Tropical diseases, travel medicine and vaccines · 2026
Assessing the impact of routine malaria vaccination on total disease burden in Cameroon: a nationwide difference‑in‑differences analysis using health district surveillance data (2023-2025).
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Bekolo Cavin Epie, Ngouenko Nina, Dipepa Nwall Esther Laura Nyame, Ewane Leonard
Аннотация
BACKGROUND: Cameroon introduced the RTS, S/AS01 malaria vaccine into routine expanded immunisation (EPI) in 2024, targeting 42 priority health districts. We assessed changes in total malaria burden between intervention and non-intervention districts over 2023-2025.
METHODS: We conducted a retrospective, quasi-experimental, ecological longitudinal study using a difference-in-differences (DiD) approach on routine district-level surveillance data from 206 districts (42 intervention, 164 non-intervention) for 2023-2025. Outcomes included severe malaria rate (per 1,000 children < 5), uncomplicated malaria rate, all malaria-related hospitalisations, and malaria mortality rate (per 100,000). Crude pre-post changes and DiD were calculated. Adjusted linear DiD models with district and year fixed effects and cluster-robust standard errors were also fitted. Subgroup analyses examined interactions with seasonal malaria chemoprevention (SMC), intermittent preventive treatment in infants (IPTi), insecticide-treated nets (ITNs), and ecological region.
RESULTS: Baseline characteristics differed significantly: intervention districts had higher ITN coverage (60.2% vs. 45.5%, p = 0.006), higher IPT coverage (35.1% vs. 24.4%, p = 0.001), and larger populations (median 121,284 vs. 89,592, p = 0.029). From 2023 to 2025, intervention districts experienced larger declines in all outcomes. Crude DiD showed a 2.6 per 1000 (15%) reduction in severe malaria, 8.1 per 1000 (22%) reduction in uncomplicated malaria, 5.3 per 1000 (28%) reduction in hospitalisations, and 4.1 per 100,000 (26%) reduction in malaria deaths. Adjusted linear DiD estimates were not statistically significant (e.g., severe malaria coefficient - 0.54, 95% CI - 11.07 to 9.99, p = 0.920). Subgroup analyses indicated the largest effects in the Sahel (crude rate ratio 0.78) and added benefit when the vaccine was combined with SMC (additional - 5.6 per 1000 reduction). In 2025 alone, vaccination averted an estimated 7,200 severe cases, 12,800 uncomplicated cases, 5,300 hospitalisations, and 77 deaths.
CONCLUSION: Crude trends show favourable declines in malaria burden in intervention districts, but adjusted estimates were null, likely due to selection bias and low power. These findings support continued vaccine scale-up and use of routine data for monitoring, while acknowledging the limitations of non-randomised evaluations.
METHODS: We conducted a retrospective, quasi-experimental, ecological longitudinal study using a difference-in-differences (DiD) approach on routine district-level surveillance data from 206 districts (42 intervention, 164 non-intervention) for 2023-2025. Outcomes included severe malaria rate (per 1,000 children < 5), uncomplicated malaria rate, all malaria-related hospitalisations, and malaria mortality rate (per 100,000). Crude pre-post changes and DiD were calculated. Adjusted linear DiD models with district and year fixed effects and cluster-robust standard errors were also fitted. Subgroup analyses examined interactions with seasonal malaria chemoprevention (SMC), intermittent preventive treatment in infants (IPTi), insecticide-treated nets (ITNs), and ecological region.
RESULTS: Baseline characteristics differed significantly: intervention districts had higher ITN coverage (60.2% vs. 45.5%, p = 0.006), higher IPT coverage (35.1% vs. 24.4%, p = 0.001), and larger populations (median 121,284 vs. 89,592, p = 0.029). From 2023 to 2025, intervention districts experienced larger declines in all outcomes. Crude DiD showed a 2.6 per 1000 (15%) reduction in severe malaria, 8.1 per 1000 (22%) reduction in uncomplicated malaria, 5.3 per 1000 (28%) reduction in hospitalisations, and 4.1 per 100,000 (26%) reduction in malaria deaths. Adjusted linear DiD estimates were not statistically significant (e.g., severe malaria coefficient - 0.54, 95% CI - 11.07 to 9.99, p = 0.920). Subgroup analyses indicated the largest effects in the Sahel (crude rate ratio 0.78) and added benefit when the vaccine was combined with SMC (additional - 5.6 per 1000 reduction). In 2025 alone, vaccination averted an estimated 7,200 severe cases, 12,800 uncomplicated cases, 5,300 hospitalisations, and 77 deaths.
CONCLUSION: Crude trends show favourable declines in malaria burden in intervention districts, but adjusted estimates were null, likely due to selection bias and low power. These findings support continued vaccine scale-up and use of routine data for monitoring, while acknowledging the limitations of non-randomised evaluations.