Can dual active ingredient Interceptor® G2 insecticide-treated net (ITN) replace indoor residual spraying (IRS)...

Following three successful rounds of indoor residual spraying (IRS) implementation in the district of Sakassou (Côte d'Ivoire), IRS was withdrawn and replaced by insecticide-treated nets (ITNs). This study evaluated the entomological and epidemiological impacts of Interceptor (IG2) ITNs distributed in Sakassou to determine whether the protection offered by IG2 ITNs was adequate to suppress malaria transmission post-IRS withdrawal.

This study is a quasi-experimental evaluation using historical data and additional data collections on entomological indicators and malaria incidence to assess malaria transmission trends in Sakassou. The vector control optimization model was adapted to evaluate the effectiveness of the IRS and IG2 ITN deployment on malaria transmission dynamics. Additionally, we used an interrupted time series model to analyze routinely reported malaria cases in the District Health Information Management System (DHIS2) to determine the epidemiological impact of both interventions. Counterfactual trends were generated for the post-IRS withdrawal period during which IG2 ITNs were distributed.

The results showed a 55.4% (95% CI 48.3-62.4%) reduction in the human biting rate (HBR) when IRS was deployed and 48.8% (95% CI 42.8-54.6%) when IG2 ITNs were distributed, compared with standard pyrethroid-only nets. No statistical difference was recorded between the HBR of IG2 ITNs and IRS (P = 0.164) during the implementation of IG2 ITNs and the counterfactual of IRS. Similarly, IRS resulted in a 64.7% (95% CI 56.6-72.8%) decline in EIR while IG2 ITNs resulted in a comparable reduction of 61.9% (95% CI 54.2-69.6% ;P = 0.616) over the same period. Furthermore, a 26% reduction in malaria cases was recorded immediately after spraying (IRR = 1.02; 95% CI 1.00-1.04; P = 0.005) with cumulative impact over time and spray rounds and was similar to IG2 performance (IRR = 1.03; CI 1.00-1.07; P = 0.040).

The study findings suggest that IG2 ITNs provided entomological efficacy comparable to clothianidin-based IRS but could not adequately suppress malaria cases after IRS withdrawal, possibly due to plastic-vector feeding behavior and late timing of IG2 deployment. Overall, the study shows how the dynamics of malaria transmission and operational decisions could impact the effectiveness of both IRS and ITNs as vector control tools. These findings provide key information for malaria programs and policymakers to consider when deploying vector control interventions as countries work toward malaria elimination.