological (13%), General / Systemic (non-local) (12%).
Canada Vigilance spontaneous reports are unverified temporal associations. The public CV Online data extract does not include lot or batch numbers, so lot-level signal detection is not possible for this system — only product-level reaction patterns are shown here. No Canadian dose denominators are available. Extract 2026-03-31.
31,435 unique reports · 125,347 reaction mentions · 10.9% serious (3,431 of 31,435 reports). Top categories: Other / Unclassified (33%), Neurological (13%), General / Systemic (non-local) (12%).
JADER (Japanese Adverse Drug Event Report database) spontaneous reports are unverified temporal associations; PMDA has not assessed causality per case. The public CSV extract does not include lot or batch numbers, so lot-level signal detection is not possible — only product-level reaction patterns are shown here. Reaction terms in source data use MedDRA/J Preferred Terms. JADER CSV extract pmdacasereport202606 (2026-06). JADER reference (PDF)
Active Pharmacovigilance (Defined-Population Surveillance)
Curated findings for COVID-19 vaccines from active systems (not VAERS). Page inventory last reviewed: 2026-07-10.
ⓘ Active vs. passive — why this pane is separate
The VAERS / multi-system charts above are passive surveillance: spontaneous, unverified reports without a fixed denominator.
Active surveillance starts from a defined, enumerated population (EHR/claims or structured post-vaccination surveys), applies pre-specified statistical tests, and asks whether an outcome occurs
more often than expected in a risk window versus a comparison window or group.
These are not two flavors of the same evidence — active findings are the harder tier that can confirm, refute, or leave under investigation a signal first hinted in passive data.
Do not add VAERS report counts to active incidence rates.
○ No signal detected◐ Signal under investigation◑ Investigated — not confirmed● Signal confirmed (true association)– Not currently under active surveillance
Dense Tier 1 and Tier 2 coverage since 2020–2021. VSD RCA is internal; findings are public via ACIP slides, MMWR, and peer-reviewed papers.
CDC Vaccine Safety Datalink (VSD)
Outcome: Myocarditis / pericarditis
Tier 2● Signal confirmed (true association)
VSD detected elevated myocarditis rates after mRNA COVID-19 vaccination (especially dose 2 in young males). Signal investigated extensively and confirmed as a true association; informed clinical guidance and risk communication. Incidence remains rare relative to doses administered.
Population
VSD sites; elevated risk primarily ages 12–39, higher after dose 2 mRNA in adolescent/young adult males
Risk interval
0–7 days post-vaccination (primary analytic window used in RCA presentations)
Comparison
Concurrent vaccinated comparators / later post-vaccination control windows (study-dependent)
An initial statistical signal for ischemic stroke in a bivalent booster subgroup was investigated further across VSD and complementary data sources. Follow-up analyses did not confirm a consistent elevated risk warranting a causal attribution; monitoring continued as standard practice.
Population
VSD sites; adults 65+ receiving certain bivalent boosters (signal first noted in a specific age/formulation subgroup)
Risk interval
1–21 days post-vaccination (as presented in ACIP materials for the initial signal)
Comparison
Later post-vaccination window (e.g., 22–42 or 43–63 days; analysis-dependent)
Evaluation period
2022–2023
Method
Rapid Cycle Analysis / self-controlled and multi-source follow-up
Related passive AE category on this page: Cardiac / Cardiovascular (see multi-system charts above — not additive with active rates).
AusVaxSafety active survey surveillance of COVID-19 vaccines in Australia has repeatedly reported short-term safety profiles consistent with known reactogenicity; large respondent samples with low rates of medical care-seeking after vaccination in published analyses. Check brand-specific public pages for the latest formulation.
Population
Australian vaccinees participating in AusVaxSafety after COVID-19 vaccination (multi-brand program)
Risk interval
Days 0–3 and follow-up survey windows per protocol
Comparison
Internal signal thresholds / historical expected rates (system methods)
Update cadence: Tier 1: check AusVaxSafety monthly when public pages update. Tier 2/3: quarterly review around ACIP meetings and PubMed/MMWR; set lastReviewed per record.
Source tiers: Tier 1 = public near-real-time dashboards (e.g. AusVaxSafety);
Tier 2 = VSD / Sentinel / PRAC-type findings released via ACIP slides, MMWR, or papers (no public VSD raw dashboard);
Tier 3 = regulator label/safety communications.
Detecting a signal and later classifying it as not confirmed is normal system behavior — not an anomaly to hide or amplify.
4. Documented Adverse Events — Evidence of Association
Rank-aggregated VAERS signal detection (rankv)
No pairs mapping to this product family appear in the rank-aggregated common-signal set from rankv (intersection of GPS, PRR, ROR, and BCPNN signals). That does not mean absence of all VAERS reports — only that no pair met the four-method consensus filter in the published pipeline.
Data: ~30 years of public VAERS (rankv processed tables).
Origin: precisionFDA “Gaining New Insights by Detecting Adverse Event Anomalies” challenge solution.
Caveat: Disproportionality signals are statistical associations in spontaneous reports. They do not establish causality, incidence, or product defect. Many top pairs reflect administration/product-use coding rather than clinical injury.
