One Full or Two Fractional Doses of Inactivated Poliovirus Vaccine for Catch-up Vaccination in Older Infants: A Randomized Clinical Trial in Bangladesh

Abstract

The polio eradication endgame called for the removal of trivalent oral poliovirus vaccine and introduction of bivalent (types 1&3) OPV (bOPV) and inactivated poliovirus vaccine (IPV). However, supply shortages have delayed IPV administration to tens of millions of infants, and immunogenicity data are currently lacking to guide catch-up vaccination policies. We conducted an open-label randomized clinical trial assessing two interventions, full or fractional-dose IPV (fIPV, 1/5 of IPV), administered at age 9-13 months with a second dose given two-months later. Serum was collected at days 0, 60, 67, and 90 to assess seroconversion, priming, and antibody titer. None received IPV or poliovirus type 2-containing vaccines before enrolment. A single fIPV dose at age 9-13 months yielded 75% (95%CI:68-82) seroconversion against type 2, whereas two fIPV doses resulted in 100% seroconversion compared with 94% (95%CI: 89-97) after a single full dose (p < 0.001). Two doses of IPV resulted in 100% seroconversion. Our study confirmed increased IPV immunogenicity when administered at an older age, likely due to reduced interference from maternally derived antibodies. Either one full dose of IPV or two doses of fIPV could be used to vaccinate missed cohorts, two fIPV doses being antigen-sparing and more immunogenic. This trial was registered with ClinicalTrials.gov, number NCT03890497