Key result
Two doses of nOPV2 elicit a type 2 immune response in ~62% of children.
Why the study?
Novel oral polio vaccine type 2 (nOPV2) was used to respond to a circulating vaccine-derived poliovirus type 2 outbreak in Kenya, but the immunogenicity of one and two doses administered during outbreak response required assessment.
Does two doses of nOPV2 improve immune response in children aged 6-59 months during an outbreak response?
Cohort (n=461)
Yes
Does two doses of nOPV2 improve immune response in children aged 6-59 months during an outbreak response?
Two doses of nOPV2 during an outbreak response achieved an immune response in only 62% of children, suggesting it may be insufficient for high population immunity in sub-Saharan Africa.
Should not yet change outbreak protocols; leaves open questions on nOPV2 dosing in real-world settings.
BACKGROUND: In 2023, novel oral polio vaccine type 2 (nOPV2) was used to respond to an outbreak of circulating vaccine-derived poliovirus type 2 (cVDPV2) in Kenya. We assessed the immunogenicity of one and two doses of nOPV2 administered during outbreak response. METHODS: An observational cohort study was conducted from October to December 2023 in Kitui and Tana River counties in Kenya. Children aged 6-59 months were enrolled. Two nOPV2 doses were administered. Dried blood spots (DBS) were collected at enrollment, four-weeks after the first nOPV2 dose, and two- and four-weeks after the second nOPV2 dose. The DBS cards were tested at the US Centers for Disease Control and Prevention (CDC), Atlanta for the presence of poliovirus neutralizing antibodies using microneutralization assays. The primary endpoint was cumulative immune response after two nOPV2 doses. FINDINGS: Of the 475 participants followed in the study, 461 (97%) completed all study visits and were included in the analysis. Four weeks after two nOPV2 doses, a cumulative type 2 immune response was observed in 285 (62%; 95% CI 57-66) of 461 participants. After one nOPV2 dose, type 2 immune response was observed in 196 (43%, 95% CI 38-47) of 461 participants. Type 2 seropositivity (titers ≥1:8) increased from 19% at enrollment to 72% after two nOPV2 doses. INTERPRETATION: The study demonstrated an immune response in 62% of the participants following two nOPV2 outbreak vaccination rounds. These findings suggest that two nOPV2 doses may be insufficient to achieve high population immunity during poliovirus type 2 outbreak response in sub-Saharan Africa.
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Anand et al. (2026) conducted a cohort in circulating vaccine-derived poliovirus type 2 (cVDPV2) (n=461). novel oral polio vaccine type 2 (nOPV2) was evaluated on cumulative immune response after two nOPV2 doses (95% CI 57-66). Two doses of novel oral polio vaccine type 2 (nOPV2) elicited a cumulative type 2 immune response in 62% (95% CI 57-66) of children aged 6-59 months during an outbreak response in Kenya.
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