Giving low doses of the generic steroid drug dexamethasone to patients admitted to hospital with Covid-19 reduced death rates by around a third among those with the most severe cases of infection, trial data showed.
The results, described as a "major breakthrough" by scientists leading the UK-led clinical trial known as RECOVERY, suggest the drug should immediately become standard care inpatients treated in hospital with the disease, researchers said.
"This is a result that shows that if patients who have Covid-19 and are on ventilators or are on oxygen are given dexamethasone, it will save lives, and it will do so at a remarkably low cost," said Martin Landray, an Oxford University professor who is co-leading the trial.
His co-lead investigator, Peter Horby, said dexamethasone - a generic steroid widely used in other diseases to reduce inflammation - is "the only drug that's so far shown to reduce mortality - and it reduces it significantly."
"It is a major breakthrough," he said.
There are currently no approved treatments or vaccines for Covid-19, the illness caused by the new coronavirus which has killed more than 431,000 globally.
For Covid-19, the World Health Organization says data to date suggests that 80% of infections are mild or asymptomatic; 15% are a severe infection, requiring oxygen and 5% are critical, requiring ventilation.
Generally, you need to be 15 minutes or more in the vicinity of an infected person and within 2 metres of them, to be considered at-risk, or a close contact.