Evidence for shifting hepatitis B virus population epidemiology after nearly two decades of universal hepatitis B vaccination in South Africa

Abstract

Background: The heptitis B vaccine has been part of the South African Expanded Programme on Immunization since April 1995 but its long-term impact remains unknown. Methods & Materials: This study tested 1206 sera collected frompatients aged1 to25years fromvarioushealth facilities across the country for HBV serologicalmakers andHBVDNA. Based on the year thevaccinewas introduced, sampleswere stratifiedbyage into preand post-vaccine introduction populations, which were then compared for evidence of immunity and chronic carriage using the chi-square test.WhereHIV statuswas known, subset analyseswere performed. Results: Immunity to HBV infection increased from 13.0% in the preto 57.0% in the post-vaccine introduction population (p<0.001). This decreased with increasing age within the postvaccine introduction population (76.1% for 1-5 year olds, 50.0% for 6-10 year olds and 46.3% for 11-16 year olds). In addition HBV chronic carriage was significantly (p=0.003) reduced in the post(1.4%) compared to the pre-vaccine introduction population (4.2%) but increased with increasing age (0.5% in 1-5 year olds, 1.3% in 6-10 year olds and 2.2% in 11-16 year olds). The difference in prevalence of activeHBV infection in the serologically exposed preversus post-vaccine introduction populations was not statistically significant. Subset analyses showed that evidence of immunitywas significantly (p<0.001) higher in the HIV negative compared to the HIV positive subset in both populations. Conclusion: Universal hepatitis B vaccination has been a remarkable success, with a significant increase in immunity to HBV infection. The observation that HBV chronic carriage increases as immunitywanes over time calls into questionwhether the timehas come to consider a pre-adolescence vaccine booster dose policy.