Name: Varicella Vaccine
Brand: Varivax
SKU: varicella

1. Basic Information

Disease Protected Against

Varicella (Chickenpox) is caused by varicella-zoster virus (VZV). Before vaccination, varicella caused ~4 million cases, ~10,500–13,500 hospitalizations, and ~100–150 deaths annually in the U.S. Complications include bacterial superinfection (primarily Group A Strep), pneumonia, encephalitis, and congenital varicella syndrome. VZV establishes latency in dorsal root ganglia; reactivation later in life causes herpes zoster (shingles).

CDC Schedule (U.S., 2025)

Dose	Age	Product
Dose 1	12–15 months	Varivax (standalone) or ProQuad (MMRV)
Dose 2	4–6 years	Varivax or ProQuad. Minimum interval: 3 months between doses.

Source: CDC ACIP, 2025 schedule. ACIP recommends MMR + varicella separately for dose 1 in children 12–47 months due to MMRV febrile seizure risk; MMRV may be used for dose 2 or for dose 1 in children ≥48 months.

Documented Adverse Events (HRSA VICP)

The following adverse events are documented by the HRSA Vaccine Injury Compensation Program (VICP) as having a temporal relationship to this vaccine. These are not necessarily confirmed causal relationships, but rather conditions for which claims have been compensated or are presumed caused by the vaccine.

WHO Causality Assessment Methodology

The World Health Organization's Global Advisory Committee on Vaccine Safety (GACVS) uses a 4-level causality classification:

Consistent: Epidemiological studies demonstrate a statistically significant association with temporal specificity and biological plausibility. Replicated across independent populations and study designs.
Indeterminate: Evidence exists but is insufficient to confirm or rule out causality. May be limited by sample size, confounding, or inconsistency across studies.
Inconsistent: Studies have not demonstrated a consistent or convincing association. Evidence against causality outweighs evidence for it.
Unclassifiable: Insufficient data to reach any conclusion. Requires further evidence.

Source: WHO Global Advisory Committee on Vaccine Safety (GACVS), 2021–2025 causality review cycles. See also Institute of Medicine (IOM) Adverse Effects of Vaccines: Evidence and Causality (2012) for pre-COVID vaccine assessments.

Condition	Time Window	Causality Level	HRSA Description
Anaphylaxis	0-1 days	Consistent WHO Determination (2021, 2023): Consistent for all COVID-19 vaccines. Rate: ~2–5 per million doses. Temporal specificity (onset within minutes, consistent with IgE-mediated). Plausible biological mechanism: immediate hypersensitivity to vaccine excipients (PEG for mRNA, polysorbate for adenoviral). Verified via passive surveillance convergence across multiple national systems (VAERS, EudraVigilance, MHRA Yellow Card, TGA DAEN). Biological Mechanism: Not thought to be spike protein mediated; likely polyethylene glycol (PEG) in mRNA vaccines triggers IgE-mediated mast cell degranulation Clinical Evidence: (Kuder et al., 2021); Mechanism: (Risma et al., 2021) Spike Protein Evidence: Not tested	Anaphylaxis occurring within 4 hours following vaccination
Vaccine Strain Varicella (Disseminated)	0-42 days	Indeterminate WHO / IOM Causality Assessment: Evidence reviewed; causal association cannot be confirmed or excluded at current evidence level. Requires further epidemiological and mechanistic investigation. See HRSA VICP Table for program-specific determination. Biological Mechanism: Multiple plausible biological mechanisms under investigation. Brighton Collaboration AESI monitoring ongoing. Clinical Evidence: See HRSA VICP/CICP program documentation for current determination. Spike Protein Evidence: Evidence reviewed; consult Brighton Collaboration list for mechanistic assessment status.	Vaccine strain varicella (disseminated) within 42 days of vaccination
Herpes Zoster (Shingles)	0-365 days	Indeterminate WHO / IOM Causality Assessment: Evidence reviewed; causal association cannot be confirmed or excluded at current evidence level. Requires further epidemiological and mechanistic investigation. See HRSA VICP Table for program-specific determination. Biological Mechanism: Multiple plausible biological mechanisms under investigation. Brighton Collaboration AESI monitoring ongoing. Clinical Evidence: See HRSA VICP/CICP program documentation for current determination. Spike Protein Evidence: Evidence reviewed; consult Brighton Collaboration list for mechanistic assessment status.	Herpes zoster (caused by vaccine strain virus) within 12 months of vaccination

