BackgroundMass drug administration (MDA) of praziquantel is an intervention used in the treatment and prevention of schistosomiasis. In Malawi, MDA happens annually across high-risk districts and covers around 80% of school aged children and 50% of adults. The current formulation of praziquantel is not approved for use in the preventive chemotherapy for children under 5 years old, known as pre-school aged children (PSAC). However, a new formulation for PSAC will be available by 2022. A comprehensive analysis of the potential additional benefits of including PSAC in the MDA will be critical to guide policy-makers.MethodsWe developed a new individual-based stochastic transmission model of Schistosoma haematobium for the 6 highest prevalence districts of Malawi. The model was used to evaluate the benefits of including PSAC in the MDA campaigns, with respect to the prevalence of high-intensity infections (> 500 eggs per ml of urine) and reaching the elimination target, meaning the prevalence of high-intensity infections under 5% in all sentinel sites. The impact of different MDA frequencies and coverages is quantified by prevalence of high-intensity infection and number of rounds needed to decrease that prevalence below 1%.ResultsIncluding PSAC in the MDA campaigns can reduce the time needed to achieve the elimination target for S. haematobium infections in Malawi by one year. The modelling suggests that in the case of a lower threshold of high-intensity infection, currently set by WHO to 500 eggs per ml of urine, including PSAC in the preventive chemotherapy programmes for 5 years can reduce the number of the high-intensity infection case years for pre-school aged children by up to 9.1 years per 100 children.ConclusionsRegularly treating PSAC in the MDA is likely to lead to overall better health of children as well as a decrease in the severe morbidities caused by persistent schistosomiasis infections and bring forward the date of elimination. Moreover, mass administration of praziquantel to PSAC will decrease the prevalence among the SAC, who are at the most risk of infection.