Summary Little is known of the course of COVID‐19 and the antibody response to infection or vaccination in patients with hairy‐cell leukaemia (HCL). Among a total of 58 HCL cases we studied in these regards, 37 unvaccinated patients, mostly enjoying a relatively long period free from anti‐leukaemic treatment, developed COVID‐19 between March 2020 and December 2021 with a usually favourable outcome (fatality rate: 5/37, 14%); however, active leukaemia, older age and more comorbidities were associated with a worse course. Postinfection ( n = 11 cases) and postvaccination ( n = 28) seroconversion consistently developed, except after recent anti‐CD20 or venetoclax therapy, correlating with perivaccine B‐cell count. Vaccination appeared to protect from severe COVID‐19 in 11 patients with breakthrough infection.