By Ransdell Pierson

Nov 11 (Reuters) - Gilead Sciences Inc on Tuesday said its new Harvoni drug for hepatitis C achieved cure rates of 96 percent to 97 percent in a study of patients who had cirrhosis and had failed to benefit from prior treatments.

The data bolsters the attractiveness of Harvoni, a combination drug that U.S. regulators approved last month and whose $95,000 cost for a course of treatment has raised complaints from insurers and politicians.

The Gilead study involved 155 patients with cirrhosis and the most common genotype 1 form of the liver virus. They previously had failed to benefit from standard older treatments that included protease inhibitors as well as interferon and ribavirin, drugs that can cause harsh side effects and must be taken for almost a year.

All patients received Harvoni, a once-daily pill containing Gilead's Sovaldi and ledipasvir. The combination eliminates the need to take interferon and ribavirin with Sovaldi.

In one group taking Harvoni alone for 24 weeks, the cure rate was 97 percent. It was 96 percent for patients who received Harvoni plus ribavirin for 12 weeks.

Three far smaller Gilead studies evaluated Sovaldi, a so-called nucleotide, in combination with the company's experimental NS5A inhibitor GS-5816, with and without ribavirin for eight or 12 weeks.

Of patients taking the combination for 12 weeks without ribavirin, sustained cures were seen in 100 percent of genotype 1 patients, with and without cirrhosis, and in 88 percent of those with the less common genotype 3 form of the virus, with cirrhosis.

Shares of Gilead were up 1.4 percent at $108.54 in morning trading.

(Reporting by Ransdell Pierson; Editing by Lisa Von Ahn)