Very inconsistent': 2 allergic reactions in the UK to COVID-19 vaccine puzzle 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.

Allergic reactions were not a significant problem in the U.S. trial in which more than 20,000 people have received both two doses of the vaccine, but the U.S. trials kept out subjects who have had severe allergic reactions, said Moncef Slaoui, co-head of Operation Warp Speed – the government program tasked with developing, manufacturing and distributing COVID-19 vaccines.