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

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

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.

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.

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.