Epidemiology of Plasmodium falciparum infection and clinical malaria among infants in Malawi

Abstract

Background: Few malaria interventions are designed to target infants under six months. The burden of malaria in infancy and its long-term health impact needs to be better characterized to inform surveillance and treatment guidelines for this age group. Objectives: The aims of this study were to (a) assess the effect of intermittent preventive treatment during pregnancy (IPTp) regimens on the risk of malaria in infancy, (b) characterize P. falciparum infection and clinical malaria in the first six months and the risk of subsequent malaria, and (c) assess effects of P. falciparum infection and clinical malaria exposure in first six months on weight and hemoglobin concentration after six months. Methods: Longitudinal cohort data collected from infants in southern Malawi between 2016 and 2019 was analyzed using Cox proportional hazards models, Poisson generalized estimating equations with a log link function, and linear mixed effects models. Results: Maternal IPTp regimen had no effect on infant incidence of clinical malaria (IRR=1.03; 95%CI: 0.58–1.86) or incidence of P. falciparum infection (IRR=1.18; 95%CI: 0.92–1.55) before two years. Maternal IPTp was not significantly associated with infant’s time to first infection (HR=1.05; 95%CI: 0.8–1.39) or clinical malaria (HR=0.92; 95%CI: 0.58–1.48). Exposure to any malaria before six months was associated with higher incidence of any malaria (IRR=1.27; 95%CI: 1.06–1.52) and clinical malaria (IRR=1.76; 95%CI: 1.42–2.19) between 6 and 24 months. Clinical malaria exposure before first six months was also associated with higher incidence of any malaria (IRR=1.64; 95%CI: 1.38–1.94) and clinical malaria (IRR=1.85, 95%CI:1.48–2.32) between 6 and 24 months. Exposure to asymptomatic P. falciparum infection before six months was associated with lower weight-for-age z-scores during follow-up (p=0.02) and exposure to clinical malaria before six months was associated with lower hemoglobin concentrations during follow-up (p=0.02). Conclusion: Prevention of malaria during pregnancy does not reduce infant risk of malaria and malaria infection before six months is associated with higher malaria incidence, lower weight-for-age Z-scores, and lower hemoglobin concentrations in early childhood. Early malaria infection may be an indication of high exposure risk and a marker for downstream health outcomes.