Should the WHO withdraw support for mass deworming?

  • Croke K
  • Hicks J
  • Hsu E
  • et al.
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In April 2016, the World Health Organization (WHO)'s Control of Neglected Tropical Dis-eases (NTD) department and Nutrition for Health and Development (NHD) department con-vened a Guidelines Development Group meeting to review the WHO's recommendations for the control of soil-transmitted helminths in high-risk groups. Subsequent to this meeting, the WHO will announce whether it will reaffirm its long-standing recommendation of mass drug administration (MDA) in areas with more than 20% prevalence of soil-transmitted helminths (hookworm, whipworm, and roundworm). We recently released a new meta-analysis [1] working paper focusing on the effect of MDA on weight gain for children, which was pre-sented at this WHO convening. There is consensus that the relevant drugs are safe and effective. Indeed, they are the stan-dard of care for those known to be infected. Since individual collection and testing of stool samples prior to treatment is prohibitively expensive and logistically impractical in many low-income contexts, the relevant question for policy is whether the expected benefits of MDA exceed its costs, taking into account uncertainty. The literature on long-run educational and economic impacts of deworming of children in several high-prevalence settings suggests that this is the case [2]. However, the 2015 Cochrane review meta-analysis [3] disputes this view. They estimate that treatment of those known to be infected increases weight by 0.75 kg (95% confidence interval 0.24–1.26, p = 0.0038) but conclude that there is " substantial evidence " of no impact of mass treatment on weight or other outcomes at community level. This has led some to suggest that the long-term impacts discussed above are logically impossible and that the WHO policy is mistaken [4]. The new meta-analysis [1] working paper first examines statistical power in the recent Cochrane Review on deworming [3]. Next, we update the analysis in [3] by including studies omitted from that analysis and extracting additional data from included studies. To do this, we follow procedures outlined in the Cochrane Handbook for Systematic Reviews of Interventions [5], such as deriving standard errors from p values when the standard errors are not reported in the original article and contacting original study authors for clarification when necessary. The updated, full sample in [1] includes twice as many trials as analyzed by [3], substantially improving statistical power. We find that the 2015 Cochrane Review analysis [3] is statistically underpowered; that is, its analysis of nutritional outcomes would likely conclude that MDA has no effect even if the true effect were large enough (given relevant treatment cost data) to be cost-effective relative to other interventions in similar populations. The hypothesis of a common zero effect of




Croke, K., Hicks, J. H., Hsu, E., Kremer, M., & Miguel, E. (2017). Should the WHO withdraw support for mass deworming? PLOS Neglected Tropical Diseases, 11(6), e0005481.

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