The United States Food and Drug Administration is investigating around five allergic reactions that happened after people were administered Pfizer Inc and BioNTech SE’s Covid-19 vaccine in the United States this week, a top FDA official has said.

Dr Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said at a press conference that the allergic reactions had been reported in more than one state, including in Alaska.

Marks also said that a chemical called polyethylene glycol (PEG) that is an ingredient in the Pfizer vaccine — as well as the Moderna Inc vaccine authorised on Friday — “could be the culprit” causing the reactions.