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Hepatitis A vaccine is highly immunogenic with >95% of adults having protective levels of antibody within one month after vaccination and there are data to indicate most vaccinated persons have levels of antibody considered protective within 2 weeks of vaccination. However, it is not known whether everyone with early "protective antibody" levels actually has neutralizing antibody; one study suggested that early after vaccination most antibody is not neutralizing (i.e., actually protective). In addition there are data indicating that the immunogenicity of hepatitis A vaccine is somewhat lower in older persons (age >40 years). Although the package insert for both hepatitis A vaccines indicates that protection is present 2 weeks after vaccination, to be safe, the ACIP has recommended that persons traveling to areas where they will be immediately at risk of HAV infection be vaccinated at least ONE MONTH prior to travel, and depending on the travel destination and situation, administration of immune globulin (IG) in addition to hepatitis A vaccine should be given in order to provide optimum protection. Back to Frequently asked Questions
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