Immunogenicity of oral poliovirus vaccine administered in mass campaigns versus routine immunization programmes.

Reported are the results of a study to investigate the immunogenicity of oral poliovirus vaccine (OPV) when administered in mass campaigns compared with that following routine immunization programmes. For this purpose, paired sera were collected from a cohort of children before and after a mass vaccination with OPV in Morocco in 1987. Serum samples and information on vaccination status and other confounding factors that could influence antibody responses to OPV were collected. Neutralizing antibody titres to poliovirus types 1, 2 and 3 were determined using a standardized assay. OPV doses administered exclusively during the mass campaign were consistently associated with higher type-specific seroprevalence rates than the same number of doses administered in the routine programme. These findings could not be attributed to differences in confounding factors. Enhanced secondary spread of vaccine virus may have occurred but could not be demonstrated because of limitations in the study design. Mass campaigns appear to be highly effective in raising the dose-related poliovirus type-specific immunity of the population above that achieved by the routine immunization programme. Our findings support the continued use of mass campaigns as an adjunct to routine programmes in order to both enhance and catalyse current efforts to achieve the global eradication of poliomyelitis by the year 2000.

PIP: Reported are the results of a study to investigate the immunogenicity of oral poliovirus vaccine (OPV) when administered in mass campaigns compared with that following routine immunization programs. For this purpose, paired sera were collected from a cohort of children before and after a mass vaccination with OPV in Morocco in 1987. Serum samples and information on vaccination status and other confounding factors that could influence antibody responses to OPV were collected. Neutralizing antibody titers to poliovirus types 1, 2, and 3 were determined using a standardized assay. OPV doses administered exclusively during the mass campaign were consistently associated with higher type-specific seroprevalence rates than the same number of doses administered in the routine program. These findings could not be attributed to differences in confounding factors. Enhanced secondary spread of vaccine virus may have occurred but could not be demonstrated because of limitations in the study design. Mass campaigns appear to be highly effective in raising the dose-related poliovirus type-specific immunity of the population above that achieved by the routine immunization program. These findings support the continued use of mass campaigns as an adjunct to routine programs in order to both enhance and catalyze current efforts to achieve the global eradication of poliomyelitis by the year 2000. (author's)

On the role of the World Health Organization in the development of Sabin vaccines.

The World Health Organization has played a major part in the development, surveillance and distribution of attenuated poliovirus vaccines. At a time when most of the United States' efforts concerned the introduction of Salk-type vaccines, WHO initiated studies that set standards and permitted the large scale trials of Sabin and other attenuated vaccines. Independent expert review validated studies in countries such as the U.S.S.R. which helped lead to the adoption of Sabin vaccines for worldwide usage. Surveillance by WHO Collaborative Centres established the safety of Sabin vaccines and identified issues of reversion primarily concerning type 3 viruses, initiating studies which have elucidated the molecular mechanism of reversion. Efforts by the Biological Unit of the World Health Organization have ensured worldwide acceptable standards to control the safety and manufacture of vaccines. Revision of neurovirulence test methods has ensured adequate safety testing of vaccine lots, reduced the costs of such studies and the numbers of primates needed, important ethical and conservation issues. Finally, the World Health Organization has played a major part in the worldwide supply of vaccines at affordable prices and has been the repository of, and had the exclusive license, to Sabin vaccines since 1972.

Availability of vaccines of an assured quality.

In establishing standards of quality for vaccines used in vaccination programmes, it is necessary to protect the recipients without demanding unnecessarily high specifications and standards of purity. Such standards reduce profitability, jeopardizing further vaccine supplies and future research, and also diminish the probability of vaccine manufacture outside the industrialized countries. Funds will be needed to encourage research and local manufacture, and internationally accepted procedures of quality assurance must be established.