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During a large community-wide outbreak of hepatitis A in two adjoining villages in Slovakia with a total of 5,000 inhabitants we administered to schoolchildren the first commercially available vaccine against hepatitis A (HAVRIX, Smith-Kline Beecham Biologicals, Rixensart, Belgium) in an attempt to control the progress of the epidemic. Soon after the start of the vaccination programme, an abrupt decrease in the occurrence of cases in the school was observed. In the village school with 624 schoolchildren, 404 had received a first dose of 360 enzyme-linked immunosorbent assay (ELISA) units (EL.U) and 373 a second dose 1 month later. Subsequent to the start of vaccination there were eight clinical cases of hepatitis A among the 157 children without a history of hepatitis A who remained unvaccinated and only 1 case in the vaccinated school children, giving attack rates of 5.1% and 0.25% in the two groups, respectively. Among the remaining 63 children, one was found seropositive when screened and 62 had a history of hepatitis A at the start of the vaccination programme. These 63 children were not offered vaccine. No cases occurred in that group. During the epidemic, three cases occurred an average of 20 days following its administration among 19 children who received immune globulin (IG). Cases in the whole population of the villages also ceased soon after the vaccination of the children had started. The vaccine was found more effective than postexposure IG in interrupting the epidemic in the whole community.