This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax email@example.com with numerous contributions by others.
A single dose of the vaccine induced antibodies in 88% to 96% of
subjects by two weeks and in 97% to 100% by one month. Completion of
the full vaccine schedule is recommended to ensure high antibody
levels and long-term protection. Efficacy trials in children and
adolescents show it is 94% (or more) effective against endemic
hepatitis A virus.
According to the AAP recommendation for hepatitis A, on December,
1996: "Clinical studies suggested a possible herd-immunity effect if
more than 80% of the estimated susceptible individuals were
vaccinated. A single dose of Havrix in Alaskan native villages with
endemic HAV disease resulted in a dramatic decrease in cases within 8
weeks of vaccination. A similar abrupt decrease in HAV cases was
observed after two doses of vaccine in two Slovak Republic villages
experiencing a large community outbreak. In the Vaqta trial in New
York State, no cases of clinical and confirmed hepatitis A occurred in
vaccine groups more than 21 days after the first dose, and the
calculated protective efficacy was 100%. "