Micronutrient and protein-energy supplementation enhance vaccine responses in undernourished children: Evidence from a systematic review

Background Malnutrition impairs immune function and vaccine responses, particularly in low-income settings. This can lead to reduced seroconversion rates and compromised herd immunity in children. Nutritional interventions have been proposed to enhance vaccine immunogenicity, yet evidence remains scattered and context specific. Objective This systematic review assesses the impact of nutritional interventions—especially vitamin A, zinc supplementation, and protein-energy rehabilitation—on serological responses to routine childhood vaccines among malnourished children in low- and middle-income countries. Methods Following PRISMA guidelines, we searched PubMed, Embase, Cochrane Library, and WHO Global Health Library for studies published between 2000 and 2024. Eligible studies included randomized trials, cohort studies, and systematic reviews reporting on nutritional supplementation and vaccine seroconversion outcomes in malnourished children. Narrative reviews and retracted articles (e.g., Chandra RK) were excluded. Results From 3,245 records, 29 studies met the inclusion criteria. Vitamin A supplementation improved measles vaccine seroconversion by 35%, especially among deficient children. Zinc enhanced responses to oral vaccines (rotavirus and OPV) by 20%. Protein-energy rehabilitation significantly increased seroconversion rates for BCG and measles vaccines, particularly in children recovering from severe acute malnutrition. Evidence for iron supplementation and inactivated vaccines remained inconsistent. Conclusion Nutritional interventions can improve vaccine immunogenicity among malnourished children. Vaccination should not be delayed in malnourished children; instead, integrated strategies combining immunization and nutrition services should be prioritized to address immunity gaps in vulnerable populations.