[Infectiousness of a 4-year-old hepatitis B virus carrier and and active immunization of his playmates].

Screening the contacts of a 33-year-old father with acute hepatitis B virus (HBV) infection revealed that this four-year-old adopted son was a persistent HBV carrier with massive viremia. The infection did not occur until they had been in contact for three and a half years. Serological findings from the wife, daughter and one of the children's playmates indicated previous hepatitis B infections which had been healed with a positive immune response. It is highly probable that the son induced these infections. The history of the child with persistent HBV infection as well as the clinical course indicate a perinatally acquired HBV infection. To prevent this infection from spreading further, seven playmates with an average age of five years were actively vaccinated against hepatitis B. The success of this vaccination was compared to a control group of adults. After applying the vaccine three times at four-week intervals, the seroconversion to anti-HBs occurred earlier and the antibody titres were higher in the children. 71% of the children had produced anti-HBs after the first vaccination compared to only 13% of the adults (mean age: 33 years). The rate of seroconversion was 100% for the children after the second vaccination, compared to only 93% for the adults four to six weeks after the third vaccination.