Ethics dictate always using the smallest viable cohort to show that giving the treatment regimen (in this case dosage for a drug known to be effective) isn't obviously worse than the thing it's supposed to treat, even if we're already pretty sure. This also keeps the costs of running the studies down so we can effectively conduct more studies for more treatments.

We also already have data about its use in babies over 11 lbs, and this is just going even smaller to 4.4 lbs, so a strong baseline has already been demonstrated.

Statistical power. Malaria doesn’t go away on its own. They know the treatment should be overwhelmingly effective if dosed correctly, it’s merely a measure of determining dosage vs negative effects.

Also they apparently didn't use a control group, the study was terminated early, and after the 43 day test window 9 of the 28 participants are listed as having the adverse event of malaria.

I'm particularly confused by that last one. How is malaria considered an adverse event when testing an anti-malaria treatment? Other data in the study shows that 1 participant had malaria again with matching DNA, meaning the original infection likely came back. 6 others were reported as getting malaria again but with different DNA. So what does it mean to have 9 with the adverse event of malaria?

This particular one is mostly about dosing, the available medicines were weight based, with lowest dosages in the 5-15kg range. This brings dosages lower allowing more precise dosing for the lighter babies.

Edit: it's a very welcome addition. Limits side effects.

As opposed to what?

Isn't that how medicine works?