The major challenge to development of an all-oral, interferon-free treatment for hep C is drug resistance.
Hep C circulates as a mixture of viruses with various sequences. It has been estimated that pre-existing drug resistance variants with one, two, three and even four mutations may be present in most hep C-infected patients and account for the rapid development of drug resistance on exposure to direct-acting antiviral drugs ((DAAs)).
For a successful interferon-free treatment maybe necessary to use several DAAs concurrently, and each of these should have potent antiviral activity, possess nonoverlapping resistance profiles, and have limited or manageable drug interactions and minimal adverse effects.
It means that there may be room in the market for a range of combos, which would explain the presence of so many combo studies going on at the same time.