1. Basic Information
Disease Protected Against
Hepatitis A is an acute liver infection caused by hepatitis A virus (HAV), transmitted via the fecal-oral route. Illness ranges from asymptomatic (especially in children <6) to acute liver failure (rare; ~0.3–0.5% case-fatality overall; higher in older adults). Unlike hepatitis B and C, HAV does not cause chronic infection. Before vaccination, the U.S. experienced cyclical epidemics every 10–15 years. The last major epidemic was 1995–1996. Universal childhood vaccination was recommended in 2006.
CDC Schedule (U.S., 2025)
| Dose | Age | Notes |
|---|---|---|
| Dose 1 | 12–23 months | First dose recommended at 1 year of age |
| Dose 2 | ≥6 months after dose 1 | 2-dose series. Both Havrix and Vaqta are interchangeable. |
Source: CDC ACIP, 2025 schedule. Catch-up vaccination recommended for children 2–18 years not previously vaccinated. Also recommended for adults at increased risk and anyone seeking protection.
2. Pre-Licensure Clinical Trial Data
Havrix (GSK) was licensed in 1995; Vaqta (Merck) in 1996. Both are inactivated whole-virus vaccines. The pivotal trial for Vaqta enrolled ~1,000 children in a community with high HAV incidence and demonstrated ~100% efficacy. Havrix efficacy was demonstrated in ~40,000 Thai children (~94–97% efficacy).
| Metric | Data |
|---|---|
| Pre-licensure safety database (combined) | ~10,000+ across both products |
| Efficacy | ~94–100% in pivotal trials; seroprotection >97% after 2 doses |
| Most common reactions | Injection site pain (~20–50%), erythema (~10–20%), fever (~5–10%), headache (~5–15%) |
Key Limitations
- Pre-licensure trial sizes were modest by modern standards.
- Duration of protection is not fully characterized beyond ~20–25 years of follow-up data, though modeling suggests long-term protection.
3. Post-Licensure Safety Data
Hepatitis A vaccines have >30 years of post-licensure safety data. VSD and VAERS surveillance have not identified unexpected safety signals. The vaccine is one of the least reactogenic on the pediatric schedule aside from injection site reactions. IOM (2012) did not identify safety concerns specific to hepatitis A vaccine. No confirmed post-licensure safety signals have been identified.
⚠ Critical Caveat
VAERS data represent unverified reports. A report to VAERS does not mean the vaccine caused the event.
4. Documented Adverse Events
▶ Strong Evidence
- Injection site reactions: Pain (20–50%), erythema (10–20%). Self-limited. Strong
- Fever: 5–10% (low-grade). Strong
- Anaphylaxis: ~1 per million doses. Strong
5. Disease Prevention Benefits
| Metric | Pre-Vaccine Era | Post-Vaccine Era |
|---|---|---|
| Annual HAV cases (U.S.) | ~30,000–60,000 (1980s–1990s); ~57,000 in the 1995 peak | ~3,000–6,000 reported cases (2015–2020); >95% reduction from peak |
| HAV incidence (children) | Highest incidence in children 5–14 years | >98% reduction in vaccinated age cohorts |
| HAV-related mortality | ~100–150 deaths/year | <50 deaths/year |
Source: CDC Pink Book; MMWR. However, the U.S. has experienced large person-to-person outbreaks since 2016 among unvaccinated adults (homeless populations, persons who inject drugs, MSM), reminding that population immunity depends on maintaining high vaccination coverage.
6. Evidence Summary
Hepatitis A vaccine has a well-established safety profile with >30 years of post-licensure data. It is among the least reactogenic vaccines on the pediatric schedule. No significant safety signals have been identified. Effectiveness is high (>94%). The main evidence gap is the duration of protection beyond 25 years, though immunologic memory is expected to provide long-term protection even after antibody levels wane.
7. Key References
- IOM. Adverse Effects of Vaccines: Evidence and Causality. National Academies Press; 2012.
- CDC. Pink Book — Hepatitis A chapter. cdc.gov/pinkbook
- Innis BL, et al. Protection against hepatitis A by an inactivated vaccine. JAMA. 1994;271(17):1328–1334. (Havrix pivotal trial)
- CDC. VSD. cdc.gov/vaccine-safety/about/vsd.html
- CDC/FDA. VAERS. vaers.hhs.gov