BACKGROUND: In the treatment of acute malnutrition (AM), non-response is considered a treatment failure for not meeting recovery criteria within a therapeutic window of 12-16 weeks, but this category of children is misunderstood. As current research emphasizes ways to simplify and optimize treatment protocols, non-response emerges as a new issue to enhance program efficiency. METHODS: A prospective cohort study was conducted from 2019 to 2020 at two health centres in Mirriah, Niger among children aged 6-59 months with uncomplicated AM treated under the Optimising treatment for Acute MAlnutrition (OptiMA) protocol. Children who did not meet recovery criteria by 12 weeks (mid-upper arm circumference (MUAC) ≥125 mm without oedema for two consecutive weeks) were classified as non-responders. Non-responders received a home visit six-months post-discharge. Logistic regression was used to analyze factors associated with non-responders compared with children who recovered. RESULTS: Of the 1,112 children enrolled, 909 recovered and 139 were non-responders, of which 127 (80.6%) had significant MUAC gain (mean: +9.6 mm, sd = 5.1) at discharge. Girls (adjusted hazard ratio (aHR) = 2.07, 95% CI 1.33-3.25), children <12 months of age (aHr = 4.23, 95% CI 2.02-9.67), those with a MUAC <115 mm (aHR = 11.1, 95% CI 7.23-17.4) or severe stunting (aHR = 2.5, 1.38-4.83) at admission and a negative or flat MUAC trajectory between admission and week 4 (aHR = 4.66, 95% CI 2.54-9.13) were more likely to be non-responders. The nutritional status of non-responders had generally improved 6 months after discharge, but only 40% had achieved MUAC ≥125 mm. CONCLUSION: Non-responders are not a homogeneous group; while most children ultimately show significant nutritional improvement, rapid hospital referral is crucial for those not gaining MUAC early in treatment. As efforts to expand MUAC-based programming progress, adapting exit criterion and/or providing additional food supplementation with smaller daily ration for children with risk factors discussed here may help improve programme efficiency without adding to the cost of treatment.< Réduire