Evidence state
For each outcome: the specific question, what controlled studies found, and how certain that evidence is on the GRADE scale (high, moderate, low, very low). Ratings are editorial judgments by the site applying GRADE to the studies in the table below — observational evidence starts at low and is rated up for large, consistent effects or a dose/age gradient, and down for inconsistency or imprecision (Methods). Where an effect is confined to a subgroup (for example young males), the question says so. "Not searched" means no controlled study has been compiled here yet; it is not a finding that the outcome is rare or caused by the vaccine.
| Outcome & question | Finding & certainty | Why this rating |
|---|---|---|
| Guillain-Barré syndrome Abrysvo and Arexvy, adults 60+ | increased risk (about 5–18 extra cases per million doses) Low certainty | Two independent US analyses (FDA/CMS Medicare; EHR platform) agree on an excess; estimates imprecise. Studies: FDA 2025, Fry 2025. See table |
| Pregnancy outcomes Abrysvo (RSVpreF) in pregnancy | no increase in preterm birth detected in the licensure trial or a US cohort; a different (unlicensed) GSK maternal candidate increased preterm birth in its trial Moderate certainty | Randomized evidence starts high; −1 imprecision (trial not powered for preterm birth; numerical imbalance). FDA licensed maternal use only at 32–36 weeks of gestation. Studies: Kampmann 2023, Son 2024, Dieussaert 2024. See table |
| Immune thrombocytopenia Abrysvo and Arexvy | no increased risk detected Low certainty | One large self-controlled analysis. Studies: Fry 2025. See table |
| Anaphylaxis | Not searched | No controlled-study result is compiled for this outcome yet. |
| Myocarditis or pericarditis | Not searched | No controlled-study result is compiled for this outcome yet. |
| Febrile seizure | Not searched | No controlled-study result is compiled for this outcome yet. |
1. Basic Information
Respiratory syncytial virus (RSV) is a leading cause of bronchiolitis and pneumonia in infants and a significant cause of morbidity in older adults. U.S. prevention now includes three distinct product classes — not interchangeable:
| Product | Type | Who | Manufacturer |
|---|---|---|---|
| Arexvy | Adjuvanted recombinant RSV vaccine (GSK) | Adults ≥60; pregnancy indication (maternal immunization) | GSK |
| Abrysvo | Bivalent recombinant RSV prefusion F vaccine (Pfizer) | Adults ≥60; maternal immunization (32–36 wks) | Pfizer |
| Beyfortus (nirsevimab) | Long-acting RSV monoclonal antibody — not a vaccine | Infants & toddlers (seasonal) | AstraZeneca / Sanofi |
Source: FDA prescribing information; CDC RSV pages (2024–2026). Beyfortus reports in VAERS may appear under RSV product labels.
Licensed RSV vaccine products
Each product has its own page with package-insert ingredients, side-effect data, lot lookup and comparisons with the other brands.
Ingredients (Package Insert)
Structured composition for 2 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.
Arexvy GlaxoSmithKline Biologicals · Recombinant protein
Delivery
Route: Intramuscular (IM)
Form: Lyophilized powder (reconstitute)
Dose volume: 0.5 mL
Presentation: antigen vial + AS01E adjuvant suspension
Encapsulation / delivery vehicle
Liposome — AS01E is a liposomal adjuvant system (half-dose AS01 relative to AS01B).
| Component | Role | Amount |
|---|---|---|
| DOPC | liposomal phospholipid | 0.5 mg |
| Cholesterol | cholesterol | 0.125 mg |
Antigens
| Antigen | Type | Amount / dose |
|---|---|---|
| Recombinant RSV prefusion F glycoprotein (RSVPreF3) | Recombinant protein | 120 mcg |
Adjuvants
- AS01E — MPL 25 mcg + QS-21 25 mcg
- MPL — 25 mcg
- QS-21 — 25 mcg
Preservatives
- None — Single-dose presentation; label states no preservative.
