Hepatitis A Vaccine

Hepatitis A vaccine protects against acute hepatitis A by stimulating the production of neutralising IgG antibodies against the HAV capsid. The inactivated whole-virion antigen is presented on an aluminium hydroxide adjuvant that enhances and prolongs the antigen depot at the injection site and recruits antigen-presenting cells, supporting a robust T-cell-dependent B-cell response with memory.

Mechanism of Action

• Antigen presentation and B-cell activation: the inactivated whole-virion antigen is engulfed by dendritic cells and macrophages at the injection site, processed, and presented on MHC-II to CD4⁺ helper T cells. These in turn provide help to HAV-specific B cells, driving class-switching and affinity maturation toward neutralising IgG and the generation of memory B cells.
• Aluminium hydroxide adjuvant: creates an antigen depot, activates the NLRP3 inflammasome, and recruits innate immune cells — substantially increasing antibody titre and persistence compared with unadjuvanted protein.
• Humoral protection: anti-HAV IgG generated after vaccination neutralises HAV virions at the gut–blood interface and within the bloodstream, preventing systemic infection.
• Onset: anti-HAV IgG above the protective threshold (~10–20 mIU/mL by commercial assay) is reached in approximately 95% of recipients within 2 weeks of the first dose, and in essentially all healthy recipients within 4 weeks.
• Booster and duration: a single dose provides protection for at least 1 year; a second dose 6–12 (up to 18 in some schedules) months after the first produces antibody titres that mathematical models predict will persist for at least 20–25 years and probably for life.

Pharmacokinetics

Conventional pharmacokinetics do not apply. Relevant immunological parameters:

• Seroconversion: 95–100% after a single dose by day 28 in healthy adults; >99% after the second dose.
• Geometric mean titres: rise substantially after the booster (4- to 10-fold), supporting durable memory.
• Duration of protection: predicted ≥20–25 years from current cohort data; lifelong protection plausible.

• Pre-travel prophylaxis: travellers to any country with intermediate or high HAV endemicity (most of Africa, Asia, Latin America, parts of Eastern Europe) — first dose ideally ≥2 weeks before exposure, though even later administration is worthwhile.
• Occupational exposure: laboratory workers handling HAV, sewage and wastewater workers, food handlers in selected settings, healthcare workers in some regions.
• Risk groups: men who have sex with men (MSM), people who inject drugs (PWID), individuals with chronic liver disease, hepatitis B or C co-infection (where acute HAV super-infection causes worse outcomes), recipients of blood-product replacement therapy, residents and staff of certain institutional settings.
• Household and sexual contacts of acute HAV cases: post-exposure vaccination within 14 days of exposure is effective; for older adults and immunocompromised contacts, co-administration with human normal immunoglobulin may be recommended.
• Outbreak control: ring vaccination in defined outbreak settings.
• Routine childhood immunisation: in many countries with intermediate endemicity (e.g., Argentina, Israel, US, parts of Europe) — included in the national immunisation schedule from age 12 months.

• Hypersensitivity to hepatitis A vaccine, any of the excipients (including aluminium, polysorbate 20), or to neomycin (trace residue).
• For Twinrix specifically: hypersensitivity to yeast-derived products (recombinant hepatitis B antigen is yeast-produced).
• Acute febrile illness or active uncontrolled infection — defer until resolution.

Very common (≥1/10): injection-site soreness, erythema, induration, headache, irritability (children), fatigue, malaise.

Common (≥1/100 to <1/10): low-grade fever, myalgia, arthralgia, nausea, decreased appetite (children), diarrhoea, vomiting.

Uncommon (≥1/1,000 to <1/100): pruritus, rash, urticaria, lymphadenopathy, dizziness, paraesthesia.

Rare to very rare: hypersensitivity reactions including anaphylaxis (very rare), serum-sickness-like reactions, neurological events (Guillain-Barré syndrome, optic neuritis, encephalomyelitis — temporal association reported, causality not established), thrombocytopenia, vasculitis.

Combination products (Twinrix) carry the additive reactogenicity profile of both component vaccines but are no more reactogenic than separate administration.

• Other vaccines: hepatitis A vaccine can be co-administered with most other inactivated and live vaccines at separate sites with separate syringes. Common co-administrations include hepatitis B, typhoid (oral or injectable), yellow fever, rabies, meningococcal vaccines, MMR, varicella, and routine childhood immunisations.
• Immunoglobulins: simultaneous administration of human normal immunoglobulin (e.g., for post-exposure prophylaxis or other indications) does not abolish the response but may modestly reduce final antibody titres; combined use is appropriate in older or immunocompromised post-exposure contacts.
• Immunosuppressive therapy (DMARDs, biologics, high-dose corticosteroids, chemotherapy, transplantation): may attenuate vaccine response; vaccinate ahead of planned immunosuppression where possible; consider post-vaccination serology to confirm response in patients who cannot defer therapy.
• No clinically significant small-molecule interactions.

