The impact of Seasonal Malaria Chemoprevention and relationship to parasite drug resistance in a nomadic pastoralist community in Northern Kenya

IntroductionFollowing WHOs updated guidelines for SMC, countries beyond the Sahel region are exploring the suitability of SMC to protect children in areas with sharply seasonal transmission. Sulphadoxine-pyrimethamine with amodiaquine (SPAQ) is the standard regimen, leading to concerns about the efficacy of SMC in areas with higher levels of SP resistance. Here we report the impact of an SMC program implemented in Turkana Central, an area with moderate-to-high SP resistance. We examine the relationship between parasite resistance and breakthrough infections in children receiving SMC. MethodsWe conducted a parallel cohort study during the 2024 peak malaria season (June - October) with 10 randomly-selected villages in the SMC delivery subcounty (Turkana Central) and 10 from the adjacent subcounty (Turkana North). Community Health Promoters conducted weekly surveillance of malaria symptoms. Symptomatic children were tested with a Rapid Diagnostic Test and blood spot samples were collected. Using Poisson regression, an incidence rate ratio was used to measure SMC efficacy where the primary outcome was malaria-like symptoms with a positive diagnostic test. Pf positive samples from symptomatic infections were tested for SP resistance alleles within the Pfdhfr and Pfdhps genes. Results398 children were followed from 2 weeks prior to SMC until four weeks after the final cycle. In Turkana Central, 145/198 (73%) children received complete SMC. There was a 71% reduction in malaria incidence attributable to SMC (Adjusted IRR 0.29, 95% CI:0.13-0.67). There were 156 Pf-positive samples collected during active surveillance of which 68 were fully characterized at all three codons. The proportion of infections with mutations in the Pfdhps gene was significantly higher in children receiving SMC and increased with increasing cycles of SMC received. ConclusionSMC with SPAQ is highly effective for preventing malaria in areas with moderate prevalence of SP resistance. Despite this, infections in children who received SMC were more likely to harbor resistant parasites.