G'day Jen,
Nope, doubt it. The announcement of this potential vaccine has no fundamental impact on CST.
Just one of those irrational little runs. You know the story, somebody sells, somebody else panics, stops hit etc etc. Just that beast the irrational market - the business value has not changed one iota.
Note that it has turned around now. Shows that there are plenty of folk out there willing to pick themselves up an early Christmas present.