(Reuters) - Gilead Sciences Inc’s shares surged 16% in after hours trading on Thursday following a media report detailing encouraging partial data from trials of the U.S. company’s experimental drug remdesivir in severe COVID-19 patients.

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 in less than a week, according to medical news website STAT here.

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

UChicago Medicine, also in an email, said “partial data from an ongoing clinical trial is by definition incomplete and should never be used to draw conclusions.”

The university said information from an internal forum for research colleagues concerning work in progress was released without authorization.

Gilead expects results from its Phase 3 study in patients with severe COVID-19 at the end of this month, and additional data from other studies to become available in May.

The University of Chicago is one of 152 locations participating in Gilead’s trial involving severe COVID-19 patients, which is “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.

There are currently no approved treatments for COVID-19, the highly contagious respiratory illness caused by the novel coronavirus that has infected over 2 million people worldwide.

STAT reported that UChicago Medicine recruited 113 people with severe COVID-19 into Gilead’s trial. It said most of them have been discharged and two patients 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,” RBC Capital Markets analyst Brian Abrahams said in a research note. “Nonetheless, there are major limitations to contextualizing and interpreting this data.”

Interest in Gilead’s drug amid the ongoing coronavirus pandemic has been high. The New England Journal of Medicine last week published an analysis showing that 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, the patient numbers were small, the details being disclosed were 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 a placebo. Those results are not expected until after Gilead’s trial reads out.

Shares of Gilead, which closed at $76.54 in regular trading, were up 16% at $89.10 after hours.