If You're Allergic to 1 of These 2 Things, Beware Which Vaccine You Get

These compounds could be behind the rare instances of anaphylaxis, the CDC says.

If you're one of the many Americans who suffer from allergies—or worse, you've experienced anaphylaxis—you might be hesitant to get vaccinated against the coronavirus. But the good news is, severe allergic reactions to the COVID vaccine are extremely rare. Only 2 to 5 patients per million vaccinated in the U.S. against COVID were found to have severe allergic reactions, the Centers for Disease Control and Prevention (CDC) told NBC News.

"CDC recommends that people get vaccinated even if they have a history of severe allergic reactions not related to vaccines or injectable medications," the agency says on its website. However, "if you have had an immediate allergic reaction—even if it was not severe—to a vaccine or injectable therapy for another disease, ask your doctor if you should get a COVID-19 vaccine."

And, to be extra cautious, anyone who gets vaccinated is monitored for 15 minutes after their injection to be sure they're not having a severe allergic reaction. Additionally, if you've ever had an anaphylactic reaction to a vaccine and your doctor advises you to get the COVID shot, you'll tell your vaccine site and they'll monitor you for 30 minutes to be sure you're OK. Still concerned that you could react poorly to the shot? Read on to learn the two ingredients that tend to be causing these very infrequent reactions to the COVID vaccines, and for more on how you can prepare, check out Don't Do This the Night Before Your Vaccine Appointment, Experts Say.

Though it's not conclusive, two ingredients are the "likely culprits" behind severe allergic reactions to the COVID vaccine.

covid vaccine in small glass bottles
M-Foto / Shutterstock

We don't yet know which vaccine ingredients trigger allergic reactions in different people for certain, but Meredith Moore, MD, a physician at the Charleston Allergy and Asthma in South Carolina, told NBC News that "polyethylene glycol and polysorbate are the more likely culprits when you look at the ingredients in those two vaccines."

She said her clinic is conducting polyethylene glycol and polysorbate allergy tests to learn more, but the physician has advised her patients with known allergies not to be frightened about possible allergic reactions to COVID vaccines.

The Mayo Clinic describes some symptoms of anaphylaxis as difficulty breathing, a weak or rapid pulse, nausea, vomiting, a skin rash, swelling of your tongue and throat, and dizziness or fainting.

For more on what to look for, know that If This Happens After Your Vaccine, the FDA Says You Should Call 911.

If you're allergic to polyethylene glycol, don't get the Pfizer or Moderna vaccine.

Doctor in protective face mask wearing surgical gloves injecting vaccine to a patient in medical lab.

Pfizer-BioNTech and Moderna are behind the two approved mRNA vaccines that instruct your cells to make a protein that sparks an immune response against a virus via messenger RNA. One of the ingredients they include is polyethylene glycol (PEG), which is used as a protective coating for the vaccine's messenger RNA and is believed to cause an allergic reaction in a small percentage of people.

The CDC advises, "If you are allergic to PEG, you should not get an mRNA COVID-19 vaccine. Ask your doctor if you can get the J&J/Janssen vaccine."

PEG is a petroleum-based compound that is commonly used in cosmetics "as thickeners, solvents, softeners, and moisture-carriers" and in pharmaceuticals as laxatives, according to the David Suzuki Foundation in Vancouver. So there's a chance you've been exposed to it before.

"Colleagues of mine who have been practicing allergy for 20 to 30 years can count on one hand the number of patients that they've seen with polyethylene glycol reactions," Paul Williams, MD, an allergist at Northwest Asthma and Allergy Center in Seattle, told NBC News.

Despite the rarity of polyethylene glycol-induced allergic reactions, "PEG has never been used before in an approved vaccine, but it is found in many drugs that have occasionally triggered anaphylaxis," Science Magazine reports. "Some allergists and immunologists believe a small number of people previously exposed to PEG may have high levels of antibodies against PEG, putting them at risk of an anaphylactic reaction to the vaccine."

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If you're allergic to polysorbate, don't get the Johnson & Johnson vaccine.

A female healthcare workers fills a syringe with COVID-19 vaccine

Meanwhile, the third approved COVID vaccine in the U.S.—from Johnson & Johnson/Janssen—has a synthetic ingredient known as polysorbate. Polysorbate, which has been approved by the FDA, is commonly used in chewing gum, ice cream, cosmetics, and medicines to improve the consistency of gel capsules and to make the contents of your pills disperse throughout your stomach.

However, according to the National Library of Medicine, a 2005 study about polysorbate in medical products concluded the ingredient was "identified as the causative agent for the anaphylactoid reaction" of a patient lacking immunity.

The CDC says, "If you are allergic to polysorbate, you should not get the J&J/Janssen COVID-19 vaccine. Ask your doctor if you can get an mRNA COVID-19 vaccine," meaning Pfizer or Moderna.

And for more on which vaccine tends to produce fewer side effects, check out This COVID Vaccine Has the Lowest Rate of Side Effects, Data Shows.

People with a history of allergic reactions "without any known cause" are candidates to get tested for allergies to these compounds.

A woman appears to have allergic reaction, itchy arm
Albina Gavrilovic / Shutterstock

Some clinics in the U.S.—like Moore's Charleston Allergy and Asthma in South Carolina—are able to test whether patients will have an allergic reaction to polyethylene glycol or polysorbate, but it is not recommended that everyone get checked. Moore told NBC News that she recommends that only people who have a "history of allergic reactions without any known cause" get their allergies tested. But those who have a known history of allergic reactions don't need to get tested.

However, John Grabenstein, PhD, a former Defense Department immunologist who also spoke with NBC News, said there's no evidence allergy tests for polyethylene glycol or polysorbate can reduce the risk of a vaccine-triggered allergic reaction. Experts note that a positive or negative allergy test should not be the deciding factor as to whether or not you get vaccinated.

And if you haven't gotten your shot yet, but are planning to do so in the near future, check out Don't Do This for 2 Days After Your COVID Vaccine, Doctors Say.

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