'Very inconsistent': Allergic reaction by 2 in UK to COVID-19 vaccine puzzles researchers

Two British people with severe allergies apparently had allergic reactions to Pfizer/BioNTech's COVID-19 vaccine, raising questions about whether it is safe for people with preexisting allergies. In response, British regulators advised those with severe allergies to avoid the vaccine. It was not immediately clear what triggered the allergic reactions. Unlike some vaccines, in the Pfizer/BioNTech vaccine there are no preservatives or egg products, which have been known to trigger reactions with other types of vaccines.