Countries have been urged not to “rush” to make changes to clinical care following the UK breakthrough on a coronavirus treatment.

The World Health Organisation (WHO) praised British scientists after they found that a cheap steroid could help reduce the risk of death for some of the sickest Covid-19 patients in hospital.

But the global health body said “this is not the time to rush to change clinical practice”.

It said that the full data from the trial is yet to be released and published in a peer-reviewed journal.

The WHO said it was convening an expert group to assess the results before it changes its clinical advice to countries around the world.

On Tuesday a team of researchers at the University of Oxford were hailed for their “major breakthrough”.

The study of dexamethasone suggests it is the first drug to reduce deaths from coronavirus, and has been described as the most important trial result for Covid-19 so far.

Researchers found the drug reduced deaths by up to a third among patients on ventilators, and by a fifth for those on oxygen.

It has been immediately approved to treat all UK hospitalised Covid-19 patients requiring oxygen, including those on ventilators.

In a press conference in Geneva, officials from the WHO welcomed the news but stressed that it must be used in specific clinical circumstances.

Dr Tedros Adhanom Ghebreyesus, WHO director general, said: “Yesterday there was the welcome news of positive initial results from the RECOVERY trial in the United Kingdom.

“Dexamethasone, a common steroid, has been shown to have a beneficial effect on those patients severely ill with Covid-19.

“According to the early findings shared with WHO, for patients on oxygen alone the treatment was shown to reduce mortality by about one fifth.

“And for patients requiring a ventilator, mortality was reduced by about one third.

“However, dexamethasone was shown to not have a beneficial effect for those with milder disease, who did not need respiratory support.

“This is very welcome news for those patients with severe illness, these drugs should only be used under close clinical supervision.

“We need more therapeutics that can be used to tackle the virus, including those with milder symptoms.”

Dr Mike Ryan, executive director of the WHO’s health emergencies programme, said: “It’s exceptionally important that the drug is used under medical supervision – this is not for mild cases, this is not for prophylaxis. This is a very, very powerful anti-inflammatory drug.

“It can rescue patients who are in very serious condition where their lungs and their cardiovascular system around the lungs may be very inflamed.

“So this allows possibly the patients are able to continue getting oxygen into the blood from the lungs for a very critical period by rapidly reducing inflammation and a critical period in the illness.

“It is not a treatment for the virus itself, it is not a prevention for the virus.

“In fact, steroids, particularly powerful steroids, can be associated with viral replication. In other words, they can actually facilitate the division and replication of viruses in human bodies. So it’s exceptionally important in this case, this drug is reserved for use in severely critical patients.”

He added: “It is one of the many breakthroughs we’re going to need in order to effectively deal with Covid-19 and as such we should celebrate that today but it’s still just preliminary data from one study, it is very significant, but we also have to see the real, full data.

“We thank our colleagues in the UK and they will be working very hard over the coming days to release the detailed data to get this published in peer-reviewed journals so everybody can see what the results are.”

Dr Ryan added: “We will pull together the necessary expert group to look at all of that, both on the research and the clinical side, and come to a conclusion around our clinical advice to countries.

“And it’s important that each country takes that measured approach as well.

“This is not the time to rush to change clinical practice in a too rushed a fashion.

“People need training, we need to understand what doses to be used, how patients are going to be clinically assessed, we need to make sure there are supplies of the drug, we need to look at a lot of things.

“So while we’re very pleased today, we still need to see the final data, we need to adjust the clinical guidelines that will be needed and we need to support countries to both access and utilise this drug in the most appropriate way possible.”

Meanwhile, a WHO official confirmed that the Solidarity trial involving the malaria drug hydroxychloroquine had been halted after results from other trials showed no benefit.