From Dec. 21, 2020, to Jan. 10, 2021, the Vaccine Adverse Event Reporting System (VAERS) detected 10 cases of severe anaphylaxis after immunization with the Moderna COVID-19 vaccine, the Centers for Disease Control and Prevention (CDC) reported.

Ten cases coming out 4,041,396 first doses of the vaccine translates to 2.5 cases per million shots administered. “In nine cases, onset occurred within 15 minutes of vaccination,” the CDC stated. “No anaphylaxis-related deaths were reported.”1

In all 10 cases, patients received epinephrine as part of initial emergency treatment. Six patients were hospitalized, including five in intensive care. Four of the ICU patients required endotracheal intubation.

“Nine of the 10 anaphylaxis case reports included a patient history of allergies or allergic reactions, including to drugs (six), contrast media (two), and foods (one),” the CDC reported. “Five patients had experienced an episode of anaphylaxis in the past, none of which was associated with receipt of a vaccine. No geographic clustering of anaphylaxis cases was observed, and the cases occurred after receipt of doses from multiple vaccine lots.”

The CDC previously reported that from Dec. 14 to Dec. 23, 2020, vaccine surveillance systems picked up 21 cases of anaphylaxis after administration of a reported 1.8 million first doses of the Pfizer-BioNTech COVID-19 vaccine. No deaths were reported, but four patients were hospitalized, including three in intensive care. Another 17 were treated in an emergency department. The Pfizer cases come to a rate of 11.1 cases per million doses. Overall, the rate of anaphylactic shock for established vaccines is approximately one case per million immunized.2

“Locations administering COVID-19 vaccines should adhere to CDC guidance, including screening recipients for contraindications and precautions, having necessary supplies and staff members available to manage anaphylaxis, implementing recommended postvaccination observation periods, and immediately treating suspected anaphylaxis with intramuscular epinephrine injection,” the CDC recommended.

The CDC will continue enhanced monitoring for anaphylaxis among recipients of COVID-19 vaccines and will review case reports to VAERS.

“For both vaccines, symptom onset after vaccination occurred quickly, usually within minutes,” the CDC concluded. “A strong female predominance of anaphylaxis case reports exists for both vaccines. Finally, many persons experiencing anaphylaxis after receiving either vaccine had a history of allergies or allergic reactions, with several having experienced an anaphylaxis episode in the past.”

All patients should be advised to immediately seek medical care if they develop signs or symptoms of an allergic reaction after their vaccination observation period ends and they have left the location.


  1. CDC COVID-19 Response Team; Food and Drug Administration. Allergic reactions including anaphylaxis after receipt of the first dose of Moderna COVID-19 vaccine — United States, December 21, 2020-January 10, 2021. MMWR Morb Mortal Wkly Rep 2021;70:125-129.
  2. CDC COVID-19 Response Team; Food and Drug Administration. Allergic reactions including anaphylaxis after receipt of the first dose of Pfizer-BioNTech COVID-19 vaccine — United States, December 14-23, 2020. MMWR Morb Mortal Wkly Rep 2021;70:46-51.