CDC Director Dr. Rochelle Walensky didn't say what those plans were. However, should Americans require booster shots, the U.S. would likely need to make arrangements with drugmakers to supply additional doses and make plans for vaccine distribution. Walensky told CNBC that U.S. health officials are "thinking ahead" in the event that vaccine-induced immunity against the coronavirus begins to wane. Officials still don't know if that will happen or if booster shots will be needed, "but we are planning for it just in case," she said. "Right now, if you have two doses of the mRNA vaccines, you are...