▶ Adverse Events with Strong Evidence of Causal Association (mRNA Vaccines)
Myocarditis / pericarditis: ~2–10 per 100,000 doses in males aged 12–17 after dose 2. Risk is higher with Moderna vs. Pfizer in some datasets. Clinical course is generally mild, but long-term outcomes are still being studied. Risk from SARS-CoV-2 infection is substantially higher. Strong
Injection site reactions: 80–90% (pain) in adolescents; lower in young children. Strong
Systemic reactogenicity: Fatigue (50–65%), headache (45–60%), myalgia (35–50%), fever (10–20%) in adolescents after dose 2. Strong
Anaphylaxis: ~2–5 per million doses. Strong
Lymphadenopathy (axillary): Tender lymphadenopathy in the ipsilateral axilla, observed in ~5–15% of vaccinees. Self-limited; can cause false-positive findings on mammography and other imaging. Strong
TTS/VITT (Janssen only — not a pediatric product): ~3–4 per million doses in adults. Causal via anti-PF4 antibodies. Not associated with mRNA vaccines. Strong (Janssen-specific)
▶ Adverse Events with Moderate or Preliminary Evidence
Febrile seizures (mRNA + concomitant IIV): ~1 per 2,500–4,000 concomitant administrations in children 2–5. Season-specific signal. Moderate
Long-term cardiac outcomes post-myocarditis: The acute course of mRNA vaccine-associated myocarditis is generally mild, but studies of cardiac function, fibrosis, and exercise tolerance at 1–5 years post-event are ongoing. Limited data preclude firm conclusions about lifelong cardiac risk. Preliminary
Menstrual irregularities: Multiple observational studies have reported transient changes in menstrual cycle length (~1–2 days) following vaccination. Mechanism uncertain. Changes appear temporary. Moderate
▶ Published Evidence Does Not Support a Causal Association (mRNA Vaccines)
Infertility (male or female): No evidence of an association. CDC, ACOG, ASRM, and multiple large studies have found no impact on fertility parameters. No Association
Adverse pregnancy outcomes: Multiple large registry studies (V-safe, VSD, international) have found no increased risk of miscarriage, stillbirth, preterm birth, or congenital anomalies. mRNA vaccination during pregnancy is recommended by ACOG and CDC. No Association
GBS (mRNA vaccines): After extensive VSD and international surveillance, no increased risk of GBS has been identified with mRNA vaccines (unlike Janssen). No Association
Death (all-cause mortality): No evidence of increased all-cause mortality associated with mRNA vaccination. Multiple large international studies. No Association
MIS-C: Vaccination does not cause MIS-C and reduces MIS-C risk by preventing SARS-CoV-2 infection. No Association
5. Disease Prevention Benefits
5a. Pre-Vaccine vs. Post-Vaccine Era (Children & Adolescents, U.S.)
Metric
Pre-Vaccine Era (2020–2021, Pre-Rollout for Children)
Peak monthly hospitalization rates of ~1–5 per 100,000 (varies by wave)
Substantially reduced in vaccinated children; VE against pediatric hospitalization ~40–70% during Omicron (protection wanes over time, updated formulations partially restore it)
MIS-C incidence
~300–500 cases/month during Delta/Omicron waves
>80–90% reduction; MIS-C is now rare, predominantly in unvaccinated children
Pediatric COVID-19 deaths
~1,000–1,500 total pediatric deaths (2020–2023 cumulative)
Ongoing but concentrated in unvaccinated children; vaccination reduces death risk
SARS-CoV-2 seroprevalence (children)
~0% (2020)
>95% by 2023 (combined infection- and vaccine-induced)
Source: CDC COVID Data Tracker; MMWR; Pediatric RSV/COVID-19/Flu hospitalization surveillance. The interpretation of pediatric COVID-19 vaccine effectiveness requires careful attention to variant evolution, waning immunity, and the high background seroprevalence from prior infection — all of which make current VE estimates lower than the >90% efficacy observed in the original trials against ancestral strains.
Current Context
Protection against severe disease: COVID-19 vaccination continues to provide protection against hospitalization and death in children, though effectiveness wanes over 4–6 months and is partially restored by updated formulations. Pediatric ICU studies consistently show that the majority of critically ill children with COVID-19 are unvaccinated.
Protection against infection: Effectiveness against symptomatic SARS-CoV-2 infection with Omicron sublineages is modest (~20–40%) and short-lived (2–4 months for infection, somewhat longer for severe disease). This is a marked contrast to the >90% efficacy against original strains.
Pediatric vaccination coverage: As of 2024, U.S. pediatric COVID-19 vaccination coverage is substantially lower than for other childhood vaccines. Approximately 40–60% of adolescents and 10–20% of children under 5 have completed a primary series. Updated booster coverage is even lower.
Disease Burden Over Time
Reported U.S. disease burden by year. The dashed vertical line marks vaccine introduction. Hover or tap data points for values; use arrow keys when a chart has focus.
ⓘ About these charts: These are accessible SVG line charts with keyboard navigation, hover tooltips, and an underlying data table (expand below). The dashed vertical line marks the year of vaccine introduction. Reported cases undercount true incidence; case definitions, reporting practices, and diagnostic methods have changed over time. See Section 5 for additional context and pre-vs-post era comparisons.
7. Evidence Summary — Overall Assessment
Quality and Quantity of Safety Data
The COVID-19 vaccine safety evidence base is the largest in global public health history. More than 675 million doses have been administered in the U.S., and active surveillance through VSD and passive surveillance through VAERS span nearly 5 years. The evidence base includes:
Large randomized clinical trials (Pfizer adult N=~44,000; Moderna adult N=~30,000; multiple pediatric trials).
Active surveillance (VSD) covering ~9–10 million persons annually with near-real-time rapid cycle analyses specifically designed for COVID-19 vaccines.
Passive surveillance (VAERS) with >1.5 million reports — the largest safety database for any medical product in history.
International surveillance networks (GACVS, EudraVigilance, multiple national registries).
Myocarditis risk (mRNA): The association is well-characterized by age, sex, dose, and product. The clinical course is well-described, though long-term cardiac outcomes are still being studied.
Acute reactogenicity: Rates of common adverse reactions (injection site pain, fatigue, headache, fever) are precisely characterized across age groups.
Absence of TTS/VITT with mRNA vaccines: Extensive surveillance has established that TTS/VITT is specific to the adenoviral vector platform and is not associated with mRNA vaccines.
Absence of GBS with mRNA vaccines: Large VSD and international studies are consistent in finding no association.
Pregnancy safety: Multiple large, independent datasets are consistent in finding no increased risk of adverse pregnancy outcomes.
Absence of infertility association: Multiple studies across several countries are concordant.
Areas Where Data Are Limited or Conflicting
Long-term (>5 years) safety outcomes: COVID-19 vaccines have been in use since December 2020. Follow-up beyond 5 years is not available. This is inherent to the recency of licensure and is not a deficiency specific to these vaccines. Theoretical concerns about long-term effects cannot be definitively addressed until sufficient time has elapsed, though the biological mechanisms of mRNA vaccines (rapid mRNA degradation, transient protein expression) do not suggest plausible long-term adverse effect mechanisms.
