Testing indoor residual spraying coverage targets for malaria control, Bioko, Equatorial Guinea.

Objective: To test 50% indoor residual spraying coverage (percentage of households sprayed) for non-inferiority against the recommended 80% coverage for malaria control.

Methods: Indoor residual spraying was done in 2021 and 2022 on Bioko, Equatorial Guinea, in a control arm (80% coverage) and intervention arm (50% coverage) with 37 clusters each. We assessed malaria infection in a representative sample of the population during annual surveys using rapid diagnostic tests. We compared the change in the odds of Plasmodium falciparum infection between baseline and post-intervention using difference-in-differences analysis within a survey-weighted binomial generalized linear model. Given differences between the arms at baseline, we adjusted the model for indoor residual spraying coverage at baseline.

Findings: Relative to baseline, the odds of malaria infection post-intervention were 1.11 (95% confidence interval, CI: 0.81-1.52) in the 80% arm and 0.97 (95% CI: 0.72-1.29) in the 50% arm. In the adjusted model, the change in the odds of P. falciparum infection was no greater in the intervention arm than in the control arm (odds ratio: 0.89; 95% CI: 0.58-1.36), with the upper CI being lower than the non-inferiority margin of 1.43.

Conclusion: There was no evidence that 50% coverage was inferior in preventing malaria, which supports the use of this target in settings where this level makes indoor residual spraying feasible by increasing the cost-effectiveness and equity of the intervention.