NEW YORK (NYTIMES) - The malaria drug hydroxychloroquine helped to speed the recovery of a small number of patients who were mildly ill from the coronavirus, doctors in China reported this week.

Cough, fever and pneumonia went away faster, and the disease seemed less likely to turn severe in people who received hydroxychloroquine than in a comparison group not given the drug. The authors of the report said that the medication was promising, but that more research was needed to clarify how it might work in treating coronavirus disease and to determine the best way to use it.

"It's going to send a ripple of excitement out through the treating community," said Dr William Schaffner, an infectious disease expert at Vanderbilt University.

The study was small and limited to patients who were mildly or moderately ill, not severe cases. Like many reports about the coronavirus, it was posted at medRxiv, an online server for medical articles, before undergoing peer review by other researchers.

But the findings strongly support earlier studies suggesting a role for the drug, Dr Schaffner said.

"I think it will reinforce the inclination of many people across the country who are not in a position to enter their patients into clinical trials but have already begun using hydroxychloroquine," he said.

Previous reports from China and France that the drug seemed to help patients, along with enthusiastic comments from US President Donald Trump, have created a buzz around hydroxychloroquine and the closely related chloroquine, which are decades-old drugs used to treat malaria and autoimmune diseases like lupus and rheumatoid arthritis.

A resulting spike in demand has led to hoarding and shortages, and left patients who rely on the drugs for chronic diseases wondering whether they will be able to fill their prescriptions.

With no proven treatment for the coronavirus, many hospitals have simply been giving hydroxychloroquine to patients, reasoning that it might help and probably will not hurt, because it is relatively safe.

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The earlier reports from France and China drew criticism because they did not include control groups to compare treated versus untreated patients. Researchers called the reports anecdotal and said the lack of controls made it impossible to determine whether the drugs worked.

Among health officials who declined to endorse the drugs, and who called for clinical trials, were some members of the US President's coronavirus task force - including Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, and Dr Stephen Hahn, commissioner of the Food and Drug Administration.

The new study, of 62 patients with an average age of about 45, did have a control group. It was conducted at the Renmin Hospital of Wuhan University, in Wuhan, China. The patients were carefully chosen to exclude people with medical problems that could be made worse by hydroxychloroquine, like abnormal heart rhythms, certain eye diseases, and liver or kidney problems.

Half the subjects - the controls - received just the usual care given to coronavirus patients, and half had usual care plus hydroxychloroquine. The usual care included oxygen, antiviral drugs, antibiotics and other treatments.

Their disease was considered mild, even though all had pneumonia that showed up on CT scans. After giving informed consent, they were assigned at random to either the hydroxychloroquine or the control group. They were treated for five days, and their fevers and coughing were monitored. They also had chest CT scans the day before the study treatment began and the day after it ended.

Coughing and fever eased a day or so earlier in the patients who received hydroxychloroquine, and pneumonia improved in 25 of 31, as opposed to 17 of 31 in the controls.

The illness turned severe in four patients - all in the control group.

Two patients had minor side effects from hydroxychloroquine: One had a rash, and another had a headache.

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Dr Schaffner cautioned that the results applied only to patients with relatively mild illness, like the ones in the study, and could not be generalised to advanced cases.

"If you want to treat people who are already seriously ill, we don't know how well this will work," he said.

If the drug is helping, it is not clear how. There are two possible ways. In laboratory studies, it can stop the virus from invading cells. But hydroxychloroquine can also dial back an overactive immune system, which is why it can treat autoimmune diseases. And a powerful immune reaction to the coronavirus is suspected of playing a role in some of the severest cases of the disease.

"We don't know which of the pharmacologic aspects of hydroxychloroquine are most active, the antiviral part or the immunomodulatory part," Dr Schaffner said. "We don't know, but it does reinforce the notion, as the authors say briefly, it reinforces the thinking about the nature of many of these pneumonias we are seeing, which seem to have an immune basis, as opposed to being secondary bacterial pneumonia, which we see so often in influenza."