Shares of Gilead Sciences Inc’s shares jumped by 16% following news reports that its experimental drug remdesivir is proving to be effective in U.S. trials of patients who have been severely afflicted by the COVID-19 disease caused by the coronavirus.

According to a report from medical news website STAT, a University of Chicago hospital participating in a study of the antiviral medication said it is seeing rapid recoveries in fever and respiratory symptoms, with nearly all patients discharged from the hospital in less than a week.

In an e-mailed statement, Gilead said “the totality of the data need to be analyzed in order to draw any conclusions from the trial.”

By the end of April 2020, Gilead is expecting additional data from its Phase 3 study in patients with severe COVID-19 infection.

The University of Chicago is among the 152 locations participating in Gilead’s trial involving severe COVID-19 patients; this is a “single arm” meaning it does not measure the drug against a matched group of patients treated with a placebo.

A trial of patients with moderate COVID-19 symptoms has 169 study locations.

Currently, there are no approved treatments for COVID-19.

In a report, STAT said the University of Chicago Medicine has recruited 113 people with severe COVID-19 into Gilead’s trial. While most of them have been discharged, two of the patients have died.

The “anecdotal data … looks promising on the surface and continues to support some potential for the drug to be active in certain COVID-19 patients,” said RBC Capital Markets analyst Brian Abrahams in a research note.

“Nonetheless, there are major limitations to contextualizing and interpreting this data.”

Last week, the New England Journal of Medicine published an analysis indicating that over two-thirds of a small group of severely ill COVID-19 patients saw their condition improve after treatment with remdesivir.

The paper’s author called the findings “hopeful,” but cautioned it is difficult to interpret the results since they do not include comparison to a control group, as would be the case in a randomized clinical trial. Furthermore, the sample size of patients was also small, the details being disclosed are limited, and the follow-up time was relatively short.

The U.S National Institute of Allergy and Infectious Disease in February began an 800-patient trial that randomly assigns patients to treatment with either remdesivir or with a placebo to enable a controlled comparison of outcomes. These results are expected to come out after Gilead’s trial reads out.