Shrinking the malaria map in Indonesia: progress of subnational control, elimination, and future strategies.

Background: Indonesia has a complex pattern of malaria transmission alongside a highly decentralized system of governance. Indonesia applies a subnational elimination strategy to achieve nationwide malaria elimination by 2030. This review describes Indonesia's subnational verification process, assesses progress towards subnational elimination over the past several decades, and explores strategies to accelerate achievement of elimination, including the challenges of high transmission in lowland Papua region and zoonotic malaria in Sumatra and Kalimantan islands.

Methods: Published and unpublished data, reports, and grey literature in Indonesian and English from 1950 to 2023 were collected and analyzed. These reports document strategies, geographic coverage, and malaria metrics. Most of the unpublished data and reports are from the Ministry of Health of Indonesia, including the guidelines describing processes for certification of district-level malaria elimination.

Results: While the number of malaria cases has fluctuated over the years, cases decreased significantly by 2015 but increased during the Coronavirus disease-19 (COVID-19) pandemic. Nonetheless, as of 2023, 389 of 514 districts and five of 38 provinces had been verified as having no local transmission of malaria, with the most rapid progress observed in western Indonesia. We describe the malaria elimination verification process in detail, including the criteria used and challenges encountered. Malaria cases are now localized in the Papua region, which reports more than 90% of cases in the country. The lowland Papua region experiences high transmission with malaria incidence of over 400 cases per 1000 person-years due to its efficient vectors and high year-round rainfall. Expansion of malaria transmission to highland Papua due to climate change is likely happening. In the west, pockets of transmission persist in remote areas and among mobile and migrant populations. Further, frequent outbreaks occur in malaria-free districts, with two districts now experiencing re-established transmission. In addition, reports of zoonotic Plasmodium knowlesi infections in humans are increasing.

Conclusions: Existing interventions will need to be well-managed, and new combinations of interventions implemented if Indonesia is to achieve its goal of malaria elimination by 2030, particularly in high-endemic Papua, which will remain a source of importation of malaria to other regions of Indonesia if malaria there is not eliminated.