© Chris Landsberger / Associated Press
Scientists are looking for a possible culprit that causes allergic reactions to the vaccine Pfizer Inc. and BioNTech SE Covid-19: the polyethylene glycol compound, also known as PEG.
Six serious allergic reactions to the vaccine have been reported in the United States, according to the Centers for Disease Control and Prevention, of 272,001 doses administered through December 19. At least two cases of anaphylaxis have also occurred in the United Kingdom. People in the US started receiving the vaccine from Moderna Inc. on 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 after vaccination”. The company said its prescribing information includes a warning that “appropriate medical treatment and supervision should always be available in the event of a rare anaphylactic event following administration of the vaccine”.
Scientists are pointing to PEG as a potential suspect, although health officials say they are still investigating the incidents and plan to study the matter further. The compound is found in other drugs and is known to trigger anaphylaxis on rare occasions.
“Although I think we are just speculating here … it is known that one of the components that is present in both vaccines – polyethylene glycol – may be associated, in an unusual way, with allergic reactions,” said Peter Marks, director of Food and the Drug Administration’s Center for Biological Products Research and Evaluation, at a press conference on December 18.
“What we are learning now is that these allergic reactions may be a little more common than the highly unusual ones we thought, because people are exposed to polyethylene glycol in various pharmaceutical preparations,” he said, adding that the FDA also plans to watch the launch. of the Modern vaccine “very closely”, since both vaccines contain PEG.
In the Pfizer-BioNTech and Moderna vaccines, PEG is part of the fatty envelope that surrounds messenger RNA, the main ingredient in the vaccine. Once the mRNA reaches the cells, it teaches them to make a protein that resembles the spike protein found on the surface of the coronavirus. This induces a specific immune response that strengthens the body’s defenses when it is exposed to the real virus. The fatty envelope containing PEG helps to ensure that mRNA crosses the cell membrane and enters cells.
Allergies to PEG are extremely rare, say allergists and immunologists, and it is possible that the few people who had reactions after receiving the Pfizer-BioNTech vaccine reacted to something else. The compound is found in a variety of products, they say, like cosmetics, food and medicines. Some vaccines also contain compounds similar to PEG, they note.
Some types of PEG are more likely to cause allergic reactions than others, say the scientists.
“They are all in one big family, but in terms of their allergic potential, they are not the same,” said Elizabeth Phillips, director of the Center for Drug Safety and Immunology at Vanderbilt University Medical Center. Heavier types of PEG are generally more likely to cause allergic reactions than others, she said.
At the same time, “PEG in vaccines is different from what was previously associated with allergic reactions,” said James Baker, an immunologist who runs the Michigan Institute of Nanotechnology for Medicine and Biological Sciences at the University of Michigan.
“The overall structure is very different from everything that exists in a vaccine before,” he said. This makes it difficult to say how allergic reactions to PEG in Covid-19 vaccines will be compared to allergic reactions to other PEGs, such as those in certain laxatives, that have caused rare allergic reactions in the past.
Allergy experts say it is still unclear whether the reactions seen so far were classic allergic reactions, that is, immunological reactions involving an antibody called immunoglobulin E, or IgE, which is part of the so-called adaptive arm of the immune system, which learns to recognize specific intruders. The reactions may also be due to a failure in the innate immune system, causing a cascade of reactions in what is known as the body’s complement system.
“We have to look at all the possibilities,” said Dr. Baker.
He and Dr. Phillips recently attended a virtual meeting organized by the National Institute of Allergy and Infectious Diseases to discuss allergic reactions to the Covid-19 vaccine. The agency said it is preparing a study to look more closely at the issue.
“We plan to study highly allergic individuals with previous episodes of anaphylaxis, as well as some other groups, such as [as] patients with known PEG allergy, ”said Daniel Rotrosen, director of NIAID’s Allergy, Immunology and Transplant Division, by email. The study will include healthy individuals for comparison, he said, and the researchers will collect biological samples before and after vaccination to monitor any immunological changes induced by the vaccine.
Although PEG is a possible culprit, “we need to keep an open mind about other possibilities,” he added.
For now, the CDC says that people with a history of severe allergic reactions to any component of the Pfizer-BioNTech or Moderna vaccines should not receive the vaccine, and those who experience a severe allergic reaction after the first dose should not receive the second.
People with severe allergies to any other vaccine or injectable may receive the vaccine, but they should speak to their doctors before weighing the risks of an allergic reaction with the benefits of receiving the vaccine, the agency advises.
There is no reason why people with a history of mild or severe allergic reactions to food, pets, oral medications or environmental allergens should not receive the vaccine, says the CDC.
The agency also says that people who get the vaccines 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, he says.
The FDA requires that appropriate medical treatment for allergic reactions be immediately available in the event of an acute anaphylactic reaction.
Write to Sarah Toy at [email protected]
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