COVID-19: Allergic reactions to Pfizer vaccine are rare
Researchers estimate a rate of 11.1 cases of anaphylaxis for every million first doses of the Pfizer-BioNTech COVID-19 vaccine.
Anaphylaxis is a life threatening allergic reaction that some people have after exposure to a specific substance, such as venom or a particular food or medication (including vaccines).
Symptoms include difficulty breathing and swallowing, facial swelling, and a rapid heart rate.
Scientists at the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) reviewed reports of adverse reactions to the Pfizer-BioNTech vaccine in the United States shortly after the FDA authorized its use on December 11, 2020.
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Over the same period, about 1,893,360 people in the U.S. received their first dose of this vaccine. This equates to 11.1 cases of anaphylaxis for every million doses.
Out of the 21 people who experienced anaphylaxis, four were hospitalized, with three needing intensive care. The treatment of the remaining 17 people took place in an emergency department.
At the time of reporting to VAERS, 20 of the patients had left the hospital or recovered. There were no reported deaths.
Of the 21 individuals, 17 (81%) had a documented history of allergies, and seven (33%) had experienced anaphylaxis in the past.
Over the same period, the researchers note, there were 83 cases of milder allergic reactions to the vaccine that did not meet the criteria for anaphylaxis.
Commonly described symptoms of these reactions included:
pruritus (itchy skin)
itchy and scratchy sensations in the throat
mild respiratory symptoms
Tom Shimabukuro from the CDC and Narayan Nair from the FDA have published their findings in the journal JAMA.
In their report, they emphasize the benefits of vaccination against COVID-19:
“Mortality from COVID-19 in populations at high risk is substantial, and treatment options are limited. Widespread vaccination against COVID-19 with highly effective vaccines represents an important tool in efforts to control the pandemic.”
The Pfizer vaccine is an mRNA vaccine, which means that it contains genetic material that instructs the cells to make a harmless piece of the virus’ spike protein.
This fragment of protein cannot cause COVID-19, but it provokes an immune response that provides protection against the disease.
The CDC have issued general advice to healthcare professionals about mRNA COVID-19 vaccines and specific guidelines on the management of anaphylaxis after COVID-19 vaccination.
These recommendations include screening vaccine recipients to identify anyone with contraindications to its ingredients.
The CDC also advise a period of observation after administration. They recommend 15 minutes for most people but 30 minutes for anyone who has a history of anaphylaxis or has had a previous allergic reaction to any vaccine or injectable therapy.
In cases of suspected anaphylaxis, the CDC say, healthcare professionals should administer an immediate injection of epinephrine.
Epinephrine, also known as adrenaline, is a hormone that counters the effects of anaphylaxis. People who have experienced such a reaction in the past often carry an auto-injector that delivers a shot of the hormone in emergencies.
The authors of the new study conclude with this advice to healthcare professionals:
“All patients should be instructed to seek immediate medical care if they develop signs or symptoms of an allergic reaction after their observation period ends and they have left the vaccination location.”
In the United Kingdom, the Medicines and Healthcare Products Regulatory Agency (MHRA) initially recommended that certain people — individuals who have previously had a significant allergic reaction to a vaccine, medicine, or food and those who have received medical advice to carry an epinephrine auto-injector — should not receive the Pfizer vaccine.
Following a thorough investigation of the potential of the vaccine to cause anaphylaxis, however, the MHRA withdrew this advice.
The agency still say that the vaccine is not suitable for individuals who have a history of allergic reactions to any of its ingredients or experience anaphylaxis after their first dose.
The agency also advise closely observing everyone who receives the vaccine for at least 15 minutes afterward.
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