Immunogenicity and immune persistence in 4-year-old children completing four doses of Sabin strain or wild strain inactivated poliovirus vaccine: A phase IV, open-labeled, parallel-controlled observational study

Sabin strain inactivated poliovirus vaccine (hereinafter as “sIPV”) has been marketed globally in recent years, and more data on its immune persistence are needed. This is a phase IV, open-labeled, parallel-controlled observational study based on phase III clinical trial as required by the China National Medical Products Administration (NMPA). At least 450 subjects aged four years (48–54 months) who received four doses at 2, 3, 4 and 18 months of age of sIPV or wild strain poliovirus vaccine (wIPV) in phase III clinical trial enrolled at a 2:1 ratio and collected blood samples for neutralizing antibody testing. A total of 500 subjects of four years old (334 in the sIPV group and 166 in wIPV group) were finally enrolled. The seropositivity rates (≥1:8) of neutralizing antibodies against serotype I-III were all 100.00% in all participants, and the geometric mean titers (GMT) were 1117.33 vs. 337.77 against serotype I, 632.72 vs. 267.34 against serotype Ⅱ, 1665.98 vs. 923.02 against serotype III in the sIPV group and wIPV group respectively at 4 years old. The seropositivity rates and GMTs of neutralizing antibodies in the test group were non-inferior to that of the control group against all three serotypes at different time points (P