Introduction

Novel vaccine used as one of the vaccines for the final eradication of polios worldwide, complete data on the consistency and immunogenicity characteristics of the inactivated poliomyelitis vaccine made from the Sabin strain (sIPV) and its safety in large-scale populations are required to support the future use of this vaccine worldwide. A phase IV clinical trial was conducted to perform an immunogenicity evaluation of lot-to-lot consistency of three commercial batches of sIPV in 1200 infants and to investigate the vaccine’s safety on a large-scale in 20,019 infants for active monitoring and 29,683 infants for passive monitoring through the Adverse Event Following Immunization (AEFI) reporting system in China.

In the immunogenicity evaluation, the average seroconversion rates for type I, type II and type III of the three groups were 99.83%, 98.93% and 99.44%, respectively. No differences in the seroconversion rate and the GMT ratios were noted in the pair-to-pair comparisons. In the large-scale safety evaluation, most adverse reactions occurred 0–30 days after the first doses, and the common local and systemic reactions were similar to those in the phase III clinical trial, with low incidence in both activated and passive monitoring. In conclusion, sIPV exhibits good lot-to-lot consistency and safety in large-scale populations; thus, it is qualified to serve as one of the vaccines for use in eradicating all wild and vaccine-derived polioviruses worldwide in the near future.

Following the achievement of polio eradication, all countries, especially developing countries that use OPV in routine vaccinations, are revising their routine schedule from OPV only to a sequential IPV-OPV schedule and will ultimately revise to a full IPV schedule [2], [3]. These schedules will ultimately change to the full IPV schedule to create a polio-free world according to the requirements of the WHO Global Polio Eradication & Endgame Strategic Plan. The presently used wIPV together with the new sIPV that was debuted in 2015 are required to meet worldwide vaccination needs. In the present study, we reported on the immunogenicity and safety of large-scale population vaccination in this first phase IV clinical trial of sIPV to provide important data for guiding its future use together with wIPV and monovalent OPV (emergency storage) in the eradication of polio.

To investigate AEs of routine vaccination in the future EPI schedule, we collected safety data from the CDC AEFI monitoring system. Similar to the active monitoring results, most AEs occurred 24 h after the first dose, but the incidence rates decreased sharply. Local and systematic reactions were similar between these two investigations, with low incidences reported in AEFI monitoring. Of note, among 119 AE cases, 50 occurred during concomitant administration with other vaccines, and 39 occurred at the second and third doses of sIPV administration with the first dose of DTaP and DTaP-Hib. In Shanghai city, where the present study was performed, the AEFI incidence has been reported as 486.93/100000, 617.84/100000 and 1117.47/100000 for DTaP, DTaP-Hib and DTaP-IPV-Hib, respectively, while it was 390.80/100000 in the present sIPV passive monitoring.

Conclusion

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