A study published on Wednesday in the CDC's weekly report on death and disease looking at cases between December 14 and December 23, identified 21 cases of anaphylaxis after the administration of 1,893,360 doses of the Pfizer-BioNTech vaccine.
Almost 140 000 people in Hebei province have taken COVID-19 vaccine doses, said Cui Gang, a National Health Commission official, part of China's vaccination scheme targeting specific groups of high infection risk.
"A good value proposition for someone to get vaccinated is their risk from Covid and poor outcomes from Covid is still more than the risk of a severe outcome from the vaccine", she said.
Of the 21 cases reviewed in MMWR, 18 had documented allergies or allergic reactions to drugs, medical products, food, or insect stings, and seven had experienced anaphylaxis in the past, including one following a rabies vaccine and one following an influenza A (H1N1) vaccine. Almost all of these patients were treated with epinephrine following their reaction to the COVID-19 vaccine, and all 21 recovered.
"This averages out to a rate of 11.1 anaphylaxis cases per one million doses administered", senior CDC official Nancy Messonnier told reporters.
Speaking further, the minister said that the simulation of the entire inoculation process has been conducted, the staff concerned has been familiarised with all the aspects of the actual administration of the vaccine, the operational aspects have been thoroughly reviewed and feasibility of the CoWIN Portal has also been monitored.
Officials attributed the difference largely to the fact that the Pfizer-BioNTech vaccine was authorized earlier than the Moderna shot, and said the precautions apply to both. Symptoms can include skin rash, nausea, vomiting, difficulty breathing and shock.
Even though the rate of anaphylaxis tied to COVID-19 vaccines is about 10 times higher than what's seen with flu vaccines, "it's still exceedingly rare", Messonnier said. Moreover, comparing these to the numbers for flu "misses the point" when there are over 2,000 deaths from COVID-19 every day in the U.S.
All COVID-19 vaccine recipients should be observed for at least 15 minutes after getting the shot.
Exactly what's causing these reactions is unclear, and "tremendous efforts" are underway to better understand the cause, Messonnier said.
Up to 20 percent of people who are vaccinated experience mild side effects including redness around the injection site, low-grade fevers, chills, and headaches.
The agency recommends that people not receive the Pfizer or Moderna vaccine if they have a known allergy to an ingredient in these vaccines, including polyethylene glycol; and people should not receive a second dose if they have a serious reaction to the first.