OptiMAx Will Test Whether SQ-LNS Incentivises Vaccination Uptake in Rural Chad and Niger, With a Cost Effectiveness Analysis. It Will Also Look at Whether Having Received SQ-LNS Before Becoming Malnourished Leads to Better Outcomes for Children Treated Under the OptiMA Protocol.

Inclusion Criteria: * All non-malnourished children between 6 and 12 months of age will be eligible for SQ-LNS supplementation until they reach 18 months of age. For the annual household surveys, * Children aged 6 to 59 months will be surveyed on MUAC status and other malnutrition-related issues, while the immunization analysis will focus on children aged 12 to 23 months; * With the informed oral consent of the parents or legal guardian ; * Reside in the neighborhoods included in the study. For the mixed-methods process evaluation and gender sub-study (to be carried out in the months following implementation). Inclusion criteria * OptiMAx intervention personnel (e.g. healthcare staff) * A group of mothers of children benefiting from the intervention * Male partners/spouses of parents * Community members from the sites targeted by the intervention will be recruited for the focus groups. * Non-adherents or parents who choose not to continue nutritional supplementation and/or vaccination despite their availability under the program will be recruited for interviews. * Husbands/male partners of non-members will also be surveyed. Exclusion Criteria: * Age-eligible children with MUAC \<125 or edema will first be treated for acute malnutrition with OptiMA and then resume supplementation with SQ-LNS. There is no exclusion criteria for the annual household surveys Exclusion criteria for the mixed-methods process evaluation \- Parents or guardians under 15 years of age.