Ali O. Alil^1,, Khadija F. Ali¹, Bakar O. Khatib¹, Fatma A. Massoud¹, Talib S. Khatib¹, Kali A. Omar¹, Huba H. Ali¹, Ramla M. Haji¹, Makame H. Makame¹, Zamzam J. Pandu¹, Nufayla H. Nassor¹, Shija J. Shija¹, Maulid I. Kassim¹, Makame M. Kombo¹, Elison Kemibala², Nicodem J. Govella³

Background: Zanzibar has achieved major reductions in malaria transmission through expanded coverage of insecticide-treated net (ITNs), indoor residual spraying (IRS), strong malaria surveillance systems (epidemiological and entomological), and effective case management with Artemisinin-based Combination Therapy (ACT). However, residual transmission remains a challenge, driven by both local and imported infections that continue to threaten malaria elimination efforts. This study aimed to assess the contribution of entomological surveillance and key malaria vector control interventions, particularly ITNs and IRS, in supporting malaria elimination efforts in Zanzibar. Methods: Data on entomological surveillance, key malaria interventions and malaria epidemiological data from across elven (11) districts of Unguja and Pemba from 2015–2023 were assessed retrospectively Negative binomial regression was applied to monthly district-level counts of confirmed malaria cases to estimate the impact of interventions, using the “negbin” command in STATA and zero-inflated negative binomial (ZINB) regression model was also considered. Result: 1,188 malaria incidences were analyzed. Malaria vector density steadily increased from 2015 to 2023 with no significant correlation with malaria cases. Substantia malaria incidence differed slightly between Unguja (48.29 cases per 100,000 population) and Pemba (28.04 cases per 100,000 population), but this difference was not statistically significant (p = 0.186). In contrast incidence varied significantly across district (p < 0.001). ITNs distributions significantly associated with reductions in malaria incidence (p < 0.05), with IRRs decreasing by 50% to 99% following distribution, IRS had no statistically significant effect on malaria incidences (p = 0.806). Conclusion: Sustaining entomological surveillance and timely, targeted interventions particularly before rainy seasons and in high-risk areas—remains crucial for addressing residual transmission and advancing Zanzibar’s malaria elimination goal. However, further research should conducted to assess integration of ITNs, IRS, and behavioral interventions using modeling to predict trends and explore strategic interventions.

Entomology, Surveillance, malaria interventions, elimination, malaria trend, Zanzibar