1987 yellow fever epidemics in Oyo State, Nigeria: a survey for yellow fever virus haemagglutination inhibiting antibody in residents of two communities before and after the epidemics.

A survey for yellow fever haemagglutination inhibiting antibody was carried out before and after the 1987 yellow fever epidemics in Nigeria in two localities in Oyo State, namely: Ibadan and Ogbomosho. A total of 129 sera were collected from the two localities before the epidemic. The overall prevalence of yellow fever HI antibody was 37%. A breakdown of positive sera showed that 30/100 and 18/29 sera tested in Ibadan and Ogbomosho respectively were positive. There was a higher prevalence of HI antibody in males (43%) than in females (32%). Of the 48 yellow fever positive sera 23(47%) contained HI antibody to West Nile and 26(52%) to Potiskum viruses. Following the epidemic and the subsequent mass vaccination campaign with the 17D yellow fever vaccine, 200 sera were randomly collected from the same localities. The overall prevalence of yellow fever HI antibody was 67%. The percentage of positive sera in the individual locality was 63% in Ibadan and 73% in Ogbomosho. No statistical difference was observed in the prevalence of yellow fever antibody in both sexes following the yellow fever vaccination campaign (P greater than 0.05). Tests on yellow fever HI antibody positive sera collected after the vaccination campaign showed that 74% and 82% were positive for West Nile and Potiskum HI antibody respectively. Results of this study showed that despite the massive antiyellow fever vaccination campaign there was still a high percentage of seronegative persons in the two communities.