Primary and booster vaccination with an inactivated poliovirus vaccine (IPV) is immunogenic and well-tolerated in infants and toddlers in China.

INTRODUCTION Replacing live-attenuated oral poliovirus vaccines (OPV) with inactivated poliovirus vaccines (IPV) is part of the global strategy to eradicate poliomyelitis. China was declared polio-free in 2000 but continues to record cases of vaccine-associated-poliomyelitis and vaccine-derived-poliovirus outbreaks. Two pilot safety studies and two larger immunogenicity trials evaluated the non-inferiority of IPV (Poliorix™, GSK Vaccines, Belgium) versus OPV in infants and booster vaccination in toddlers primed with either IPV or OPV in China. METHODS In pilot safety studies, 25 infants received 3-dose IPV primary vaccination (Study A, www.clinicaltrial.gov NCT00937404) and 25 received an IPV booster after priming with three OPV doses (Study B, NCT01021293). In the randomised, controlled immunogenicity and safety trial (Study C, NCT00920439), infants received 3-dose primary vaccination with IPV (N=541) or OPV (N=535) at 2,3,4 months of age, and a booster IPV dose at 18-24 months (N=470, Study D, NCT01323647: extension of study C). Blood samples were collected before and one month post-dose-3 and booster. Reactogenicity was assessed using diary cards. Serious adverse events (SAEs) were captured throughout each study. RESULTS Study A and B showed that IPV priming and IPV boosting (after OPV) was safe. Study C: One month post-dose-3, all IPV and ≥ 98.3% OPV recipients had seroprotective antibody titres towards each poliovirus type. The immune response elicited by IPV was non-inferior to Chinese OPV. Seroprotective antibody titres persisted in ≥ 94.7% IPV and ≥ 96.1% OPV recipients at 18-24 months (Study D). IPV had a clinically acceptable safety profile in all studies. Grade 3 local and systemic reactions were uncommon. No SAEs were related to IPV administration. CONCLUSION Trivalent IPV is non-inferior to OPV in terms of seroprotection (in the Chinese vaccination schedule) in infant and toddlers, with a clinically acceptable safety profile.