Duration of Seroimmunity After Poliomyelitis Vaccination

The persistence of the effects of immunization against poliomyelitis was studied in 139 children three years after primary inoculation and two years after booster inoculation with inactivated poliomyelitis vaccine. The criterion was the titer of neutralizing antibodies for the three immunological types of poliomyelitis virus, as measured colorimetrically by the protection of monkey-kidney cell suspensions from the metabolic inhibitory influence of the virus. School-age children who had received primary vaccination during the nationwide field trial of 1954 showed an average loss of only threefold to fourfold in antibody titer during the two-year period after secondary immunization and still had high levels indicative of protection. The levels of protection found appeared to be independent of the extent of primary stimulation. The younger children had markedly lower levels of antibody after the booster injection, but the mean loss of antibodies was of the same order of magnitude in the three groups. The degree of immunity and extent of loss during the two-year interval closely duplicated the values reported by others for patients convalescing from the disease itself.