evidence: A national study has found that a significant proportion of clinically at-risk patients with certain immunocompromised or immunosuppressed conditions, mount a low, or undetectable, immune response after two doses of the same COVID-19 vaccine. The ongoing multi-centre OCTAVE study is evaluating the immune responses following COVID-19 vaccination in patients with immune-mediated inflammatory diseases such as cancer, inflammatory arthritis, diseases of the kidney or liver, or patients who are having a stem cell transplant. Initial data from the study have been published on the Lancet pre-print site. [...] The study used a variety of state-of-the-art immune tests performed on blood samples taken before and/or after COVID-19 vaccination in around 600 people recruited across the UK. OCTAVE's early data show that 40% of people in the patient groups studied mounted a low serological immune response after two SARS-CoV-2 vaccines.