Serious allergic reactions after the COVID-19 vaccines are probably more common than the following serious reactions flu vaccines, but are still very rare, according to a new report.
The authors of the report, the Centers for Disease Control and Prevention (CDC), analyzed data on the first 1.9 million doses of the COVID-19 vaccine administered in the United States from December 14 to 23. For most of that time, only the Pfizer-BioNTech COVID-19 vaccine was available in the USA
The researchers identified 21 cases of people who experienced anaphylaxis – a potentially fatal allergic reaction – shortly after receiving the COVID-19 vaccine.
This is a rate of about 11 cases of anaphylaxis per 1 million doses of vaccine administered. For comparison, the rate of anaphylaxis after influenza vaccination is 1.3 cases per million people, said Dr. Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases, during a news conference on Wednesday (6 January).
Even though the rate of anaphylaxis linked to COVID-19 vaccines is about 10 times higher than what is seen with flu vaccines, “it is still extremely rare,” said Messonnier. Overall, the vaccine’s benefits outweigh the potential risks, she said.
Related: 7 weird signs you’re having an allergic reaction
Of the 21 cases described in the report, 17 had a history of allergies or allergic reactions, including reactions to drugs, food and insect bites; and seven of those people had experienced anaphylaxis in the past. Almost all of these patients were treated with epinephrine after their reaction to the COVID-19 vaccine, and all 21 recovered.
Although the new report only includes cases of the Pfizer COVID-19 vaccine, the CDC is also aware of confirmed cases of anaphylaxis linked to the Modern COVID-19 vaccine.
Exactly what is causing these reactions is unclear and “tremendous efforts” are underway to better understand the cause, said Messonnier. A possible culprit is polyethylene glycol, an ingredient in both Pfizer and Modern vaccines, Live Science previously reported.
However, having allergies does not necessarily increase the risk of reactions to COVID-19 vaccines. Allergies are common in the United States, but serious reactions to vaccines are not.
The CDC recommends that people with a history of reactions to vaccines or anaphylaxis from any cause be observed by the health team for 30 minutes after receiving the COVID-19 vaccine. (In the report, patients experienced anaphylaxis on average about 13 minutes after the COVID-19 injection.)
The agency recommends that people not receive the Pfizer or Moderna vaccine if they have a known allergy to an ingredient in these vaccines, including polyethylene glycol; and people should not receive a second dose if they have a severe reaction to the first.
Originally published on Live Science.