Hepatitis A Vaccine Dosing Schedule
For an adult with immunity to hepatitis B (anti-HBs positive) and no hepatitis C infection, administer the standard 2-dose hepatitis A vaccine series: either Havrix at 0 and 6-12 months or Vaqta at 0 and 6-18 months. 1, 2
Standard Dosing Regimens
The two single-antigen hepatitis A vaccines available have the following schedules:
- Havrix (adults): 1.0 mL (1440 ELISA units) intramuscularly, followed by a second 1.0 mL dose administered 6-12 months later 2, 3
- Vaqta (adults): 1.0 mL (50 units) intramuscularly, followed by a booster dose 6-12 months later 3
Both vaccines should be administered in the deltoid muscle in adults 2
Why Not Twinrix?
Do not use Twinrix (combination hepatitis A and B vaccine) in this patient. 4 Since your patient already has documented immunity to hepatitis B (anti-HBs 30.14 IU/mL, which is above the protective threshold of 10 mIU/mL), using Twinrix would expose them to unnecessary hepatitis B antigen without clinical benefit 4
Twinrix is specifically reserved for patients who need protection against both hepatitis A and hepatitis B viruses simultaneously 1, 4
Clinical Context for Hepatitis A Vaccination
Consider hepatitis A vaccination for adults with any of the following indications 1:
- Travel-related: Persons traveling to or working in countries with high or intermediate hepatitis A endemicity 1
- Behavioral risk factors: Men who have sex with men, persons who use injection or noninjection illicit drugs 1
- Occupational exposure: Persons working with HAV-infected primates or with HAV in research laboratory settings 1
- Medical conditions: Persons with chronic liver disease, persons who receive clotting factor concentrates 1
- Homelessness: Added as a routine indication in 2018 1
- General protection: Any person seeking protection from hepatitis A without a specific risk factor 5
Important Administration Details
- Timing of protection: Protective antibody levels are reliably present by 4 weeks after the first dose and may afford protection as soon as 2 weeks after immunization 1
- Route: Administer intramuscularly only; do not give intravenously, intradermally, or subcutaneously 2
- Interchangeability: If the vaccine series is started with one brand, it is preferable to complete with the same brand, but the vaccines are interchangeable if necessary 1
Common Pitfalls to Avoid
- Do not use Twinrix simply because it contains hepatitis A vaccine—this patient does not need hepatitis B vaccination 4
- Do not administer in the gluteal region, as this may result in suboptimal immune response 2
- Do not delay the second dose beyond 18 months, though some flexibility exists in the 6-18 month window 1, 2
- Do not routinely perform pre-vaccination serologic testing for hepatitis A antibodies in young adults, as it is not cost-effective in most populations 1, 6