What to Know About Allergic Reactions to Pfizer’s Vaccine

People with a history of anaphylaxis should wait for further guidance, but there’s no need to panic

Yasmin Tayag
Medium Coronavirus Blog


Image: Iryna Veklich / Getty Images

On Tuesday, a 90-year-old woman named Margaret Keenan received Pfizer’s Covid-19 vaccine in the U.K., kicking off the country’s historic Covid-19 vaccination campaign. The U.K. approved Pfizer’s vaccine last week, making it the first nation in the Western world to approve a Covid-19 vaccine for widespread use. Canada and Bahrain soon followed suit, and the United States is expected to do the same after a Food and Drug Administration advisory panel on Thursday.

As thousands more in the U.K. were vaccinated this week, a couple complications emerged: Two people — health care workers who have experienced serious allergies in the past — had reactions to the Pfizer vaccine.

On Wednesday, Stephen Powis, the national medical director for England’s National Health Service, issued a statement saying: “As is common with new vaccines the MHRA (Medicines and Healthcare products Regulatory Agency) have advised on a precautionary basis that people with a significant history of allergic reactions do not receive this vaccination after two people with a history of significant allergic reactions responded adversely yesterday.” He noted that both people were “recovering well.”

The MHRA later clarified this guidance by specifying that people with a history of anaphylaxis should not get the vaccine. Anaphylaxis is a severe allergic reaction to an antigen to which the body has become hypersensitive. The strong, potentially life-threatening reactions some people have to bee stings or peanuts are examples of anaphylaxis. People who have these allergies usually carry an injection of adrenaline (also known as epinephrine), like an EpiPen, to counter the effects of anaphylaxis in emergency situations.

“Any person with a history of anaphylaxis to a vaccine, medicine, or food should not receive the Pfizer BioNTech vaccine. A second dose should not be given to anyone who has experienced anaphylaxis following administration of the first dose of this vaccine,” said June Raine, chief executive of the MHRA on Thursday.

The MHRA guidance for health care professionals administering the vaccine notes: “As with all injectable vaccines, appropriate medical treatment and supervision should always be readily available in case of a rare anaphylactic event following the administration of the vaccine.”

The wording of this guidance is significant: “As with all injectable vaccines” acknowledges the fact that all vaccines have the potential to elicit an allergic reaction in some people. In other words, it’s not abnormal that some people were allergic to the Pfizer vaccine because allergies to vaccines do happen. In a paper about vaccine allergies published in the Journal of Allergy and Clinical Immunology in 2018, researchers with the Centers of Disease Control and Prevention explained:

“Vaccine-associated hypersensitivity reactions are not infrequent. Fortunately, most reported vaccine-associated adverse reactions are not serious, and many are not immunologically mediated or even reproducible on reexposure. Serious anaphylactic or cutaneous adverse reactions do occur but are extremely rare.”

This context is especially important as many people have still expressed hesitancy about taking the vaccine due to safety concerns.

Infectious diseases expert Anthony Fauci, MD, head of the National Institutes of Allergy and Infectious Diseases, acknowledged in a webcast conversation with Sanjay Gupta, MD, on Wednesday that the allergic reactions were concerning but also par for the course.

“These are the kinds of things that happen when you implement large vaccine programs [on millions of people],” he said. “You may start seeing effects in some that might not have been picked up when you were dealing with thousands.”

Allergies to the Pfizer vaccine are likely “unusual and rare,” he said, but people with a history of allergic reaction should be aware. “So if I were a person that had an underlying allergic tendency,” he said, “I might want to be prepared that I might get a reaction and therefore be ready to treat it.”

As of Thursday, the most up-to-date guidance from MHRA is that people with a “history of a significant allergic reaction to a vaccine, medicine, or food” should not receive the Pfizer vaccine and that vaccines should only be administered in facilities where resuscitation measures are available.

In his conversation with Gupta, Fauci said that the vaccine’s potential for allergic reaction highlighted why it’s important to test many different vaccines. If it does turn out that the Pfizer vaccine has consistent allergy issues, he said, “we’ll always have other vaccine platforms that you can use and hopefully you will not see that with those other platforms.”

In an interview with AP, Ashish Jha, MD, dean of the school of public health at Brown University, offered simple advice to those at risk of allergic reaction: “The cautionary approach is to say to people who have had severe reactions to other things, ‘just hold.’”



Yasmin Tayag
Medium Coronavirus Blog

Editor, Medium Coronavirus Blog. Senior editor at Future Human by OneZero. Previously: science at Inverse, genetics at NYU.