The UK’s medicine regulator has warned people with significant allergies to a vaccine, medicine or food not to get Pfizer-BioNTech’s COVID-19 vaccine after two people suffered adverse reactions in the early rollout.

Starting with the elderly and front-line workers, Britain began mass vaccinating its population on Tuesday. 

NHS medical director Professor Stephen Powis said the advice had been changed as a precaution after two NHS workers reported anaphylactoid reactions from the vaccine.

“Two people with a history of significant allergic reactions responded adversely yesterday. Both are recovering well,” Professor Powis said.