Anaphylaxis is an overreaction of the body’s immune system that may sometimes be life threatening. It causes throat swelling, breathing trouble and difficulty in swallowing. Britain’s medicines regulator has advised people with a history of significant allergies not to get the Pfizer-BioNTech COVID-19 vaccine after receiving two reports of anaphylaxis and one report of a possible allergic reaction since the rollout commenced. Pfizer has not included people with a history of significant adverse reaction to vaccines or its vaccine ingredients from the later-stage trials.