Even if the most optimistic projections hold true and a Covid-19 vaccine is cleared for U.S. use in November, the vast majority of Americans won’t be able to get the shots until spring or summer next year at the earliest. That likely timeline, based on interviews and remarks from top specialists including Anthony Fauci of the White House Coronavirus Task Force, means businesses, schoolchildren and families will continue to wait. The reasons are many. U.S. health regulators will have only a tiny sliver of the usual safety and efficacy data. The leading products require two doses, which will limit how many people early supplies can help. And government health officials are still developing a plan for who will get the shots, how they’ll be distributed, and how their effectiveness and safety will be tracked afterward. “For three, to six, to nine months, there will be more people wanting a vaccine than there are vaccines,” said Stephane Bancel, chief executive officer of Moderna Inc., the biotechnology company developing one of the furthest-along inoculations. Bancel said he expects his company’s product may get an emergency authorization from the Food and Drug Administration for “a very narrow population at very high risk.” Vaccines for the general population will need full FDA approval, which will likely take significantly longer, he said in an interview.