IMMUNOGENICITY OF ORAL POLIOVIRUS VACCINE ADMINISTERED IN MASS CAMPAIGNS VERSUS ROUTINE IMMUNIZATION PROGRAMS

Reported are the results of a study to investigate the immunogenicity of oral poliovirus vaccine (OPV) when administered in mass campaigns c ompared with that following routine immunization programmes, For this purpose, paired sera were collected from a cohort of children before a nd after a mass vaccination with OPV in Morocco in 1987, Serum samples and information on vaccination status and other confounding factors t hat could influence antibody responses to OPV were collected. Neutrali zing antibody titres to poliovirus types 1, 2 and 3 were determined us ing a standardized assay. OPV doses administered exclusively during th e mass campaign were consistently associated with higher type-specific seroprevalence rates than the same number of doses administered in th e routine programme. These findings could not be attributed to differe nces in confounding factors. Enhanced secondary spread of vaccine viru s may have occurred but could not be demonstrated because of limitatio ns in the study design. Mass campaigns appear to be highly effective i n raising the dose-related poliovirus type-specific immunity of the po pulation above that achieved by the routine immunization programme. Ou r findings support the continued use of mass campaigns as an adjunct t o routine programmes in order to both enhance and catalyse current eff orts to achieve the global eradication of poliomyelitis by the year 20 00.