POLIOVIRUS NEUTRALIZING ANTIBODY PERSISTENCE AFTER VACCINATION WITH THE SABIN VACCINE - A FOLLOW-UP-STUDY

In 1976, a cohort survey on the persistence of neutralizing antibodies in children regularly immunized 1 to 4 years earlier with the Sabin attenuated vaccine (OPV) was undertaken in the Venice mainland. Subsequent serological evaluations in the same cohort were carried out in 1983 and 1993. A macroneutralization test using a 1:4 initial serum dilution was utilized in the 1976 and 1983 survey years. In the 1993 survey a microneutralization test using a 1:2 initial dilution was utilized. In this survey, however, sera were tested using both the latter microneutralization test and the former test. Using the former method, the results indicate that the OPV-induced humoral immunity to poliovirus 1 and 2 remain fairly stable after the initial decrease, whereas antibodies to poliovirus 3 are further declining. Using the latter more sensitive method the seropositivity rates were found to be equal or close to 100 percent. The results of our follow-up survey thus indicate that the OPV-induced humoral immunity is long-lasting when tested with a highly sensitive and reproducible method. The clinical protection that ensues after OPV-immunization is probably lifelong similar to that which follows the natural infection.