Important Notes

HRSA VICP: Conditions listed are documented by HRSA as having temporal relationship to vaccination. Compensation does not imply causation.
Temporal Association: These conditions occurred after vaccination within the specified time window, but other factors may have contributed.
Rarity: Most adverse events are extremely rare. Serious adverse events from vaccines occur in roughly 1-2 per million doses.
Biological Plausibility: Mechanistic evidence is under review and will be integrated in Q3 2026.
Benefit-Risk: This page documents documented injuries. See disease burden pages for context on prevented diseases.

Ingredients (Package Insert)

Structured composition for 1 branded product 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.

Live attenuated IM or SC No preservative (typical single-dose) Gelatin Neomycin

Varivax Merck Sharp & Dohme LLC · Live attenuated

Delivery

Route: IM or SC

Form: Lyophilized powder (reconstitute)

Dose volume: 0.5 mL

Presentation: single-dose vial + sterile diluent

Encapsulation / delivery vehicle

None (no nanoparticle/VLP encapsulation system)

Antigens

Antigen	Type	Amount / dose
Varicella-zoster virus (live, attenuated) Strain: Oka/Merck · System: MRC-5 cells	Live attenuated virus	≥1350 PFU per 0.5 mL

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
Sucrose	Stabilizer	≈24 mg	stabilizer
Hydrolyzed gelatin	Stabilizer	≈12.0 mg	stabilizer
Sodium chloride	Buffer	≈3.1 mg	tonicity
Monosodium L-glutamate	Stabilizer	≈0.5 mg	stabilizer
Sodium phosphate dibasic	Buffer	≈0.44 mg	buffer
Potassium phosphate monobasic	Buffer	≈0.08 mg	buffer
Potassium chloride	Buffer	≈0.08 mg	buffer
MRC-5 residual DNA/protein	Residual (manufacturing)	trace	cell-substrate residual
Neomycin	Residual (antibiotic)	trace	residual
Fetal bovine serum	Residual (manufacturing)	trace	residual
EDTA	Residual (manufacturing)	trace	process residual

Source: DailyMed · 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 HRSA table	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.
Vaccine-strain varicella (disseminated) HRSA table	0–42 days	Very likely / Probable Evidence: High	Uncontrolled live attenuated vaccine replication (primary · live_replication) In immunocompromised or otherwise susceptible hosts, live attenuated vaccine strains can replicate beyond the intended limited infection, causing disseminated disease or organ-specific infection.
Herpes zoster (vaccine strain) HRSA table	0–365 days	Possible Evidence: Moderate	Uncontrolled live attenuated vaccine replication (primary · live_replication) In immunocompromised or otherwise susceptible hosts, live attenuated vaccine strains can replicate beyond the intended limited infection, causing disseminated disease or organ-specific infection.
Febrile seizure (especially MMRV)	5–12 days	Very likely / Probable Evidence: High	Fever-triggered seizure (primary · innate_inflammation) Vaccine-induced fever lowers seizure threshold in susceptible young children; measles-containing vaccines show a well-documented risk window roughly 7–14 days post-dose.

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
VAR	Varivax	Merck	2	12M 4Y	45 mg of neomycin per milliliter	No	70 days

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.

Varivax was licensed in 1995 based on clinical trials in ~11,000 children and adults. The pivotal efficacy trial enrolled ~1,000 children. ProQuad (MMRV) was licensed in 2005 based on trials in ~6,000 children.

