A COMPREHENSIVE INVESTIGATION OF IMMUNITY TO POLIOMYELITIS IN A DEVELOPING COUNTRY

A comprehensive nationwide surveillance program of serologic immunity of two-year-old black children, combined with evaluation of vaccine quality and distribution, was carried out in South Africa during 1983–1984. Sera were randomly collected from urban and rural groups and cluster samples collected from the semi-urban group. The sample represented 0.23% of the total target population. Satisfactory levels of immunity were found in the urban (80%) and semi-urban (71%) groups but a disquietingly low level was found for the rural group (59%). Individual districts in the rural group could be singled out for directed cluster sampling at a later stage. History and documentation of immunization corresponded well to serologic findings and revealed also a fairly substantial level of natural immunization among individuals who, on history, had received no vaccine. Some 95% of random samples of vaccine recalled from the field showed satisfactory levels of potency. An immunity surveillance program such as this is ideally suited and highly cost-effective for developing countries with incomplete immunization to prevent large-scale buildup of immunity deficit. The technique, however, is too insensitive to detect localized community immunity defects.