Both sofosbuvir in combination with ribavirin and sofosbuvir in combination with GS-5885 and ribavirin were well tolerated in the ELECTRON study. In the sofosbuvir combined with GS-5885 and ribavirin groups, there was one discontinuation due to an adverse event unrelated to study drugs. Despite stopping therapy at week 8, this patient also achieved SVR4.The most common adverse events were headache, fatigue, upper respiratory tract infection and nausea. The most common clinically significant grade 3/4 laboratory abnormality was a hemoglobin reduction. Additional Safety Data for GS-5885 In a poster presentation at The Liver Meeting on Sunday, November 11 th, investigators will report combined safety data for more than 1,000 patients who have received at least one dose of GS-5885, in combination with other HCV medicines, in six ongoing Phase 2 clinical trials. In this analysis, 616 patients received a 30 mg dose and 423 patients received the 90 mg dose of GS-5885, which is being assessed in Phase 3 research. More than 700 patients completed at least 12 weeks of treatment with GS-5885. Approximately 70 percent of patients were treatment-naïve and 70 percent had HCV genotype 1a infection. Researchers concluded that GS-5885 is safe and well tolerated. No laboratory abnormalities or other safety signal of concern has been observed in the GS-5885 development program. Sofosbuvir and GS-5885 are investigational products and their safety and efficacy have not yet been established. About Gilead Sciences Gilead Sciences is a biopharmaceutical company that discovers, develops and commercializes innovative therapeutics in areas of unmet medical need. The company’s mission is to advance the care of patients suffering from life-threatening diseases worldwide. Headquartered in Foster City, California, Gilead has operations in North America, Europe and Asia Pacific. Forward-Looking Statement This press release includes forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 that are subject to risks, uncertainties and other factors, including the possibility that the proportion of patients who maintain a sustained virologic response 12 weeks post-treatment will not be as favorable as the sustained virologic response rates reported in this press release, the possibility that results from the arm of the ELECTRON study evaluating the efficacy and safety of sofosbuvir, GS-5885 and ribavirin in genotype 1 previous null responder patients will not be favorable once four and 12 week post-treatment data from all nine patients are available and the possibility of unfavorable results from additional arms of the ELECTRON study and subsequent clinical trials involving sofosbuvir and GS-5885 with and without ribavirin. As a result, sofosbuvir and GS-5885 as single agents or as a fixed-dose combination may never be successfully commercialized. Further, Gilead may make a strategic decision to discontinue development of the compounds or the fixed-dose combination regimen if, for example, Gilead believes commercialization will be difficult relative to other opportunities in its pipeline. These risks, uncertainties and other factors could cause actual results to differ materially from those referred to in the forward-looking statements. The reader is cautioned not to rely on these forward-looking statements. These and other risks are described in detail in Gilead’s Annual Report on Form 10-K for the quarter ended September 30, 2012, as filed with the U.S. Securities and Exchange Commission. All forward-looking statements are based on information currently available to Gilead, and Gilead assumes no obligation to update any such forward-looking statements.