Vulnerability-Based Adult Vaccination: Beyond Chronological Age in Geriatric Prevention

The COVID-19 pandemic demonstrated that vulnerability, rather than chronological age alone, is a major determinant of severe infectious-disease outcomes; yet adult vaccination policies remain largely based on age and selected medical conditions. This narrative review examines vulnerability as a multidimensional framework for adult vaccination and explores its implications for vaccine policy, healthy aging, and pandemic preparedness. We conducted a non-systematic search of PubMed, Scopus, and Google Scholar (January 2020–June 2026), complemented by a targeted consultation of institutional reports, and synthesized evidence on the biological, clinical, functional, and social determinants of vulnerability and their relationship to vaccination. Vulnerability emerged as a multidimensional construct in which immunosenescence, multimorbidity, frailty, and social disadvantage were consistently identified as major contributors to susceptibility to, and adverse outcomes of, infectious diseases such as COVID-19, influenza, respiratory syncytial virus, pneumococcal disease, and herpes zoster; these dimensions also shaped vaccine uptake, access, and effectiveness; and appeared to identify at-risk populations more accurately than age alone. Adult vaccination policies should therefore complement age-based recommendations with person-centered approaches incorporating multidimensional vulnerability assessment, which may improve vaccine equity, optimize protection among high-risk groups, help preserve functional independence, and strengthen pandemic preparedness. The development of a practical Vaccination Vulnerability Index warrants further investigation.