The Moderna Covid-19 vaccine, like the one made by Pfizer and BioNTech, appears to induce rare anaphylactic reactions in a small number of people who receive the vaccine, new data from the Centers for Disease Control and Prevention suggest.
As of Jan. 19, there have been 15 confirmed cases of anaphylaxis after receipt of Moderna’s vaccine and 45 confirmed cases of anaphylaxis after receipt of the Pfizer vaccine, the CDC said in a statement to STAT. That works out to a rate of 2.1 cases per million doses of the Moderna vaccine and 6.2 cases per million doses of the Pfizer, according to the agency.
Anaphylaxis is a severe allergic reaction that can be life-threatening if not treated quickly.
“Early monitoring of both the Moderna and the Pfizer-BioNTech Covid-19 vaccines indicate that anaphylaxis following vaccination is a rare event, and although anaphylaxis is serious, it occurs shortly after vaccination (usually within minutes), is readily diagnosed, and effective treatments are available,” the agency said via email.
It noted that the rates at which anaphylaxis is reported following vaccination is likely to change as more vaccine doses are given. In fact, they already have. The first report on U.S. cases of anaphylaxis following administration of the Pfizer vaccine suggested it occurred at a rate of 11.1 cases per million doses given.
In a report published Friday on anaphylaxis cases among people who received the Moderna vaccine between Dec. 21 and Jan. 10, the CDC detailed 10 cases, all of which occurred in women. During the period of study, more than 4 million doses of the Moderna vaccine were administered.
In Friday’s report, six of the 10 people who developed anaphylaxis were hospitalized and four of them needed to be intubated to assist their breathing. None of the people died, the CDC reported. To date there have been no reports of fatal cases of anaphylaxis associated with Covid vaccines in the United States.
All 10 of the people who developed anaphylaxis were given epinephrine, the drug in EpiPens that is used to combat severe allergic reactions. The CDC has said that those administering Covid vaccines need to be equipped to treat anaphylaxis, including having epinephrine injections on hand.
Anaphylaxis occurred quickly in the people affected, with the median time to the start of symptoms being 7.5 minutes. People who receive Covid-19 vaccines are supposed to be monitored for 15 minutes after the injection, with that period extended to 30 minutes for people with a history of severe allergies or anaphylaxis.
Nine of the 10 people had a history of allergies and five of them had previously experienced an anaphylactic reaction.
This story has been updated with additional data and comment from the CDC.