A small randomized control trial last year by psychiatrists at the Washington University School of Medicine in St. Louis was a spectacular success: None of the 80 participants who started fluvoxamine within seven days of developing symptoms deteriorated. In the placebo group, six of the 72 patients got worse, and four were hospitalized. The results were published in November 2020 in the Journal of the American Medical Association and inspired a real-world experiment.

Soon after the study was published, there was a Covid outbreak among employees at the Golden Gate Fields horse racing track in Berkeley, Calif. The physician at the track offered fluvoxamine to workers. After 14 days, none of the 65 patients who took it were hospitalized or still had symptoms. Of the 48 who didn’t take the drug, six, or 12.5%, were hospitalized and one died. Twenty-nine had lingering symptoms, which might have resulted from inflammatory damage to their organs. Those who took the placebo were more likely to be asymptomatic when they tested positive, so they would have been expected to fare better.

The studies drew the attention of Francis Collins, director of the National Institutes of Health. “A big need right now is for a drug that you could take by mouth, that you could be offered as soon as you had a positive test, and that would reduce the likelihood that the virus is going to make you really sick,” he said in an interview with “60 Minutes” in March. “Fluvoxamine could certainly be something you want to put in the tool chest,” Dr. Collins added. “It looks as if it has the promise to reduce the likelihood of severe illness.”