Sero-epidemiology of hepatitis A in black South African children.

A community-based sero-epidemiological survey was undertaken to determine the age-specific prevalence rates of hepatitis A virus (HAV) infection in a representative sample of 782 urban black children aged from newborn to 13 years. Among children aged 0-5 months, the prevalence of anti-HAV was 68.8% (95% confidence interval (CI) 60.6-77.0%); this fell to a low of 2.5% (CI 0.1-4.9%) in those aged 6-11 months, implying the presence of maternal antibody in the first few months of life. By the age of 2 years, 51.2% (CI 45.7-56.7%) had anti-HAV, by age 4 the prevalence had risen to 81.4% (CI 75.5-87.3%) and by age 6, the prevalence of anti-HAV was almost 100% (CI 90.5-96.7%), reflecting the poor socio-economic and environmental conditions these children live in. The lowest prevalence of HAV infection among urban black South African children was during infancy, before the age at which the incidence rate rose sharply; e.g. 1 out of 5 children was already infected with HAV by its 2nd birthday. Vaccination in infancy will therefore have the biggest impact on the spread of HAV. However, before HAV vaccination in infancy is advocated, vaccine immunogenicity in infancy and the possible detrimental effect of maternal antibodies on the immunogenicity of the vaccine need clarification.