Pick a reason, there is truth in a few probably.
My opinion, many stocks are down, biotech may be down generally. If some are green today it is after getting killed on friday. : )
Look at a GILD 1 or 2 year chart. Last year we had a rotation out of biotech. Please also pay attention to what happened after all the weak hands were flushed out. This could be a replay of that.
Lots of fear in HCV, lots of uncertainty by uninformed investors. They get scared out causing more to reflexively abandon their positions.
IMHO, GILD, ABBV, and ENTA will soon be showing better than expected sales in next quarterly reports and the tide will turn.
Until we see actual numbers and profits people will likely remain unsettled and we may see erosion of SP. I think people are feeing uncertain about their HCV investments and I think possibly some larger players are *helping* undermine their resolve to stay put.
Personally, I see the prices going back up. IF you look at GILD, ENTA and ABBV on a 1 year chart you'll see they all dipped and all recovered quite nicely. All three of these companies should soon report record sales and profits.
It's just my perspective.