Seasonal malaria chemoprevention

What the evidence says

Seasonal malaria chemoprevention (SMC) is well tested. A 2012 Cochrane review pooled seven trials with 12,589 participants, all in West Africa. Giving young children antimalarial drugs through the transmission season prevented about three quarters of clinical malaria episodes (rate ratio 0.26) and a similar share of severe malaria. The reviewers rated both findings high-quality evidence. The trials were too small to settle the effect on deaths: the estimate pointed to fewer deaths, but its confidence interval included no effect. The most-studied drug pair, amodiaquine plus sulfadoxine-pyrimethamine, made vomiting more common.

Delivery at scale has been measured too. The ACCESS-SMC project gave about 12.5 million monthly treatments in 2015 and 25.1 million in 2016 across seven countries. Case-control studies found 88 percent protection in the 28 days after a treatment. Confirmed outpatient malaria cases fell by between about 25 percent (Nigeria) and 55 percent (The Gambia) in high-transmission periods, and hospital malaria deaths fell by 42 percent in Burkina Faso and 57 percent in The Gambia. Coverage was imperfect: only 53 to 55 percent of eligible children received all four monthly rounds. Four rounds cost about $3.63 per child.

GiveWell describes a large real-world study that found case reductions of about 25 to 55 percent, smaller than in the trials, and it still treats the trial results as the better guide. In 2022 WHO widened its recommendation. SMC is no longer limited to the Sahel or to children under 6, and the number of monthly rounds is no longer capped at four. In 2021, programs reached roughly 45 million children in 15 African countries.

Where it sits on the depth scale

SMC is prevention (depth 2). It stops malaria in the children who receive it, but protection fades within about a month, so campaigns have to return every season. It doesn’t change the conditions that let malaria persist, such as mosquito habitats or weak health systems. In that way it resembles bed nets: it saves lives now, and the benefit lasts only as long as the funding.

Open questions

• What a new dollar achieves depends on whether another funder would have paid for the same campaign. GiveWell puts that chance at 10 to 65 percent, depending on location. That is one form of the counterfactual problem.
• ACCESS-SMC found drug-resistance markers at low levels but saw selection for one linked to sulfadoxine-pyrimethamine resistance, which needs monitoring. GiveWell says it has not reviewed resistance data since 2020.
• Malaria vaccines are being rolled out. GiveWell notes this could make SMC either more or less cost-effective.