Fig. 4

Optimal deployment of IRS. a Effectiveness of IRS depends on both IRS half-life and timing of spray campaigns relative to the peak biting season. Timing has the strongest impact on moderately long-lasting IRS. Top: daily count of adult vectors and EIR. Bottom: fractional reduction in prevalence one year after an IRS campaign with 50% coverage in a population with homogeneous transmission. Mean and standard deviation of 50 stochastic realizations are shown for each half-life and campaign start date. b The matrix of shaded boxes represents prevalence reduction in a population experiencing heterogenous dry-season biting with the coverage in population experiencing dry-season biting along the vertical axis, and the fraction of the same population in the entire population along the horizontal axis. Each box within the matrix is shaded to reflect the mean number of clinical cases averted during the year after the campaign is started for 50 stochastic realizations. The optimal start month for each campaign given the coverage and fraction of the group experiencing dry-season biting is indicated in the box. Regions shaded with gray oblique lines indicate coverage in the total population was either above or below the target 50% overall coverage for the corresponding coverage and fraction of the group with dry season biting