Vaccination with the CHAT strain of type 1 attenuated poliomyelities virus in Leopoldville, Belgian Congo. 1. Description of the city, its history of poliomyelitis, and the plan of the vaccination campaign.

A trial of the CHAT, type 1, attenuated poliovirus strain of Koprowski was begun in August 1958 in Léopoldville, a city of 350 000 people, and possessing modern medical facilities, including an institute of public health.Paralytic poliomyelitis is endemic in the city; since 1951 there has been an average annual incidence of 63 cases, and a rate of 19.4 cases per 100 000 inhabitants. More than 80% of the cases have occurred in African children less than 3 years old. Consequently, a plan to vaccinate African infants and children was formulated and put into operation.Vaccination was performed by squirting virus into the mouths of the children at medical dispensaries or special clinics. The innocuity of the vaccine was checked by follow-up visits to the homes of a large number of children one and two weeks after virus feeding. Blood specimens were taken before and after virus administration to determine the initial susceptibility of the population and their response to live-virus vaccination. The results of vaccination are presented in the following paper.