Poliovirus shedding after sequential immunization of Sabin-strain inactivated polio vaccines and oral attenuated polio vaccines

The identification of poliovirus in stool samples post-Oral Poliovirus Vaccine (OPV) immunization is essential for implementing post-eradication monitoring of poliomyelitis. This research presents the inaugural assessment of the virus shedding rate and the genetic diversity of OPV shedding strains across different Inactivated Poliovirus Vaccine (IPV)-OPV sequential immunization schedules. Our findings revealed that the shedding rate of different serotypes in each sequential immunization groups peaked within 7 days following the initial administration of OPV, and then gradually decreased. Prior vaccination with OPV reduced the rate and shortened the duration of virus shedding. Additionally, we observed a slight increase in the shedding rate of type3 after the removal of type2 from trivalent oral poliovirus vaccine (tOPV). The comprehensive analysis of the whole-genome high-throughput sequencing results for the shedding strain revealed that the variation sites among samples from different sequential immunization groups were distributed throughout the entire genome. The mutation frequencies within the 5'NCR, 2 C, 3 A, 3 C, and 3D regions were elevated of type1 and type3, while type2 had higher frequencies within the 5'NCR, VP1 and 3D regions. Consequently, it is imperative to expedite the transition from OPV to IPV, and to discontinue OPV as soon as wild poliovirus strains and vaccine-derived poliovirus (VDPVs) are eliminated.