Effectiveness of hepatitis-B vaccination in Ivory Coast: the case of the Grand Bassam health district.

ABSTRACT

Ivory Coast has a high prevalence of infection with hepatitis B virus (HBV). The effects of a control programme based on the anti-HBV vaccine, which has formed part of the national Expanded Programme on Immunization (EPI) since 2000, have recently been evaluated in the country, for the first time. In this, cross-sectional investigation, two-stage cluster sampling stratified by age was used to assess the impact of the programme of universal childhood HBV vaccination in the Grand Bassam health district. The seroprevalences of carriage of the HBV surface antigen (HBsAg) and of antibodies to this antigen (HBsAb) and to the core antigen of HBV (HBcAb) were estimated among children aged 12-59 months and their mothers. Serology was successful for 1038 children (of 1172 in the original sample) and 836 mothers. Of the children enrolled, 46.8% had had a standard vaccination (completed before the age of 6 months, with the correct schedule), 4.6% had had no vaccination against HBV, and the rest had received incomplete or incorrectly timed vaccination. The prevalence of HBsAg carriage was 0.7% among the tested children and 9.9% among the tested mothers. The prevalence of seroprotection (i.e. an HBsAb titre of >10 mIU/ml), which was 74.2% overall, was strongly correlated with the number of vaccination doses, ranging from 16.7% in the unvaccinated infants to 85.5% in the children who had each received four doses. Circulation of the virus (indicated by seropositivity for HBcAb) was much higher among the unvaccinated children (10.4%) than the fully vaccinated ones (2.9%). The prevalences of both HBsAg and HBcAb were higher in rural areas, where vaccine coverage was relatively low, than in the urban areas. It appears that HBV vaccine is highly effective within the framework of the EPI in Ivory Coast, where it has already had a positive impact in reducing HBsAg carriage among children under 5 years of age. Improving vaccination coverage in the rural areas of the country is now a public-health priority.