When researchers at pharmaceutical companies around the world started developing COVID-19 vaccines, experts reminded everyone to temper expectations. Vaccines usually take years. The frontrunners were made using unproven technology, and there were dozens of ways things could go wrong. The Food and Drug Administration said it would be fine with anything over 50 percent effective.
Then, last month, Pfizer announced that it had a vaccine, and it was 95 percent effective. Moderna did too. It was better news than anyone dared hope for. Stéphane Bancel, chief executive at Moderna, said he cried when he first heard the data. With the FDA’s blessing, which came in late Friday night, health care workers in the United States could start getting...