Excipients & residuals
| Ingredient | Category | Amount | Role |
|---|---|---|---|
| Trehalose | Stabilizer | 14.7 mg | stabilizer |
| Sodium chloride | Buffer | 4.4 mg | tonicity |
| Potassium dihydrogen phosphate | Buffer | 0.83 mg | buffer |
| Dipotassium phosphate | Buffer | 0.26 mg | buffer |
| Polysorbate 80 | Surfactant | 0.18 mg | surfactant |
| Disodium phosphate anhydrous | Buffer | 0.15 mg | buffer |
Source: FDA package insert · Verified 2026-07-09
Abrysvo Pfizer Inc. · Recombinant protein
Delivery
Route: Intramuscular (IM)
Form: Lyophilized powder (reconstitute)
Dose volume: 0.5 mL
Presentation: single-dose vial + sterile water diluent / prefilled presentations per labeling
Encapsulation / delivery vehicle
None (no nanoparticle/VLP encapsulation system)
Antigens
| Antigen | Type | Amount / dose |
|---|---|---|
| RSV prefusion F (bivalent: subgroup A and B) System: CHO cells | Recombinant protein | 60 mcg each antigen (120 mcg total) |
Adjuvants
None listed on the package insert for this product (common for live attenuated and some inactivated whole-virus vaccines).
Preservatives
- None — Single-dose presentation; label states no preservative.
Excipients & residuals
| Ingredient | Category | Amount | Role |
|---|---|---|---|
| Tromethamine / tromethamine hydrochloride | Buffer | label quantity | buffer |
| Sucrose | Stabilizer | label quantity | stabilizer |
| Mannitol | Stabilizer | label quantity | stabilizer |
| Polysorbate 80 | Surfactant | label quantity | surfactant |
| Sodium chloride | Buffer | label quantity | tonicity |
Unadjuvanted protein subunit RSV vaccine (contrast Arexvy AS01E).
Source: FDA package insert · Verified 2026-07-09
ⓘ How to read this section
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.
| Condition | Time window | Causality | Potential mechanism(s) |
|---|---|---|---|
| Anaphylaxis | 0–1 days |
Very likely / Probable
Evidence: High |
IgE-mediated hypersensitivity (anaphylaxis) (primary · hypersensitivity) 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. |
| Local/systemic reactogenicity | 0–3 days |
Very likely / Probable
Evidence: High |
Adjuvant-driven local and systemic reactogenicity (primary · innate_inflammation) Aluminum or other adjuvants (e.g., AS01B) amplify innate immune signaling, producing injection-site inflammation and transient systemic symptoms (fever, myalgia, fatigue). |
| Guillain-Barré Syndrome | 0–42 days |
Possible
Evidence: Low |
Molecular mimicry → Guillain-Barré syndrome (primary · molecular_mimicry) Vaccine- or infection-triggered immune responses cross-react with peripheral-nerve gangliosides or myelin components, producing demyelinating or axonal polyneuropathy. Temporal association — mechanism unknown (alternative · unknown) Reports show temporal clustering after vaccination but a specific pathogenic pathway is not established; alternative (coincidental) explanations remain plausible. |
| 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). |
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.
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.
- Methods combined: BCPNN (IC), GPS/EBGM, PRR, ROR — then rank aggregation.
- 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.
Source: nanx.me/rankv · Code: github.com/nanxstats/rankv (MIT) · Built: 2026-07-30.
2. Pre-Licensure Clinical Trial Data
Licensure trial design (ICAN / OpenVAERS)
This vaccine is not listed in ICAN’s childhood-schedule No Placebo Table (which covers CDC routine pediatric injectable products). Pre-licensure trial comparators for travel, adult, or specialty vaccines should be taken from FDA review documents and product labels in the sections below.
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.
| Product | Pivotal evidence | Common reactogenicity (trials) |
|---|---|---|
| Arexvy (AReSVi-006) | ~82–89% efficacy vs. RSV-LRTD in adults ≥60 over one season | Injection-site pain, fatigue, myalgia, headache, arthralgia |
| Abrysvo (MATISSE maternal) | ~82% efficacy vs. severe RSV disease in infants through 90 days when given in pregnancy | Maternal: injection-site pain, headache, myalgia; infant outcomes monitored in trials |
| Beyfortus (HARMONIE / MELODY) | ~74–80% reduction in medically attended RSV LRTI in infants | Rash, injection-site reactions (mAb, not live virus) |
Trial efficacy is against RSV disease endpoints — distinct from VAERS adverse-event report counts post-licensure.
3. Post-Licensure Safety Data
RSV preventives licensed in 2023–2024; post-marketing databases are still accumulating. Guillain-Barré syndrome signal monitoring was highlighted in FDA communications for older-adult RSV vaccines — see primary FDA reviews for context.
