Lay summary
Shingles (zoster) and its complications place a heavy burden on people, their families, and the healthcare system. Current treatments have limited success, especially for individuals with weakened immune systems. These patients are of interest due to potential immune system suppression or over-activation caused by the primary disease or treatment, affecting vaccine effectiveness. The shingles vaccine is available and included in national immunisation programmes in many countries. To reduce the burden and improve quality of life, understanding the vaccine's performance in medical practice is crucial. Most trials exclude individuals with weakened immune systems, so evidence from clinical practice is necessary to complement findings from these trials. We aim to summarise international evidence on the effectiveness of the shingles vaccine in preventing shingles-related outcomes in people with weakened immune systems. This information will provide policymakers, practitioners, and the general public with a better understanding of the benefits of shingles vaccination.