At the height of last summer, New York Federal Reserve President John Williams temporarily roiled markets when he argued that central banks running low interest rates should act boldly to inoculate their economies against unfolding ailments.

"When you only have so much stimulus at your disposal, it pays to act quickly to lower rates at the first sign of economic distress," he said in a speech that the New York Fed later clarified was not meant to be a policy signal. You want to "vaccinate against further ills."

As Williams and his colleagues prepare for a monetary policy meeting next week, the mounting economic impact of the coronavirus is turning his academic theorizing into a practical consideration for policy: Should the Fed cut interest rates to zero? And, if so, how soon should it act?