The epidemiology and molecular characterstics of hepatitis B virus infection in children from a hyperendemic area of South Africa, including a field trial of the hepatitis B immunization programme and its impact on infection in this population

Abstract

Three studies were done in children from the Eastern Cape Province of South Africa, an area highly endemic for hepatitis B virus (HBV) infection. The objective of the first study was to investigate the epidemiology and age of acquisition of HBV infection in a community based, age stratified sample of children from 0-6 years of age (n=2299), to provide a pre-immunisation baseline measure of this infection in the population targeted for HBV immunisation in South Africa. The results suggest that there is a significant burden of HBV infection in the population targeted for immunisation (overall, 10.4% HBsAg positivity and 15.7% positive 61-72 month age group) with a high rate of chronic carriers in the early age groups of 0-6 (8.1%) and 7-12 (8.9%) months. In the second study the HBV genotypes in a randomly selected group of chronically infected individuals from the same population (n=57) was determined. The aim was to supply information regarding the naturally circulating HBV genotypes in children from this area similarly, to provide baseline information to enable the future detection of escape mutants after low dose HBV immunisation had been introduced. The predominant HBV genotype identified was A' (85.7%), genotype D was found in 11.4% and A in 2.9% of the amplified specimens. These findings suggest a unique circulation of HBV genotypes in the Eastern Cape compared to the other genotypes currently identified in South Africa. In the final study, the effectiveness under field conditions of a low-dose plasma derived (LDPD) HBV vaccine chosen for the EPI programme in South Africa was assessed. Children presenting for routine immunisations at 6 weeks of age were randomly assigned to receive either LDPD HBV vaccine through the normal clinic route (n=119) or a recombinant paediatric HBV vaccine (n=108) given under controlled conditions. Both vaccines were administered at 6 ,1 0 and 14 weeks of age. At one month after the last vaccination, LDPD vaccine induced levels of anti-HBs s 10 mlU/ml in 42.2% (95% Cl 27.99-57.77) of immunised infants whereas recombinant vaccine induced protective antibody levels in 88.6% (95% Cl 74.66-95.74) of immunised infants. These results suggest a poor performance of the LDPD vaccine under field conditions in Eastern Cape infants.