Iron deficiency and vaccine efficacy: A mini-review of immunological interplay and evidence across vaccine types.

Iron deficiency (ID), the world's most prevalent micronutrient disorder, is known to impair immune function. However, its influence on vaccine efficacy remains under-explored. This mini-review examines the interplay between iron status and immunological responses to vaccines, synthesizing evidence from human and animal studies across various vaccine types. We highlight key immune mechanisms affected by iron, such as T-cell proliferation, B-cell differentiation, and cytokine modulation, and examine how these disruptions alter vaccine responsiveness. While some studies show clear negative effects of iron deficiency, particularly in pediatric and animal models, others find minimal impact, particularly with mRNA and COVID-19 vaccines. Iron supplementation appears to improve immune outcomes in several studies, though evidence varies by pathogen, vaccine type, and severity of deficiency. These findings carry important implications for global immunization strategies, especially in iron-deficient populations. We recommend that future vaccine policy and research incorporate iron status as a critical factor in optimizing vaccine effectiveness.