Malaria Surveillance Performance and Persistent Transmission During the Elimination Phase in Mizoram, India, 2017-2024

Background: Despite substantial progress towards malaria elimination in India, Mizoram continues to experience persistent and fluctuating transmission. Previous studies have established the spatial concentration of malaria in high-burden districts. However, recent changes in transmission in relation to routine surveillance performance remain insufficiently understood. Objectives: To assess temporal changes in malaria transmission and surveillance performance in Mizoram during 2017-2024 and examine the relationship between surveillance indicators and malaria incidence Methods: A retrospective ecological study was conducted using district-level malaria surveillance data from the National Vector Borne Disease Control Programme for 2017-2024. Annual Parasite Incidence (API), Annual Falciparum Incidence, Slide Positivity Rate (SPR), Plasmodium falciparum percentage, Annual Blood Examination Rate (ABER), blood-slide collection and examination, confirmed cases, and malaria deaths were analysed. Temporal trends and district-level variation were assessed using descriptive statistics, Spearman’s rank correlation, and multivariate linear regression. Results: Malaria transmission declined during 2017-18 but resurged from 2019, with marked increases during 2022-2024. Transmission remained concentrated in Lawngtlai, Mamit and Lunglei, while several districts maintained low incidence. Rising API coincided with increasing SPR, whereas ABER declined after 2022, indicating that increased malaria burden was accompanied by higher parasite positivity despite changing surveillance intensity. SPR showed the strongest positive association with API (ρ=0.99, p<0.001) and remained statistically significant after adjustment. Falciparum-related mortality persisted, although the case fatality rate declined from 0.09 per cent in 2019 to 0.05 per cent in 2024. Conclusion: Malaria resurgence in Mizoram during the elimination phase reflects persistent focal transmission despite sustained routine surveillance. The close association between API and SPR indicates continuing transmission intensity, while changing surveillance patterns highlight the need to strengthen timely diagnostic processing and case detection. Elimination strategies should prioritise surveillance responsiveness and targeted transmission reduction in persistently affected districts.