A nurse prepares a shot of the Pfizer-BioNTech COVID-19 vaccine at Guy’s Hospital in London, Tuesday, Dec. 8, 2020, as the U.K. health authorities rolled out a national mass vaccination program. U.K. regulators said Wednesday Dec. 9, 2020, that people who have a “significant history’’ of allergic reactions shouldn’t receive the new Pfizer/BioNTech vaccine while they investigate two adverse reactions that occurred on the first day of the country’s mass vaccination program. (AP Photo/Frank Augstein, Pool)