The figure was calculated by the Centers for Disease Prevention and Control (CDC), which identified 21 cases of anaphylactic shock, a severe allergic reaction, out of a total of 1,893,360 vaccine injections made between the 14th and the 14th. December 23. “On average, this represents a rate of 11.1 anaphylactic shocks per million doses administered,” Nancy Messonnier, a CDC official, told reporters.
For comparison, influenza vaccines cause about 1.3 anaphylactic shock per million doses.
Even though the rate for Pfizer-BioNTech’s coronavirus vaccine is about ten times higher, the number of cases of severe allergic reactions remains “exceedingly rare” and the population has every interest in being vaccinated, the risks of the pandemic of Covid-19 being much larger, insisted Ms. Messonnier.
“We know how to treat anaphylactic shock and we have put in place procedures at the vaccination sites” to react if necessary, she added.
The 21 cases identified by the CDC involved people aged 27 to 60, with a median age of 40. All but two were treated with epinephrine, which is commonly used to treat severe allergies.
No deaths were recorded 19 cases (90%) of allergic shock occurred in women and symptoms occurred between two and 150 minutes after injection of the vaccine (median time 13 minutes). These symptoms included rash, hives, a feeling of suffocation, swelling of the tongue, difficulty breathing, swollen lips, nausea, and a persistent dry cough.
Four patients (19%) were hospitalized, including three in intensive care, and the other 17 were treated in an emergency department.
There were no deaths and all but one were well at the time of the study. Ms Messonnier said investigations were underway to determine the cause of the allergic reactions.
One of the hypotheses concerns the presence in the vaccine of a substance, polyethylene glycol (PEG), which is used in many common products such as laxatives, shampoos or toothpaste but has never yet been used in vaccines.
Currently, the US authorities have authorized two vaccines, one developed by Pfizer and another produced by Moderna. Both use a new technology, called messenger RNA (mRNA), which had never been approved in a vaccine until now, and contain PEG.
There are still insufficient data to determine the rate of anaphylactic shock after injection of Moderna vaccine.