Effect of inactivated poliovirus vaccine on nasal mucosal immunity and pharyngeal shedding following novel oral poliovirus vaccine type 2 challenge: A randomized, open-label trial.

BACKGROUND: Impact of prior inactivated poliovirus vaccine (IPV) doses on nasal and pharyngeal viral replication following subsequent poliovirus exposure remains unclear. Circulating vaccine-derived poliovirus detection in IPV-only countries necessitates better understanding of IPV's role in inducing nasal and pharyngeal mucosal immunity. METHODS: This multicenter, randomized, open-label, parallel-group trial (9 November 2023-25 August 2024; ClinicalTrials.gov identifier: NCT05677256) was conducted in Bangladesh in 500 polio vaccine-naïve infants aged 6-8 weeks. Two infant cohorts (vaccinated with 3 doses of either IPV or bivalent oral poliovirus vaccine [bOPV]) were challenged at 18-20 weeks with novel OPV type 2 (nOPV2). Pharyngeal and fecal viral shedding, and nasal, intestinal, and serum immune responses were measured post-nOPV2-challenge. RESULTS: Poliovirus type 2 (PV2) pharyngeal shedding was minimal post-challenge (1.7% of IPV-vaccinated and 2.6% of bOPV-vaccinated infants). Nasal PV2-specific neutralizing antibody titers were higher in the IPV group post-nOPV2-challenge (day 14; geometric mean titers [GMT]: IPV, 7.5 [95% CI: 5.1-11.1] vs bOPV, 0.6 [95% CI: 0.3-1.2]). Stool PV2-specific neutralization titers were comparable at day 14 (GMT: IPV, 124.0 [95% CI: 54.7-281.0] vs bOPV, 127.3 [95% CI: 74.0-218.9]). Serum PV2 neutralizing antibody titers were consistently higher in IPV group, peaking at day 28 (GMT: IPV, 4347.4 [95% CI: 2378.2-7947.2] vs bOPV, 259.9 [95% CI: 115.5-584.9]). CONCLUSIONS: nOPV2 pharyngeal shedding was low following IPV or bOPV vaccination, whereas IPV induced higher nasal and serum, and comparable intestinal PV2-specific immunity, suggesting a potential role for IPV in poliovirus outbreak response in IPV-only settings.