One-Year Decline of Poliovirus Antibodies Following Fractional-Dose Inactivated Poliovirus Vaccine.

BACKGROUND: Fractional dose (one-fifth of full intramuscular dose) of inactivated poliovirus vaccine (fIPV) administered intradermally is used as IPV dose-sparing strategy. We compared the rate of decline of poliovirus antibodies (PVA) in recipients of 2 doses of fIPV or IPV. METHODS: A community-based randomized controlled trial was conducted in Karachi, Pakistan. Children aged 14 weeks were randomized into fIPV or full IPV (study arms A, B) and received 1 vaccine dose at age 14 weeks and 1 at age 9 months. PVAs were measured at age 14, 18 weeks and 10, 21 months. RESULTS: Seroprevalence of poliovirus type 2 antibodies in 170/250 (68%) children after 2 IPV or fIPV doses at age 10 months in A and B reached 100% vs 99% (P = .339), and at 21 months, 86% vs 67% (P = .004). Between age 10 and 21 months antibody log2 titers dropped from ≥ 10.5 to 6.8 in A and from 9.2 to 3.7 in B. CONCLUSIONS: There was a significant decline in antibody titers 12 months following the second IPV dose. The slope of decline was similar for full IPV and fIPV recipients. The results provide further evidence that fIPV is a viable option for IPV dose-sparing. CLINICAL TRIALS REGISTRATION: NCT03286803.