The long wait to approve the vaccines is similar. F.D.A. officials are acting as if most Americans are experts in the nuances of their approval process and will be shocked if the agency expedites it. In reality, many Americans know almost nothing about that process. But some are understandably confused by the mixed messages that the F.D.A. is sending.Hundreds of millions of people around the world have been vaccinated. Tens of thousands of them were followed for months in clinical trials. And F.D.A. officials have repeatedly urged other Americans to get vaccinated. “In the history of medicine, few if any biologics (vaccines, antibodies, molecules) have had their safety and efficacy scrutinized to this degree,” Dr. Eric Topol of Scripps Research wrote in The Times.Yet the agency still has not given formal approval to those same vaccines.Big costs, few benefitsThink of it this way: In the highly unlikely event that the evidence were to change radically — if, say, the vaccines began causing serious side effects about 18 months after people had received a shot — Americans would not react by feeling confident in the F.D.A. and grateful for its caution. They would be outraged that Woodcock and other top officials had urged people to get vaccinated.The combination means that the F.D.A.’s lack of formal approval has few benefits and large costs: The agency has neither protected its reputation for extreme caution nor maximized the number of Americans who have been protected from Covid. “In my mind, it’s the No. 1 issue in American public health,” Topol told me. “If we got F.D.A. approval, we could get another 20 million vaccinated,” he estimated.Rebecca Robbins, who covers the vaccines for The Times, says she is less sure about the size of the impact. But she agrees that full approval, whenever it happens, is “probably going to be the catalyst for many new mandates.”My colleague Noah Weiland says: “Right now, it appears a full approval for the Pfizer vaccine could come in September, with Moderna not far behind.”In the meantime, more Americans may get sick from Covid. About 34 percent of Americans who are eligible for the vaccines have not yet gotten a shot. The number of new cases has roughly tripled this month, largely because of the Delta variant. The number of deaths has almost doubled in the past two weeks.