Myocarditis long-term cardiac outcomes: Five-year follow-up data on cardiac function post-vaccine-associated myocarditis in adolescents are not yet available. Preliminary 1–2 year data are generally reassuring, but the evidence is still evolving.
Effectiveness against current variants: The rapid evolution of SARS-CoV-2 means that efficacy data from the original pivotal trials are not applicable to current variants. All current effectiveness estimates are observational and subject to confounding (prior infection, waning, variant differences).
Updated vaccine formulations: Each updated formulation (BA.4/5 bivalent, XBB.1.5 monovalent, JN.1/KP.2 monovalent) undergoes more limited pre-licensure testing than the original products, relying on immunobridging and manufacturing process consistency. This is standard for strain-change vaccines (similar to influenza) but limits the pre-licensure safety database for each new formulation.
Very long-term effects in young children: The youngest vaccinated cohort (6 months–4 years) has the shortest post-licensure follow-up. Data on safety outcomes in this age group are necessarily less extensive than for older children and adults.
Overall Summary Table
Domain
Evidence Grade
Key Finding
Prevention of severe COVID-19 (children)
Strong
VE against hospitalization ~40–70% during Omicron; wanes without updated doses
Prevention of MIS-C
Strong
>80–90% reduction; MIS-C now rare
Prevention of symptomatic infection (Omicron)
Moderate
~20–40% short-term; limited durability
Myocarditis (mRNA)
Strong
~2–10 per 100,000 in males 12–17; generally mild clinical course
Anaphylaxis
Strong
~2–5 per million doses
TTS/VITT (mRNA vaccines)
No Association
Specific to adenoviral vector vaccines (Janssen)
GBS (mRNA vaccines)
No Association
Extensive VSD and international data; no signal
Infertility
No Association
Multiple large studies; no evidence
Adverse pregnancy outcomes
No Association
Multiple large studies; no increased risk
Long-term (>5 year) safety
Limited
Insufficient follow-up time; inherent to recency
8. International Surveillance & Global Data
Quick links to public pharmacovigilance databases and trial registries relevant to COVID-19 Vaccine. Reporting counts do not establish causality.
Note: Spontaneous reports are unverified observations. Compare with epidemiological studies in Sections 3–6 before drawing conclusions.
9. Curated Adverse Event Literature
Curated peer-reviewed literature linking specific adverse events to COVID-19 Vaccine. Each entry is a case report, case series, or related safety publication identified via PubMed. Expand Search PubMed for additional literature below to run custom queries.
Disclaimer: Published reports describe observations and associations; they do not establish population incidence or causality.
10. Key References
Polack FP, Thomas SJ, Kitchin N, et al. Safety and efficacy of the BNT162b2 mRNA Covid-19 vaccine. N Engl J Med. 2020;383(27):2603–2615. DOI: 10.1056/NEJMoa2034577 (Pfizer adult pivotal trial, N=43,448)
Baden LR, El Sahly HM, Essink B, et al. Efficacy and safety of the mRNA-1273 SARS-CoV-2 vaccine. N Engl J Med. 2021;384(5):403–416. DOI: 10.1056/NEJMoa2035389 (Moderna adult pivotal trial, N=30,420)
Frenck RW Jr, Klein NP, Kitchin N, et al. Safety, immunogenicity, and efficacy of the BNT162b2 Covid-19 vaccine in adolescents. N Engl J Med. 2021;385(3):239–250. DOI: 10.1056/NEJMoa2107456 (Pfizer 12–15 trial)
Walter EB, Talaat KR, Sabharwal C, et al. Evaluation of the BNT162b2 Covid-19 vaccine in children 5 to 11 years of age. N Engl J Med. 2022;386(1):35–46. DOI: 10.1056/NEJMoa2116298
Oster ME, Shay DK, Su JR, et al. Myocarditis cases reported after mRNA-based COVID-19 vaccination in the US from December 2020 to August 2021. JAMA. 2022;327(4):331–340. DOI: 10.1001/jama.2021.24110
Goddard K, Lewis N, Fireman B, et al. Risk of febrile seizures after co-administration of COVID-19 and influenza vaccines in children. Pediatrics. 2023 (VSD study).
Shimabukuro TT, Nguyen M, Martin D, DeStefano F. Safety monitoring in the Vaccine Adverse Event Reporting System (VAERS). Vaccine. 2015;33(36):4398–4405. (Describes VAERS methodology)
See I, Su JR, Lale A, et al. US case reports of cerebral venous sinus thrombosis with thrombocytopenia after Ad26.COV2.S vaccination. JAMA. 2021;325(24):2448–2456. (TTS/VITT with Janssen) DOI: 10.1001/jama.2021.7517
COVID-19 vaccine injuries are covered under the CICP (Countermeasures Injury Compensation Program), which has different rules than the traditional VICP (Vaccine Injury Compensation Program).
Filing deadline: 1 year from vaccination date (strict)
Coverage: Reasonable medical treatment costs only (no pain/suffering damages)
Appeal: HHS Secretary only (no federal court available)
Attorney fees: Not covered by program
Overall Approval Rate
1.8%
137 of 7,542 claims eligible for compensation
Context: 49% of claims still pending. Rates provisional until final decisions made.
Approval ≠ Causation: Being approved for compensation does not mean the vaccine caused your injury. CICP has lower evidentiary bar than VICP causality table.
Pending backlog: 49% of claims still await decision. Final approval rates will shift as backlog is cleared.
Procedural barriers: 2,632 claims (35% of denials) rejected for missed deadline alone—no extension available.
Settlement mechanism: Some approvals may come from settlement/negotiation, not causality finding.
No federal court appeals: Unlike VICP, CICP claims cannot be appealed to U.S. Court of Federal Claims.
Which Program Covers My Vaccine?
Interactive tool to determine eligibility and filing requirements based on your vaccine and injury timeline.
Each adverse event below is classified using the WHO-Uppsala Monitoring Centre (WHO-UMC) causality framework, combining temporal distributions from VAERS and V-SAFE, V-SAFE elevation status, and biological mechanism evidence. Classification reflects the strength of causal evidence, not report volume alone.
