This study is a open-labelled study conducted based on an already finished phase 2 study of the investigational sIPV in 600 healthy infants aged 2-months old. The purpose of this study is to evaluate the cross-neutralization capacity of the serum immuned by the investigational sIPV against 10 individual virus strains. Paired pre-immune and post-immune serum from 250 participants of the phase 2 trial, with 50 in each group including the low-, medium- and high- dosage group, control wild poliovirus vaccine (wIPV) group and control sIPV group, was selected and sent to China Center for Disease Control and Prevention (CDC) for the cross-neutralization assay to determine the neutralizing antibody titer against 10 individual virus strains including Sabin strains (type 1, 2, and 3), Salk strains (Mahoney, MEF-1, and Saukett), cVDPV (type 1, 2, and 3) and Xinjiang wild strain of type 1(Xinjiang wIPV1).~All the subjects in this study had been vaccinated at the schedule of month 0,1, and 2 in the phase 2 clinical trial.
This study is a supplementary study of an already finished randomised, double-blinded, and placebo controlled phase 2 clinical trial of an Sabin strain inactivated poliovirus vaccine (sIPV) manufactured by Sinovac Biotech Ltd., Beijing China. The purpose of this study is to evaluate the cross-neutralization capacity of the serum immuned by the investigational sIPV against 10 individual virus strains.