Third primary SARS-CoV-2 prophylactic mRNA vaccines enhances antibody responses in the majority of patients with haematological malignancies: Results from the MARCH study (preprint)

SARS-CoV-2 infection, and resulting disease, COVID-19, has a high mortality amongst patients with haematological malignancies. Global vaccine rollouts have successfully reduced hospitalisations and deaths, but the efficacy of vaccination in patients with haematological malignancies is known to be reduced. The UK-strategy offered a third, mRNA-based, vaccine as an extension to the primary course in these patients. Here we quantify serological responses following these vaccines in a cohort of 381 patients with haematological malignancies attending routine haematology outpatient clinics. By comparison with healthy controls, we report suboptimal responses following two primary vaccines, with significantly enhanced responses following the third primary dose. These responses however are heterogeneous and determined by haematological malignancy sub-type and therapy. We identify a group of patients with continued sub-optimal vaccine responses who may benefit from additional doses, as well as early intervention with monoclonal therapies in the event of developing SARS-CoV-2 infection.