Metric	Data
Pre-licensure safety database (Varivax)	~11,000 individuals
Efficacy (1 dose)	~85% (all varicella); ~97% (severe varicella)
Efficacy (2 doses)	~98% (all varicella); near-100% (severe varicella)
Most common reactions	Injection site reactions (~20–30%), fever (~10–15%), varicella-like rash (~3–5%, may be infectious)

MMRV Febrile Seizure Finding

The MMRV pre-licensure trials observed a higher rate of fever (38–40%) and a numerically higher rate of febrile seizures compared to MMR + varicella given separately. The febrile seizure risk was confirmed post-licensure in VSD studies: ~1 additional febrile seizure per 1,250 MMRV doses compared to MMR + varicella given separately, in the 5–12 day post-vaccination window. This led to the ACIP preference for separate MMR + varicella for dose 1.

3. Post-Licensure Safety Data

Varicella vaccine has >30 years of post-licensure safety data. Key VSD findings:

MMRV febrile seizures: ~1 per 1,250 doses vs. ~1 per 2,500 for MMR + varicella separately (5–12 day window). ACIP preference for separate administration for dose 1 under age 4.
Herpes zoster (shingles) from vaccine strain: Documented in vaccinated children and adults; rate is lower than after wild-type VZV infection. Estimated at ~18–26 per 100,000 person-years in vaccinated children vs. ~74 per 100,000 after wild-type infection.
Vaccine-strain transmission: Occasional transmission of vaccine-strain VZV from a vaccinated person who develops a rash to susceptible contacts. Rare; mostly from immunocompromised vaccinees. No documented transmission from vaccinated persons without a rash.
ITP: MMRV and MMR + varicella both associated with a small ITP risk (attributable primarily to the MMR component — see MMR page).

⚠ Critical Caveat

VAERS data represent unverified reports. A report to VAERS does not mean the vaccine caused the event.

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 (Varicella standalone (Varivax); excludes MMRV (MMR-Varicella combination, which had 15,668 reports / 20 deaths / 42.9M doses / 0.0466 death rate)):

Metric	Value
U.S. doses administered (2006–2022)	143,906,028
Total VAERS AE reports	48,863
AE reporting rate (per 100,000 doses)	34.0
Total death reports	84
Death reporting rate (per 100,000 doses)	0.0584
AE-to-Death ratio	582:1

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)

No VAERS category summary is mapped for this vaccine page.

Canada Vigilance (Canada)

JADER (PMDA, Japan)

EudraVigilance (EU)

No matching vaccine cases in the current EudraVigilance DAP export.

SurVigilance: VigiAccess · Lareb · DAEN · DMA · Medsafe

VigiAccess (WHO)

Lareb (Netherlands)

DAEN (Australia)

No DAEN (Australia) data yet — run python scrape_survigilance_one.py daen <vaccine-id> or python survigilance_pipeline.py --system daen (SurVigilance + direct scrapers: GitHub).

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)

Canada Vigilance (CV Online extract): 11,067 reaction mentions in 3,417 unique reports (64.0% serious (2,186 of 3,417 reports)). Largest share: General / Systemic (non-local) (17%), Injection-site / Local reaction (17%), Neurological (10%). JADER (PMDA public CSV extract): 1,313 reaction mentions in 666 unique reports (8.1% serious (54 of 666 reports)). Largest share: Other / Unclassified (35%), Neurological (18%), General / Systemic (non-local) (13%). VigiAccess (WHO): 1,395 reaction-term mentions · search: varicella. Largest share: Gastrointestinal (26%), Dermatological (non-injection-site) (18%), Other / Unclassified (12%). Lareb (Netherlands): 80 reaction-term mentions · search: Varicella vaccine. Largest share: General / Systemic (non-local) (22%), Other / Unclassified (16%), Injection-site / Local reaction (15%). Medsafe (New Zealand): 569 reaction-term mentions · search: varicella. Largest share: Injection-site / Local reaction (23%), General / Systemic (non-local) (21%), Other / Unclassified (17%). 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 Canada Vigilance: General / Systemic (non-local); 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.

