Wealth-related immunization inequality and circulating vaccine-derived poliovirus occurrence and burden in Africa from 2015 to 2024

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Introduction Despite Africa’s certification as wild poliovirus-free in 2020, circulating vaccine-derived poliovirus (cVDPV) continues to threaten eradication progress. National immunization coverage averages may conceal socioeconomic pockets of under-immunized children. This study examined whether wealth-related inequality in immunization coverage was associated with cVDPV occurrence and burden across African countries and territories Methods A longitudinal ecological panel study was conducted across 58 African countries and territories from 2015 to 2024. The primary analytical sample included 402 country-years from 44 countries and territories with usable wealth-quintile immunization data and survey lag ≤7 years. The exposure was the survey-assigned third dose of diphtheria-tetanus-pertussis-containing vaccine (DTP3) wealth gap, defined as richest-quintile minus poorest-quintile coverage and scaled per 10 percentage-point increase. cVDPV occurrence was defined as any confirmed case in a country-year; burden was the annual confirmed case count. Generalized estimating equation logistic regression and negative binomial regression were used, adjusting for national third dose of polio-containing vaccine (Pol3) coverage, survey lag, conflict/fragility status, calendar year, and population structure as appropriate. Results Ninety-nine of 402 country-years (24.6%) had at least one confirmed cVDPV case. Occurrence increased across DTP3 wealth-gap quartiles from 10.6% to 12.4%, 25.0%, and 50.5%. Each 10 percentage-point increase in the survey-assigned DTP3 wealth gap was associated with higher odds of cVDPV occurrence (odds ratio [OR] 1.47, 95% confidence interval [CI] 1.13–1.91) and higher cVDPV burden (incidence rate ratio [IRR] 1.38, 95% CI 1.11–1.71). Findings were broadly robust across sensitivity analyses. Conclusion Wealth-related immunization inequality was associated with both cVDPV occurrence and burden in Africa. Equity-disaggregated immunization monitoring may complement national coverage and surveillance indicators in polio risk assessment and eradication planning.