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With millions of people around the world under lockdown because of Covid-19, the race is on to find a drug or vaccine that will stop the virus – which has killed more than 225,000 people – in its tracks. 

Amid all the tests and trials, in the past few days you may have heard of one drug being hailed as a possible treatment for coronavirus – remdesivir.

On Wednesday, officials testing the effect of the drug on Covid-19 called preliminary results from a US trial “highly significant”, with evidence suggesting it could cut down the duration of coronavirus symptoms by almost a third. 

“What it has proven is that a drug can block this virus,” said Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases (NIAID), which ran the trial. 

“This will be the standard of care,” he added. 

What actually is remdesivir – and what impact does it have on coronavirus? Here’s what you need to know.

So, what is remdesivir? 

Remdesivir is an anti-viral drug that was originally developed to treat Ebola – a virus with a fatality rate of around 50%. 

It was dropped from Ebola trials after other drugs were found to be more effective in treating the disease. 

But the experimental drug – which is produced by US pharmaceutical company Gilead – has been revived as a potential treatment for coronavirus. 

Unlike a vaccine, which would prevent people from developing the disease, it is hoped remdesivir could be used to treat the symptoms of the virus. 

Scientists thought it could be used to fight Covid-19 after animal trials showed it had some impact fighting Mers and Sars – other strains of coronavirus that also cause respiratory issues in humans. 

What did the US-led trial show? 

Remdesivir was tested in a US-led international clinical trial, with more than 1,000 Covid-19 patients in hospitals around the world taking part. 

During the trial, patients were given the antiviral drug – or a placebo – every day for 10 days while they remained in hospital.

The first results from the trial showed that the recovery time of coronavirus patients given remdesivir was almost a third faster than those given a placebo. 

The NIAID – which carried out the trial – said remdesivir coronavirus patients recovered in 11 days, compared to 15 days for placebo patients. 

In the study, scientists defined recovery as a patient being well enough to come off oxygen, being discharged from hospital or returning to normal activity levels.  

Preliminary results also showed a trend toward better survival rates for the drug – 8% of patients given remdesivir died, compared to 11.6% in the placebo group. 

However, scientists admitted that the difference was not significant enough that they could be sure it was down to the effect of the drug. 

According to Reuters, the full results of the trial could come by the middle of May.  

But didn’t a remdesivir trial in China fail? 

If it feels like you heard about remdesivir before the results of the clinical trial were published on Wednesday, it’s probably because you did.

Just a week ago, the BBC – among others – published the story: “Hopes dashed as coronavirus drug remdesivir ‘fails first trial’.”

It was about how draft documents accidentally published by the World Health Organisation revealed that a Chinese trial of remdesivir had found the drug ineffective in treating coronavirus and reducing Covid-19 deaths. 

However, Gilead insisted that the trial in Wuhan was terminated early because of low enrolment, and was therefore not statistically meaningful. 

On Wednesday, the authors of the study themselves wrote in The Lancet that the true effectiveness of remdesivir remained unclear for this reason. 

Leader of the research Professor Bin Cao said it was not the outcome his team had hoped for but added that he recognised they were limited in the patients they could sign up.

Nonetheless, the Chinese study has led some scientists to question the effectiveness of remdesivir. 

What don’t we know about the drug? 

While the preliminary results of the US-led remdesivir clinical trial are hopeful, there are still a lot of things that are unknown about the anti-viral drug.

The Guardian quotes Dr Elena K Schneider-Futschik – from the University of Melbourne’s department of pharmacology and therapeutics – saying it was not clear who might benefit from the drug. 

“It might highly depend on when and at what stage of the infection patients receive the drug,” she said. “We can say it is currently not clear who is benefiting from remdesivir.

“Is it helping patients who would have recovered anyway, recover quicker? Is remdesivir more beneficial for younger compared [with] older patients? At what stage of the infection does treatment yield the best outcomes?” 

Professor Mahesh Parmar – who oversaw the EU portion of the trial – said scientists would continue to gather data while the early results are reviewed by regulators. 

“These results are very promising indeed,” Parmar said. “They show that this drug can clearly improve time to recovery.

“Before this drug can be made more widely available, a number of things need to happen: the data and results need to be reviewed by the regulators to assess whether the drug can be licensed and then they need assessment by the relevant health authorities in various countries.

“While this is happening, we will obtain more and longer term data from this trial, and other ones, on whether the drug also prevents deaths from Covid-19.”

If the drug is successful, will it be available for everyone? 

The World Health Organisation (WHO) has made it clear it wants any treatment or vaccine for coronavirus to be made available to people in countries across the world – not just the populations of rich countries. 

On Friday, the public health agency announced a £6.5bn programme to unite and speed up access to safe, affordable and universal coronavirus vaccines and medicines. 

The Access to Covid Tools Accelerator programme will be officially launched on May 4.  

“Past experience has taught us that even when tools are available, they have been not been equally available to all – but we cannot allow that to happen,” said WHO director general Dr Tedros Adhanom Ghebreyesus. 

Meanwhile, Antonio Guterres, secretary general of the United Nations – of which WHO is an agency – said a vaccine or treatment must be safe, affordable and “available for everyone, everywhere”.

“In an interconnected world, none of us is safe until all of us is safe,” he said. “Coronavirus anywhere is a threat to all of us everywhere.”

The UK has said it will support the accelerator programme.

But campaigners have called on the government to apply conditions to the public funding given to pharmaceutical companies for coronavirus treatments and vaccines, saying drug companies must not be able to charge whatever they want for any successful treatments.