No proven treatment is available for severely ill COVID-19. Therapeutic use of COVID-19 convalescent plasma (COPLA) is under investigation.

To compare the efficacy of COPLA with standard medical therapy (SMT) alone in severe COVID-19 patients.

A multicentric, open-labelled, phase-III randomised controlled trial conducted at two treatment centres with COPLA collected at the third dedicated centre in North-India, the coordinating centre during trial from June 2020 to December 2020. The study population comprised 400 participants in the ratio of 1:1 in each treatment group.

One group received COPLA with SMT (n=200), and another group received SMT only (n=200).

Primary outcome was time to clinical improvement measured by a two-point reduction in the ordinal scale. Secondary outcomes included duration of O₂ therapy, the proportion of patients on mechanical ventilation at day-7, mortality, SARS-CoV-2 antibody levels, cytokine levels and incidence of adverse events.

The median time to a two-point reduction in the ordinal scale in both groups was 9 days (IQR=7–13) (p=0.328). The median duration of O₂ therapy was 8 days (IQR=6–12) in COPLA and 10 days (IQR=6–12) in SMT group (p=0.64). The PaO₂/FiO₂ ratio showed significant improvement at 7 days in COPLA group(p=0.036). There was no difference in mortality till 28 days in both groups (p=0.62). However, if COPLA was given within 3 days of hospital admission, a significant reduction in ordinal scale was observed (p=0.04). Neutralising antibody titres in COPLA group (80 (IQR 80–80)) were higher than SMT group (0 (IQR 0–80)) at 48 hours (p=0.001). COPLA therapy led to a significant reduction in TNF-α levels at 48 hours (p=0.048) and D-dimer at 7 days (p=0.02). Mild allergic reactions were observed in 3 (1.5%) patients in COPLA group.

Convalescent plasma with adequate antibody titres should be transfused in COVID-19 patients along with SMT in the initial 3 days of hospitalisation for better clinical outcomes.

NCT04425915.