Hepatitis A Vaccine

Type and Preparation

• Harrison's Principles of Internal Medicine 22E, p. 2705

Immunogenicity and Efficacy

• 94-100% of adults, adolescents, and children achieve protective antibody levels 1 month after a single dose.
• Havrix showed 94% efficacy after two doses in a large double-blind RCT.
• Vaqta showed 100% efficacy after one dose in a placebo-controlled RCT.
• Twinrix achieved 99.6% seroprotection for HAV at 1 month post-final dose.
• Protective levels of anti-HAV persist in >97% of vaccinees 15-17 years after primary vaccination, with mathematical models predicting protection lasting at least 20 years.
• Booster doses are not required based on long-term follow-up data.
• Yamada's Textbook of Gastroenterology 7e, p. 1903

Vaccine Schedule

• The primary inoculation provides adequate protection beginning 4 weeks after the dose.
• For international travelers, vaccines offer protection starting within weeks; the full 2-dose series provides durable immunity.

Indications (Who Should Be Vaccinated)

• All children aged 12-23 months
• Travelers to or workers in countries with high or intermediate HAV endemicity
• Persons anticipating close contact with international adoptees (within 60 days of arrival from high-endemicity countries)
• Men who have sex with men (MSM)
• Users of injection and non-injection drugs
• Persons with chronic liver disease (including chronic hepatitis B or C)
• Persons with clotting factor disorders
• Laboratory workers with HAV-infected primates or HAV research materials
• Persons experiencing homelessness (>1 year of age)
• Anyone wishing to obtain immunity
• Yamada's Textbook of Gastroenterology 7e, Box 86.1

Post-Exposure Prophylaxis (PEP)

• Hepatitis A vaccine (not immune globulin) is now the preferred PEP for all persons aged ≥12 months, administered within 14 days of exposure.
• For immunocompromised adults and persons with chronic liver disease: administer both hepatitis A vaccine AND immune globulin (IG) 0.1 mL/kg at different IM sites.
• For infants <12 months: use IG (0.1 mL/kg) since vaccine is not indicated for this age group.
• For persons with contraindications to vaccination: use IG only.
• Harrison's Principles of Internal Medicine 22E, p. 2705

Pre-Exposure Prophylaxis for Travel

• Hepatitis A vaccine is the preferred approach for travelers to endemic areas.
• Infants aged 6-11 months traveling internationally should receive the vaccine, but this dose is not counted toward the universal 2-dose childhood schedule.
• If vaccine is contraindicated: IG 0.1 mL/kg (up to 1 month), 0.2 mL/kg (up to 2 months), repeated every 2 months for extended travel.

Passive Immunization (Immune Globulin)

• IG provides 80-90% protection if given within 2 weeks of exposure; later administration attenuates but does not prevent disease.
• Dose: 0.1 mL/kg IM for both pre- and post-exposure prophylaxis.
• Pre-exposure: 0.1 mL/kg (up to 1 month), 0.2 mL/kg (up to 2 months).
• Now largely supplanted by the vaccine except in outbreaks, infants <12 months, and contraindicated patients.

Safety and Adverse Effects

• Overall, the vaccine is very well tolerated.
• Local injection site reactions (pain, redness, swelling) are most common.
• Serious adverse events are rare: anaphylaxis, Guillain-Barre syndrome, brachial plexus neuropathy, transverse myelitis, encephalopathy, and erythema multiforme have been reported but are uncommon.
• Safe in chronic liver disease patients.
• In HIV-positive individuals, response rates range from 47-88% and are lower in those with low CD4 counts.
• Because the vaccine is inactivated, it is expected to be safe in pregnancy (risk to fetus is low), though formal pregnancy safety studies are limited.
• Can be safely co-administered with hepatitis B vaccine without reduced immunogenicity.
• Yamada's Textbook of Gastroenterology 7e, p. 1903

Special Notes

• Pre-vaccination serology is not recommended (adds cost; vaccination carries no risk even if the person is already immune).
• Post-vaccination serology is also not routinely recommended due to high response rates.
• HAV vaccine does not interfere with immune globulin co-administration when given at different sites.
• Live attenuated vaccines should be postponed ~2 weeks if IG was recently given (IG may impair live vaccine response).