The impact of Indoor Residual Spraying (IRS) withdrawal in the Lake Zone Regions in Mainland Tanzania. Should Tanzania withdrawal its IRS program?

Abstract

Abstract Background: Indoor Residual Spray (IRS) has proven to be one of the most effective malaria vector control interventions in reducing malaria transmission mainly in areas with high transmission. With the support from the US President’s Malaria Initiative (PMI), Tanzania has gone through expansion of IRS implementation with different insecticides from one district in 2007 to 18 districts in 2012. However, due to financial constraints this was followed by IRS withdrawal to 6 districts by 2021 - with planned further withdrawal in 2022 – 2023 down to 2 districts. Method: The retrospective analysis is performed to understand the impact of IRS withdrawal based on DHIS2 malaria incidence per 1000 population data. Data is subjected to interrupted time series (ITS) based on monthly periods to investigate whether the effect due to IRS withdrawal is statistically significant or not. The analysis helps to examine the changes in level and/or trend before, during, and after IRS withdrawal. Results: Visual inspections on yearly time series plots indicate that withdrawing IRS after one, two, three, or even four rounds of IRS implementation results into resurgence of malaria incidence. The interrupted time series statistical model results based on monthly data show that the difference between the trend during IRS and after withdrawal is negative and statistically significant (p < 0.001) indicating that monthly malaria incidence decreases over time during IRS. The immediate effect after the IRS is withdrawn is positive and statistically significant (p < 0.001), indicating that withdrawing IRS resulted in increased malaria incidence. The sustained effect after IRS withdrawal is positive and statistically significant (p < 0.001), indicating that each day that passes after IRS is withdrawn, the malaria incidence increases. Overall, malaria resurgence is observed in almost all the districts in which IRS was prematurely withdrawn. Such malaria rebounds costs human lives and therefore may go beyond epidemiological concerns, raising ethical, moral and human rights issues. Conclusion: Any decision to withdrawal IRS should ensure its replacement with an equally effective or superior intervention. There is currently no data to support that the new nets being rolled-out in the country are suitable alternatives to IRS; especially in areas of high malaria transmission with reported insecticide resistance. This calls for a need for endemic countries to continue collecting data in local setting on the performance of current and forthcoming “new net” products to ascertain their suitability to replace IRS.