Following implementation of vaccination, reports of anaphylaxis after the first dose of the Pfizer-BioNTech COVID-19 vaccine emerged.
Anaphylaxis is a life-threatening allergic reaction that occurs rarely
after vaccination, with onset typically within minutes to hours.
Notifications and reports of suspected severe allergic reactions and anaphylaxis following vaccination were captured in the Vaccine Adverse Event Reporting System (VAERS), the national passive surveillance (spontaneous reporting) system for adverse events after immunization.

Physicians at the US Centers for Disease Control and Prevention (CDC) evaluated these reports and applied Brighton Collaboration case definition criteria to classify case reports as anaphylaxis or not anaphylaxis.

Nonallergic adverse events, mostly vasovagal or anxiety-related, were excluded from the analysis.

Anaphylaxis and nonanaphylaxis allergic reaction cases with symptom onset occurring later than the day after vaccination were also excluded because of the difficulty in clearly attributing allergic reactions with delayed onset after vaccination.

Because the Moderna COVID-19 vaccine was only available beginning December 21, 2020, this article focuses on the PfizerBioNTech COVID-19 vaccine.

During December 14 to 23, 2020, after administration of a reported 1 893 360 first doses of Pfizer-BioNTech COVID-19 vaccine (1 177 527 in women, 648 327 in men, and 67 506 with sex of recipient not reported), CDC identified 21 case reports submitted to VAERS that met Brighton Collaboration case definition criteria for anaphylaxis, corresponding to an estimated rate of 11.1 cases per million doses administered.

Four patients (19%) were hospitalized (including 3 in intensive care), and 17 (81%) were treated in an emergency department; 20 (95%) are known to have been discharged home or had recovered at the time of the report to VAERS.

No deaths from anaphylaxis were reported.

Median interval from vaccine receipt to symptom onset was 13 minutes (range, 2-150 minutes); 15 patients (71%) had onset within 15 minutes; 18 (86%) had onset within 30 minutes.

The most common symptoms and signs were urticaria, angioedema, rash, and a sense of throat closure. Seventeen (81%) of 21 patients with anaphylaxis had a documented history of allergies or allergic reactions, including to drugs ormedical products, foods,and insect stings;7 (33%)
had experienced an episode of anaphylaxis in the past, including one
after receipt of rabies vaccine and another after receipt of influenza
A(H1N1)vaccine.

During the same period,VAERS identified83 cases of nonanaphylaxis allergic reactions after Pfizer-BioNTech COVID-19 vaccination.

Commonly reported symptoms in nonanaphylaxis allergic reactions included pruritus, rash, itchy and scratchy sensations in the throat, and mild respiratory symptoms.