Shifts in Indonesia's Malaria Landscape: an Analysis of 2010-2019 Routine Surveillance Data

Background: Indonesia faces challenges in achieving its goal of eliminating malaria by 2030, with cases stagnating between 2015 and 2019 despite a decline in 2013. This study aims to analyse epidemiological trends and demographic changes in malaria cases regionally from 2010 to 2019, considering differences in surveillance across the country. Methods: We used national and sub-national malaria routine surveillance data, applying statistical models to derive insights for future interventions. The analysis focused on metrics such as malaria incidence, test positivity, case demographics, and parasite species. Findings: We estimate a progressive decline in malaria incidence in six of seven Indonesian regions over the study period, adjusting for increased testing from 2015 onwards. In these regions, cases have shifted to older, predominantly male demographics, suggesting a move from household-based to occupational transmission. However, in Papua, cases remain high and concentrated in children. Although Papua comprises just 2% of Indonesia's population, its share of national malaria cases increased significantly from 40% to 90% between 2010 to 2019. Interpretation: Since 2010, malaria trajectories in Indonesia have diverged, influencing sub-national control priorities. In most regions, progress towards elimination requires targeted interventions for high-risk populations and inter-district cooperation. In contrast, Papua struggles with high transmission rates despite mass insecticide-treated net campaigns. Achieving similar progress in Papua as in other regions is challenging yet crucial. Therefore, Papua could be a prime candidate for enhanced malaria management, maximising efforts towards larval source reduction, education, chemopreventive intervention, and vaccine. Funding: Medical Research Council and Wellcome Africa Asia Programme Vietnam. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement BAD, ESS, TSC and PW acknowledge funding from the MRC Centre for Global Infectious Disease Analysis (reference MR/X020258/1), jointly funded by the UK Medical Research Council (MRC) and the UK Foreign, Commonwealth & Development Office (FCDO), under the MRC/FCDO Concordat agreement and is also part of the EDCTP2 programme supported by the European Union. ESS is funded by a UKRI Future Leaders Fellowship from the Medical Research Council (MR/T041986/1). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes 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 All data used in the present study are owned by the malaria working team at the Ministry of Health of the Republic of Indonesia. Requests for access to the relevant data may be made directly to the team.