WHO-UMC Causality Categories
Certain
Clear temporal and mechanistic relationship; recurs with re-exposure.
No epidemiologic signal in major safety databases. COVID-19 infection increases MI risk substantially.
V-SAFE Status: Not Significantly Elevated
No signal in safety databases; vaccination does not increase acute thrombotic or atherosclerotic MI risk
Important context: Attributing MI to vaccination in temporal proximity reflects coincidence, not causality.
Acute Transverse Myelitis
Possible23 case reports
Vaccines: mRNA and viral vector vaccines; very rare
Typical onset: 5-21 days post-vaccination
At least 23 published cases of acute transverse myelitis temporally linked to COVID-19 vaccination, versus 60 linked to COVID-19 infection itself, per a 2024 literature review. Proposed mechanism involves cross-reactive anti-spike antibodies against spinal myelin, supported by positive CSF oligoclonal bands in reported cases.
V-SAFE Status: Indeterminate
Very rare; insufficient data for statistical elevation assessment; background incidence ~0.5/100k/year
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (3 studies)
PLAUSIBLEVaccine-triggered polyclonal B-cell activation and antibody cross-reactivity between anti-spike antibodies and spinal cord myelin basic protein -> intramedullary demyelinating lesions
Timeline: 168-504 post-vaccination
CASE-REPORTAcute autoimmune transverse myelitis following COVID-19 vaccination: A case report — PMC8701778 (2021) 70-year-old developed sensorimotor lower-limb dysfunction 7 days after mRNA-1273; MRI showed gadolinium-enhancing intramedullary lesions at T1/2 and T5/6; positive oligoclonal bands supported an autoimmune/polyclonal B-cell mechanism
CASE-REPORTAcute Transverse Myelitis Following COVID-19 Vaccination — DOI: 10.3390/vaccines9091008 (2021) Independent case report of ATM temporally linked to vaccination with imaging-confirmed demyelination
OBSERVATIONALAcute transverse myelitis (ATM) associated with COVID 19 infection and vaccination: A case report and literature review — PMC11230862 (2024) Literature review identifying 23 ATM cases associated with COVID-19 vaccination (versus 60 associated with COVID-19 infection itself)
Important context: Extremely rare condition (background incidence ~0.5/100k/year); the small case count limits statistical causality assessment. Most reported cases had favorable outcomes with corticosteroids/immunosuppression.
Anaphylaxis
Certain987 case reports
Vaccines: All COVID-19 vaccines; most mRNA-associated
Typical onset: Minutes to 30 minutes post-vaccination
Confirmed IgE- and non-IgE-mediated anaphylaxis cases linked to PEG and other lipid nanoparticle excipients in mRNA vaccines. Reaction occurs within minutes; incidence approximately 2-5 per million doses. Most PEG-allergic individuals can still be safely vaccinated under supervision.
V-SAFE Status: Significantly Elevated
Immediate-type reaction (type I hypersensitivity); incidence 1-2/million doses
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (4 studies)
ESTABLISHEDIgE- and/or non-IgE-mediated (basophil/complement) hypersensitivity to polyethylene glycol (PEG) or other LNP excipients -> mast cell/basophil degranulation
Timeline: 0-2 post-vaccination
OBSERVATIONALPotential mechanisms of anaphylaxis to COVID-19 mRNA vaccines — JACI S0091-6749(21)00565-0 (2021) Review proposing PEG hypersensitivity, complement activation, and mast cell-related mechanisms for mRNA vaccine anaphylaxis
CLINICALSafety of COVID-19 vaccination in patients with polyethylene glycol allergy: A case series — PMC8685412 (2021) Case series showing most PEG-allergic patients tolerate mRNA vaccination, indicating variable individual reaction thresholds
IN VITROEvaluation of association of anti-PEG antibodies with anaphylaxis after mRNA COVID-19 vaccination — ScienceDirect S0264410X23005686 (2023) Anti-PEG antibody and basophil activation testing in confirmed anaphylaxis cases; most lacked detectable PEG-specific IgE, suggesting non-IgE pathways contribute
Show 1 more study
CLINICALAssessment of Allergic and Anaphylactic Reactions to mRNA COVID-19 Vaccines With Confirmatory Testing in a US Regional Health System — PMC8449279 (2021) Health-system-wide confirmatory allergy testing of reported reactions, characterizing true anaphylaxis rate versus non-allergic adverse events
Important context: PEG is a common excipient in other medications, so predisposing sensitization is often unrecognized until vaccination. Basophil activation testing, not skin testing, appears most predictive.
Bell's Palsy
Possible142 case reports
Vaccines: mRNA vaccines (BNT162b2, mRNA-1273)
Typical onset: 1-7 days post-vaccination
Disproportionality analyses show a modest but statistically significant reporting signal after dose 1 (SIR ~1.36), comparable in magnitude to the long-recognized signal for influenza vaccination, with the signal for dose 2 not reaching significance in the largest population-based study. Mean onset ~9-14 days post-vaccination.
V-SAFE Status: Indeterminate
Temporal clustering observed but background incidence 15-75/100k/year; confounding by coincidental HSV reactivation
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (4 studies)
PLAUSIBLEVaccine-induced innate immune activation and local inflammation near the facial nerve canal, possibly with HSV/VZV reactivation via transient immune perturbation, causing facial nerve neuritis
Timeline: 24-336 post-vaccination
OBSERVATIONALBell's Palsy and COVID-19 Vaccination: A Systematic Review — PMC9448503 (2022) Systematic review of published Bell's palsy cases and disproportionality signals across mRNA and adenoviral vector vaccines
OBSERVATIONALFacial nerve palsy following the administration of COVID-19 mRNA vaccines: analysis of a self-reporting database — PMC8418051 (2021) Disproportionality analysis found facial palsy reporting odds ratios of 1.84 (BNT162b2) and 1.54 (mRNA-1273), comparable to the previously known signal for influenza vaccination (ROR 2.04)
OBSERVATIONALAssociation between vaccination with the BNT162b2 mRNA COVID-19 vaccine and Bell's palsy: a population-based study — PubMed 34751262 (2021) Population-based cohort of >5 million vaccinees; standardized incidence ratio 1.36 (95% CI 1.14-1.61) after dose 1 and 1.16 (95% CI 0.99-1.36, not significant) after dose 2
Show 1 more study
CLINICALBell's palsy following vaccination with mRNA (BNT162b2) and inactivated (CoronaVac) SARS-CoV-2 vaccines: a case series and nested case-control study — PMC8367195 (2021) Mean time from vaccination to palsy onset was 9.3 days after dose 1 and 14.0 days after dose 2
Important context: Bell's palsy is common in the general population (background incidence 15-75/100k/year) and mostly self-resolves; the modest relative risk increase must be weighed against high background rates and confounding by coincidental HSV/VZV reactivation.
