Malaria persists as a major public health burden in Namibia's Zambezi Region. Indoor residual spraying (IRS) is a core intervention, but insecticide resistance necessitates rotating chemical classes. The optimal rotation schedule requires empirical evaluation to maximise programme impact. This policy analysis evaluated the effectiveness of different IRS insecticide rotation schedules on malaria incidence in the Zambezi Region. It aimed to determine if specific rotational patterns were associated with improved disease control outcomes. A retrospective time-series analysis was conducted using routine surveillance data on monthly malaria case counts. The study period covered multiple rotation cycles of different insecticide classes. Interrupted time-series analysis compared incidence trends following rotations to a pyrrole-based insecticide versus rotations to other WHO-recommended classes. Rotations incorporating a pyrrole-based insecticide were associated with a more pronounced and sustained reduction in malaria incidence compared to other rotation patterns. A relative reduction in cases was observed in the period following such rotations, after accounting for seasonal trends. The insecticide class chosen within a rotation schedule significantly influences IRS programme effectiveness in this setting. A strategic, evidence-based rotation policy is critical for maintaining intervention efficacy and mitigating resistance. Namibia's malaria control programme should prioritise including pyrrole-based insecticides in rotation schedules where operationally feasible. Policy should be informed by continuous resistance monitoring and local transmission dynamics to optimise rotation timing. malaria control, indoor residual spraying, insecticide resistance, policy analysis, time-series analysis, Namibia, vector control This analysis provides evidence to support national policy decisions on IRS insecticide rotation and offers a methodological approach for evaluating vector control strategies in similar endemic settings.
Hamukoto et al. (Mon,) studied this question.