The impact of mass deworming programmes on schooling and economic development: an appraisal of long-term studies

Background Documents from advocacy and fund-raising organizations for child mass deworming programmes in low- and middle-income countries cite unpublished economic studies claiming long-term effects on health, schooling and economic development. Methods To summarize and appraise these studies, we searched for and included all long-term follow-up studies based on cluster-randomized trials included in a 2015 Cochrane review on deworming. We used Cochrane methods to assess risk of bias, and appraised the credibility of the main findings. Where necessary we contacted study authors for clarifications. Results We identified three studies (Baird 2016, Ozier 2016 and Croke 2014) evaluating effects more than 9 years after cluster-randomized trials in Kenya and Uganda. Baird and Croke evaluate short additional exposures to deworming programmes in settings where all children were dewormed multiple times. Ozier evaluates potential spin-off effects to infants living in areas with school-based deworming. None of the studies used pre-planned protocols nor blinded the analysis to treatment allocation. Conclusions In the context of reliable epidemiological methods, all three studies are at risk of substantial methodological bias. They therefore help in generating hypotheses, but should not be considered to provide reliable evidence of effects.