According to the federal agency, anaphylaxis from mRNA COVID-19 vaccinations is a rare event.
US Centers for Disease Control and Prevention (CDC) research has determined that anaphylaxis rates from vaccination against the coronavirus 2019 (COVID-19) were lower than original estimates, according to a paper published in JAMA Insights.
Investigators from the CDC used the Vaccine Adverse Event Reporting System (VAERS) in order to report rates of anaphylaxis in those who have been vaccinated against COVID-19 with either the Pfizer-BioNTech or Moderna vaccine. VAERS is a passive national surveillance tool that captures adverse events following immunization, including reports of suspected anaphylaxis.
The US Food and Drug Administration authorized the mRNA-based Pfizer-BioNTech and Moderna vaccines in December 2020 via their Emergency Use Authorization. Originally, the estimation for anaphylaxis in those receiving the vaccine were 11.1 cases per million doses administered of the Pfizer-BioNTech vaccine and 2.5 cases per million doses administered of the Moderna vaccine, according to the study authors. But since those were merely generated estimates, they aimed to conduct more concrete reporting using VAERS.
During the period of December 14, 2020 to January 18, 2021, nearly 10 million doses of the Pfizer-BioNTech vaccine and about 7.5 million doses of the Moderna vaccine were reported to be administered in the U.S, according to the CDC data. The agency identified 66 case reports through VAERS that met definition criteria for anaphylaxis, levels 1, 2, or 3. Of those, 47 were from individuals who received the Pfizer-BioNTech vaccine (for a reporting rate of 4.7 cases per million doses administered), the study authors said. The remaining 19 cases followed Moderna vaccine administration, for a reporting rate of 2.5 cases per million doses administered, the study authors found.
The clinical characteristics of anaphylaxis cases for both vaccines were similar, the investigators observed. Additionally, there were no differences between anaphylaxis cases with symptom onset within 30 minutes and those with symptom onset after 30 minutes, they said. They also noted that a 15-minute observation period post-vaccination period is recommended for all persons and a 30-minute observation period post-vaccination is recommended for those with a history of certain allergic reactions.
Common signs and symptoms of anaphylaxis cases were generalized urticaria, diffuse erythematous rash, angioedema, respiratory and airway obstruction symptoms, and nausea, the study authors noted. A third of those who experienced anaphylaxis noted a prior episode of anaphylaxis from other exposures, which included vaccines for rabies and the flu, contrast media, unspecified infusions, sulfa drugs, penicillin, prochlorperazine, latex, walnuts, unspecified tree nuts, jellyfish stings, and unspecified exposures.
All of the patients who experienced anaphylaxis were treated in health care settings, and a majority received epinephrine as part of emergency treatment, the study authors wrote. About half were treated in the emergency department and half were hospitalized. There were 7 patients that required intubation, and of those, median time to symptom onset was 6 minutes. All of the intubated patients except 1 had symptom onset within 11 minutes, the study authors noted. Those patients received epinephrine, 6 of them received corticosteroids, and 5 received antihistamines. Hospitalization for those patients ranged from 1 to 3 days.
The study authors wrote that no deaths from anaphylaxis post-vaccination with either brand were reported.
“Continued safety monitoring of mRNA COVID-19 vaccines in the US has confirmed that anaphylaxis following vaccination is a rare event,” the study authors wrote, while adding that any facility providing COVID-19 vaccination should have supplies and trained medical personnel for the management of anaphylaxis. “When considered in the context of morbidity and mortality from COVID-19, the benefits of vaccination far outweigh the risk of anaphylaxis, which is treatable. Because of the acute, life-threatening nature of anaphylaxis, immediate epinephrine administration is indicated for all cases.”