Remdesivir cut the duration of symptoms from 15 days down to 11 in clinical trial at hospitals around the world.
The full details have not been published, but experts said it would be a “fantastic result” if confirmed, but not a “magic bullet” for the disease.
A drug would have the potential to save lives, ease pressure on hospitals and allow parts of lockdown to be lifted.
Remdesivir was originally developed as an Ebola treatment. It is an antiviral and works by attacking an enzyme that a virus needs in order to replicate inside our cells.
The trial was run by the US National Institute of Allergy and Infectious Diseases (NIAID) and 1,063 people took part. Some patients were given the drug while others received a placebo (dummy) treatment.
Dr Anthony Fauci who runs the NIAID said: “The data shows remdesivir has a clear-cut, significant, positive effect in diminishing the time to recovery.”
He said the results prove “a drug can block this virus” and were “opening the door to the fact that we now have the capability of treating” patients.
The impact on deaths is not as clear cut. The mortality rate was 8% in people given remdesivir and 11.6% in those given a placebo, but this result was not statistically significant, meaning scientists cannot tell if the difference is real.
It is also not clear who is benefiting. Is it allowing people who would have recovered anyway to do so more quickly? Or is it preventing people from needing treatment in intensive care? Did the drug work better in younger or older people? Or those with or without other diseases? Do patients have to be treated early when the virus is thought to peak in the body?
These will be important questions when the full details are eventually published, as a drug could have the twin benefit of saving lives and helping to lift lockdown.