Safety and cross-neutralization capacity of a Sabin strain-based inactivated polio vaccine: a randomized, double-blind, positive-control clinical trial in 2-month-old infants

Abstract Background The Sabin strain-based inactivated poliovirus vaccine (sIPV) assists in completely eradicating poliovirus transmission, especially in developing countries. Sera from sIPV-immunized individuals can neutralize wild poliovirus strains, primarily indicating its protective potential, though clinical efficacy data are required for confirmation. In the present trial, which used 2-month-old infants as study subjects, we aimed to assess the cross-neutralization capacity of test-sIPV (Wuhan Institute of Biological Products) against a panel of epidemiologically relevant poliovirus strains. Methods We performed a double-blind, randomized, positive-controlled trial including 300 healthy infants who fell into three groups (1:1:1) in a random manner. These subjects received the test-sIPV, control-sIPV, or control-wIPV when they were 2, 3, or 4 months old, respectively. The neutralizing ability of serum samples collected before the 1st dose and 28 days after the 3rd dose of vaccination against 10 individual polio strains, including Sabin, Salk, and recently circulating poliovirus strains, was evaluated. We noted the solicited systematic and local reactions within 7 days and the unsolicited adverse events (AEs) within 28 days following each vaccination and monitored the serious adverse events (SAEs) up to 6 months after the 3rd vaccination. Results A total of 282 infants who finished the entire vaccination process and provided blood samples before and after immunization within the time window underwent immunogenicity analysis after being included in the pre-protocol population. The seroconversion rates induced by the test-sIPV group, control-sIPV group, and control-wIPV against the 10 poliovirus strains were 91.58–100.0%, 87.23–98.94%, and 94.62–100.0%, respectively. Moreover, the geometric mean antibody titers (GMTs) against the 10 polioviruses were 40.24–2876.29, 25.85–1658.58, and 116.2–958.12, respectively. The test-sIPV, control-sIPV, and control-wIPV systems showed acceptable safety. Fever was the most common systemic solicited reaction, followed by irritation. Pain at the injection site was a representative local solicited AE with the test-sIPV. Conclusions Our findings suggest that the test-sIPV effectively induces neutralizing antibody response against the Sabin and wild poliovirus strains, with seroconversion rates exceeding 90%.GMTs against most wild-type strains were higher than those of control-sIPV but lower than those of control-wIPV for several strains. Safety profile was acceptable, with no vaccine-related serious adverse events, although the test-sIPV group experienced a higher incidence of mild-to-moderate adverse reactions compared with both control groups, which are already registered for sale. The broad cross-neutralization capacity and favorable safety profile of test-sIPV suggest that it could play a valuable role in global polio eradication strategies, particularly in developing countries transitioning from OPV to affordable IPV-based immunization schedules. Trial registration Clinical trial number: CTR20211257, registered on 7 June 2021 in the China Drug Clinical Trial Registration and Information Disclosure Platform. http://www.chinadrugtrials.org.cn .