Scientists are eyeing a potential culprit causing the allergic reactions to the Pfizer Inc. and BioNTech SE Covid-19 vaccine: the compound polyethylene glycol, also known as PEG.
Six severe allergic reactions to the vaccine have been reported in the U.S., according to the Centers for Disease Control and Prevention, out of 272,001 doses administered through Dec. 19. At least two cases of anaphylaxis have also occurred in the U.K. People in the U.S. began receiving Moderna Inc.’s vaccine Monday, and no allergic reactions to it have been reported so far.
In a statement, Pfizer said it “will closely monitor all reports suggestive of serious allergic reactions following vaccination.” The company said its prescribing information includes a warning that “appropriate medical treatment and supervision should always be readily available in case of a rare anaphylactic event following the administration of the vaccine.”
Scientists are homing in on PEG as a potential suspect even as health authorities say they are still investigating the incidents and plan to study the issue further. The compound is found in other drugs and is known to trigger anaphylaxis on rare occasions.