Immunocompromised patients show wide variability in vaccine-induced protection, and several biomarkers help predict who will mount a robust response. Clinical studies link measures of both humoral and cellular immunity to outcomes after vaccination, guiding individualized strategies such as additional doses or passive immunization.
Cellular and humoral biomarkers
Low B cell counts and recent anti-CD20 therapy strongly predict poor antibody responses in solid organ transplant and autoimmune patients according to Brian J. Boyarsky Johns Hopkins Medicine. Total serum IgG levels and baseline immunoglobulin replacement requirements also correlate with reduced serologic responses in patients with hematologic disease as reported by research groups studying vaccine responses in oncology clinics. Quantitative neutralizing antibody titers are the most direct humoral correlate of protection against infection and severe disease, with work by Rafi Ahmed Emory University and colleagues demonstrating relationships between neutralization, memory B cell generation, and clinical protection. On the cellular side, CD4+ T cell counts and functional assays such as interferon gamma ELISpot or intracellular cytokine staining predict durable cellular immunity and improved outcomes in populations with impaired B cell function according to John Wherry University of Pennsylvania.
Causes, relevance, and consequences
Causes of poor biomarker profiles include B cell–depleting agents like rituximab, high-dose corticosteroids, cytotoxic chemotherapy, and underlying lymphoid malignancies that reduce naive and memory B cell pools. T cell–targeting therapies and advanced HIV disease reduce CD4+ T cell help and impair vaccine-induced class switching and affinity maturation. The consequence is increased risk of breakthrough infection and attenuated durability of protection, prompting clinicians to consider additional vaccine doses, timing vaccination relative to immunosuppressive therapy, and use of monoclonal antibody prophylaxis in high-risk patients.
Practical considerations and equity
Measurement of neutralizing antibodies, B cell counts, and T cell assays can inform personalized care but access is uneven. High-resource centers can perform detailed immunophenotyping and functional assays while many regions rely on standard IgG or antibody screening. This uneven availability has cultural and territorial implications for who receives tailored protection strategies and highlights the need for pragmatic algorithms that combine readily available biomarkers with clinical risk factors. Clinicians should collaborate with immunology and infectious disease specialists to interpret biomarkers in the context of treatment timing, exposure risk, and patient values.