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Early data from yet another study of the antimalaria drug hydroxychloroquine in Covid-19 patients is interesting, and perhaps promising, but doesn’t clear up questions about the therapy’s efficacy, analysts say.

The study, conducted by scientists at the Renmin Hospital of Wuhan University and distributed before peer review on Monday, is among the first randomized, double-blind clinical trials of hydroxychloroquine in Covid-19 patients.

The drug has received enormous attention as an experimental Covid-19 treatment after President Trump highlighted its perceived potential in media briefings and on Twitter, and the Food and Drug Administration authorized its use to treat Covid-19 on an emergency basis under certain circumstances.

The Renmin study, which involved 62 patients, 31 of whom were given hydroxychloroquine, found that the patients who received the drug recovered about one day faster than patients who did not. Of the 62 patients, 4 developed severe illness, all of them in the control group.

But analysts who reviewed the study wrote in notes that key questions remain. “While these pre-print data are interesting, we caution against over-interpreting,” UBS analyst Navin Jacob wrote on Tuesday.

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Jacob noted that the severity of illness at the start of the study wasn’t balanced between the patients who received hydroxychloroquine and those who didn’t. “Progression severity of early stage patients vs. natural subsiding of disease in more severe patients could account for the efficacy difference,” Jacob wrote. “Furthermore, it’s possible the HCQ arm had a greater proportion of patients on other therapies that were beneficial vs. the control arm.”

Evercore ISI analyst Umer Raffat, who has been tracking the hydroxychloroquine question closely, also raised concerns about details missing from the preprint paper. “This trial design reads pretty decent,” he wrote Monday. “However, the way in which results were reported (and omitted) makes it hard to draw definitive conclusions.”

There have been significant weaknesses in the design of the two Covid-19 hydroxychloroquine studies that preceded this one. The French trial that received tremendous attention last week was small and not randomized, meaning that all patients received the treatment. Patients from another treatment center, and patients from the same center who refused the hydroxychloroquine, were used as a control group in that study.

Jacob wrote that he is waiting on data from far larger hydroxychloroquine trials being conducted. “While full publication could provide some clarity, we don’t hold out hope that it will change our view—that we need large clinical trials to establish HCQ’s benefit,” he wrote.

Write to Josh Nathan-Kazis at josh.nathan-kazis@barrons.com