The benefits of the experimental antiviral remdesivir in cutting time to recovery in patients severely ill with COVID-19 might not extend to those requiring mechanical ventilation, US researchers say.

The highly anticipated preliminary findings from the randomised controlled trial, published in the New England Journal of Medicine on Friday (US local time), also address a controversial decision to change the primary outcome midway through the study.

The trial, conducted by the US National Institute of Allergy and Infectious Diseases (NIAID), compared the effects of the antiviral with placebo in 1063 patients hospitalised with COVID-19 in the US, Europe and Asia.

Dr Anthony Fauci, director of the NIAID, announced the trial results last month ahead of publication in a peer-reviewed journal, leading to the FDA granting an emergency use authorisation for the drug.