ALISTAIR SMOUT BRITAIN’S medicine regulator has advised that people with a history of significant allergies do not get Pfizer-BioNTech's COVID-19 vaccine after two people reported adverse reactions on the first day of rollout. Starting with the elderly and frontline workers, Britain began mass vaccinating its population on Tuesday, part of a global drive that poses one of the biggest logistical challenges in peacetime history. National Health Service medical director Stephen Powis said the advice had been changed after two NHS workers reported anaphylactoid reactions associated with receiving the vaccine. They were among the thousands who received the shot on Tuesday.…