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.

Malnutrition and infectious disease form a vicious circle, posing a double threat to vulnerable children in low- and middle-income countries. Malnutrition makes children more vulnerable to infectious diseases, while infectious diseases increase the risk of malnutrition. When caught in this cycle, children are far more likely to die or suffer adverse effects on their health and development. High rates of wasting and low immunization coverage also constitute a weakening double burden for already fragile health systems. Every year in these contexts, hundreds of thousands of children are treated for severe wasting, while at the same time suffering repeated and prolonged epidemics of vaccine-preventable diseases such as measles. Rural areas of Chad and Niger are at the heart of this dynamic, recording some of the worst indicators of malnutrition and low vaccination coverage rates. Small-quantity lipid-based nutritional supplements (SQ-LNS) are a category of ready-to-use, nutrient-dense food supplements fortified with micronutrients, designed to prevent malnutrition and improve child survival, growth and development. A recent meta-analysis on SQ-LNS reveals that giving a child just one sachet of SQ-LNS a day for a year can reduce the risk of mortality by 27%, iron-deficiency anemia by 64%, severe wasting by 31% and severe stunting by 17%. The recent World Health Organization (WHO) guideline on complementary feeding of infants and young children aged 6 to 23 months recently recommended the use of SQ-LNS in certain contexts of food insecurity, based on evidence deemed "very safe". The distribution of SQ-LNS is also promising as an incentive for vaccination, as well as for other health services, such as participation in infant growth monitoring programs. Various operational experiences suggest that it is likely to have an impact on increasing vaccination coverage, and a modeling simulation suggests that it would lead to a significant reduction in measles morbidity and mortality. The main objective of OptiMAx is to estimate the effectiveness of a mass SQ-LNS supplementation program coupled with the routine immunization program compared with the routine immunization program alone in terms of vaccination coverage against pentavalent 1 (Niger) and measles 1 (Chad), after 12 months of program implementation, in children aged 12 to 23 months as part of an annual cross-sectional household survey. Secondary objectives include: * Estimate the effectiveness of a mass SQ-LNS supplementation program combined with the routine Essential Program on Immunization (EPI) compared with the routine EPI alone in children aged 6-18 months, after 12 months of program implementation, in terms of 1) coverage of pentavalent 3 vaccine, malaria and other childhood vaccines, 2) on-time immunization for age-eligible children. * Evaluate the feasibility and reliability of combining measles and pentavalent coverage measurements during annual MUAC-family training campaigns;. * Evaluate outcomes of acutely malnourished children who received SQ-LNS supplementation prior to RUTF treatment (as part of their inclusion in the OptiMA study) versus those who did not receive SQ-LNS supplementation The specific objectives of the process evaluation (with a sub-study on gender), modeling and economic evaluation are as follows: 1. Conduct a process evaluation of the OptiMAx intervention to understand how it works, for whom and where; 2. Understand to what extent and how gender-related facilitations and barriers affect the interaction and uptake of intervention, both on the demand side (health-seeking/intervention behaviors) and the supply side (provision of intervention services). 3. Estimate the health impact of the OptiMAx intervention, in terms of nutrition and vaccine-preventable diseases, using mathematical modeling approaches. 4. Quantify the relative costs associated with the OptiMAx intervention compared with the costs associated with existing vaccination activities in Mirriah, Niger, and Ngouri, Chad. 5. Estimate the cost-effectiveness of the OptiMAx intervention in Mirriah, Niger, and Ngouri, Chad.