After boosting its full-year hepatitis C revenue guidance last month, Gilead Sciences‘ (NASDAQ: GILD) share price has been rallying. However, the Food and Drug Administration approved AbbVie’s (NYSE: ABBV) next-generation hepatitis C drug Mavyret this week, and AbbVie has priced it to sell. Could Mavyret deliver a big blow to Gilead Sciences’ hopes for higher hepatitis C sales?