After staying in the green for most of the day, the Dow and the S&P 500 look set to finished the day in the red. The Dow Jones Industrial Average dropped 123.77 points, or 0.5%, to 26,957.59, while the S&P 500 fell 0.4% to 3116.39. The Nasdaq Composite closed up 0.2% at 8980.77.

Just as was the case on Tuesday, when a CDC official spooked the market, Wednesday’s drop seems to be a function of another official speaking, this time from the FDA. “For all intents and purposes, I think it’s fair to say we’re on the cusp of the...