As Gilead Sciences Inc. began the roll-out for its newly approved hepatitis C virus (HCV) drug, Harvoni, following FDA approval Friday, analysts continued to weigh in on prospects for the once-daily pill, which combines a dose of sofosbuvir – the active ingredient in the company's blockbuster HCV drug Sovaldi – with ledipasvir, a direct-acting macrocyclic antiviral agent and inhibitor of NS5A serine protease.