Allergic Reactions After First Dose of Pfizer-BioNTech COVID-19 Vaccine
- Following administration of ~1.9 million first doses of the Pfizer-BioNTech COVID-19 vaccine, 21 anaphylactic reactions were identified by the CDC (estimated rate, 11.1 cases per million doses).
- A majority of events (86%) occurred within 30 minutes of vaccine administration.
- No fatal allergic reactions were reported.
What is the rate of anaphylactic reactions following one’s first dose of the Pfizer-BioNTech coronavirus disease 2019 (COVID-19) vaccine?
Data were obtained from the Vaccine Adverse Event Reporting System (VAERS), the national passive surveillance (spontaneous reporting) program. Physicians at the Centers for Disease Control and Prevention (CDC) evaluated all suspected allergic reaction events following receipt of the first dose of the Pfizer-BioNTech COVID-19 vaccine and classified them as anaphylaxis and non-anaphylaxis. Non-allergic adverse events, such as vasovagal reactions, were excluded. Events with symptom onset >1 day following vaccination were also excluded.
From December 14-23, 2020, following administration of 1,893,360 doses of vaccine, the CDC identified 21 case reports meeting criteria for anaphylaxis (estimated rate, 11.1 cases per million doses). Four patients (19%) were hospitalized, including three in intensive care, and 17 (81%) were treated in an emergency department. At the time of reporting, 20 patients (95%) were known to have recovered or been discharged, and no deaths were reported. Median interval from vaccine receipt to symptom onset was 13 minutes (range, 2-150 minutes), with 71% of events occurring within 15 minutes and 86% within 30 minutes. The most common signs and symptoms were urticaria/rash, angioedema, and a sense of throat closure. A history of allergies or allergic reactions to food, drugs, vaccines, and/or insect stings was present in 17 patients (81%). Non-anaphylactic adverse reactions occurred in 83 patients; these included pruritus, rash, itchy/scratchy sensation in the throat, and mild respiratory symptoms.
Anaphylactic reactions to the first dose of the Pfizer-BioNTech COVID-19 vaccine are rare, usually occur within 30 minutes of administration, and are readily treatable.
By way of comparison, cdc.gov reports that the rate of anaphylaxis following influenza vaccines is 1.31 per million doses, so the rate with the COVID vaccine is ~8.5-fold greater. However, these initial data regarding the Pfizer vaccine in real-world settings remain encouraging, and the risk of anaphylaxis with vaccination will be far outweighed by the risk of severe COVID-19 without vaccination for most patients. Based on the fact that most anaphylactic reactions occurred soon after vaccination, current CDC recommendations for post-vaccination monitoring (15 minutes minimum, and 30 minutes for people with a history of anaphylaxis) seem appropriate. While it would appear that a history of allergies is a risk factor for vaccine-related anaphylaxis, further study will be needed to determine the magnitude of increase in risk. A limitation of VAERS is that the onus of adverse event reporting is on patients and clinicians, so some adverse events may be underreported, though providers are required by law to report all life-threatening events.
Keywords: Adverse Drug Reaction Reporting Systems, Anaphylaxis, Angioedema, Coronavirus, COVID-19, Critical Care, Emergency Service, Hospital, Exanthema, Influenza Vaccines, Patient Discharge, Primary Prevention, Risk Factors, Vaccination
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