The Effects of Indoor Residual Spraying on Prevalence of Malaria among Under-five Children in Zambia; A Retrospective Cohort Study

ABSTRACT Introduction Malaria remains a global challenge despite the efforts to eliminate it by 2030 by the WHO and its partner countries. About 93.6% of the malaria cases and 95.4% of the deaths occurred in Africa. Zambia is one of the top 20 highly endemic countries with about a third (29.3%) of all children aged 6 to 59 months having malaria in 2021 and it accounts for about 1.4% of the global malaria incidence and mortality. Among the interventions used to eliminate malaria is Indoor Residual Spraying (IRS). Existing literature has shown the effects of IRS on malaria prevalence and incidence by comparing IRS versus no IRS intervention. This study assessed the effects of IRS on malaria prevalence over time from when it was done in three monthly cohorts over a period of one year. Methods This study was a retrospective cohort study. Data was collected retrospectively covering a period of 12 months when the IRS was done in the households where the Malaria Indicator Survey of 2021 was carried out. The study then compared malaria prevalence in closed cohorts of three months. Data was analysed in Stata version 14, descriptive statistics were summarized as counts and percentages, cross-tabulations between the dependent variable and independent variables were done and measures of association were assessed using univariate and multivariable logistic regression. The level of significance was set at 0.05. Results The study included 1,786 children aged six to 59 months and more of these were female 52.5% (938/1786). Among the children, 14.7% (263/1786) were in the 0 to 3 months cohort, 59.3% (1059/1786) were in the 4 to 6 months cohort, 16.2% (289/1786) in the 7 to 9 months cohort and 9.8% (175/1786) in the 10 to 12 months cohort. The malaria prevalence was 33.4%. There were no significant statistical differences in the malaria prevalence among children in the four cohorts. Conclusion This study found that over a period of one year, the protective effect of Indoor Residual Spraying was not statistically different among under-five children whether it was done within zero to three months, four to six months, seven to nine months or ten to twelve months. This implies that the protective effects of IRS on malaria prevalence extended equally over a period of 12 months.