Accessibility, safety, and early effect of the malaria vaccine in routine immunisation practice among children under 36 months in the Soa Health District, Cameroon

Abstract

Malaria remains a leading cause of child mortality in sub-Saharan Africa. Cameroon introduced the RTS,S/AS01 malaria vaccine in 2024, but real-world evidence on its early effects, coverage, and safety remains limited. This study evaluated these parameters among children under 36 months in the high-transmission Soa Health District. A community-based analytical cross-sectional study was conducted from February to May 2025. Households were selected by stratified cluster sampling (62 clusters, 622 participants). Children aged < 36 months who had resided in the district for ≥ 3 months were eligible. Vaccination status and malaria episodes (confirmed by rapid diagnostic test or microscopy) during the preceding six months were abstracted from cards. Primary exposure was ≥ 2 doses of RTS,S/AS01; primary outcome was documented malaria episodes. Multivariable modified Poisson regression with robust standard errors was used to estimate risk ratios (RR) adjusted for age, breastfeeding, insecticide-treated net (ITN) use, and intermittent preventive treatment in infancy (IPTi). The effect of the vaccine was measured as (1–adjusted RR) × 100. Coverage and adverse events were also assessed. Among 622 children (mean age 17.9 months, 51.4% female), documented coverage of dose 1 was 56·8% (95% CI 53.5–61.7), dropping to 46·6% for dose 2 and 39·0% for dose 3. Perceived free access (aRR 1.97, 95% CI 1.47–2.64) and knowledge of a nearby vaccination facility (aRR 1.86, 95% CI 1.41–2.45) were strongly associated with uptake. In the cross-sectional analysis, children who received ≥ 2 doses were associated with a 50% lower occurrence of malaria episodes (aRR 0.50, 95% CI 0.34–0.73, p = 0.001) compared with those receiving ≤ 1 dose. Minor adverse events occurred in 27% (fever 93%, injection site swelling 10%). In this high-burden Cameroonian setting, two or more doses of RTS,S/AS01 were associated with a lower occurrence of malaria episodes favourable safety profile. Coverage remains suboptimal, and dropout is high. Ensuring free access and strengthening community awareness are critical for maximising vaccine uptake.