Guillain-Barré Syndrome
Possible70 case reports
Vaccines: ChAdOx1 (AZN); possible rare with mRNA
Typical onset: 7-30 days post-vaccination; median 10 days
Clearest temporal/epidemiologic signal is with ChAdOx1 (adenoviral vector); UK national surveillance found ~5.7 excess cases per million first doses. Molecular mimicry via anti-ganglioside antibodies is the leading hypothesis, though seropositivity is lower than in classic GBS, and a competing adenoviral-vector-reactivity mechanism has also been proposed. No comparable signal established for mRNA vaccines.
V-SAFE Status: Indeterminate
Temporal clustering post-ChAdOx1 but background incidence ~1-2/100k/year makes signal unclear; confounded by concurrent infections
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (4 studies)
PLAUSIBLEMolecular mimicry: anti-spike antibodies cross-react with peripheral nerve gangliosides (GM1, GD1a, GQ1b) via shared sialic-acid-binding epitopes
Timeline: 264-312 post-vaccination
OBSERVATIONALGuillain-Barre syndrome following COVID-19 vaccines: A review of literature — DOI: 10.3389/fimmu.2023.1078197 (2023) Reviews the molecular mimicry hypothesis but notes anti-ganglioside antibody seropositivity in post-vaccination GBS (~20%) is much lower than in classic infection-triggered GBS (80-90%), suggesting the mechanism may be more complex
OBSERVATIONALGuillain-Barré syndrome after COVID-19 vaccination: A systematic review and analysis of case reports — ScienceDirect S0303846724000702 (2024) Systematic synthesis of published case reports characterizing onset timing, vaccine type distribution, and clinical course
CASE-REPORTGuillain-Barré syndrome following ChAdOx1 nCoV-19 COVID-19 vaccination: A case series — PubMed 34548920 (2021) UK case series establishing a facial-palsy-predominant GBS variant with onset 11-13 days after ChAdOx1 first dose; UK surveillance estimated ~5.7 excess cases per million first doses
PLAUSIBLEAdenoviral vector reactivation of latent adenovirus-specific immunity, cross-reacting with peripheral nerve antigens (adenoviral-vector-specific hypothesis, distinct from spike mimicry)
Timeline: 168-720 post-vaccination
OBSERVATIONALEnhanced adenoviral reactivity in Guillain-Barré syndrome after SARS-CoV-2 infection and vaccination — Brain (Oxford) 149(5):1718 (2026) Patients with post-vaccination GBS show enhanced immune reactivity to adenoviral antigens, proposing an adenoviral-vector-specific mechanism distinct from spike-protein molecular mimicry
Important context: Background GBS incidence ~1-2/100k/year; vaccine-attributable risk for mRNA vaccines specifically remains uncertain and is confounded by concurrent respiratory/GI infections, a well-established independent GBS trigger.
Hepatitis
Unlikely
Vaccines: No established causality
Typical onset: Not established
No epidemiologic signal for vaccine-associated hepatitis.
V-SAFE Status: Not Significantly Elevated
No hepatitis signal in safety data
Important context: Background hepatitis incidence confounds any temporal cluster.
Menstrual Disorder
Possible3,421 case reports
Vaccines: mRNA vaccines (temporal reports only)
Typical onset: Changes within 1-7 days; typically resolve within 2 cycles
Multiple independent cohort designs (cross-sectional, self-controlled case series, case-control) consistently document a temporary post-vaccination change in menstrual cycle characteristics in roughly half of respondents, with IL-1B-mediated HPO-axis perturbation as the leading mechanism. The self-controlled case series design is particularly informative because it removes between-person confounding.
V-SAFE Status: Possibly Elevated
Post-vaccination menstrual changes documented; most resolve within 2 cycles; self-limited reports
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (4 studies)
PROBABLEVaccine-induced acute immune response -> pro-inflammatory cytokine release (notably IL-1B) -> transient perturbation of the hypothalamic-pituitary-ovarian (HPO) axis and endometrial signaling -> altered cycle length/flow
Timeline: 24-168 post-vaccination
OBSERVATIONALInflammatory mechanisms of menstrual cycle changes following COVID-19 vaccination in adolescents — PubMed 41554246 (2026) IL-1B identified as a key pro-inflammatory cytokine explaining cycle shortening after vaccination in adolescent girls
OBSERVATIONALThe prevalence of menstrual changes in COVID-19 vaccinated women: A cross-sectional study — PMC11261097 (2024) 54.7% of respondents reported a menstrual change post-vaccination, most commonly cycle length, followed by number of bleeding days and flow volume
OBSERVATIONALMenstrual cycle changes increased following COVID-19 mRNA vaccination: Social media validation and self-controlled case series analysis — medRxiv 2023.10.26.23297643 (2023) Self-controlled case series design (each person as their own control) confirming a within-person increase in cycle changes temporally linked to vaccination, most pronounced when vaccinated during the follicular phase
Show 1 more study
OBSERVATIONALCOVID-19 vaccination and menstrual cycle changes: A United Kingdom (UK) retrospective case-control study — medRxiv 2021.11.23.21266709 (2021) UK retrospective case-control study among the earliest to quantify menstrual cycle change association with vaccination
Important context: Background menstrual irregularity from stress, illness, and other causes is common; changes documented are generally within-normal-range shifts (~1-2 days in cycle length) that resolve within 1-2 cycles. No evidence of impact on long-term fertility.
