Scientists have hailed a cheap steroid as a “major breakthrough” in the fight against Covid-19 after it was found to reduce deaths by up to a third among patients suffering the worst effects of the virus.

The mortality rate of those who end up on a ventilator is above 40%, but this was reduced by a third among people prescribed dexamethasone.

More than 11,500 patients from 175 NHS hospitals have been enrolled on the Recovery trial since it was set up in March to test a range of potential coronavirus treatments.

In the dexamethasone study, 2,104 patients received 6mg of dexamethasone once a day by mouth or intravenous injection for 10 days.

Their outcomes were compared with a control group of 4,321 patients.

Over a 28-day period, the mortality rate among patients requiring ventilation was 41%, and for those needing oxygen it was 25%.

Among those not requiring respiratory intervention the figure was 13%.

The study revealed the steroid reduced deaths by a third in ventilated patients and a fifth in people needing oxygen.

There was no change in deaths among patients who did not require respiratory support.

It is a major breakthrough. Dexamethasone is inexpensive, on the shelf, and can be used immediately to save lives worldwide

The Recovery trial – which stands for Randomised Evaluation of COVid-19 thERapY – was co-ordinated by scientists from the University of Oxford.

Peter Horby, professor of emerging infectious diseases at the university’s Nuffield Department of Medicine, and one of the chief investigators for the trial, described it as “an extremely welcome result”.

“This is the only drug that has so far shown to reduce mortality, and it reduces it significantly. It is a major breakthrough, I think,” he said.

“Dexamethasone is inexpensive, on the shelf, and can be used immediately to save lives worldwide.”

Martin Landray, professor of medicine and epidemiology at the Nuffield Department of Population Health, and another chief investigator, said: “Covid-19 is a global disease – it is fantastic that the first treatment demonstrated to reduce mortality is one that is instantly available and affordable worldwide.

“It’s been around for probably 60 years.

“It costs in the order of £5… for a complete course of treatment in the NHS, and substantially less – probably less than one dollar – in other parts of the world, for example in India.”

The research team is working to publish the full results of the study as quickly as possible.