No food, alcohol, or driving interactions.

Administer intramuscularly into the deltoid muscle in adults and older children, or into the anterolateral thigh in infants and toddlers. Do not inject into the gluteal region (reduced immune response). Subcutaneous administration is acceptable in patients with bleeding disorders.

Monovalent Hepatitis A Vaccine (Havrix, Vaqta, Avaxim)

• Adults (≥19 years, Havrix 1,440 EL.U. or Vaqta 50 U or Avaxim 160 U): single 1.0 mL dose at month 0, followed by booster at month 6–12 (up to 18 months).
• Paediatric (1–18 years, Havrix 720 EL.U. or Vaqta 25 U or Avaxim 80 U): single 0.5 mL dose at month 0, followed by booster at month 6–12 (up to 18 months).
• A single dose offers good protection from approximately 2 weeks post-dose; the booster ensures durable protection.

Twinrix (HAV + Hepatitis B) — Adults and Adolescents ≥16 Years

• Standard schedule: 0, 1, and 6 months (three doses of 1.0 mL).
• Accelerated schedule: 0, 7, 21–30 days, with a booster at 12 months (four doses total) — useful for time-pressed travellers.

Twinrix Junior / Paediatric — Children 1–15 Years (Region-Dependent Age Range)

• Standard schedule: 0, 1, and 6 months (three doses of 0.5 mL).

Vivaxim / ViATIM (HAV + Vi Polysaccharide Typhoid) — Adults

• Single 1.0 mL dose: provides protection against both diseases for combined travel purposes; booster doses required at intervals appropriate to each component (hepatitis A booster at 6–12 months; typhoid revaccination every 3 years).

Post-Exposure Prophylaxis

• Healthy individuals aged 12 months to 40 years within 14 days of HAV exposure: a single dose of monovalent vaccine is recommended.
• Adults >40 years, immunocompromised individuals, or those with chronic liver disease: vaccine plus human normal immunoglobulin (separate site) within 14 days of exposure.

Renal/Hepatic Impairment

No dose adjustment.

Missed Dose

If the booster dose is delayed beyond the schedule, give it as soon as possible — the first dose does not need to be repeated, regardless of the elapsed interval.

Cold-Chain Handling

Maintain 2–8 °C throughout distribution, storage, and patient handling. Do not freeze — freezing destroys the aluminium-adjuvanted vaccine. Discard if the product has been frozen or if cold chain has been compromised beyond the manufacturer-specified limits.

Pre-Vaccination Serology

Routine pre-vaccination serology is not cost-effective in most populations and is not recommended. In selected adults from highly endemic regions, prior natural HAV infection (anti-HAV IgG positive) is common — pre-vaccination testing may be considered to avoid unnecessary vaccination in this group.

Post-Vaccination Serology

Not routinely indicated in immunocompetent recipients. Consider in immunocompromised individuals (e.g., people with HIV, solid-organ transplant recipients, patients on biologics) to confirm protection; revaccination or extended dosing may be needed.

Pregnancy and Lactation

• Pregnancy: inactivated vaccine — generally considered safe; recommended where indication exists. No teratogenic signals from accumulated data.
• Breastfeeding: compatible.

Immunocompromised Hosts

Response may be attenuated. Consider post-vaccination serology and additional doses if titres are below the protective threshold.

Patient Counselling

Even after vaccination, travellers should observe standard food and water hygiene (avoid uncooked seafood, peel fruit, drink bottled or boiled water, avoid ice in high-risk regions). Vaccine protection is high but not absolute.

Anaphylaxis Preparedness

Standard immunisation safety precautions: observation for 15 minutes after administration; epinephrine and resuscitation equipment readily available.

Effect on Driving

No effect.

Refrigerate at 2–8 °C in the original carton; do not freeze; protect from light. Stable for the labelled shelf life under proper storage. If accidentally frozen, discard. Some products tolerate brief excursions to room temperature; refer to the specific product Stability Data Statement.

Typically 36 months from manufacture for unopened pre-filled syringes and vials. Do not use after the expiry date printed on the packaging.

Prescription required (Rx) in most jurisdictions; included in many national immunisation programmes for routine childhood, occupational, and travel indications. Cold-chain logistics required for distribution.