How long does the hepatitis A vaccine provide protection?
Research has indicated that the hepatitis A vaccine is highly effective. Most people will develop protective levels of antibody within one month after a single dose of vaccine. And after two doses, the protection may be 20 years or more.
According to the World Health Organization:
The protective efficacy of the vaccine against clinical disease was determined in two large trials. Among almost 40 000 Thai children aged 1-16 years the protective efficacy was 94% (95% confidence intervals: 82%-99%) following two doses of vaccine given one month apart. Among approximately 1000 children aged 2-16 years, living in a highly disease-endemic community in the United States, the efficacy of one dose of vaccine was 100% (95% confidence intervals: 87%-100%).Source: Immunization, Vaccines and Biologicals, World Health Organization (WHO), www.who.int/vaccines/en/hepatitisa.shtml.
Although one dose of vaccine provides at least short-term protection, the manufacturers currently recommend two doses to ensure long-term protection. In studies evaluating the duration of protection of two or more doses of hepatitis A vaccine, 99%-100% of vaccinated individuals had levels of antibody indicative of protection five to eight years after vaccination. Kinetic models of antibody decay indicate that the duration of protection is likely to be at least 20 years, and possibly lifelong. Post-marketing surveillance studies are needed to monitor vaccine-induced long-term protection, and to determine the need for booster doses of vaccine. This is especially true in areas of low disease endemicity where natural boosting does not occur.