Gilead Sciences Inc.’s market value is on track to reach US$100 billion as the biotech jumped before the Thursday market open. But Wall Street is sounding the alarm for investors that the good times may not last.

Plans to start two late-stage studies for remdesivir, an experimental treatment for the coronavirus, are spurring fresh gains for Gilead. A month-long frenzy driven by hope that the biotech may eventually come up with a cure for the rapidly spreading Covid-19 virus has spurred a roughly 18 per cent, or US$20 billion, gain for the biotech.

“Be warned, the more it goes up, the more it has to fall at any sign of resolution,” RW Baird analyst Brian Skorney cautioned Gilead investors in a note. He rates the stock neutral.

“While we hope remdesivir proves efficacious, and believe it may have a good shot to do so, the commercial opportunity here is largely unknown,” Skorney said.

The stock jumped 7.1 per cent before the bell.

Baird wasn’t the only firm on Wall Street cautioning against Gilead optimism. “The stock is extended here,” Jared Holz, a health-care trading desk strategist at Jefferies warned. And the run-up may not be over yet, in “the current landscape with most of the S&P components reeling from macro-related pressures, stocks with theoretical benefits/upside (despite significant financial impact) may continue to ride for a bit.”

And Barclays started research coverage of Gilead at underweight late Wednesday, saying the stock surge “seems overdone.”

Small-cap companies that have touted their potential to treat coronavirus or prevent its spread are also rallying. Alpha Pro Tech Ltd., Co-Diagnostics Inc. and Novavax Inc. all surged 30 per cent or more in pre-market trading. Inovio Pharmaceuticals Inc., Sorrento Therapeutics Inc. and Moderna are all producing double-digit gains in early trading.

Skorney was critical of their efforts, too. “Of all the companies with massive upside moves on Covid-19 interventions, Gilead is, by far, the most plausible to achieve anything besides an overpriced follow-on offering.”

As if on cue, Co-Diagnostics this morning announced the sale of an additional 470,000 shares at US$9 each.