Myocarditis
Probable180 case reports
Vaccines: mRNA-1273, BNT162b2 (dose 2 especially)
Typical onset: 1-5 days post-vaccination; median 2-3 days
mRNA vaccines cause myocarditis in adolescents/young adults, especially after dose 2. Biopsy-confirmed lymphocytic infiltrate (macrophages, CD8+ T cells, B cells); peak onset 2-4 days post-vaccination. Causality is now considered established by national vaccine safety reviews (e.g., US National Academies evidence review).
V-SAFE Status: Significantly Elevated
3.1x elevation for chest pain + dyspnea cluster within 3 days (95% CI 2.4-4.0); peak day 2-3
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (6 studies)
ESTABLISHEDmRNA LNP delivery -> spike antigen expression in cardiomyocytes/pericytes -> TLR4/inflammasome/IL-1B/IL-18 activation -> lymphocytic myocardial infiltration (CD8+ T cells, macrophages, B cells)
Timeline: 24-72 post-vaccination
OBSERVATIONALMyocarditis following COVID-19 vaccination: incidence, mechanisms, and clinical considerations — PMC9115793 (2022) Vaccine safety monitoring across multiple countries supports a causal association between mRNA COVID-19 vaccines and myocarditis; describes TLR4/inflammasome/IL-1B/IL-18 pathway activation
OBSERVATIONALMyocarditis, Pericarditis, and COVID-19 Vaccines — Evidence Review of the Adverse Effects of COVID-19 Vaccination and Intramuscular Vaccine Administration — NCBI Bookshelf NBK607369 (2024) National Academies evidence review concluding the evidence establishes a causal relationship between mRNA vaccination and myocarditis/pericarditis
CLINICALClinical Characteristics of Patients with Myocarditis following COVID-19 mRNA Vaccination: A Systematic Review and Meta-Analysis — PMC9369856 (2022) Pooled case data: chest pain in ~90% of cases, troponin elevation in >80%, median onset day 2-4 after dose 2; biopsy-confirmed lymphocytic infiltrate with macrophage and T/B cell involvement
Show 1 more study
OBSERVATIONALThe Epidemiology of COVID-19 Vaccine-Induced Myocarditis — DOI: 10.1155/2024/4470326 (2024) Updated 2024 epidemiologic synthesis of incidence by age, sex, dose number, and vaccine product
PROBABLESpike-protein-directed CD8+/Th1 CD4+ T-cell response, analogous to antiviral cytotoxic clearance, cross-reacting with antigen-bearing cardiomyocytes
Timeline: 24-96 post-vaccination
OBSERVATIONALMyocarditis Following COVID-19 Vaccine: What Did We Learn? — PMC12220863 (2024) 2024/2025 review of the CD8+/Th1-CD4+ T-cell hypothesis and comparison with viral myocarditis pathophysiology
IN VITROExploring ceRNA mechanisms in COVID-19 mRNA vaccine-induced myocarditis: implications for future vaccine design — PMC12586086 (2025) Competing endogenous RNA (ceRNA) network analysis proposing transcriptional mechanisms underlying myocardial immune activation after mRNA vaccination
Important context: Background myocarditis ~1-10/100k/year; vaccine-associated rate estimated 10-70/million doses in young males. Clinical course is generally mild and self-limiting; most cases resolve within 1-12 weeks, though long-term cardiac follow-up data remain limited.
Myopericarditis
Probable23 case reports
Vaccines: mRNA-1273, BNT162b2
Typical onset: 2-4 days post-vaccination
Concurrent myocarditis and pericarditis (myopericarditis) occurs in a subset of mRNA vaccine recipients with cardiac adverse events, sharing the same inflammatory mechanism and a similar 2-4 day onset window as isolated myocarditis.
V-SAFE Status: Significantly Elevated
Combined myocarditis + pericarditis; 3.4x elevation for cardiac symptoms within 3 days
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (2 studies)
PROBABLECombined myocardial and pericardial immune-mediated infiltration from the same TLR4/inflammasome-driven inflammatory response underlying isolated myocarditis and pericarditis
Timeline: 24-72 post-vaccination
CLINICALCOVID-19 Vaccination-Induced Myopericarditis: An Imager's Perspective — PMC8800170 (2022) Cardiac MRI series demonstrating combined myocardial and pericardial inflammation/effusion in the same patients
CASE-REPORTA Case Series of Myocarditis Related to the COVID-19 Vaccine — PMC9631103 (2022) Four-case series with 5-month follow-up: three cases fully recovered within 1-12 weeks, one had persistent LV systolic dysfunction
Important context: Represents a subset of myocarditis cases; diagnosis requires imaging or biomarker evidence of both myocardial and pericardial involvement. Course is generally benign with most cases recovering within 1-12 weeks.
Myositis
Possible49 case reports
Vaccines: mRNA vaccines
Typical onset: 3-14 days post-vaccination
A 2023 literature review identified 49 published cases of vaccine-associated myositis, predominantly after mRNA vaccines, with biopsy-confirmed inflammatory infiltrate and elevated creatine kinase in the more severe cases. Most patients responded to immunosuppressive treatment.
V-SAFE Status: Possibly Elevated
Temporal signal in days 3-7 window with muscle pain/inflammation reports
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (3 studies)
PLAUSIBLEVaccine-triggered immune-mediated inflammatory myopathy with macrophage/lymphocyte infiltration of skeletal muscle, elevated creatine kinase, and myofiber degeneration
Timeline: 24-336 post-vaccination
CASE-REPORTClinicopathological Characteristics of Inflammatory Myositis Induced by COVID-19 Vaccine (Pfizer-BioNTech BNT162b2): A Case Report — PMC8938612 (2022) 30-year-old with muscle swelling/pain 6 days after second BNT162b2 dose; CPK 842 U/L (ref 58-348); muscle biopsy showed multifocal macrophage infiltration and degenerated myofibers
OBSERVATIONALCOVID-19 vaccine-associated myositis: a comprehensive review of the literature driven by a case report — PubMed 36928720 (2023) Review of 49 published cases (mean age 56.6, 59% women, 70% after mRNA vaccines); muscle biopsy/MRI/autoantibody findings varied, and immunosuppressive treatment was successful in most cases
CASE-REPORTCOVID-19 vaccine-associated myositis – a case report — PMC9465691 (2022) Additional case documenting mild CK elevation and clinical myositis following vaccination
Important context: Rare; background viral/post-infectious myositis is a common alternative explanation, and biopsy was not performed in many reported cases, limiting mechanistic certainty. Most cases are self-limited or resolve with treatment.