⚠ Critical Caveat
VAERS reports are unverified temporal associations. High report volume for new products partly reflects stimulated reporting and large rollout scale.
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 files on this site are built from the public VAERS download. FAERS figures use the public quarterly FAERS files. Counts are mentions or reports, not incidence.
VAERS (United States)
No VAERS category summary is mapped for this vaccine page.
Canada Vigilance (Canada)
No matching vaccine reports in the current Canada Vigilance extract.
JADER (PMDA, Japan)
No matching vaccine reports in the current JADER public extract.
EudraVigilance (EU)
No matching vaccine cases in the current EudraVigilance DAP export.
SurVigilance: VigiAccess · Lareb · DAEN · DMA · Medsafe
VigiAccess (WHO)
This system’s totals are not in this panel. Published counts, when this site has them, are in the surveillance section.
Lareb (Netherlands)
This system’s totals are not in this panel. Published counts, when this site has them, are in the surveillance section.
DAEN (Australia)
This system’s totals are not in this panel. Published counts, when this site has them, are in the surveillance section.
DMA (Denmark)
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)
Compare AE patterns across all vaccines →
VAERS Lot-Level Reports
2,808 VAERS reports with usable lot data (U.S.). Signal flags are hypothesis-generating only — not proof of an unsafe lot. Full dashboard →
What controlled safety studies found
Unlike VAERS counts, these studies compare vaccinated people with a control group or control time window, so they can estimate whether a risk is raised and by how much. 12 results for RSV vaccines: 5 found an increased risk of a specific outcome, 5 found no increased risk.
| Outcome | Design & population | Estimate (95% CI) | Excess per million doses | Finding | Source |
|---|---|---|---|---|---|
Guillain-Barre syndrome RSV disease (infection comparator, not a vaccine) | SCCS (Medicare claims 2011-2024) Adults >=65 y with medically attended RSV, US (452,471) | IRR (adjusted) 2.11 (1.01–4.37) | — | increased risk | Liang C et al., 2026, Clin Infect Dis doi:10.1093/cid/ciaf621; PMID 41234154 |
Guillain-Barre syndrome Abrysvo (RSVpreF, Pfizer) | SCCS (FDA/CMS Medicare claims, chart review when available) Medicare beneficiaries >=65 y, US May 2023-Jul 2024 | attributable risk per million doses 9 | 9 | increased risk | FDA Safety Communication, 'FDA Requires Guillain-Barre Syndrome (GBS) Warning in the Prescribing Information for RSV Vaccines Abrysvo and Arexvy', 2025-01-07 source |
Guillain-Barre syndrome Arexvy (RSVPreF3+AS01, GSK) | SCCS (FDA/CMS Medicare claims, chart review when available) Medicare beneficiaries >=65 y, US May 2023-Jul 2024 | attributable risk per million doses 7 | 7 | increased risk | FDA Safety Communication, 'FDA Requires Guillain-Barre Syndrome (GBS) Warning in the Prescribing Information for RSV Vaccines Abrysvo and Arexvy', 2025-01-07 source |
Guillain-Barre syndrome Abrysvo (RSVpreF) | SCCS (US EHR data platform, >270 million patients) US adults >=60 y (4,746,518 RSV vaccine recipients, both products) | excess cases per million doses 18.2 | 18.2 | increased risk | Fry SE et al., 2025, JAMA Netw Open doi:10.1001/jamanetworkopen.2025.8322; PMID 40343698 |
Preterm birth GSK RSVPreF3-Mat (candidate maternal vaccine; never licensed) | randomized controlled trial (phase 3, stopped early) Pregnant women 18-49 y, 24-34 wk (5328) | RR 1.37 (1.08–1.74) | — | increased risk | Dieussaert I et al., 2024, N Engl J Med doi:10.1056/NEJMoa2305478; PMID 38477988 |
