Boosting immune responses following fractional-dose inactivated poliovirus vaccine: A randomized, controlled trial

Abstract

Background. Fractional-dose administration of inactivated poliovirus vaccine (fIPV) could increase IPV affordability and stretch limited supplies. We assessed immune responses following fIPV administered intradermally, compared with full-dose IPV administered intramuscularly, among adults with a history of oral poliovirus vaccine (OPV) receipt. Methods. We conducted a randomized, controlled noninferiority trial in Cuba. fIPV or IPV were administered on days 0 and 28; serum was collected on days 0, 7, 28, and 56 for analysis by a neutralization assay. The primary end point was seroconversion or a ≥4-fold rise in antibody titer. The noninferiority limit was 10%. The secondary end point was safety, assessed by the number and intensity of adverse reactions. Results. A total of 503 of 534 enrolled participants (94.2%) completed all study requirements. Twenty-eight days after the first dose, 94.8%, 98.0%, and 98.0% of fIPV recipients had an immune response to poliovirus types 1, 2, and 3, respectively, compared with 98.1% (P = .06), 98.0% (P = 1.00), and 99.2% (P = .45) in the IPV arm. Noninferiority was achieved on days 7, 28, and 56 for all serotypes. No serious adverse events were reported. Conclusion. fIPV induced similar boosting immune responses, compared with full-dose IPV. This suggests that fIPV would be an effective strategy to boost population immunity in an outbreak situation. Clinical Trials Registration. ACTRN12615000305527.