A new report from STAT News on Gilead's experimental drug Remdesivir serves as an encouraging update on the drug's potential to fight Covid-19, however analysts argue it's largely anecdotal and should be interpreted with caution.

Remdesivir was one of the first medicines identified as a contender to treat Covid-19 given it showed promise in the past in treating SARS and MERS, both caused by coronaviruses.

According to the report from an ongoing phase three trial at a University of Chicago hospital, patients showing severe Covid-19 symptoms who were given the drug saw rapid recoveries in fever and respiratory symptoms, with nearly all patients discharged in less than one week.

Gilead commented that, "the totality of the data need to be analysed in order to draw any conclusions from the trial," in a statement to Reuters. A statement from the University of Chicago Medicine said that "drawing any conclusions at this point is premature and scientifically unsound."

Jefferies equity analyst Michael J. Yee published in a research note that this Chicago report provides an "incremental positive" but he assumes this significant short-term move in Gilead's share price will probably pull back a bit given eventual broader awareness that this is not the actual phase three data and that this is overdone in the near term.

JPMorgan biotechnology equity analysts wrote in a published research note Thursday that "this clinical trial experience appears to represent another encouraging, albeit largely anecdotal, data point for this high-profile drug candidate."

Meanwhile, the Barclays health-care team called the update "encouraging" but note that questions persist.

The report from the Chicago hospital comes amid mounting anecdotal evidence supporting the drug's potential effectiveness in treating the virus. Last week, the New England Journal of Medicine published an analysis showing that two thirds of a small group of severely ill patients saw their condition improve after taking the drug. These patients were given Remdesivir as part of a compassionate use program which allows doctors to provide patients with unauthorized treatments when no other treatment is available.

There was no control group in the University of Chicago study. As CNBC's Meg Tirrell has highlighted, this is not controlled clinical trial data it is a glimpse into what one of the sites that is running the trial is seeing.

The information reported by STAT News came from an internal discussion among faculty members at a University of Chicago hospital captured on video, it was not official data released by Gilead or any other trial leader.

Furthermore, this data comes from a single trial site. The Barclays health-care equity research team wrote: "While these data are encouraging, they are uncontrolled and from a single center."

Jefferies echoes this point: "Similar to the NEJM publication last week, yesterday's reports are based on one site and there is no placebo."

There is also debate around the severity of the patients included in the study. This data is part of an ongoing phase three trial of patients with severe Covid-19 symptoms. However, the patients were not intubated to start the study. Barclays adds that there will be debate around the patient population and how they compare to past cohorts.

"There's still a great deal we don't know, and thus we hesitate to put too much into the results generated at a single center without a control group," said JPMorgan.

"Fortunately, we don't have to wait long for a Phase 3 readout in severe patients."

Gilead expects results from its trials with patients with severe Covid-19 later this month. Data from its trials on patients with moderate symptoms is expected in May.

In addition to these two trials being run by Gilead, there are several others underway concurrently to evaluate Remdesivir, including a phase two trial run by the National Institute of Health which is an adaptive, randomized, double-blind, placebo-controlled trial.

Barclays adds that data from Gilead's clinical trials on severe cases due at the end of this month could support approval or expanded use authorization. A treatment is not going to end the pandemic. But it will provide a critical bridge to the ultimate panacea a vaccine.

CNBC's Berkeley Lovelace contributed to this article.

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Investors should be cautious on the potential for Gilead's drug Remdesivir, analysts say - CNBC