The first treatment for coronavirus in the community has been approved by the Department of Health after Oxford University found that a cheap asthma drug cuts illness times by three days.
There is currently no specific treatment for coronavirus, with patients usually being advised to take paracetamol to reduce their fever, or cough medicine.
However, Oxford University found that in the most at-risk patients, inhaled budesonide clears up the infection far more quickly and may even prevent hospitalisation and long Covid.
On Monday, an alert was sent to the NHS saying the drug can now be used off-label for the treatment of coronavirus for the over 65s, or at risk over 50s.
Scientists chose to trial the corticosteroid budesonide after noticing that people with asthma were under-represented in hospitalised Covid patients, which is not the case in other respiratory illnesses, such as seasonal flu.
Researchers suspected it could be the asthma treatments which were preventing the virus from progressing.
The trial showed that on average the 971 patients who had been assigned inhaled budesonide recovered three days more quickly than nearly 2,000 people who received standard care. Nearly a third got better within two weeks compared to just 22 per cent of the control group.
Associate Professor Gail Hayward, co-lead investigator of the Principle trial and a practicing GP, said: "For the first time in the pandemic I now have evidence for a treatment to offer my patients, the ones who are at home, not hospital, who develop Covid.
"This does have significant implications for the world because this is the first time we’re showing some benefit for patients in the community and the majority of patients who get Covid are in the community. Something that can make them feel better three days sooner is significant.
"We found that for patients at higher risk of severe Covid-19, we can shorten the duration of their illness, improve their wellbeing and they do better when they’ve recovered. We can certainly see a better future for patients with a high risk of severe Covid."
The researchers said budesonide could be rolled out quickly because it is cheap, widely available and has very few side effects. One inhaler costs just £14.
All patients enrolled in the Principal trial were aged over 50 with an underlying health condition that put them at a higher risk of serious Covid, or aged over 65.
Patients were asked to inhale 800 micrograms twice a day for 14 days and were followed-up for 28 days.
The study also showed that just 8.5 per cent of the budesonide group were hospitalised within 28 days, compared with 10.3 per cent of the control group - a 17 per cent decrease - although the researchers said it was difficult to tell if the effect was real because cases were dropping in Britain during the trial.
Describing how the drug works, Professor Mona Bafadhel, from Oxford University's Nuffield Department of Medicine, said: "We know that inhaled budesonide is a topical anti-inflammatory, so it works at the site of where the virus is likely to be causing its biggest effect.
"More recently from experimental laboratory analysis, they’ve been shown in cells to reduce viral replication and reduce the expression of the Ace-2 receptor, and we know that’s an important receptor, allowing the virus to enter the cell."
Joint chief investigator Professor Richard Hobbs, Head of Oxford University’s Nuffield Department of Primary Care Health Sciences, said the results were a "significant milestone" in the pandemic.
"For the first time we have high-quality evidence of an effective treatment that can be rolled out across the community for people who are at most risk of developing more severe illness from Covid-19," he said.
"Unlike other proven treatments, budesonide is effective as a treatment at home and during the early stages of the illness. This is a significant milestone for this pandemic and a major achievement for community-based research."
Professor Fiona Watt, executive chair of the Medical Research Council, which co-funded the study, added: "People around the world will be helped to recover faster thanks to these exciting new results."