This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax email@example.com with numerous contributions by others.
Firm data on long-term protection are limited because the vaccine was
under investigation for only 4 years before being approved in
1995. Estimates of antibody persistence derived from kinetic models of
antibody decline suggest that the protective levels of anti-HAV could
persist for at least 20 years.