Vaccine Adjuvants in the Immunocompromised Host: Science, Safety, and Efficacy.

Vaccine adjuvants are essential for enhancing immune responses to vaccines, particularly in immunocompromised populations who typically demonstrate suboptimal responses to standard vaccination. This narrative review evaluates the safety and efficacy of approved and candidate adjuvants in immunocompromised hosts, with emphasis on solid organ and hematopoietic cell transplant recipients. We examine conventional aluminum-based adjuvants alongside modern adjuvant systems such as AS01_B, MF59, and AS04, analyzing their mechanisms of action and clinical applications. The review synthesizes current evidence on the safety profiles of approved adjuvanted vaccines in immunocompromised individuals and explores emerging adjuvant candidates, including saponin complexes and toll-like receptor agonists. By examining factors that influence adjuvant immunogenicity and safety in these vulnerable populations, we identify critical knowledge gaps and future research priorities. This comprehensive analysis provides clinicians and researchers with an updated perspective on the rapidly evolving landscape of vaccine adjuvants and their specific applications in immunocompromised hosts.