Further observations on 17D-yellow fever vaccination by scarification, with and without simultaneous smallpox vaccination

Abstract

A trial among Nigerian school children is described, in which simultaneous vaccination with scratch 17D yellow fever and smallpox vaccines at separate sites, and two vaccinations with scratch yellow fever vaccine at an interval of 14 days, were performed. For comparison, a group vaccinated by a single yellow fever scratch vaccination, and a group vaccinated with an inert substance, were included, the latter for comparison with the other groups, to investigate the occurrence of reactions. The results showed that both yellow fever and smallpox vaccines could be applied at separate sites, without any reduction in the efficacy of either immunizing agent, and without detecting any reactions among over 60,000 children involved. A positive reaction to the smallpox component occurred in 94.5 per cent. of cases, and to the yellow fever component in 93.1 per cent. of previously non-immune cases. The double yellow fever vaccination fully protected 98.0 per cent. of children previously non-immune. The control, single scratch yellow fever vaccinated group gave a result (94.2 per cent. conversions from negative to positive protection), somewhat better than previously obtained—a possible reason for this is discussed.