Trial finds broad poliovirus-neutralizing responses in infants

A Sabin strain-based inactivated poliovirus vaccine elicited neutralizing antibody responses against Sabin, Salk and recently circulating poliovirus strains in a randomized trial involving 300 healthy infants who received their first dose at two months of age. Among 282 infants who completed the full vaccination course and provided paired blood samples within the required interval, the test vaccine produced seroconversion rates of 91.58% to 100% against the ten virus strains tested. The trial also found an acceptable safety profile, with no vaccine-related serious adverse events reported, although mild-to-moderate reactions occurred more frequently in the test-vaccine group than in either control group.

The study was designed as a double-blind, randomized, positive-controlled clinical trial. Participants were allocated in a 1:1:1 ratio to receive either the test Sabin strain-based inactivated poliovirus vaccine, developed by the Wuhan Institute of Biological Products, a control inactivated poliovirus vaccine or a control wild-type inactivated poliovirus vaccine. Vaccinations were administered when the infants were two, three and four months old. Blood samples were collected before the first dose and 28 days after the third dose, then tested for neutralizing activity against ten individual poliovirus strains. The immunogenicity analysis used a pre-protocol population comprising the 282 infants who finished all three vaccinations and supplied both pre- and post-immunization samples within the specified time window.

The test vaccine’s seroconversion rates across the ten strains ranged from 91.58% to 100%. The corresponding ranges were 87.23% to 98.94% for the control inactivated vaccine and 94.62% to 100% for the control wild-type vaccine. Geometric mean antibody titers were 40.24 to 2,876.29 for the test vaccine, 25.85 to 1,658.58 for the control inactivated vaccine and 116.2 to 958.12 for the control wild-type vaccine. Against most wild-type strains, the test vaccine’s geometric mean titers were higher than those of the control inactivated vaccine but lower than those induced by the control wild-type vaccine for several strains. These laboratory measurements showed that the test vaccine stimulated antibodies capable of neutralizing the panel of polioviruses included in the assay; they did not directly establish protection against infection, transmission or paralytic disease.

Investigators assessed solicited systemic and local reactions for seven days after each vaccination, unsolicited adverse events for 28 days after each dose and serious adverse events for up to six months after the third vaccination. Fever was the most common solicited systemic reaction, followed by irritation, while injection-site pain was a representative solicited local adverse event in the test-vaccine group. The investigators characterized the safety profiles of all three study groups as acceptable and reported no vaccine-related serious adverse events. The test vaccine nevertheless had a higher incidence of mild-to-moderate adverse reactions than both registered control vaccines, making reactogenicity an important distinction alongside the favorable antibody-response results.

Overall, the findings support the immunogenicity and short-term safety of the test Sabin strain-based inactivated vaccine in the population studied. The authors said its broad cross-neutralization capacity could make it potentially useful in global polio-eradication strategies, particularly for countries transitioning from oral polio vaccine toward affordable schedules based on inactivated vaccine. That conclusion remains a potential application rather than a demonstrated effect of this trial. The study did not measure whether the vaccine prevented poliovirus infection, reduced community transmission or lowered the incidence of paralytic polio, and its findings therefore cannot establish clinical efficacy against those outcomes. The trial was registered as CTR20211257 on 7 June 2021 on the China Drug Clinical Trial Registration and Information Disclosure Platform.

Subject of Research: Immunogenicity and safety of a Sabin strain-based inactivated poliovirus vaccine in infants

Article Title: 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

Article References: Lu, W., Zhao, L., Zhang, Z., Wu, C., Guo, H., Li, Q., Chen, W., Li, G., Zhao, W., Dong, X., Yu, G., Li, G., & Li, X. (2026). 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. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14411-2

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14411-2

Keywords: poliovirus, inactivated polio vaccine, Sabin strain, cross-neutralization, seroconversion, neutralizing antibodies, infant immunization, vaccine safety, polio eradication, Safety, capacity, Sabin