Trends in uncomplicated and severe malaria following seasonal malaria chemoprevention administration in Nouna, Burkina Faso: a quasi-experimental pre-post study.

backgroundWhile Seasonal Malaria Chemoprevention (SMC) has been adopted as a malaria control strategy in regions with seasonal transmission, continued monitoring and evaluation of its effectiveness across diverse ecological, epidemiological, and healthcare settings remain critical for optimizing the intervention. This study aims to assess the ongoing population-level impact of SMC under routine programme conditions by evaluating rates of uncomplicated and severe malaria following four rounds of administration.

methodsA pre-post analysis was conducted using real-world surveillance data from clinic visits in 285 villages in Nouna District, Burkina Faso, along with National Malaria Control Programme data on SMC administration. Estimates of the population used for person-time calculations were derived from a census conducted as part of a randomized controlled trial. Malaria rates for children under 5 were analyzed for each epidemiological week in 2021, for each health post in the study area. Negative binomial regression models were used, with person-time at risk used as an offset and standard errors clustered by health post, to obtain incidence rate ratios (IRRs) and rate differences. Changes in diagnoses were estimated from the administration weeks to each of the three weeks post- administration within the same population. Injury rates were used as a negative control outcome to assess potential unmeasured confounding.

resultsAlthough SMC was administered during peak malaria transmission weeks within each cycle, both uncomplicated and severe malaria rates remained high through December, following the fourth and final round of SMC. There was a substantial reduction in infection rates in the 3 weeks post SMC, with gradual increases in rates across the three weeks. The rates of uncomplicated and severe malaria per 1000 person-weeks in the administration weeks were 8.5 (95% CI 7.0 to 10.1) and 0.31 (95% CI 0.22 to 0.40), respectively. Uncomplicated malaria rates were lower by 41%, 95%CI (31-50%), 34% (23-43%) and 22% (12-31%) in the first, second and third weeks after administration, respectively. Severe malaria rates declined by 47% (21-64%), 47% (31-59%) and 34% (17-47%) in the three weeks post-administration. Injury rates, the negative control outcome, did not change significantly across the three weeks.

conclusionIn programme settings, at the population level, SMC administration was associated with a substantial reduction in uncomplicated and severe malaria, though this effect was limited to the immediate weeks following administration. The gradual increase in malaria rates by the third week suggests a shorter duration of protection than previously observed. Extending the areas where 5 rounds of distribution occur may be necessary to effectively prevent malaria infections in regions with a longer transmission season. Regular evaluation of local malaria trends and impact of SMC can help further tailor and optimize SMC programmes for specific regional contexts.