11 prespecified outcomes (e.g., stroke, atrial fibrillation, anaphylaxis, encephalomyelitis; GBS reported separately) Arexvy (RSVPreF3+AS01) and Abrysvo (RSVPreF) | SCCS (FDA/CMS Medicare) Medicare beneficiaries >=65 y, US 2023-2024 (3.82 million vaccinated) | — | — | no increased risk detected | Lloyd PC et al., 2026, Vaccine doi:10.1016/j.vaccine.2026.128459; PMID 41833132 |
Guillain-Barre syndrome Arexvy (RSVPreF3+AS01) | SCCS (US EHR data platform) US adults >=60 y | excess cases per million doses 5.2 | 5.2 | inconclusive | Fry SE et al., 2025, JAMA Netw Open doi:10.1001/jamanetworkopen.2025.8322; PMID 40343698 |
Hypertensive disorders of pregnancy Abrysvo (RSVpreF) in pregnancy | retrospective cohort (2 NYC hospitals) Pregnant individuals, US 2023-2024 | HR (time-dependent) 1.43 (1.16–1.77) | — | inconclusive | Son M et al., 2024, JAMA Netw Open doi:10.1001/jamanetworkopen.2024.19268; PMID 38976271 |
Immune thrombocytopenic purpura Arexvy and Abrysvo | SCCS (US EHR data platform) US adults >=60 y (4,746,518 recipients) | — | — | no increased risk detected | Fry SE et al., 2025, JAMA Netw Open doi:10.1001/jamanetworkopen.2025.8322; PMID 40343698 |
Maternal and infant adverse events Abrysvo (RSVpreF) in pregnancy (MATISSE trial) | randomized controlled trial (phase 3) Pregnant women 24-36 wk, 18 countries (3682 vaccine, 3676 placebo) | — | — | no increased risk detected | Kampmann B et al., 2023, N Engl J Med doi:10.1056/NEJMoa2216480; PMID 37018474 |
Preterm birth Abrysvo (RSVpreF) in pregnancy | retrospective cohort (2 NYC hospitals) Pregnant individuals delivering >=32 wk, US 2023-2024 (2973) | HR (time-dependent) 0.93 (0.64–1.34) | — | no increased risk detected | Son M et al., 2024, JAMA Netw Open doi:10.1001/jamanetworkopen.2024.19268; PMID 38976271 |
Preterm birth and other adverse pregnancy outcomes Maternal RSV vaccination (Abrysvo, 32-36 wk) | systematic review (RCTs + comparative observational studies) Pregnant individuals, US-licensed products | — | — | no increased risk detected | Senerth E et al., 2026, JAMA doi:10.1001/jama.2026.17871; PMID 42684247 |
Benefit and risk on the same scale (per million)
Bars are drawn to scale within each comparison. Disease risks are per case of the disease; vaccine risks are the excess above background per dose, from controlled studies. How likely someone is to catch the disease, without vaccination, decides how these weigh up for an individual.
No single study measured both risks in the same population for this vaccine, so no side-by-side ratio is shown; the two lists below come from different studies, eras and populations.
Excess risk after vaccination (per million doses)
| Guillain-Barre syndrome Abrysvo (RSVpreF) | 18.2 | US adults >=60 y (4,746,518 RSV vaccine recipients, both products) · doi:10.1001/jamanetworkopen.2025.8322; PMID 40343698 |
| Guillain-Barre syndrome Abrysvo (RSVpreF, Pfizer) | 9 | Medicare beneficiaries >=65 y, US May 2023-Jul 2024 · source |
| Guillain-Barre syndrome Arexvy (RSVPreF3+AS01, GSK) | 7 | Medicare beneficiaries >=65 y, US May 2023-Jul 2024 · source |
| Guillain-Barre syndrome Arexvy (RSVPreF3+AS01) | 5.2 | US adults >=60 y · doi:10.1001/jamanetworkopen.2025.8322; PMID 40343698 |
Compiled from study abstracts and FDA/CDC pages, verified 2026-10-09; full table with every source on vaccine safety studies. Data: active_surveillance_results.json, disease_risks.json.
