Serious allergic reactions to Pfizer’s COVID-19 vaccine are “rare,” says CDC

Serious allergic reactions to Pfizer and BioNTech’s COVID-19 vaccine were “rare” across the country in the first 10 days of its launch, according to a new report from the Centers for Disease Control and Prevention.

A total of 21 cases of anaphylaxis – none of which were fatal – were confirmed among nearly 1.9 million doses administered, CDC researchers wrote in Wednesday’s weekly report on morbidity and mortality. That corresponds to 11.1 cases per 1 million doses.

Anaphylaxis is a severe allergic reaction that can be triggered by a vaccine, food, medicine, insect bites, and latex. The reaction can be fatal if not treated immediately, typically with an injection of epinephrine to open the airways in the lungs.

The reports of anaphylaxis and other side effects of the Pfizer BioNTech vaccine were sent to the Vaccine Adverse Event Reporting System (VAERS), which is managed by the CDC and the Food and Drug Administration, to track safety issues after a vaccine has been manufactured for the Open to the public.


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Pfizer-BioNTech’s COVID-19 vaccine was the first to receive emergency approval from U.S. regulators. The first doses went into the arms of frontline health workers on December 14. The new CDC report is based on 1,893,360 doses administered as of December 23rd.

These doses resulted in 175 possible cases of severe allergic reactions. The investigators who reviewed these cases found that 21 of them were anaphylaxis and 86 were other allergic reactions. Sixty-one cases were not allergic reactions at all, and seven are still being studied.

Of the 21 people who had anaphylaxis, 17 had a history of allergies, including seven people who had previously had anaphylactic reactions.

17 of the 21 patients were treated in emergency rooms and four patients were hospitalized. Three of these hospital patients required intensive care.

Twenty of the patients had recovered when their cases were reported to the Vaccine Adverse Event Reporting System. Details about the 21st patient were not known, but the CDC researchers noted that there were no reports of anaphylaxis-related deaths with the Pfizer BioNTech vaccine.

The 21 patients were between 27 and 60 years old, with a mean age of 40 years. Nineteen of them – or 90% – were women. The report’s authors found that 64% of cases where the sex of a vaccine recipient was known were women. They also pointed out that during the 2009 pandemic flu, women were more likely to have “immediate hypersensitivity” to the H1N1 influenza vaccine.

After receiving the COVID-19 vaccine, the fastest anaphylactic reaction occurred in just two minutes, and the slowest occurred in 150 minutes. The vast majority of reactions were rapid, with 15 occurring within the first 15 minutes after injection and three more occurring between 15 and 30 minutes.

Nineteen of the patients were treated with adrenaline.

The 21 cases were not grouped into a single geographic area and were tied to doses from multiple lots of the vaccine.

Among the other cases of allergic reactions, more than four in five were classified as “not serious”. The most common reactions reported to VAERS were rash or itchy skin, itchy or itchy throat, and mild respiratory problems. Half of these reactions occurred within 12 minutes of receiving the vaccine, and 90% of those affected were women.

In total, VAERS received 4,393 reports of any type of adverse event during the first 10 days of the Pfizer BioNTech vaccine launch, according to the report. That is a rate of 0.2%.

The CDC has already updated its vaccine administration guidelines and a similar one developed by Moderna and the National Institutes of Health, which received emergency approval a week after the Pfizer-BioNTech product. This guide contains:

• Make sure that adrenaline is available and ready to use at the vaccination sites.

• Ask potential vaccine recipients about their history of allergic reactions to identify those at high risk.

• Keep people under surveillance for up to 30 minutes after receiving the vaccine so that cases of anaphylaxis can be treated quickly.

• Make sure that the healthcare providers delivering the vaccine are trained to recognize the early signs of anaphylaxis.

• If anaphylaxis is suspected, give an intramuscular injection of adrenaline immediately.

The first doses of the Moderna vaccine were given on December 21, and fewer than 225,000 doses were given during the 10-day period of this study. A separate report on its side effects is in the works, the CDC researchers said.

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