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.
A. Anand, Damaris Jepkosgei, C. Mwachari et al.· Vaccine· 0 citations
INTRODUCTION
From 2020 to 2023, Madagascar experienced an outbreak of circulating vaccine-derived poliovirus type 1 (cVDPV1) that notably affected adults and was associated with high mortality among paralytic cases. This atypical epidemiological pattern required adapted surveillance approaches and tailored outbreak response strategies, including vaccination campaigns targeting adult populations.
METHODS
We conducted a descriptive analysis of the cVDPV1 outbreak in Madagascar between September 2020 and September 2023. Epidemiological data on confirmed and polio-compatible cases were reviewed, including age distribution, clinical presentation, and outcomes. We also documented outbreak response strategies, particularly vaccination campaigns and operational innovations implemented to reach adult populations.
RESULTS
A total of 54 confirmed cases of paralytic polio caused by cVDPV1 were reported during the study period, including two adults presenting with fever and paralysis. Between February 2022 and March 2023, 15 adult acute flaccid paralysis cases were classified as polio-compatible by the National Polio Eradication Committee due to missing (86%) or negative laboratory specimens. Mortality among these compatible adult cases was 56%. In response, Madagascar conducted vaccination campaigns using bivalent oral polio vaccine, targeting the entire population in four regions and children under 15 years in the rest of the country. Critical role of country leadership, strategic mobilization, and effective communication in driving success and influencing risk perception during the 2023 campaigns helped achieve high coverage among adults.
CONCLUSIONS
The cVDPV1 outbreak in Madagascar demonstrated the potential for significant adult involvement and high mortality in polio outbreaks. High vaccination coverage combined with targeted innovations and strong community engagement contributed to successful outbreak control. These findings highlight the importance of inclusive vaccination strategies and tailored approaches in similar settings.
Kpandja Djawe, Eric Aigbogun, Joseph Souba Zoumanigui et al.· Vaccine· 0 citations
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