The findings confirm the results of an earlier trial, which has already led to steroids being used widely for Covid patients in intensive care.

The new results, published in JAMA, show eight lives would be saved for every 100 patients treated.

The researchers said the findings were impressive, but stressed steroids were not a coronavirus cure.

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• .What progress are we making on treatments?
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In June, the UK's Recovery trial found the first drug - a steroid called dexamethasone - that could save the lives of people with severe Covid.

The latest study brings together all clinical trials involving steroids on coronavirus patients around the world.

It confirms dexamethasone works and that another steroid, hydrocortisone, is equally effective.

"At the beginning of the year, at times it felt almost hopeless knowing that we had no specific treatments," said Prof Anthony Gordon, from Imperial College London.

"It was a very worrying time, yet less than six months later we've found clear, reliable evidence in high quality clinical trials of how we can tackle this devastating disease."

The results on 1,703 critically ill patients showed:

• .40% died when given only standard treatment
• .32% died when given steroids

The studies were on only the sickest hospital patients. Most people recover having only experienced mild symptoms.

Steroids calm down inflammation and the immune system, which is why they are already used in conditions like arthritis and asthma, as well as in some severe infections.

The drugs are not thought to be helpful in the early stages of a coronavirus infection - when symptoms include a cough, fever or a sudden loss of taste or smell.

But as the disease develops, the immune system can go into overdrive, damaging the lungs and other organs.

It is this stage of Covid that steroids are thought to help with.

"At the point at which you reach for an oxygen cylinder for a patient with Covid, you probably should be reaching for the prescription for corticosteroids," said Prof Martin Landray, from the University of Oxford.

"These results are instantly useable; they are widely available, cheap, well-understood drugs that reduce mortality."

Doctors are already using dexamethasone after the results earlier in the year, but the hope is that having the choice of different drugs will increase access to the treatment around the world.

The drugs can either be swallowed as tablets or given via intravenous drip.

The research so far has focused on low doses of steroids. There is no evidence that higher doses would be more effective.

New guidelines for doctors are expected to be released by the World Health Organization.

In the UK, NHS chief executive Sir Simon Stevens said: "Just as we did with dexamethasone, the NHS will now take immediate action to ensure that patients who could benefit from treatment with hydrocortisone do so, adding a further weapon in the armoury in the worldwide fight against Covid-19."