Dexamethasone, a cheap and widely available drug, can help save the lives of patients seriously ill with coronavirus, UK experts say.

The low-dose steroid is part of the world’s biggest trial testing existing treatments to see to see if they also work for coronavirus.

The drug cut the risk of death by a third for patients on ventilators. For those on oxygen, it cut deaths by a fifth.

Had the drug had been used to treat patients in the UK from the start of the pandemic, up to 5,000 lives could have been saved, researchers say.

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Dexamethasone could be of huge benefit in poorer countries with high numbers of Covid-19 patients.

PM Boris Johnson said there was a genuine case to celebrate “a remarkable British scientific achievement”, adding: “We have taken steps to ensure we have enough supplies, even in the event of a second peak.”

About 19 out of 20 patients with coronavirus recover without being admitted to hospital.

Of those who are admitted, most also recover but some may need oxygen or mechanical ventilation.

These are the high-risk patients dexamethasone appears to help.

Dexamethasone is already used to reduce inflammation in a range of other conditions, including arthritis, asthma and skin some conditions.

It appears to help stop some of the damage that can happen when the body’s immune system goes into overdrive as it tries to fight off coronavirus.

This over-reaction, a cytokine storm, can be deadly.

In the trial, led by a team from Oxford University, about 2,000 hospital patients were given dexamethasone and compared with more than 4,000 who were not.

For patients on ventilators, the drug cut the risk of death from 40% to 28%.

For patients needing oxygen, dexamethasone cut the risk of death from 25% to 20%.

Dexamethasone does not appear to help people with milder symptoms of coronavirus who do not need help with their breathing.