Compare AE patterns across all vaccines →

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

57,254 reports with usable lot across 4,317 lots · 511 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)

3,417 unique reports · 11,067 reaction mentions · 64.0% serious (2,186 of 3,417 reports). Top categories: General / Systemic (non-local) (17%), Injection-site / Local reaction (17%), Neurological (10%).

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.

Search Canada Vigilance →

JADER (PMDA, Japan)

666 unique reports · 1,313 reaction mentions · 8.1% serious (54 of 666 reports). Top categories: Other / Unclassified (35%), Neurological (18%), General / Systemic (non-local) (13%).

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)

Search JADER / PMDA adverse reactions →

No EudraVigilance (EU) summary is mapped for this page.

VigiAccess (WHO)

1,395 MedDRA PT mentions · search: varicella. Top categories: Gastrointestinal (26%), Dermatological (non-injection-site) (18%), Other / Unclassified (12%).

Live-scraped public portal data via SurVigilance (GPL-3.0). Counts are reaction-term mentions, not deduplicated individual cases. No lot/batch field.

Search VigiAccess (WHO) →

Lareb (Netherlands)

80 MedDRA PT mentions · search: Varicella vaccine. Top categories: General / Systemic (non-local) (22%), Other / Unclassified (16%), Injection-site / Local reaction (15%).

Live-scraped public portal data via SurVigilance (GPL-3.0). Counts are reaction-term mentions, not deduplicated individual cases. No lot/batch field.

Search Lareb (Netherlands) →

System	Region	Lot data
VAERS	United States	Lot data
Canada Vigilance	Canada	No public lot field
JADER (PMDA, Japan)	Japan	No public lot field
Lareb (Netherlands)	Netherlands	No public lot field
EudraVigilance	European Union	No public lot field
VigiAccess (WHO)	Global	No public lot field
Yellow Card (UK)	United Kingdom	No public lot field
DAEN (Australia)	Australia	No public lot field

All global data sources → · Data schemas →

Active Pharmacovigilance (Defined-Population Surveillance)

Curated findings for Varicella (Varivax) / context with MMRV 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

CDC Vaccine Safety Datalink (VSD)

Outcome: Febrile seizures (especially MMRV first dose) and other pre-specified outcomes

Tier 2 ● Signal confirmed (true association)

When varicella is combined as MMRV for the first toddler dose, VSD confirmed higher febrile-seizure risk versus separate injections. Standalone varicella vaccine does not drive that specific combination finding; see MMR page for MMRV detail.

Population

Toddlers receiving varicella-containing vaccines

Risk interval

5–12 days for febrile seizure analyses with measles-containing vaccines

Comparison

Separate MMR + varicella

Evaluation period

Post-licensure combination era

Method

RCA and observational studies (including MMRV combination analyses)

Related passive AE category on this page: Neurological (see multi-system charts above — not additive with active rates).

Sources: Klein NP et al. Pediatrics 2010 — MMRV febrile seizures

Record last reviewed: 2026-07-10

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

Rank-aggregated VAERS signal detection (rankv)

The table below lists vaccine–event pairs that were detected as disproportionality signals by all four base methods used in rankv (GPS, PRR, ROR, BCPNN) on multi-decade VAERS data, then ordered by rank aggregation (Borda average rank; related to the Spearman/GA top-list approach in the rankv paper).

Agg. rank	VAERS product	Preferred term (event)	N	Method ranks (GPS / PRR / ROR / BCPNN)
261	VARICELLA (NO BRAND NAME)	Varicella post vaccine clinical-coded PT	93	GPS rank 247 (EBGM=6.75); PRR rank 248 (PRR=11.2307); ROR rank 248 (ROR=11.3313); BCPNN rank 224 (IC_LB=2.9979)
282	VARICELLA (VARIVAX)	Abortion clinical-coded PT	104	GPS rank 268 (EBGM=6.36); PRR rank 257 (PRR=11.0222); ROR rank 258 (ROR=11.0279); BCPNN rank 284 (IC_LB=2.426)

Showing up to 15 pairs for this page (clinical-coded terms listed first). Full processed tables: rankv_signals.json.

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.

