According to GiveWell's Cost-Effectiveness Analysis (CEA), mass deworming ranks among the very best global health interventions. The evidence for deworming comes primarily from a single study, which showed large economic effects which were present a full decade after treatment. However, other studies have shown little to no effect of mass deworming on weight, cognitive ability, school attendance or other health outcomes, and the weight placed on the initial paper has proved controversial.
In GiveWell's CEA, deworming benefits are modeled as being entirely due to long-term economic effects like those seen in the study mentioned above. Despite being heavily discounted due to concerns about replicability, in expectation these economic effects are expected to dominate the short term health effects of the interventions.
Givewell's position is explained, in detail, in the following two blog posts:
Some more information is available in this evidence overview, written by GiveWell, which cites several papers, and this evidence overview, which was written by Evidence Action. While Evidence Action does currently run a deworming programme, they have proved capable of changing their minds on programmes when the evidence changes.
Currently, GiveWell lists seven top charities, of which four are deworming programmes.
At the end of 2025, will any of GiveWell's top charities perform mass deworming as their primary intervention?
Resolution will be according to the GiveWell website on 2026/01/01.
If GiveWell no longer maintains a list of "top charities", but allows donors to donate funds which will be re-granted at GiveWell's discretion, this question resolves positively if at least 10% of these regrants go to deworming charities in the year 2025.
"Mass deworming" is taken to mean treating all or almost all of the individuals in a group for parasitic worms, without testing to see whether they have them. This is common practice due to the low cost and excellent safety profile of deworming medication, as well as the relative expense of testing.
If a charity has multiple programmes, but GiveWell restricts its donations to a particular programme, that programme is considered to be the "primary intervention" for the purposes of resolution. Otherwise, whichever intervention the organisation spends most on is considered the "primary intervention".
If deworming medication is administered in addition to something else, for example a vaccine or vitamin supplement, at the same time, then whether "deworming" is the primary intervention will be determined by whether the majority of the value of the programme comes from deworming, according to GiveWell's CEA.
If GiveWell ceases to exist in a similar form, such that neither of the conditions for positive resolution above make sense, this question resolves ambiguously.
Some of the text in this question has been adapted from this EA forum post, by the same author.