I think it's possible that the trial will be +, but the results could be underwhelming (e.g., low increase in %FEV, perhaps some unanticipated AEs and no stat sig improvements in secondary outcomes).
If you read the people talking about the trial on facebook, the most vocal ones seem quite negative on the trial. Are they telling the truth? who knows.
My gut feeling is that the trial will hit its primary endpoint, but I also have a feeling that there might be a quick backlash b/c the results might not be spectacular. (maybe $VRTX goes over $100 briefly and then settles in the 80-90 area).
I'm just speculating, however.
Disclosure: I have a bull spread position with max return @ $90.