About one in 100,000 people receiving the Pfizer-BioNTech COVID-19 vaccine have had severe allergic reactions, U.S. health officials said Wednesday, stressing that the benefits of immunization far outweigh the known risks.
The data comes from the Centers for Disease Control and Prevention (CDC), which documented 21 cases of anaphylaxis after taking 1,893,360 photos reported between December 14 and 23.
“This is done at an average rate of 11.1 cases of anaphylaxis per one million doses,” CDC official Nancy Messonnier told reporters.
By comparison, influenza vaccines cause about 1.3 cases of anaphylaxis per million doses administered, so the rate of anaphylaxis for the Pfizer vaccine is about ten times higher.
Messonnier added that cases of anaphylaxis were still “extremely rare” and it remains in the interest of people to get the vaccine, especially in the context of the COVID-19 pandemic, which poses a much greater danger to their health.
“A good value proposition for someone to be vaccinated is the risk of COVID, and the poor results of COVID are even more than the risk of a severe vaccine outcome,” 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, with a median age of 40 years and all but two were treated with epinephrine.
Nineteen cases (90 percent) occurred in women, and the mean 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. It was known that all but one were discharged at home or recovered at the time of the study and there were no deaths.
Symptoms include rash, tightness in the throat, swollen tongue, hives, difficulty breathing, hoarseness, swollen lips, nausea and persistent dry cough.
Investigations are ongoing
The United States has so far authorized two emergency vaccines – 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 both similar warning labels, advising people with a known history of allergic reactions to vaccine ingredients to avoid their administration.
People who have a severe reaction to the first dose are also asked not to take a second dose.
Messonnier said investigations are ongoing to determine what may be causing the allergies.
There is not yet enough data to know the rate of anaphylaxis for the Moderna vaccine, which was approved in the US a week after the Pfizer shot or if there will be a significant difference between the two vaccines.
A preliminary hypothesis for the reactions is the presence of the compound polyethylene glycol (PEG), which has not been used so far in an approved vaccine, but is found in everyday products, including laxatives, shampoos and toothpastes.
Both Pfizer and Moderna vaccines use PEG molecules as part of the protective shell around their main ingredient, the mRNA that carries the genetic instructions to the cells.
© Agence France-Presse