Officials at the Centers for Disease Control and Prevention (CDC) said that the reactions, known as anaphylaxis, are happening at a rate of 11.1 per million vaccinations. With flu vaccines, anaphylaxis occurs at a rate of 1.3 per 1 million injections.
"The anaphylaxis rate for COVID-19 vaccines may seem high compared to flu vaccines, but I want to reassure you, this is still a rare outcome," Dr. Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, told reporters on a call.
Twenty-one people experienced severe allergic reactions out of those who received the first 1.89 million doses of the Pfizer-BioNTech COVID-19 vaccine, which were administered between Dec. 14 and Dec. 23, 2020.
Seventeen of the people who experienced severe allergic reactions had a history of allergies or allergic reactions. The average time between getting a shot and symptom onset was 13 minutes; most patients experienced symptoms within 15 minutes. The median age of the patients was 40 years old.
Information available for 20 of the 21 showed they'd recovered or had been discharged, the CDC said in a report.
Eighty-six other cases were determined to be allergic reactions that weren't severe. Sixty-one were considered nonallergic adverse events. The remaining seven are still under investigation.
There's no federal database of confirmed allergic reactions. The report doesn't include data for the past two weeks. Approximately 3.4 million doses have been administered since the time period studied in the report.
Hundreds of people who received one of the new vaccines, including one from Moderna, were sent to hospital emergency rooms, according to data that was reported to federal authorities through Jan. 5. Over 1,000 experienced an adverse event.
Messonnier noted that the CDC has been adapting its recommendations as it reviews reports of adverse events. The agency recently said anyone who experiences an allergic reaction to a COVID-19 vaccine shouldn't get a second dose. The agency also directed administrating officials to observe anyone with a history of allergic reactions to injectable vaccines or a history of anaphylaxis due to any cause for 30 minutes post-vaccination. The typical observation period is 15 minutes.
Anyone with a history of allergic reactions to any components of the vaccines, officials said last month, should not get them.
The benefits of the vaccines outweigh the risks, officials have stressed.
"Our vaccine safety systems haven't picked up any worrisome signals. This means that right now the known and potential benefits of the current COVID-19 vaccines outweigh the known and potential risks getting the COVID-19," Messonnier said.
"That doesn't mean, however, that we couldn't see potential serious health events in the future."
The CDC and the Food and Drug Administration (FDA), which issued emergency authorization for the Moderna and Pfizer vaccines, are reviewing all serious adverse event reports with clinicians to figure out if they're connected with vaccination. The reactions could be coincidental, as are many adverse events, according to Messoinner.
Both vaccines are new types that use Messenger RNA, a molecule that teaches a body's cells to make a spike protein that then triggers an immune response. That differs from vaccines of the past, which deliver a weakened or inactivated germ into bodies to activate a response.
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