Efficacy of hepatitis A vaccine in prevention of secondary hepatitis A infection: a randomised trial

Background Hepatitis A vaccination stops outbreaks of hepatitis A infection , but its efficacy against infection after exposure has not been proven. We investigated the use of hepatitis A vaccine to prevent secondary infection s with hepatitis A virus (HAV). Methods We did a randomised controlled trial of hepatitis A vaccine in hous ehold contacts of people with sporadic HAV infection (index cases). Househo lds (index cases and contacts) were randomly assigned to the vaccine group or unvaccinated group, according to the study week in which they were enrol led. All household contacts in the vaccine group received vaccination at th e time of entry to the study. Findings During 45 days of follow-up, secondary infection had occurred in t en (13.3%) of 75 households (two families had two cases each) in the untrea ted group and in two (2.8%) of 71 households in the vaccine group. The prot ective efficacy of the vaccine was 79% (95% CI 7-95). The number of seconda ry infections among household contacts was 12 (5.8%) of 207 in the unvaccin ated group and two (1.0%) of 197 in the vaccinated group. Therefore, 18 ind ividuals needed to be vaccinated to prevent one secondary infection. Interpretation Hepatitis A vaccine is effective in the prevention of second ary infection of HAV and should be recommended for household contacts of pr imary cases of HAV infection.