Neuralgic Amyotrophy
Possible14 case reports
Vaccines: mRNA vaccines; rare with viral vectors
Typical onset: 3-14 days post-vaccination
Multiple published case reports describe classic Parsonage-Turner syndrome (severe shoulder/arm pain followed by weakness) with onset roughly 2 weeks post-vaccination, confirmed by nerve conduction studies, EMG, and MR neurography. PTS is already a recognized post-immunization and post-infectious syndrome, making a vaccine trigger biologically plausible.
V-SAFE Status: Possibly Elevated
Temporal clustering 3-14 days suggests possible association; background incidence low (~1-3/100k/year)
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (3 studies)
PLAUSIBLEImmune-mediated inflammatory neuropathy of the brachial plexus (Parsonage-Turner syndrome), consistent with known post-infectious/post-immunization triggers of this syndrome
Timeline: 72-360 post-vaccination
CASE-REPORTParsonage-Turner syndrome of the brachial plexus secondary to COVID-19 vaccine: A case report — PubMed 36276907 (2022) Case report of PTS following COVID-19 vaccination with characteristic severe pain followed by weakness
CASE-REPORTCOVID-19 Vaccine-Induced Parsonage-Turner Syndrome: A Case Report and Literature Review — PMC9242527 (2022) 50-year-old developed PTS 15 days after second BNT162b2 dose; nerve conduction studies and EMG confirmed decreased motor unit recruitment
CASE-REPORTParsonage-Turner Syndrome Following COVID-19 Vaccination: MR Neurography — PMC8488809 (2021) MR neurography imaging documenting brachial plexus nerve inflammation/edema in a post-vaccination PTS case
Important context: Rare condition; natural history of PTS includes many non-vaccine triggers (viral infection, surgery, strenuous exercise), which limits attribution in individual cases despite plausible mechanism.
Optic Neuritis
Possible18 case reports
Vaccines: mRNA and viral vector vaccines
Typical onset: 7-30 days post-vaccination
A published case series of 18 patients found optic neuritis and related demyelinating syndromes within 14 days of vaccination across both mRNA and adenoviral vector platforms, with MRI confirmation of demyelination in most. Some cases were subsequently diagnosed with underlying MS or NMOSD unmasked by vaccination rather than a purely vaccine-caused process.
V-SAFE Status: Indeterminate
Rare post-vaccination; background incidence ~1-5/100k/year; insufficient data for statistical assessment
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (3 studies)
PLAUSIBLEVaccine-triggered CNS demyelinating event targeting the optic nerve, part of a broader spectrum of post-vaccination demyelinating syndromes (isolated optic neuritis, ADEM, NMOSD, MS relapse)
Timeline: 24-720 post-vaccination
CASE-REPORTCNS Demyelination Syndromes Following COVID-19 Vaccination: A Case Series — PMC11000968 (2024) 18-patient case series (8 male, 10 female) with neurological manifestations including optic neuritis within 14 days of Pfizer or AstraZeneca vaccination; 16/18 had MRI findings consistent with demyelinating disease
CASE-REPORTOptic neuritis after mRNA COVID-19 vaccination: a case report — PMC10675095 (2023) Isolated optic neuritis case following mRNA vaccination with MRI-confirmed demyelination
CASE-REPORTAcute disseminated encephalomyelitis with bilateral optic neuritis following ChAdOx1 COVID-19 vaccination — PMC8840677 (2022) Bilateral optic neuritis as part of ADEM following adenoviral vector vaccination, indicating the signal is not mRNA-exclusive
Important context: Very rare (background incidence ~1-5/100k/year); distinguishing genuinely vaccine-triggered cases from coincidental unmasking of pre-existing demyelinating disease is difficult with current case-level data. Most cases improve with corticosteroids/immunosuppression.
Pericarditis
Probable45 case reports
Vaccines: mRNA-1273, BNT162b2
Typical onset: 1-7 days post-vaccination
Often co-occurs with myocarditis (myopericarditis); chest pain and ST-segment changes are the most common presenting features, with a median onset of ~3 days after dose 2. Similar immune-mediated mechanism to myocarditis with pericardial extension.
V-SAFE Status: Significantly Elevated
2.8x elevation for chest pain + SOB within 3 days; often co-occurs with myocarditis
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (3 studies)
PROBABLEmRNA LNP-triggered immune activation extending from myocardium to adjacent pericardium -> inflammatory infiltration and effusion
Timeline: 24-72 post-vaccination
OBSERVATIONALIncidence, risk factors, natural history, and hypothesised mechanisms of myocarditis and pericarditis following covid-19 vaccination: living evidence syntheses and review — PMC9277081 (2022) Living systematic review of incidence, risk factors, and hypothesized shared mechanisms for myocarditis and pericarditis after vaccination
CASE-REPORTAcute Inflammatory Pericarditis following First Dose of COVID-19 Vaccine (AstraZeneca) — PMC9699737 (2022) Case report of isolated acute pericarditis after ChAdOx1, demonstrating the reaction is not mRNA-exclusive
CLINICALCOVID-19 Vaccination-Induced Myopericarditis: An Imager's Perspective — PMC8800170 (2022) Cardiac MRI/echo characterization showing pericardial effusion co-occurring with myocardial inflammation in vaccine-associated cases
Important context: Less frequent than isolated myocarditis; mostly mild and responsive to NSAIDs/colchicine.
Pulmonary Embolism
Unrelated
Vaccines: No causality established
Typical onset: Not established
Safety surveillance shows no increased PE risk post-vaccination.
V-SAFE Status: Not Significantly Elevated
No PE signal in surveillance data; COVID-19 infection increases PE risk substantially
Important context: Confounded by infection risk; attributing PE to vaccination reflects coincidence.
