Effectiveness of a dry season larviciding strategy to complement universal coverage with long-lasting insecticidal nets against malaria: a pragmatic cluster randomised controlled trial in Côte d’Ivoire

International audience Background: Malaria control has stagnated in several endemic regions despite widespread use of long-lasting insecticidal nets (LLINs). We assessed whether adding dry-season microbial larviciding to LLINs could provide additional malaria control benefit in rural West Africa.Methods: We conducted a pragmatic cluster-randomised controlled trial in northern Côte d'Ivoire. Villages were eligible if they had approximately 300 inhabitants, were separated by at least 2 km, and were accessible yearround. Sixteen villages (population 5273) were assigned to LLINs alone (eight villages) or LLINs plus weekly larval habitat treatment with Bacillus thuringiensis israelensis (Bti; eight villages). The primary outcome was malaria incidence measured through passive case detection at health centres. The secondary outcome was clinical case prevalence measured through community-based cross-sectional surveys. Data were collected over 8⋅5 months before and after randomisation. Analyses followed the intention-to-treat principle. The trial is registered with ClinicalTrials.gov (NCT03074435). Findings Between December 2016 and August 2018, 854 confirmed malaria cases were recorded over 84,446 theoretical person-months of follow-up. During the post-intervention period, malaria incidence was 23% lower in the LLIN plus larvicide group than in the LLIN-only group, although this reduction was not statistically significant (rate ratio 0⋅77 [95% CI 0⋅52-1⋅13]; p = 0⋅182). Malaria case prevalence was reduced by 40% in larvicide group (0⋅60 [95% CI 0⋅50-0⋅75]; p = 0⋅0001). No intervention-related adverse effects were reported.Interpretation Adding a microbial larviciding to LLINs reduced malaria case prevalence in a rural high-transmission setting. Further studies are needed to assess operational scalability and effectiveness across diverse transmission settings.