Severe allergic reactions to the Moderna Covid-19 vaccine are a “rare event,” according to a report published Friday by the US Centers for Disease Control and Prevention.
As of Jan. 10, among the more than 4 million people vaccinated with the first dose of the Moderna shot, only 10 people had severe allergic reactions, known as anaphylaxis, according to the CDC’s Morbidity and Mortality Weekly Report. That’s a rate of 2.5 cases per million doses administered.
A previous report on the Pfizer/BioNTech Covid-19 vaccine estimated an initial rate of 11.1 cases per million of the first doses administered.
The CDC has been monitoring for adverse reactions and collected 1,266 adverse event reports related to the Moderna vaccine. Among those reports, 108 involving allergic reactions were flagged for further review.
The CDC determined 47 of the reports were nonanaphylaxis allergic reactions, 47 were considered nonallergic reactions, four case reports didn’t have enough information.
All 10 of the anaphylaxis cases were women. Of the 10, nine had a documented history of allergies and more than half of those people had a previous history of anaphylaxis. Only one had a prior allergic reaction to a vaccine. The others had allergic reactions to a mix of things – drugs, contrast agents used in some medical imaging and one person had a food allergy.
Symptoms began at a median of seven and a half minutes after the shot. Among those for whom CDC had follow up information, all had recovered and had been discharged from the hospital and sent home.
The current CDC guidance is that people who have an immediate allergic reaction to a first dose of either the Pfizer or Moderna vaccine shouldn’t get the second. The guidance also mandates health care workers monitor people for at least 15 minutes after vaccination. Anaphylaxis is potentially life-threatening and requires immediate treatment; the CDC says vaccination sites need trained staff and supplies on hand to manage it.
“Anaphylaxis after receipt of Moderna COVID-19 vaccine appears to be a rare event; however, comparisons of anaphylaxis risk with that associated with non–COVID-19 vaccines are constrained at this time by the limited data available this early in the COVID-19 vaccination program,” the report said. “CDC and FDA will continue enhanced monitoring for anaphylaxis among recipients of COVID-19 vaccines.”