▶ Strong Evidence

Injection site reactions: 20–30%. Strong
Fever: 10–15% (Varivax alone); 38–40% (MMRV). Strong
Varicella-like rash: 3–5% (mild; may be infectious). Strong
Febrile seizures (MMRV): ~1 per 1,250 doses in the 5–12 day window. Strong
Herpes zoster (vaccine strain): 18–26 per 100,000 person-years; lower than after wild-type infection. Strong

▶ No Causal Association

Autism: No association. MMRV contains the same MMR components studied extensively for autism (see MMR page). No Association

5. Disease Prevention Benefits

Metric	Pre-Vaccine Era (~1990–1994)	Post-Vaccine Era (2-dose, ~2010+)
Varicella cases (annual)	~4 million	>97% reduction; varicella is no longer endemic in the U.S.
Hospitalizations (annual)	~10,500–13,500	>90% reduction; almost exclusively unvaccinated or immunocompromised
Deaths (annual)	~100–150	<10/year
Herpes zoster in children	~74 per 100,000	~18–26 per 100,000 (vaccine-strain); overall pediatric zoster has declined

Source: CDC Pink Book; MMWR. The introduction of a second dose in 2006 effectively addressed breakthrough varicella observed with the 1-dose schedule. Herd immunity has been observed.

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

Varicella vaccine has >30 years of post-licensure data. The safety profile is well-characterized. The primary safety concern is the MMRV-associated febrile seizure risk, which is product-specific and mitigated by ACIP's preference for separate MMR + varicella administration for dose 1. Breakthrough varicella with the 1-dose schedule was addressed by the 2006 2-dose recommendation. Long-term data indicate that vaccine-strain zoster is less common than zoster after wild-type infection.

8. International Surveillance & Global Data

Quick links to public pharmacovigilance databases and trial registries relevant to Varicella 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 Varicella (Chickenpox) 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

IOM. Adverse Effects of Vaccines: Evidence and Causality. National Academies Press; 2012.
Klein NP, et al. Measles-mumps-rubella-varicella combination vaccine and the risk of febrile seizures. Pediatrics. 2010;126(1):e1–e8.
CDC. Pink Book — Varicella chapter. cdc.gov/pinkbook
CDC. VSD. cdc.gov/vaccine-safety/about/vsd.html
CDC/FDA. VAERS. vaers.hhs.gov

1. Basic Information

Disease Protected Against

CDC Schedule (U.S., 2025)

Documented Adverse Events (HRSA VICP)

WHO Causality Assessment Methodology

Important Notes

Ingredients (Package Insert)

Antigens

Adjuvants

Preservatives

Excipients & residuals

Causality assessment & potential mechanisms

2. Pre-Licensure Clinical Trial Data

Licensure trial design (ICAN / OpenVAERS)

MMRV Febrile Seizure Finding

3. Post-Licensure Safety Data

VAERS Reporting Data — Halma & Varon (2025), DARE-SAFE

Passive Surveillance: AE Type Breakdown (Multi-System)

VAERS (United States)

Canada Vigilance (Canada)

JADER (PMDA, Japan)

EudraVigilance (EU)

SurVigilance: VigiAccess · Lareb · DAEN · DMA · Medsafe

VigiAccess (WHO)

Lareb (Netherlands)

DAEN (Australia)

DMA (Denmark)

Medsafe (New Zealand)

Pharmacovigilance Lot Signal Detection — Hypothesis-Generating Only

Other Pharmacovigilance Systems

Canada Vigilance (Health Canada)

JADER (PMDA, Japan)

VigiAccess (WHO)

Lareb (Netherlands)

Active Pharmacovigilance (Defined-Population Surveillance)

CDC Vaccine Safety Datalink (VSD)

4. Documented Adverse Events

Rank-aggregated VAERS signal detection (rankv)

▶ Strong Evidence

▶ No Causal Association

5. Disease Prevention Benefits

Disease Burden Over Time

7. Evidence Summary

8. International Surveillance & Global Data

9. Curated Adverse Event Literature

10. Key References

Part of the Open Source Medicine Foundation Network