Stroke (Ischemic)
Unlikely
Vaccines: No established causality
Typical onset: Not established
No epidemiologic signal for vaccine-caused ischemic stroke. Unvaccinated COVID-infected cohorts show higher stroke rates.
V-SAFE Status: Not Significantly Elevated
No increased ischemic stroke risk in safety surveillance; COVID-19 infection increases stroke risk substantially
Important context: Stroke multifactorial; temporal proximity often coincidental; COVID-19 itself increases stroke risk.
Thrombocytopenia (ITP)
Possible66 case reports
Vaccines: All COVID-19 vaccines; rare
Typical onset: 3-14 days post-vaccination
A systematic review identified 66 published cases of post-vaccination ITP with a consistent clinical pattern (mucocutaneous bleeding, female predominance, onset within days to three weeks). Nearly all reported patients responded to standard ITP therapy (glucocorticoids, IVIG, or thrombopoietin receptor agonists).
V-SAFE Status: Possibly Elevated
Temporal signal in days 3-7 window; unclear if vaccine-triggered ITP or coincidental
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (3 studies)
PLAUSIBLEVaccine-triggered de novo formation of anti-platelet (glycoprotein-directed) autoantibodies, or reactivation of pre-existing subclinical ITP, causing accelerated platelet clearance
Timeline: 24-504 post-vaccination
OBSERVATIONALA Systematic Review of Reported Cases of Immune Thrombocytopenia after COVID-19 Vaccination — PMC9500907 (2022) Systematic review of 66 published cases; median age 52, female predominance (60.6%), 85% presented with mucocutaneous bleeding/petechiae; onset ranged from 1-3 days (first dose) to 10-21 days (either dose)
CASE-REPORTBNT162b2 COVID-19 Vaccine Induced Immune Thrombocytopenic Purpura — PMC9019434 (2022) Case report documenting new-onset ITP temporally linked to BNT162b2 vaccination with anti-platelet antibody workup
CASE-REPORTSevere Immune Thrombocytopenia after COVID-19 Vaccination: Two Case Reports and a Literature Review — PMC9177350 (2022) Two severe cases requiring treatment, reviewed alongside prior literature on presentation and management
Important context: Background ITP incidence ~2-4/100k/year in adults; most vaccine-associated cases are new-onset rather than relapse of prior ITP, and most recover fully with treatment.
Thrombosis with Thrombocytopenia Syndrome
Probable142 case reports
Vaccines: ChAdOx1 (AZN), Ad26.COV2.S; rare with mRNA
Typical onset: 4-10 days post-vaccination; median 9 days
ChAdOx1 and Ad26.COV2.S cause VITT through vector-triggered anti-PF4 antibody formation; mechanism is now well characterized at the molecular level (stereotyped anti-PF4 IgG, integrin activation, NETosis). Exceedingly rare VITT-like cases have also been reported after mRNA vaccination.
V-SAFE Status: Significantly Elevated
Marked elevation in bleeding + thrombosis cluster 8-14 days (>10x background); peak day 9-10
Temporal Distribution: VAERS vs V-SAFE
VAERS (passive)V-SAFE (active)
Biological Mechanisms & Supporting Literature (5 studies)
ESTABLISHEDAdenoviral vector components form immunogenic PF4-polyanion complexes -> high-affinity monoclonal/oligoclonal anti-PF4 IgG -> FcgammaRIIa-dependent platelet activation and neutrophil NET release -> thrombotic microangiopathy
Timeline: 72-240 post-vaccination
IN VITROVaccine-induced immune thrombotic thrombocytopenia (VITT) is mediated by a stereotyped clonotypic antibody — medRxiv 2022.03.28.22272975 (2022) VITT antibodies are stereotyped/clonotypic anti-PF4 IgGs distinct from heparin-induced thrombocytopenia (HIT) antibodies
IN VITROAnti-PF4 (heparin-independent)/PF4 complex induces allosteric activation of integrins alphaIIbbeta3 and alphavbeta3, a potential mechanism of VITT — bioRxiv 2022.08.17.504306 (2022) Anti-PF4/PF4 immune complexes allosterically activate platelet and endothelial integrins, providing a direct biochemical mechanism for thrombosis
IN VITROReverse engineering of a pathogenic antibody reveals the molecular mechanism of vaccine-induced immune thrombotic thrombocytopenia — bioRxiv 2023.06.30.547300 (2023) Structural reconstruction of a pathogenic anti-PF4 antibody clarifying the epitope and binding geometry driving platelet activation
Show 1 more study
OBSERVATIONALVaccine-Induced Immune Thrombotic Thrombocytopenia: Clinicopathologic Features and New Perspectives on Anti-PF4 Antibody-Mediated Disorders — PMC10889051 (2024) Clinicopathologic review distinguishing VITT from HIT and other anti-PF4 antibody-mediated disorders
PLAUSIBLERare mRNA-vaccine-associated VITT-like syndrome via a distinct (non-adenoviral) immune trigger
Timeline: 72-336 post-vaccination
CASE-REPORTVaccine-Induced Immune Thrombotic Thrombocytopenia following BNT162b2 mRNA COVID-19 Booster: A Case Report — PMC10302306 (2023) Rare VITT-like presentation after an mRNA booster dose, confirming the syndrome is not exclusive to adenoviral vector vaccines though far less common
Important context: Rare: approximately 4-6 cases per million ChAdOx1 doses in early UK/EU surveillance; essentially absent in first-dose mRNA cohorts. Higher incidence reported in younger women.
Venous Thromboembolism
Unrelated
Vaccines: No established causality for any COVID-19 vaccine
Typical onset: Not established
Major safety surveillance (UK, US, EU) found NO increased VTE risk. Unvaccinated infected cohorts show higher VTE than vaccinated uninfected.
V-SAFE Status: Not Significantly Elevated
No increased VTE risk in surveillance data; COVID-19 infection itself increases VTE 10-fold
Important context: Viral infection (COVID-19) significantly increases VTE risk; confounding in observational studies.
Legend: Evidence Model Types
IN VITROIN VIVOCLINICALOBSERVATIONALCASE-REPORT
Part of the Open Source Medicine Foundation Network
