During December 14–23, 2020, after administration of 1,893,360 first doses of Pfizer-BioNTech COVID-19 vaccine ( 1,177,527 doses in females, 648,327 doses in males, and 67,506 doses missing sex ), reports of 4,393 ( 0.2% ) adverse events after receipt of the vaccine had been submitted to VAERS.
Among these, 175 case reports were identified for further review as possible cases of severe allergic reaction, including anaphylaxis, based on descriptions of signs and symptoms; 21 of these reports met the Brighton Collaboration case definition criteria for anaphylaxis, corresponding to an initial estimated rate of 11.1 cases per million doses administered.
All reports were Brighton levels 1 or 2. The median age of persons with anaphylaxis was 40 years ( range = 27–60 years ), and 19 ( 90% ) cases occurred in females.
The median interval from vaccine receipt to symptom onset was 13 minutes ( range = 2–150 minutes ); 15 ( 71% ) patients had onset within 15 minutes, three ( 14% ) within 15 to 30 minutes, and three ( 14% ) after 30 minutes.
In 19 of 21 ( 90% ) reports, patients were treated with Epinephrine as part of therapy; one patient received subcutaneous Epinephrine and the remaining 18 were confirmed or presumed to have received intramuscular Epinephrine based on the report.
Four ( 19% ) patients were hospitalized ( including three 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 report to VAERS.
No deaths from anaphylaxis were reported after receipt of Pfizer-BioNTech COVID-19 vaccine.
Seventeen ( 81% ) of 21 patients with anaphylaxis had a documented history of allergies or allergic reactions, including to drugs or medical products, foods, and insect stings; seven ( 33% ) patients had experienced an episode of anaphylaxis in the past, including one after receipt of a rabies vaccine and another after receipt of an influenza A(H1N1) vaccine.
No geographic clustering of anaphylaxis cases was observed, and the cases occurred after receipt of doses from multiple vaccine lots.
At the time of this report, investigators have been unable to obtain sufficient information to confirm or rule out anaphylaxis in seven cases despite follow-up efforts; these cases remain under investigation.
During the same period, VAERS identified 83 cases of non-anaphylaxis allergic reaction after Pfizer-BioNTech COVID-19 vaccination with symptom onset within the 0–1-day risk window, 72 ( 87% ) of which were classified as nons-erious.
Commonly reported symptoms included pruritus, rash, itchy and scratchy sensations in the throat, and mild respiratory symptoms.
The median patient age was 43 years ( range = 18–65 years ), and 75 ( 90% ) reported reactions occurred in women.
The median interval from vaccine receipt to symptom onset was 12 minutes ( range less than or equal to 1 minute–20 hours ); in 61 ( 85% ) cases, onset occurred within 30 minutes, in 11 cases, onset occurred after 30 minutes, and for 11 cases, time of onset was missing.
For 56 ( 67% ) case reports, a past history of allergies or allergic reactions was documented. ( Xagena )
Source: Morbidity and Mortality Weekly Report (MMWR) | MMWR - CDC, 2021