Immunisation against vaccine-preventable diseases in individuals receiving immunosuppressive targeted therapies

The availability and clinical use of biological and small molecule targeted therapies is rapidly expanding. The intricate nature of their mechanisms and the impact of the underlying condition make it challenging for clinicians to anticipate the infectious risks and vaccination outcomes for individuals prescribed these therapies. We aimed to summarise the current evidence focusing on the risk of infections, vaccine efficacy and vaccine safety in patients receiving targeted therapies. Our review revealed variable infection risks and vaccine responses in patients on targeted therapies, ranging from dramatic (e.g., alemtuzumab, rituximab) to negligible (e.g., mepolizumab, imatinib). Higher risks of serious infection were associated with receipt of concomitant immunosuppressive medications. Vaccine immunogenicity data were predominantly restricted to COVID-19, influenza, and pneumococcal vaccines, with fewer studies on herpes zoster and hepatitis B vaccines. Vaccine responses were often impaired by many targeted therapies, but rarely eliminated. Therapies with lymphocyte-depleting effects, however, can result in inadequate vaccine responses, and were often affected by underlying conditions and concomitant immunosuppressants. Live vaccine safety remains a prominent concern for patients prescribed targeted therapies, though serious adverse events are rare. Current evidence is largely based on non-randomised trials and observational studies, which limits the strength of conclusions that can be drawn. To address this gap and ensure accurate evaluation of vaccine immunogenicity, clinical efficacy and safety, it is essential that future trials include immunocompromised individuals. Better prediction models or biomarkers for stratifying risk and predicting vaccine efficacy are also important further steps.