COVID-19 vaccine, giving fuller guidance on an earlier allergy warning about the shot.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.The Medicines and Healthcare Products Regulatory Agency (MHRA) said there had been two reports of anaphylaxis and one report of a possible allergic reaction since rollout began.Also read: The pandemic push to the silver economy"Any person with a history of anaphylaxis to a vaccine, medicine or food should not receive the Pfizer BioNTech vaccine," MHRA Chief Executive June Raine said in a statement."Most people will not get anaphylaxis and the benefits in.