(Reuters) – A federal advisory panel recommended on Friday that the U.S. Food and Drug Administration approve Gilead Sciences Inc’s experimental hepatitis C drug sofosbuvir, paving the way for a treatment that is more effective than current therapies and takes less time.

The FDA advisory panel voted 15 to 0 in favor of approval of the drug in patients with two variants of the liver-damaging disease – genotype 2 and genotype 3 – in combination with an existing treatment, ribavirin.

If approved, it will be the first all-oral treatment for genotypes 2 and 3, obviating the need for the injectable drug interferon, which can cause debilitating side effects. Panelists called the vote “historic” and a “game-changer.”

“Our patients have been waiting for this for a long time,” said Dr. Curt Hagedorn, chief of medicine service at the Central Arkansas Veterans Healthcare Service.

The panel also voted unanimously to approve the drug in patients with genotype 1 and genotype 4 variants in combination with ribavirin and interferon in patients who have not received prior therapy.

Genotype 1 accounts for roughly 70 percent of hepatitis C cases. The FDA is not bound to follow the advice of its panels but typically does so.

“We’d already built in 100 percent chance of approval into our valuation for the company,” said Karen Andersen, an analyst at Morningstar. “Gilead is still really in the prime position looking ahead in the hepatitis C market.”

Panelists also appeared to support the use of sofosbuvir in patients who failed prior treatment, even though the company has little hard data to support such a claim.

“I did think there was a surprise upside result by the end of the panel,” said Michael Yee, an analyst at RBC Capital Markets.

Bristol-Myers Squibb Co and Abbvie Inc have advanced all-oral clinical trial programs in late-stage development, using a variety of so-called direct acting antivirals, which directly interfere with the virus’s ability to replicate. But Gilead is widely seen to be in the lead.

Chronic hepatitis C affects at least 3 million people in the United States, according to the U.S. Centers for Disease Control.

Analysts on average expect Gilead’s drug to generate sales of $1.73 billion in 2014, according to Thomson Reuters data.

Current standard treatments for genotype 1 often include a protease inhibitor. These are oral drugs that include Merck & Co Inc’s Victrelis and Vertex Inc’s Incivek.

Gilead acquired sofosbuvir, known as a nucleotide analogue inhibitor, with its $11 billion purchase of Pharmasset Inc in 2012.

Panelists urged Gilead to make the drug available to other companies to study in combination with other oral regimens waiting in the wings.

Bristol-Myers is expected to present data from a late-stage clinical trial of its interferon-free treatment of genotype 1 patients at next month’s meeting of the American Association for the Study of Liver Diseases in Washington, D.C.

The FDA is due to rule on whether to approve the drug by December 8.

(Additional reporting by Bill Berkrot; Editing by Gerald E. McCormick, Dan Grebler and David Gregorio)