NEW: U.S. Food and Drug Administration full approval of Pfizer vaccine "opens the door for more universities, businesses, corporations, even local and state governments to mandate the vaccine," Dr. Alok Patel tells ABC News. "Hopefully what this means is that people out there who wanted to wait and see, or wanted to see more safety data, got exactly what they wanted this morning," Patel says. abcn.ws/3B9ClDn | ABC News