Shifts in Indonesia's malaria landscape: an analysis of 2010-2019 routine surveillance data

BackgroundIndonesia 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. MethodsWe 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. FindingsWe 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 Indonesias population, its share of national malaria cases increased significantly from 40% to 90% between 2010 to 2019. InterpretationSince 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. FundingMedical Research Council and Wellcome Africa Asia Programme Vietnam. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSAs the country with the fourth biggest malaria burden outside of Africa, malaria control and elimination have been significant public health priorities in Indonesia, especially since the National Ministerial Decree on Malaria Elimination was passed in 2009. To understand the existing literature on malaria in Indonesia, we conducted a literature search on PubMed using the keywords MALARIA and INDONESIA for titles and abstracts from 1 January 2008 to 3 January 2024, yielding 386 results. Among these, only a few studies extensively discussed the broad landscape of malaria in Indonesia. Notably, Elyazar et al., in their series of studies published in the early 2010s, provided an in-depth look at the epidemiology of malaria in Indonesia, the history of malaria control efforts leading up to the 2009 decree, potential challenges in malaria control, and estimates of malaria prevalence across the country at the beginning of the 2010 decade. These studies laid a foundational understanding of the malaria situation in Indonesia at the start of the decade, capturing the diverse and complex nature of the elimination challenge. Sitohang et al. wrote a commentary article on the accelerated progress towards malaria elimination in Indonesia from 2007 to 2017. However, they also highlighted the persisting challenges that Indonesia faces in meeting the 2030 elimination target. Therefore, there remains a need to quantitatively assess the impact of acceleration strategies ten years after the 2009 ministerial decree and understand the shifting epidemiological patterns of malaria, especially in the context of Indonesias diverse and changing demographic and environmental landscapes. Added value of this studyOur study offers a significant contribution to understanding contemporary malaria epidemiology in Indonesia, especially after a period of acceleration in malaria elimination efforts. We did a comprehensive analysis of a decades worth of malaria surveillance data in Indonesia, revealing diverging trends in malaria incidence between regions and the changing profiles of malaria cases. We highlight the significant decline in malaria cases since 2010 in six out of seven regions in Indonesia, with cases shifted to older and predominantly male demographics, indicative of a move from household-based to occupational transmission. However, in Papua, cases remain high and concentrated in children despite efforts such as mass insecticide-treated nets distribution campaigns. In 2019, Papua contributed to 90% of malaria cases across the country, an increase from around 40% in the early 2010s despite comprising only 2% of Indonesias population. Implications of all the available evidenceThis study identifies challenges and discusses the way forward for Indonesias fight against malaria. Although there has been great progress, the findings suggest that regionally tailored strategies are needed for effective elimination efforts going forward. In areas where malaria incidence has declined and the demographics of typical malaria cases have shifted, malaria interventions should be focused on the high-risk population in respective regions, which includes mobile and migrant populations such as forest workers and indigenous people, amongst others. Furthermore, inter-district cooperation is needed to prevent malaria importations and reintroductions to districts already eliminating or achieving progress towards malaria elimination. In Papua, where malaria transmission remains high, novel and innovative interventions may be required to accelerate progress towards malaria elimination. While some malaria vaccines have proven effective in high-burden countries within Africa, severe disease numbers are lower in Papua, and sustained coverage levels with routine immunisations have been a challenge to maintain. Hence, Indonesia is hesitant to adopt such a strategy. Additionally, Indonesia also has challenges in controlling P. vivax, which presents a significant burden on the population and is a problem not seen in African countries. Therefore, in Indonesia, chemopreventive interventions (such as intermittent preventive treatment of malaria during pregnancy or IPTp), and additional vector control interventions (such as larval source reductions) may be potential tools to deliver progress for Papua and other remaining high-burden locales. Furthermore, vaccine development efforts to target adults and P. vivax may also be useful additions for controlling malaria in Indonesia in the future.