Baseline epidemiological studies for a hepatitis B vaccine trial in Kangwane.

Hepatitis B markers were determined by radioimmunoassay of serum samples from 1 495 Black subjects representative of the resident population of Kangwane, a rural area with a high incidence of chronic liver disease and hepatocellular carcinoma. Pregnant women formed an important part of the study group, since it was intended to assess the frequency of perinatal transmission and the passive immunity of their infants, two factors which would markedly influence an infant immunization programme. A high overall marker positivity rate was found, indicating that hepatitis B is endemic. The hepatitis B surface antigen (HBsAg) carrier rate was 14,6% in adult males and 4,6% in adult females, while 82.6% of adult males and 69,4% of adult females were positive for at least one marker, indicating that infection had been present at some stage. Of infants under 1 year of age 34,5% were positive for antibodies to HBsAg (anti-HBs), compared with 9,3% at 13-24 months, which indicates that transplacental transfer of anti-HBs is frequent. Other markers were acquired even in the 1st year of life, with the sharpest increase at 3-11 years. Perinatal transmission was not common, however, and horizontal transmission during early childhood seemed to play an important role. It was concluded that the risk and frequency of infection justified a vaccine trial in this population and that the target group for vaccination should be infants under 1 year of age.