What is the Hepatitis A (Hep A) vaccine?

From the Guidelines

The Hepatitis A vaccine is recommended for all individuals at risk, including children starting at age 12 months, travelers to countries where Hepatitis A is common, men who have sex with men, people with chronic liver diseases, and those who use drugs, as it provides long-term protection against the Hepatitis A virus with over 95% efficacy. The vaccine is typically given as two doses, separated by 6-18 months, and for adults, common brands include Havrix and Vaqta, with standard adult dosing being 1.0 mL intramuscularly, as stated in the study by 1. Children receive a lower dose (0.5 mL for ages 1-18), and for those needing immediate protection, such as last-minute travelers, the first dose can provide effective short-term protection, as noted in the study by 1. The vaccine works by introducing inactivated (killed) Hepatitis A virus, which cannot cause infection but stimulates the immune system to develop antibodies against the virus. Some key points to consider when administering the Hepatitis A vaccine include:

• The vaccine is highly effective in preventing Hepatitis A infection, with over 95% of recipients developing protective antibodies after completing the series, as reported in the study by 1.
• The vaccine provides long-term protection, likely lasting for decades, as stated in the study by 1.
• Side effects are generally mild and may include soreness at the injection site, headache, or fatigue, as noted in the study by 1.
• The Advisory Committee on Immunization Practices (ACIP) recommends the use of Hepatitis A vaccine for postexposure prophylaxis and for preexposure prophylaxis for international travel, as stated in the study by 1. It is essential to follow the recommended vaccination schedule and dosing to ensure optimal protection against Hepatitis A virus, as emphasized in the study by 1.

From the Research

Hepatitis A Vaccine Efficacy

• The hepatitis A vaccine is immunogenic and protective in children and adults, with a single dose inducing antibody in 88% to 96% of subjects by 2 weeks and 97% to 100% by 1 month 2.
• Completion of the full vaccine schedule is recommended to assure high antibody titers and likely long-term protection 2.
• The vaccine has been shown to be effective in preventing hepatitis A infection, with a study demonstrating that it protected against subsequent hepatitis A virus (HAV) disease occurring 21 days after receipt of the dose in a community with endemic hepatitis A infection 2.

Postexposure Prophylaxis

• Immune globulin is recommended for postexposure prophylaxis, as vaccine has not yet been demonstrated to be protective for this purpose 2.
• However, a study comparing hepatitis A vaccine with immune globulin for postexposure prophylaxis found that both provided good protection after exposure, with symptomatic infection with hepatitis A virus confirmed in 4.4% of contacts receiving vaccine and 3.3% of contacts receiving immune globulin 3.
• Another study found that administration of human serum immune globulin (Ig) is an effective means of protecting individuals against hepatitis A virus (HAV) infection and disease, with Ig providing approximately 90% efficacy in preventing hepatitis A 4.

Safety and Immunogenicity

• A study on the safety, tolerability, and immunogenicity of an inactivated hepatitis A vaccine found that it was well-tolerated and immunogenic, with anti-HAV seroconversion occurring in 100% of recipients after a single dose 5.
• The study also found that the vaccine provided long-term protection, with anti-HAV geometric mean titers (GMT) persisting in all recipients up to week 24 5.
• A systematic review of published studies on the use of hepatitis A vaccine for post-exposure prophylaxis in individuals over 40 years of age found that immunogenicity of the vaccine may be diminished in older adults, especially in the very oldest age groups 6.

Recommendations for Use

• The major pediatric indications for hepatitis A vaccine are travelers to areas with intermediate to high rates of endemic hepatitis A, children living in defined and circumscribed communities with high endemic rates or periodic outbreaks of HAV infection, and patients with chronic liver disease 2.
• The vaccine is recommended for postexposure prophylaxis in individuals over 40 years of age, with administration as soon as possible within 14 days after exposure to achieve the best possible immune response 6.