What We Know About PEG, Suspected as the Cause of Reactions to Pfizer’s COVID-19 Vaccine


Important note: This article is intended for those who understand vaccines as critical to maintaining their health and that of their families. It is NOT intended for those who are anti-vaccine and as such is NOT intended to foster a discussion on the merits of vaccines in this forum. It is also NOT intended to foster a discussion of the lethality of COVID-19 or the need for civic action to limit the spread of the disease.

To date, there have been six reported severe reactions to Pfizer’s COVID-19 vaccine after hundreds of thousands have been vaccinated despite no such reactions having been observed during phase 3 trials during which 20,000 people received the vaccine. All six developed their reactions during the prescribed observation period, all received epinephrine, and all have recovered.

As we reported, Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, told reporters Friday night that “out of caution” the agency recommends that people who have severe allergic reactions to any components of the two vaccines (Pfizer’s and the newly authorized vaccine from Moderna) should not be vaccinated with either.

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Marks indicated that focus is on a compound called polyethylene glycol (PEG) a lipid (fat) that is a component in other injectable medicines and has been known to cause allergic reactions in rare circumstances. “That could be a culprit here,” said Marks.

PEGs, a class of macrogols similar to polysorbates, are widely used compounds in medicines, foods, and cosmetics and are generally referred to by their molecular weights, e.g. PEG-2000.

According to the MIT, PEGs are basically tiny, greasy spheres that are used in COVID vaccines to protect the active ingredient (mRNA) and help it penetrate cells. It is within cells that the mRNA can go to work priming the immune system.

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PEGs have also been confirmed to cause allergic reactions in rare cases, but how rare is not known.

In an article from 2018 entitled “Can You Really be Allergic to an ‘Inactive’ Ingredient?”, the American Academy of Allergy Asthma and Immunology (AAAAI) states:

Currently, there is only limited awareness of the role of PEGs in reactions to medications where they are present as an ingredient. The degree to which PEG hypersensitivity might be a problem in the United States and the mechanism for PEG and polysorbate reactions are therefore not well understood.

The article refers to a study published in The Journal of Allergy and Clinical Immunology: In Practice where the authors found an average of 4 cases of anaphylaxis reported per year to the FDA from 2005-2017 where PEG 3350-containing bowel preparations or laxatives were the implicated culprit.

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As of this writing, the Centers for Disease Control (CDC) warns:

If you have had a severe allergic reaction—also known as anaphylaxis—to any ingredient in the Pfizer-BioNTech vaccine, you should not get vaccinated.*

*If you have had a severe allergic reaction to other vaccines or injectable therapies, ask your doctor if you should get the Pfizer-BioNTech vaccine. Your doctor will help you decide if it is safe for you to get the Pfizer-BioNTech vaccine.

PEG-2000 is an ingredient used in both the Pfizer and Moderna COVID-19 vaccines. If the compound is found to be the cause of the six allergic reactions to date, it will help the CDC hone their guidance further by narrowing the list of those that should not receive the vaccine.

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Dave Bloom
Dave Bloom
Dave Bloom is CEO and "Blogger in Chief" of SnackSafely.com.

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