Simeprevir's commercial potential in HCV would look to be limited after Johnson & Johnson agreed with FDA that genotype 1a patients should be screened for the Q80K polymorphism, a cohort where the pharma's drug did not produce a robust response as part of an interferon regimen.

But J&J also argues the effect is interferon-specific, and that additional data show the company's protease inhibitor still could be used in all-oral, IFN-free combinations.