From Children to Adults? Shifting Age Patterns of Malaria in Kenya, 2008 – 2023

Abstract Estimation of the impact of the doubled malaria funding over the past two decades targeting high-risk populations warrants use of age-attentive metrics. This study assessed temporal trends in malaria burden and parasite density across age groups in Kenya. Between 2008 and 2023, malaria burden and parasite density among symptomatic individuals were estimated and analyzed using RStudio. Up to 4,184 participants, comprising 2,737 (65.42%) Lake-endemic region, 1,278 (30.54%) highland endemic region, and 169 (4.04%) coast endemic zones were enrolled. Median age of participants was 5 years, (IQR 3–15, SD,11.68). Enrolment differed significantly across age groups: 0–5 (51.6%), 6–11 (18.8%), 12–17 (7.4%), 18–26 (13.1%), and 27–78 years (9.2%) (χ², p < 0.001). Median age increased significantly, from 4 to 13 years suggesting a shift in disease burden toward older age groups, χ² p = 0.0001. Median parasite density in parasites/µL declined significantly from 37,500/µL (n = 196, 2008) to 5,080/µL (n = 102, 2023) (Kruskal–Wallis, p = 0.0001). The age of individuals presenting with malaria symptoms increased significantly alongside a reciprocal decrease in parasite density. These changes suggest need to reassess age-targeted malaria interventions to ensure adequate protection of those at the highest risk of malaria.