A coronavirus drug which initially failed in Chinese trials is now working and could help end lockdown restrictions, scientists have said.
Remdesivir, a broad-spectrum antiviral, was developed more than a decade ago to cure an unknown "Disease X" and is currently being trialled on patients in the NHS.
In results published in The Lancet on Wednesday, Chinese scientists said the drug worked no better than placebo.
But less than 24 hours later, US health officials reported that their own trial, on more than 1,000 severely ill patients in 75 hospitals around the world, had seen recovery times cut from 15 days to 11, and mortality rates fall by nearly 30 per cent.
British scientists involved in the UK trials said the results were "exciting" and, once rolled out, the drug could help lessen the need for lockdown restrictions by removing the burden on the NHS and cutting deaths.
Patients who were being given placebo in the British trials are now being moved on to remdesivir.
Asked whether it could help end some lockdown restrictions, Professor Max Parmar, director of the medical research council clinical trials unit at University College London (UCL) said: "It will potentially be a help.
"Reducing time to recovery by about a third will be helpful because that reduces the time patients are in hospital and reduces the pressure on the departments. There is no doubt these are very promising results indeed."
Public health officials have consistently said it is unlikely that full restrictions will be lifted until a vaccine or treatment is available and Professor Chris Whitty, England's chief medical officer, has warned that disruptive measures will be in place for a long time to come.
But a new drug could alter that timeline, giving patients a much better chance of survival and freeing up hospital beds more quickly, meaning there is less chance of the NHS being overwhelmed. It could also help cut transmission rates if given as a preventative treatment.
Abdel Babiker, professor of epidemiology and medical statistics at the MRC Clinical Trials Unit at UCL and co-lead for the study said: "I think the impact on lockdown is going to depend more importantly on transmission in the community.
"Of course a treatment will help in the sense of less days in hospital, meaning there isn't as much pressure on the NHS.
"One would need to control the transmission and has this drug any role to play? We don't know that yet, but if people take this drug early, and this is speculation at this point, there will be less virus replication and maybe less transmission."
Now that remdesivir has been shown to be effective on its own, the next stage of trials will add an immunity suppressant drug to see if the two in combination could lower the death rate and speed up recovery even further.
Gilead, the pharmaceutical company that produces the drug, began ramping up production earlier in the year in anticipation of successful trial results.
A spokesman said: "We are investing very heavily in manufacturing – this is a drug that would typically take up to a year to manufacture end-to-end, but we've been trying to get that process down to about six months.
"We are working with hundreds of organisations globally to help us, so that we can be ready to treat as many patients as possible as quickly as possible, and our goal is to produce one million treatment courses by year end and several million in 2021 if required."
The new trial was sponsored by the US National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health. The drugs still need to be licensed by regulators and then passed by health authorities before they can be rolled out.
Dr Anthony Fauci, the director of NIAID said: "What it has proven is that a drug can block this virus. This will be the standard of care."
Brian Angus, professor of infectious diseases at the Nuffield Department of Clinical Medicine, University of Oxford, who has been carrying out British trials, said he was excited by the new results. "The most frustrating thing was having no treatments," he said. "The results are promising."
Speaking at Thursday's Downing Street press conference, Sir Patrick Vallance, the chief scientific adviser, said remdesivir "absolutely does hit a particular part of the virus" but warned that the drug is not a "magic bullet".
Professor Chris Whitty, the chief medical adviser, agreed that the preliminary results have been "encouraging", but cautioned against "over-interpreting" the drug's potential until a peer-reviewed study is published.He added that a combination of drugs is likely to be needed to overcome coronavirus.