Several SARS-CoV-2 vaccines are being rolled out worldwide, following testing in healthy volunteers and smaller groups of people with comorbidities, including HIV. Human T-cell leukaemia virus type 1 (HTLV-1), a retrovirus like HIV, is oncogenic and can cause chronic immune dysfunction. However, there is no established antiretroviral treatment for HTLV-1. An estimated 10 million individuals live with HTLV-1 worldwide. Two main disease patterns are recognised: lymphoproliferative immunodeficient (adult T-cell leukaemia/lymphoma) and inflammatory immunodysfunctional (HTLV-1-associated myelopathy).