Objective:To compare the polio antibody level of healthy children in Jiangsu Province before and after the conversion of (inactivated poliovirus vaccine, IPV) immunization program.Methods:200 serum samples of healthy children under 5 years old in Jiangsu Province were collected before and after the vaccine conversion, and the neutralizing antibody against poliomyelitis was measured using the micro cell neutralization test. We compared the differences in the positive rate and geometric mean titer (GMT) of polio antibody before and after vaccine conversion.Results:Before vaccine conversion, positive rates of antibody against poliovirus type Ⅰ and Ⅲ were 98.50% and 92.00%, with GMTs of 1∶100.43 and 1∶23.34, respectively. After the conversion, positive rates of polio antibody type I and Ⅲ were 99.00% and 96.00%, GMT were 1∶213.04 and 1∶121.10.Conclusions:There is a difference in immunization effect before and after the polio vaccine conversion, and the antibody level of the population after vaccine conversion is higher than that before vaccine conversion. It is recommended to gradually increase the IPV dose in order to finally achieve the whole course of IPV inoculation.

Objective:To analyze immune effects of children with different immunization schedules after the conversion of polio vaccine immunization strategy.Methods:Serum samples of children with different immunization schedules were collected in 2018 and 2021 respectively. The neutralizing antibody against poliovirus was detected by micro cell neutralization test, and the antibody positive rate and geometric mean titer (GMT) were analyzed.Results:The positive rates of neutralizing antibodies against type I and type III poliovirus in children immunized with two doses inactivated polio vaccine (IPV) and two doses bivalent live attenuated oral polio vaccine (bOPV), one dose IPV and 3 doses bOPV were both 100.00%. The GMT for type I poliovirus antibody were higher than 1∶300, and for type III poliovirus antibody were close to 1∶200. In children vaccinated with IPV, the positive rates of type I and III poliovirus antibodies were 96.72% and 95.08%, and the GMT for type I and III poliovirus antibodies were 1∶96.72 and 1∶48.72, respectively. In children vaccinated with trivalent live attenuated oral polio vaccine (tOPV) only, the positive rates of type I and III poliovirus antibodies were 98.68% and 96.05%, and the GMT for type I and III poliovirus antibodies were 1∶126.84 and 1∶68.22, respectively. In children vaccinated with three doses tOPV and one dose bOPV, the positive rates of type I and III poliovirus antibodies were 100.00% and 98.57%, and the GMT for type I and III poliovirus antibodies were 1∶214.21 and 1∶94.17, respectively.Conclusions:Children who received sequential immunization with IPV and live attenuated oral polio vaccine (OPV) have a high level of positive rate and GMT of neutralizing antibody against poliovirus type I and III.