Covid-19 vaccines have so far caused severe allergic reactions in 29 people in the US

The 29 cases are as of Jan. 5 and are of the more than 5.3 million doses administered to date, the CDC said.

The rate of 5.5 cases of anaphylaxis, a life-threatening allergic reaction, for every million Covid-19 vaccine doses administered to date, is comparable to the rate of 1.3 cases for every million doses of flu vaccine, according to the CDC.

Still, cases of anaphylaxis are “extremely rare,” said Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases, who is in charge of the agency’s vaccination efforts for Covid-19.

In a conference call Wednesday, Dr. Messonnier that the benefits of a vaccine far outweigh the possible risks.

“It’s a very safe vaccine, and we’re on the verge of 2,000 Covid deaths per day,” she said. “I continue to believe that the risk of Covid and the risk of poor outcomes, especially in seniors, makes it imperative that people go ahead and get vaccinated as soon as they get it.”

The 29 people received vaccines from Pfizer Inc.

and partner BioNTech SE,

approved by the U.S. Food and Drug Administration on Dec. 11, as well as Moderna Inc.,

whose vaccine was approved on December 18.

The CDC and the FDA are reviewing reports of serious side effects that may be related to the vaccines and are working with manufacturers to determine whether a particular component is involved in the reactions.

Anyone who has an immediate or allergic reaction to the first dose of a Pfizer-BioNTech or Moderna Covid-19 vaccine should not receive their second dose, said Dr. Messonnier. People who have previously had an immediate allergic reaction to a vaccine or injectable therapy, or who have a history of anaphylaxis, should be observed for 30 minutes after vaccination, she said. Immunization sites must be prepared to treat patients for anaphylaxis, she added.

The CDC said all other vaccine recipients should be monitored for 15 minutes after getting the injection.

Federal officials are looking for a possible cause of the severe reactions, and the National Institute of Allergy and Infectious Diseases is planning a study to find out more.

“We are studying these vaccines closely, and our adverse event systems are incredibly robust,” said Dr. Messonnier.

One potential culprit, an FDA official said last month, is polyethylene glycol, also known as PEG. The compound is found in other medical products, including laxatives and preparations taken before colonoscopies, and is known to cause anaphylaxis in rare cases.

In both the Pfizer BioNTech and Moderna vaccines, PEG is an ingredient in the fatty envelope surrounding the messenger RNA that is the primary ingredient of the vaccine.

Pfizer is closely following all reports of serious allergic reactions and updates the labeling swatch as needed, a company spokeswoman said. The prescribing information already contains a warning that treatment for anaphylaxis should be available during vaccination.

“Moderna is aware of two cases of anaphylaxis during the EUA period [emergency use authorization], one of which was reported directly to Moderna, ”said a company spokesperson. “We will continue to monitor the CDC and FDA reports pending information on any additional cases that may not have been reported directly to us.”

The CDC provided details of 21 cases of anaphylaxis on Wednesday identified from more than 1.9 million doses of vaccines administered between December 14 and 23. The rate of anaphylaxis during that period was 11.1 cases for every million doses administered, the CDC said. how easily the rate can change, given that the vaccination program is still in its infancy and data is limited.

In a study published in its Morbidity and Mortality Weekly Report, the agency said 4,393 incidents related to Covid-19 vaccination had been recorded in a federal adverse event reporting system on Dec. 23. CDC officials identified 175 as possible cases of serious allergic reactions and studied them further.

They determined that there were 21 cases of anaphylaxis, and the vast majority experienced the life-threatening event within half an hour of vaccination. Most people – 17 – had a documented history of serious reactions to one or more of the many possible allergens: medicines and other medical products, eggs and other foods, or bee or wasp stings.

Seven had previously had anaphylaxis; Their events were linked to a rabies vaccine, an H1N1 flu vaccine, a jellyfish sting, walnuts and certain drugs.

Four of them were hospitalized, including three in intensive care, while the others were treated in an emergency department. Most received epinephrine injections, the CDC said.

It’s not clear whether their previous allergic reactions were related to their anaphylaxis from the Covid-19 vaccine, said Dr. Messonnier. “Therefore, our recommendation is generally that people should consult their healthcare provider,” she said. For example, “there is a big difference between someone who had a mild allergic reaction in childhood and someone who had a severe allergic reaction last week.”

The cases came from different parts of the country and received vaccines from different lots, the CDC said, indicating the problem isn’t due to contamination or some other problem with one batch. The median age of the cases was 40, and the vast majority – 19 – were women. That may be because nearly two-thirds of the vaccinations were given to women during that time, the agency said.

Write to Betsy McKay at [email protected]