Can Antihistamines Help Stop Allergic Reactions to MRNA COVID-19 Vaccines?

Curated by Claudia Shannon / Research Scientist / ishonest

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New research has found that antihistamines may help resolve the allergic reactions some people experience after receiving the Pfizer and Moderna messenger RNA (mRNA) vaccinations against COVID-19.

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There is a small risk of experiencing a serious allergic reaction to certain ingredients in the vaccine — polyethylene glycol or polysorbate — but according to the findings, most reported reactions to the vaccines did not cause anaphylaxis.

If you experienced a reaction after your first dose, “your allergist may recommend premedicating with an antihistamine to dampen the body’s response to the histamine released in the body as a response to the vaccine, therefore lessening the severity of symptoms,” said Dr. Sanjeev Jain, a board certified allergist and immunologist at Columbia Allergy on the West Coast.

Allergy symptoms resolved with antihistamines

The study evaluated the vaccine’s effects in 189 individuals who experienced at least one allergy symptom — such as flushing, hives, or shortness of breath — within 4 hours after receiving their first dose.

The researchers sought out to explore how these individuals tolerated the second dose.

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Of the group, 159 received the second dose. Of this 159, 47 were given antihistamine medications before the shot.

All individuals, including 19 people who experienced anaphylaxis after the first dose, tolerated the second dose.

Thirty-two experienced allergy symptoms after their second dose that were self- limited and resolved with antihistamines.

Allergic reactions to the COVID-19 vaccines have been reported to be as high as 2 percent. Reports also suggest anaphylaxis is rare but can occur at a rate of up to 2.5 per 10,000 individuals.

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This study found that the vast majority of allergic reactions reported were not the type of severe reaction known to cause anaphylaxis.

According to the findings, these types of symptoms can be reduced with antihistamine premedication.

“Most people who had an immediate — within 4 hours — allergic symptoms after receiving the first COVID-19 mRNA vaccine are able to tolerate [a] second dose, after consultation with the allergy specialist,” said Dr. Blanka Kaplan, an allergy and immunology specialist with Northwell Health in Great Neck, New York.

Why some people have reactions to the vaccine

According to Jain, when you receive a vaccine, your immune system gets activated to produce a protective response against a pathogen — in this case, SARS-CoV-2.

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“As your immune system is activated, there is a transient release of inflammatory mediators that can lead to symptoms such as soreness, redness, and swelling at the injection site or of the adjacent lymph nodes as well as fever, muscle aches, and headache,” Jain said.

These symptoms typically resolve within 24 to 48 hours.

There is a small risk of developing a severe reaction if you have an allergy to polyethylene glycol or polysorbate, which are ingredients in the mRNA shots.

These types of rare severe allergic reactions, immunoglobulin E-mediated (IgE- mediated) reactions, can lead to anaphylaxis.

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During IgE-mediated reactions, the immune system releases histamines that can cause the lungs to contract and lead to hives, lowered blood pressure, wheezing, hives, and gastrointestinal symptoms, according to Jain.

Antihistamines can reduce the severity of these types of reactions by blocking histamine receptors throughout the body and preventing these symptoms.

“Based on the report in the article, it does seem likely that most reported reactions to the vaccine were not in fact true IgE-mediated reactions that have the potential to cause anaphylaxis,” Jain said.

The risk of COVID-19 is far greater than the risk of vaccine reactions

Health experts agree that the risks linked to COVID-19 are much higher than the risk of developing an allergic reaction after getting the vaccine.

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“It is well documented that anaphylaxis can be effectively treated with epinephrine and other medications including antihistamines, steroids, and inhalers,” Jain said.

“Benefits of completing a COVID-19 vaccination series outweigh the risk of getting severe COVID-19 disease due to incomplete immunization,” Kaplan said.

COVID-19 cases are surging again in the United States, with the more infectious delta variant on the rise.

If you’re concerned, talk with your doctor

For those who are concerned about developing a reaction to the vaccination, Jain recommends working with an allergist to come up with a plan to reduce any risk.

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Anyone who had an allergic reaction to the first dose or any other vaccine should consult an allergy specialist who can provide guidance for getting vaccinated.

Those who had a reaction to their first dose should be closely monitored during their second dose.

“Antihistamines can be potentially helpful, but people should not just take antihistamines after having a reaction to the first shot and get the second shot without physician’s guidance,” said Kaplan.

The bottom line

New research has found that antihistamines help resolve the allergic reactions some people experience after receiving the Pfizer and Moderna mRNA vaccines. There is a small risk of experiencing a serious allergic reaction to certain ingredients in the vaccine — polyethylene glycol or polysorbate — but most reported reactions to the vaccines were not the type of severe allergic reaction that causes anaphylaxis.

When given prior to vaccination, antihistamine treatment can help prevent allergy symptoms like hives, shortness of breath, and flushing. Anyone who developed a reaction after their first dose plus those with a history of reactions to vaccines should work with an allergy specialist to get fully vaccinated.

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