Approximately one in 100,000 people who received the Pfizer-BioNTech COVID-19 vaccine had severe allergic reactions, US health officials said on Wednesday, while emphasizing that the benefits of immunization far outweigh known risks.
The data comes from the Center for Disease Control and Prevention (CDC), which documented 21 cases of anaphylaxis after administering 1,893,360 shots reported from December 14 to 23.
“This results in an average of 11.1 cases of anaphylaxis per million doses administered,” CDC senior officer Nancy Messonnier told reporters.
In comparison, flu vaccines cause about 1.3 cases of anaphylaxis per million doses administered, and therefore the rate of anaphylaxis for the Pfizer vaccine is about ten times higher.
Messonnier added that cases of anaphylaxis are still “extremely rare” and that it remains in people’s interest to get the vaccine, particularly in the context of the COVID-19 pandemic, which is a much greater danger to their health.
“A good value proposition for someone to be vaccinated is the risk of COVID and poor COVID results are still more than the risk of a serious vaccine result,” she said.
“Fortunately, we know how to treat anaphylaxis and we have made arrangements to ensure that, at immunization sites, people who administer the vaccine are ready to treat anaphylaxis.”
The 21 cases ranged from 27 to 60 years old, with a median of 40 years old, and all but two were treated with epinephrine.
Nineteen of the cases (90 percent) occurred in women, and the average time to onset of symptoms was 13 minutes, but ranged from two to 150 minutes.
Four (19 percent) of the patients were hospitalized, including three in intensive care, and 17 (81 percent) were treated in an emergency department. All but one were discharged home or recovered at the time of the study, and there were no deaths.
Symptoms include a rash, a closed throat, swollen tongue, hives, difficulty breathing, hoarseness, swollen lips, nausea and a persistent dry cough.
Investigations in progress
The United States has already authorized two vaccines for emergency use – one developed by Pfizer and the other by Moderna.
Both are based on state-of-the-art mRNA (messenger ribonucleic acid) technology and authorities have attached warning labels similar to both, which advise people who have a known history of allergic reactions to vaccine ingredients to avoid taking them.
People who have a severe reaction to the first dose should also not take a second dose.
Messonnier said investigations are underway to determine what may be the cause of the allergies.
There is still not enough data to know what is the anaphylaxis rate of the Modern vaccine, which was authorized in the USA a week after the injection of Pfizer, or if a significant difference will appear between the two vaccines.
A preliminary hypothesis for the reactions is the presence of the compound polyethylene glycol (PEG), which has never been used in an approved vaccine, but is found in everyday products, including laxatives, shampoos and toothpastes.
The Pfizer and Moderna vaccines use PEG molecules as part of the protective envelope around their main ingredient, the mRNA that carries genetic instructions into cells.
© Agence France-Presse