Correspondence to Dr Fathimath Farah Shiham, Liverpool School of Tropical Medicine, Liverpool L3 5QA, UK; farah.shiham@doctors.org.uk Convalescent plasma treatment of severe COVID-19: potential benefit but many unanswered questions Virus-specific antibodies in convalescent plasma have demonstrated a therapeutic benefit in viral infections such as SARS and may offer similar potential in COVID-19 infection. Liu and colleagues (Nat Med 2020;26:1708) conducted a retrospective propensity score matched control study to evaluate the effectiveness of convalescent plasma therapy in 39 patients with severe or life-threatening COVID-19 within 14 days of symptom onset. For safety reasons, older participants were vaccinated after the 18–55 cohort and hence only 5 cases of COVID-19 had occurred in participants older than 55 at data lock; therefore, vaccine efficacy in this age group could not be assessed.