A leading coronavirus treatment candidate has succeeded in a critical trial, helping severe COVID-19 patients recover faster.

A new study of more than 1,000 hospitalized patients found that those taking the antiviral drug remdesivir recovered 31% faster than those taking a placebo, the US National Institutes of Health said Wednesday.

The typical COVID-19 patient taking remdesivir in the study recovered in 11 days, while those in the placebo group took 15 days to recover on average.

Gilead Sciences, the maker of remdesivir, also released data from its own study that suggested a five-day treatment course worked just as well as a 10-day regimen. This trial, however, lacked a control group to compare results against.

There are no drugs approved to treat COVID-19. Gilead did not say whether it planned to file for approval for remdesivir.

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A leading coronavirus treatment candidate succeeded in a critical trial, helping COVID-19 patients who took it recover faster than those who got a placebo.

The US National Institutes of Health on Wednesday released preliminary data from a study of just over 1,000 hospitalized patients who were randomly assigned to take either Gilead Sciences' antiviral drug remdesivir or a placebo.

The patients taking remdesivir recovered 31% faster than those taking the placebo, the NIH found. The typical patient who took remdesivir recovered in 11 days, while the typical patient in the placebo group recovered in 15 days.

Of the patients taking remdesivir, 8% died, compared with 11.6% of those in the placebo group, though the difference wasn't statistically significant.

The NIH said more information from the trial would be published "in a forthcoming report."

Remdesivir has become a leading treatment candidate as other repurposed drugs have largely disappointed with early study results. Gilead's drug has not been approved to treat any diseases but was previously tried in Ebola patients.

And remdesivir hasn't been without its own trial disappointments. A separate trial in China did not find a meaningful benefit for remdesivir compared with a placebo, according to results published Wednesday in The Lancet, a top medical journal.

That study was stopped early because of difficulty in finding enough COVID-19 patients to enroll in China, the researchers noted. Given that that study didn't reach full enrollment, the results are "inconclusive," John David Norrie, a professor at the University of Edinburgh, said in an accompanying commentary.

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Having an effective treatment would be a significant milestone in the fight against the coronavirus pandemic. So far, doctors have been testing unproven drugs in COVID-19 patients.

Remdesivir is given as an IV infusion and has been tested only in hospitalized patients. The drug has not been tested as a preventive treatment or as a way to help people with mild cases of COVID-19.

Gilead's announcement boosted the stock market on Wednesday. The S&P 500 rose 2.7%, and the biotech's shares jumped 6.3%.

Gilead on Wednesday also released data from its own trial of five-day and 10-day regimens of remdesivir in 397 patients with severe forms of COVID-19. This study did not compare patients who got the drug with patients who got a placebo, making the results more difficult to interpret.

Merdad Parsey, Gilead's chief medical officer, said Gilead's results complemented the data from the NIH's placebo-controlled trial and were intended to help figure out the right dose to give patients. The trial generated similar results for patients treated with the five-day course and those treated with the 10-day course, Gilead said.

"The study demonstrates the potential for some patients to be treated with a 5-day regimen, which could significantly expand the number of patients who could be treated with our current supply of remdesivir," Parsey said in a statement.

Using a five-day course could effectively double the number of patients who could be treated with the available supply of remdesivir. The company has already started ramping up manufacturing capacity, planning to pump out more than 1 million courses by the end of the year.

Beyond the finding that the two treatment durations produced similar results, conclusions from Gilead's study are limited by its design. Since there was no control arm, it's difficult to determine just from this data whether remdesivir helped patients.

For instance, the trial found that slightly more than half of the enrolled patients left the hospital within two weeks of starting treatment — but it's difficult to know how meaningful that finding is in a disease where most patients recover on their own anyway.