In Japan, routine polio immunization with the oral polio vaccine (OPV) was discontinued in September 2012, and an immunization program with inactivated polio vaccines (IPVs), including the conventional IPV (cIPV) derived from virulent strains and the IPV derived from Sabin strains (sIPV), was implemented. However, the immunity generated by sIPV is poorly understood. The neutralizing antibodies generated against poliovirus in patients who got OPV or IPV dosages were evaluated and compared in this study. Between 2013 and 2016, serum samples were collected as part of the National Epidemiological Surveillance of Vaccine-Preventable Disease. The neutralizing antibody titers for Sabin strain types 1, 2, and 3 were measured in 224 children aged 0 to 90 months. Seropositivity rates following OPV or IPV vaccination were greater than 90%. Neutralizing antibody titers for Sabin type 1 after IPV vaccination were lower than those for OPV, but they were considerably greater for Sabin types 2 and 3 after IPV vaccination. Analyses of antibody titer dynamics indicated that in patients vaccinated with IPV, the decay of antibody titers for Sabin types 1, 2, and 3 was steeper than in those vaccinated with OPV.
Thus, while IPV generated a substantial amount of neutralizing antibodies, the immunity established by IPV did not last as long as that caused by OPV. The findings recommended that a long-term survey for polio vaccination using IPVs be undertaken, and that booster vaccination for IPVs may be essential.