Trials, timing and other data sources
Randomized placebo-controlled trials: serious adverse events
Trials on ClinicalTrials.gov with posted results and a placebo, saline or no-vaccine control arm (37,948 vaccinated vs 40,241 controls), pooled with a random-effects model:
- Any serious adverse event: RR 1.00 (95% CI 0.96–1.03), 11 trials, I² 0% — no significant difference
- Death (any cause, including from the disease itself): RR 0.94 (95% CI 0.83–1.06), 6 trials, I² 0% — no significant difference
- by product — RSVPreF3 OA: RR 0.87 (95% CI 0.67–1.13), 4 trials, I² 37% — no significant difference
- by product — RSVpreF: RR 1.02 (95% CI 0.96–1.09), 5 trials, I² 0% — no significant difference
- by product — mRNA-1345: RR 1.01 (95% CI 0.96–1.06), 2 trials, I² 0% — no significant difference
Trials included
| Trial | Title | Vaccine: SAE/n | Control: SAE/n |
|---|---|---|---|
| NCT04886596 | Efficacy Study of GSK's Investigational Respiratory Syncytial Virus (RSV) Vaccine in Adult | 796/6,243 | 1,660/12,503 |
| NCT06551181 | A Study on the Immune Response, Safety and the Occurrence of Respiratory Syncytial Virus ( | 81/2,019 | 38/601 |
| NCT05590403 | A Study on the Immune Response and Safety of a Vaccine Against Respiratory Syncytial Virus | 27/1,150 | 8/383 |
| NCT06614725 | A Study in India on the Immune Response and Safety of a Respiratory Syncytial Virus (RSV) | 1/500 | 0/250 |
| NCT04424316 | A Trial to Evaluate the Efficacy and Safety of RSVpreF in Infants Born to Women Vaccinated | 1,310/7,357 | 1,270/7,333 |
| NCT05096208 | Clinical Lot Consistency for RSVpreF in a Population of Healthy Adults 18 to ≤49 Years of | 0/1,490 | 0/247 |
| NCT06325657 | A Study to Learn About the Vaccine RSVpreF In Pregnant Participants With HIV and Their Inf | 92/343 | 93/336 |
| NCT06593587 | A Study to Assess the Safety, Tolerability, and Immunogenicity of RSVpreF in Older Adults | 2/251 | 1/126 |
| NCT04785612 | Study of RSVpreF Vaccination and RSV Challenge in Healthy Adults | 1/105 | 1/105 |
| NCT05127434 | A Study to Evaluate the Safety and Efficacy of mRNA-1345 Vaccine Targeting Respiratory Syn | 2,773/18,369 | 2,745/18,316 |
| NCT06097299 | A Study of mRNA-1345, an mRNA Vaccine Targeting Respiratory Syncytial Virus, in Children 2 | 0/121 | 0/41 |
Only blinded, placebo-controlled periods are used (open-label, crossover, booster and extension periods excluded) and vaccine and placebo arms are matched within the same trial part. Risk ratios use participant counts, not person-time: where placebo recipients crossed over to vaccine, the placebo arm is followed for less time, which pushes count-based ratios up. Serious adverse events are sponsor-coded and include events unrelated to vaccination; trials were powered for efficacy, not rare harms; most childhood-vaccine trials use active comparators and therefore do not appear here. Code: analysis/vaccine_trial_meta.py; data: vaccine_trial_meta.json.
When do reported events start? (time to onset)
Days from vaccination to onset in U.S. VAERS reports (0–180 days). A causal reaction usually starts inside a characteristic window; but people also report what happens soon after a shot, so each event is compared with all other reports for this vaccine. The Weibull shape measures bunching (below 1 = most onsets early).
| Event | Reports | Median days | In risk window | Shape (95% CI) vs others | Reading |
|---|---|---|---|---|---|
| Syncope | 97 | 0 | 85% (others 78%) | 0.75 (0.60–1.31) vs 0.69 | same timing as other reports |
| Guillain-Barré syndrome | 74 | 9 | 86% (others 45%) | 0.96 (0.81–1.23) vs 0.69 | spread later than other reports |
| Seizure (any) | 29 | 1 | 100% (others 96%) | 0.95 (0.83–1.21) vs 0.69 | spread later than other reports |
| Stroke | 28 | 1 | 54% (others 44%) | 0.78 (0.65–1.26) vs 0.69 | same timing as other reports |
| Bell's palsy / facial paralysis | 26 | 3 | 81% (others 45%) | 0.77 (0.66–1.06) vs 0.69 | same timing as other reports |
Timing alone cannot establish causation; it can make it more or less plausible. *Fitted on a random sample of 5,000 of these reports. Data: vaers_onset.json.
4. Disease Prevention Context
RSV causes an estimated 58,000–80,000 hospitalizations and 100–300 deaths annually among U.S. children <5 years (prevention era), and substantial burden in adults ≥65. Seasonal immunization and infant mAb programs aim to reduce LRTI hospitalization — effectiveness in real-world settings is tracked separately from pharmacovigilance report counts.