The intensive care unit nurse was worried the COVID-19 vaccine would kill her.

In the past, just minutes after getting the influenza vaccine, she had hives, wheezing, and throat swelling. Her life-threatening reaction only resolved after an epinephrine injection and monitoring in the emergency room. She vowed never to get another vaccine.

With the arrival of the COVID-19 vaccine, she reconsidered her stance. Now she was in my clinic, and together we considered the options: Not get the vaccine — even though she regularly cares for COVID-19 patients — and remain unprotected from the novel coronavirus, or get the vaccine, and possibly risk another life-threatening reaction.

As an allergist/immunologist, I assured her that, with a proper evaluation, it was safe to receive the COVID-19 vaccine, even with a history of a severe allergy.

Millions of people in the United States have allergies to foods, medications, and/or bee stings. What’s more, many of these people have experienced anaphylaxis, a severe allergic reaction whose symptoms include not only hives and throat swelling, as in the ICU nurse, but also facial swelling, vomiting, a dangerously low blood pressure, or even loss of consciousness.

After the COVID-19 vaccine was approved for use in England in mid-December 2020, the media breathlessly reported that two health care workers had anaphylaxis to the vaccine on day one of administration. When the COVID-19 vaccine was rolled out in the United States two weeks later, similarly alarmist news sites documented instances of allergic reactions. Moreover, on January 17, a large cluster of reactions was reported in San Diego, so officials temporarily halted the administration of more than 300,000 Moderna vaccines, at a time when the supply was — and continues to be — disconcertingly limited.

Even though vaccine allergies are rare — literally one in a million — people were understandably nervous. Misinformation was rife on social media. As a result, physicians were deluged with messages and phone calls from patients, concerned their history of allergies prevented them from safely receiving the COVID-19 vaccine.

For COVID-19 vaccine allergies, the mechanism and the exact chemical causing these responses are still unknown. One likely culprit is polyethylene glycol (PEG), a component of both the Pfizer and Moderna vaccines. PEG is commonly found in medications, cosmetics, and food, though allergy to PEG, prior to the development of the COVID-19 vaccine, was exceedingly rare.

So how does this translate practically? Because most allergies, such as to food and medications, have nothing to do with COVID-19 vaccine reactions, the vast majority of people with severe allergies can get the COVID-19 vaccine, followed by a 30 minute observation period in a medical facility equipped to treat anaphylaxis.

However, a person with a history of allergic reactions to a vaccine or injectable therapy should be evaluated by an allergist, who can review the components in the causative vaccine or injectable therapy, and perform skin testing to determine if there are any allergies to PEG.

The skin tests are usually done on the arms and, contrary to popular belief, not that painful. If the skin tests show no reactivity to PEG, the person can receive the COVID-19 vaccine, monitoring for 30 minutes afterward.

In the future, when the vaccine supply is more plentiful, allergists may be able to give the COVID-19 vaccine to a vaccine-allergic person through the administration of rapidly increasing doses.

Recent reports from the CDC, released four days ago, are encouraging. The rate of anaphylactic reactions is 2.5 per million for the Moderna vaccine, and 11.1 per million for the Pfizer vaccine. Of note — and we don’t know why — over 90 percent of anaphylactic reactions occurred in women.

Most importantly, out of more than 14 million administered COVID-19 vaccines, there have been zero deaths associated with allergic reactions, largely because anaphylaxis is completely treatable with epinephrine injections.

Some people, especially after the second vaccine, will get fevers, chills, and muscle aches. This is not an allergic reaction, but rather well-known side effects of the vaccine — physical evidence that the immune system is mounting a robust response.

The ICU nurse agreed to skin testing, which was negative to PEG. She got her first vaccine without problems, and eagerly awaits her second one in a month. She’s now more confident she can care for COVID-19 patients, without ending up in the ICU as a patient herself.

As she pointed out, she won’t die from an allergic reaction to the COVID-19 vaccine. But getting the vaccine will prevent her from dying of COVID-19.

Charles Feng is an allergy and immunology physician.

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