By Sarah Toy
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.
"Although I think we're just speculating here...it is known that
one of the components that is present in both of the vaccines --
polyethylene glycol -- can be associated, uncommonly, with allergic
reactions," said Peter Marks, director of the Food and Drug
Administration's Center for Biologics Evaluation and Research, at a
Dec. 18 press conference.
"What we're learning now is that those allergic reactions could
be somewhat more common than the highly uncommon that we thought
they were because people do get exposed to polyethylene glycol in
various pharmaceutical preparations," he said, adding that the FDA
also plans to watch the Moderna vaccine rollout "very closely"
since both vaccines contain PEG.
In both the Pfizer-BioNTech and Moderna vaccines, PEG is part of
the fatty envelope that surrounds the messenger RNA, the main
ingredient in the vaccine. Once the mRNA gets into cells, it
teaches them to make a protein that resembles the spike protein
found on the surface of the coronavirus. That induces a specific
immune response that shores up the body's defenses for when it is
exposed to the real virus. The PEG-containing fatty envelope helps
ensure the mRNA gets across the cell membrane and into the
Allergies to PEG are extremely rare, allergists and
immunologists say, and it is possible that the few people who had
reactions after getting the Pfizer-BioNTech vaccine reacted to
something else. The compound is found in a range of products, they
say, such as cosmetics, foods and drugs. Some vaccines also contain
PEG-like compounds, they note.
Some types of PEG are more likely to cause allergic reactions
than others, scientists say.
"They're all in a big large family, but in terms of their
allergic potential, they're not equal," said Elizabeth Phillips,
director of the Center for Drug Safety and Immunology at Vanderbilt
University Medical Center. Types of PEG that are heavier are
generally more likely to elicit allergic reactions than others, she
At the same time, "the PEG in the vaccines is different than
what has been previously associated with allergic reactions," said
James Baker, an immunologist who heads the Michigan Nanotechnology
Institute for Medicine and the Biological Sciences at the
University of Michigan.
"The overall structure is very different from anything that's
been in a vaccine before," he said. That makes it hard to tell how
allergic reactions to the PEG in the Covid-19 vaccines will compare
to allergic reactions to other PEGs, like those in certain
laxatives, that have caused rare allergic reactions in the
Allergy experts say it isn't certain yet whether the reactions
seen so far were classic allergic reactions -- that is, immune
reactions involving an antibody called immunoglobulin E, or IgE,
which are part of the so-called adaptive arm of the immune system,
which learns to recognize specific intruders. The reactions could
also be due to a misfiring of the innate immune system, causing a
cascade of reactions in what's known as the body's complement
"We have to look at all the possibilities," said Dr. Baker.
Both he and Dr. Phillips recently attended a virtual meeting
hosted by the National Institute of Allergy and Infectious Diseases
to discuss the Covid-19 vaccine allergic reactions. The agency said
it is designing a study to look more closely at the issue.
"We anticipate studying highly allergic individuals with prior
episodes of anaphylaxis, as well as some other groups such [as]
patients with known PEG allergy," said Daniel Rotrosen, the
director of the Division of Allergy, Immunology and Transplantation
at NIAID, in an email. The study will include healthy individuals
for comparison, he said, and researchers will gather biologic
samples before and after vaccination to monitor for any immune
changes induced by the vaccine.
While PEG is a possible culprit, "we need to keep an open mind
regarding other possibilities," he added.
For now, the CDC says people who have a history of severe
allergic reactions to any component of the Pfizer-BioNTech or
Moderna vaccines should not receive the vaccine, and those who have
a severe allergic reaction after the first dose should not receive
People with severe allergies to any other vaccine or injectable
may receive the vaccine, but should speak with their medical
providers beforehand about weighing the risks of an allergic
reaction with the benefits of receiving the vaccine, the agency
There is no reason why people who have a history of mild or
severe allergic reactions to food, pets, oral medications or
environmental allergens shouldn't receive the vaccine, the CDC
The agency also says people who get the shots should be observed
for 15 minutes after vaccination to monitor for possible adverse
reactions. People with a history of anaphylaxis should be observed
for 30 minutes, it says.
The FDA requires that appropriate medical treatment for allergic
reactions be immediately available in the event of an acute,
Write to Sarah Toy at firstname.lastname@example.org
(END) Dow Jones Newswires
December 25, 2020 08:14 ET (13:14 GMT)
Copyright (c) 2020 Dow Jones & Company, Inc.