As I understand it the body has natural interferon and you add extra to amp up the immune system further, forming extra killer t-cells to kill the virus. The co-
drug, ribivirin, works as an adjuvant (increases the activity of the interferon), but has no effect on it's own. You need them both.
I once looked the 2 drugs up online and when I added them up for 48 weeks of treatment, it came to $27,000 total, but can't recall the interferon figure, maybe it was $150 per shot.