Deworming charities – Comprehensive Summary

Last updated: November, 2023

Problem

Parasitic infections from worms affect around a billion people in mostly low- and middle-income countries, and cause a range of health problems (WHO, 2011; Else et al., 2020). Lack of proper sanitation or health behaviours increases the risk of transmission because infected individuals can contaminate soil and water via their waste. These infections can cause a range of urinary, intestinal, nutritional, cognitive, and developmental problems.

Intervention

The World Health Organisation (WHO) recommends mass deworming as treatment for parasitic worms: providing anti-parasite drugs to a general (unscreened) population, usually schoolchildren, to control the prevalence of worms in an area (WHO, 2006, 2011, 2020; Else et al., 2020).

Organisations

A number of organisations provide deworming pills at scale, including the four evaluated by GiveWell discussed above.

We evaluated the impact of deworming as an intervention in general, rather than a specific organisation or programme, so our analysis applies across all such organisations.

Evaluation

Methods

Evidence for the long-term impact of deworming (two to 20 years post-intervention) primarily comes from one RCT¹There is another unpublished study in Uganda which found non-significant increases in height, schooling, maths, and English, seven to eight years after treatment (Croke, 2014). See Jullien et al. (2017) for a review of long-term effects.
: the Primary School Deworming Project (PSDP; Miguel & Kremer, 2004). In this study, different cohorts of schoolchildren in Kenya were assigned to receive different amounts of deworming medication (no group was assigned to zero medication) from 1998 to 2003. A longitudinal survey, the Kenya Life Panel Survey (KLPS; Baird et al., 2016; Hamory et al., 2021), has followed a sample of these children (n = ~7,500) from 2003 to 2019.

The KLPS contains measures of subjective wellbeing. We used this data to conduct the first analysis of the long-term impact of deworming on subjective wellbeing. We ran a meta-regression on the effect of having more deworming medication (vs. less deworming medication, as the control group received) on happiness over time.

Impact

The impact of deworming is unclear. Our analysis of the KLPS data finds small, non-significant effects of deworming on wellbeing that are positive at some time points and negative at others (see Figure 5). Calculating the total wellbeing effect involves many assumptions and uncertainties²Primary uncertainties include (1) how to integrate the effect over time, considering these are non-significant findings with some positive and some negative effect sizes – when taken at ‘face value’ over the time of the surveys, this leads to a negative effect; (2) how to count the short-term effect of deworming on wellbeing, considering we couldn’t find such data; and (3) how we should discount or adjust these findings, considering they come from only one study.
. Overall, we conclude that the impact of deworming is uncertain based on the available evidence. This finding is generally consistent with research on the impacts of deworming on other outcomes (e.g., health, cognition, income), which have also been small or inconclusive.

Figure 5. Differences in happiness between treatment and control groups over time (in WELLBYs)

Note. The point estimates show the difference (in Cohen’s d) in happiness between the treatment and control groups at each time point. The bars represent 95% confidence intervals. The regression line shows the trend of the difference between the treatment and control groups over time. The shaded area represents the ‘face value’ integration of the effect over time, which results in a negative total effect.

Cost

We use GiveWell’s estimates of the costs for the four organisations to calculate the average cost of the intervention: we estimate it costs $0.94 to provide one child with one year of deworming medication.

Cost-effectiveness

The cost-effectiveness of deworming programmes is extremely uncertain: there is limited evidence for the effect of deworming medication on subjective wellbeing, and the available evidence is inconclusive.

Quality of evidence

We think the quality of evidence supporting the effect of deworming is very low. The primary reasons for this are:

• Most of the long-term RCT evidence for the impact of deworming medication on any outcome (wellbeing, education, and income) is based on one trial, the PSDP (Miguel & Kremer, 2004), and its survey follow-up, the KLPS (Hamory et al., 2021).
• We used the subjective wellbeing data in the KLPS and found small, non-significant effects of deworming on the long-term wellbeing of recipients (Dupret et al., 2022). Some of these effects were positive but others were negative. This makes interpreting these findings and modelling cost-effectiveness very complicated.
• The rest of the evidence base for deworming also has many non-significant findings and has led to many debates (Taylor-Robinson et al., 2019; Welch et al., 2019). Hence, our conclusion of an uncertain long-term effect is consistent with the other evidence. Furthermore, this evidence does not provide us with a clear prior based of knowledge to make a decision.

Funding need

We use GiveWell’s estimates of how much the different deworming charities could absorb:

• SCI Foundation/Unlimit Health ($85 million)
• Evidence Action’s Deworm the World Initiative ($6.4 million)
• Sightsavers’ deworming programme ($28.7 million)
• The END Fund’s deworming programme (no evaluation of room for funding)

Conclusion

Based on this limited evidence, deworming treatment has a small, non-significant effect on happiness. Because the evidence is so uncertain, we do not recommend donations to deworming programmes for now. We would be interested to evaluate the medium-term evidence of deworming’s effect (i.e. up to three years after the intervention) but we are not aware of any.

FAQs

• Does the null evidence make HLI trust subjective wellbeing measures less for evaluating the impact of deworming?
  • No, it would make us doubt our measurement more if there was unambiguous evidence of deworming’s efficacy on health, education, or economic outcomes, but the evidence we found in those domains is very mixed. Also, the KLPS only has long-term data on deworming’s effectiveness. We think it’s plausible that deworming has short-term effects on subjective wellbeing, but there’s been no study of that topic.
• Are you recommending against donating to deworming charities?
  • No. Although we are unable to recommend any specific deworming programmes, we also don’t have strong evidence to recommend against them. The data is uncertain, which means deworming could be beneficial or not. We think better data is needed to confidently make a claim either way.

Our reports so far

We have one report on the effect of deworming on subjective wellbeing. We have also criticised GiveWell’s modelling of the effect of deworming on income.