Among 4,041,396 [Moderna COVID vaccine] doses given over 21 days, a total of 10 cases of anaphylaxis were confirmed by CDC investigators. Another four cases of possible anaphylaxis are still being investigated.
No deaths have been tied to the vaccine.
“Based on this early monitoring, anaphylaxis after receipt of Moderna COVID-19 vaccine appears to be a rare event,” the researchers wrote [January 22] in the CDC’s Morbidity and Mortality Weekly Report.
The authors calculated that there were 2.5 cases of anaphylaxis for every 1 million doses of the Moderna vaccine that were administered. A similar study of the COVID-19 vaccine developed by Pfizer and BioNTech reported that there were 11.1 cases of anaphylaxis for every 1 million doses of that vaccine during its first 10 days of administration.
The CDC advises that anyone who has an “immediate allergic reaction” to a first dose of either the Moderna vaccine or the Pfizer-BioNTech vaccine should not receive a second dose. In addition, patients should be asked about past allergic reactions before getting either vaccine, the agency says.
Vaccination sites are advised to monitor people for up to 30 minutes after they receive their injections, and to have epinephrine on hand to treat anyone who has a bad reaction to either vaccine.