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Do you need a test to tell you if you're allergic to the Covid vaccine before getting it?

Allergic reactions to the Covid-19 vaccines are incredibly rare. But some allergy clinics are offering testing.

When reports of severe allergic reactions among recipients of Covid-19 vaccines started surfacing, Angelina Giunta became worried.

Even though Giunta, 61, of Brooklyn, New York, was desperate to get the vaccine after a year in quarantine, she'd had two severe allergic reactions to medications during treatment for cancer in 2017.

"I want to get the vaccine because I want to move on with my life," Giunta said. "But I was extremely concerned."

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Two ingredients in the Covid-19 vaccines, polyethylene glycol and polysorbate 80, have been suggested as possible culprits in anaphylactic reactions related to Covid-19 vaccines. (Anaphylaxis is a severe, life-threatening allergic reaction.) To date, however, the link has not been conclusively established.

Still, some allergy clinics across the U.S. have begun to highlight that they are able to test patients for allergies to those ingredients.

But those tests, many experts say, may be a waste of time and resources — mainly because such allergies are incredibly rare.

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.

"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," said Dr. Paul Williams, an allergist at Northwest Asthma and Allergy Center in Seattle and clinical professor of pediatrics at the University of Washington.

In fact, it is likely that the vast majority of Americans have already been exposed to either polyethylene glycol or polysorbate 80.

Polyethylene glycol is a common active ingredient in over-the-counter laxatives. Pfizer-BioNTech and Moderna use it in their vaccines as a protective coating for messenger RNA, or mRNA, bits of genetic code used to teach cells how to recognize and fight the virus that causes Covid-19.

And polysorbate 80 is ubiquitous in the typical American diet, found in chewing gum, ice cream, puddings and other foods. It's used as an emulsifier to make products creamier. It's also an ingredient in the Johnson & Johnson Covid-19 vaccine identified as a potential allergen — though no allergic reactions have been reported in Johnson & Johnson vaccine recipients to date.

"There's nothing special about these vaccines in terms of allergic disease or anaphylaxis," said Dr. Mitchell Grayson, chair of the Asthma and Allergy Foundation of America's Medical Scientific Council. "Why aren't we seeing more people with polyethylene glycol or polysorbate allergy in general?"

Severe allergic reactions to the Covid-19 vaccine have occurred at a rate of "2 to 5 people per million vaccinated in the United States," the Centers for Disease Control and Prevention said in a statement to NBC News. "Fortunately, vaccination providers have medicines available to effectively and immediately treat patients who experience anaphylaxis following vaccination."

Additionally, screening and monitoring for such reactions has been factored into the Covid-19 vaccination protocol: It's why vaccine recipients are asked beforehand whether they've had a past severe allergic reaction to a vaccine and why they're told to wait for 15 to 30 minutes after receiving the vaccine, so that if a reaction does occur, medical staff on hand can respond.

Grayson said the biggest problem with Covid-19 vaccines isn't allergies, it's hesitancy. Nearly a third of those who took part in a recent Kaiser Family Foundation survey said they would rather wait and see what happens to others who get the vaccine before rolling up their own sleeves.

"My fear is that all of this is just helping to feed into that," Grayson said, referring to Covid-19 vaccine allergy testing.

Who, if anyone, needs a test?

Charleston Allergy and Asthma in South Carolina is one clinic offering testing for polyethylene glycol and polysorbate 80. The tests are done by scratching a tiny amount of the substance in question into a person's skin and watching for a reaction, like redness or itching.

"We don't know at this point exactly what [vaccine] components cause reactions in all these different individuals," said Dr. Meredith Moore, a physician practicing at the clinic. "But polyethylene glycol and polysorbate are the more likely culprits when you look at the ingredients in those two vaccines."

None of the tests administered so far among Moore's patients has been positive.

Moore said most people with allergies do not need to worry about any potential reactions to Covid-19 vaccines.

In fact, for people who carry emergency epinephrine for peanut, insect or other allergies, Moore advises against getting tested. She said allergy tests for polyethylene glycol or polysorbate 80 should be reserved for people who have a history of allergic reactions without any known cause.

John Grabenstein, a former executive director of medical affairs for vaccines at Merck and a former Defense Department immunologist, said there is no evidence the tests reduce the risk for any type of allergic reaction from the Covid-19 vaccine.

Because the ingredients have not been proven to be causes of Covid-19 vaccine allergic reactions, having a negative allergy test to polyethylene glycol or polysorbate 80 does not necessarily mean a person will be spared an allergic reaction to the vaccine. And a positive test should not preclude a person from getting the Covid-19 vaccine, experts say.

"The vast majority of the public — even people with pollen allergies, people with penicillin and bee sting allergies — don't have to worry about vaccination," Grabenstein said.

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Dr. Cascya Charlot, who offers the tests in her practice at Allergy and Asthma Care of Brooklyn, agreed.

"I'm not advocating that everybody should be skin-tested before getting the vaccine, absolutely not," Charlot said.

She sees the testing as a pathway to allaying fears of allergic reactions to the Covid-19 vaccine.

"It's a public health incentive as far as we see it, to try to get people vaccinated," Charlot said. "We don't want concerns about a potential reaction to the vaccine."

None of the allergy tests Charlot has done for polyethylene glycol or polysorbate 80 has come back positive.

The harm in relying on such testing, Grayson said, would be to have someone "avoid a vaccine that they otherwise should be able to receive."

"You're either unnecessarily excluding people from a vaccine, or you're allowing them to go ahead with a vaccine, without knowing for sure if they'll have another anaphylactic reaction," Grayson said.

The one positive effect appears to be peace of mind.

Giunta, one of Charlot's patients, tested negative and is looking forward to her Covid-19 vaccine.

"I want to move on with my life and travel, you know," Giunta said, "do the normal stuff that I did before."

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