Impact of seasonal malaria chemoprevention timing on clinical malaria incidence dynamics in the Kedougou region, Senegal

Seasonal malaria chemoprevention (SMC) with sulfadoxine-pyrimethamine and amodiaquine is recommended by the World Health Organization since 2012 for clinical malaria prevention in children in the Sahelian region of Africa. In Senegal, SMC implementation began in 2013 and is given to children under 10 years old. This study aimed to describe clinical malaria incidence in the general population during routine SMC implementation and to analyse how SMC timing impacted clinical malaria dynamics in eligible children.   We conducted an ecological study in the Kedougou region of Senegal in 27 villages included in the Bandafassi Health and Demographic Surveillance System (HDSS). We calculated weekly Plasmodium falciparum malaria incidence by age group using malaria case data recorded by community health workers and health-posts, and population denominators obtained from Bandafassi Health and Demographic Surveillance System. We used negative binomial generalized additive multilevel models to analyse the incidence of clinical episodes in children under 10 years during the expected SMC prophylactic period and at the end of the transmission period.   Malaria incidence was strongly seasonal with a high transmission period starting in June. Children under SMC presented an overall lower incidence compared to older children and young adults. Among children eligible for SMC, the incidence was lowest for approximately 3 weeks after treatment administration and increased subsequently, suggesting a gradual loss of protection.  At the end of the high transmission period, a higher malaria incidence was recorded from the 3rd  to 6th week after the week of administration of the fourth (final) SMC round.   While protecting children under 10 years, SMC warrants adjustment to reduce exposure before the next round, to increase protection of 5-9 years, and to cover the high transmission period completely. The addition of a  5th round of SMC in 2023 was necessary to cover the end of the transmission season, but individual-level studies are required to ensure that drug efficacy and adequate dosing are maintained. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was funded by the Excellence Initiative of Aix-Marseille University - A*MIDEX, a French “Investissements d’Avenir” programme: the MARS project (A*Midex International 2018). The funder has no part in the design, implementation and reporting of this study. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study is included in the "Malaria Asymptomatic Reservoir in the Sahel" research project and its protocol was approved by the National Ethics Committee for Health Research of Senegal (protocol SEN20/10, N°0000052/MSAS/DPRS/CNERS) Since 2020, an informed consent form is signed by each head of household or his/her representatives allowing the collection of demographic data by the HDSS. The consent is valid for several rounds. In 2021 and 2023, new consent forms are signed in cases where there is a new household or when the head of the household has changed. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes We are currently in the process of uploading the data respectively required to produce figures 1-4 and figure 5-7 and corresponding models on the Senegalese Statistical agency repository.