I have never heard of a relapse. Either the Harvoni works or it don't. Just so I'm clear, in my mind a relapse is different than a fail. A fail means the person never becomes totally or even close to being undetected. A relapse is when someone becomes undetected and stays undetected for a month or so and then their viral load is back with a vengeance. I have heard of only one person fail, and that was right here on this forum, but I don't remember the particulars.
Hi there, so far I have only recently seen one person who had Harvoni fail them. I did a search for Harvoni relapse and I found this, I hope this helps a bit. You can also conduct a search at the top of this page where it says "search this community"
http://www.medhelp.org/posts/Hepatitis-C/Harvoni-failure/show/2449070