More Data Indicates Anaphylaxis Is Very Rare With mRNA COVID-19 Vaccines

Pharmacies and other COVID-19 vaccine sites have to be prepared to monitor for anaphylaxis in recipients and be prepared to give them emergency treatment if they show signs of the life-threatening allergic reactions. Find out how unlikely that is to occur, however, based on new data showing that anaphylaxis is very rare with the mRNA vaccines.

ATLANTA – Pharmacists will be relieved to know that continued safety monitoring of mRNA COVID-19 vaccines in the United States confirms that anaphylaxis following vaccination is a rare event and, so far, has led to no deaths.

An Insight article in JAMA points out that rates of anaphylaxis are 4.7 cases/million Pfizer-BioNTech vaccine doses administered and 2.5 cases/million Moderna vaccine doses administered, based on information through Jan. 18, 2021.

“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,” point out the authors from the national Centers for Disease Control and Prevention. “Because of the acute, life-threatening nature of anaphylaxis, immediate epinephrine administration is indicated for all cases. CDC guidance on use of mRNA COVID-19 vaccines and management of anaphylaxis is available. All facilities administering COVID-19 vaccines should have the necessary supplies and trained medical personnel available to manage anaphylaxis.”

Cases of anaphylaxis began to be reported shortly after vaccines began with the Pfizer-BioNTech and Moderna vaccines. The life-threatening allergic reaction, which can occur after vaccination, typically has onset within minutes to hours.

The CDC notes that the initial estimated reporting rates for anaphylaxis in the US were 11.1 cases per million doses administered of the Pfizer-BioNTech vaccine (Dec. 14-23, 2020) and 2.5 cases per million doses administered of the Moderna vaccine (Dec. 21, 2020-Jan. 10, 2021).

“Since these early estimates were generated, millions more doses of both vaccines have been administered and safety monitoring has detected additional cases of anaphylaxis,” according to the report. “This analysis updates the reporting rates of anaphylaxis in individuals following receipt of either the Pfizer-BioNTech or Moderna vaccine.”

Cases were tracked by the Vaccine Adverse Event Reporting System (VAERS) and analyzed by CDC researchers who applied the Brighton Collaboration case definition for anaphylaxis to classify cases.

From Dec. 14, 2020 through Jan. 18, 2021, 9.9 million doses of the Pfizer-BioNTech vaccine and 7.6 million doses of the Moderna vaccine were reported administered in the United States. CDC investigators identified 66 case reports received by VAERS that met Brighton Collaboration case definition criteria for anaphylaxis (levels 1, 2 or 3). That includes 47 following Pfizer-BioNTech vaccine, for a reporting rate of 4.7 cases/million doses administered, and 19 following Moderna vaccine, for a reporting rate of 2.5 cases/million doses administered.

Researchers explain that cases occurred after receipt of doses from multiple vaccine lots. CDC physician reviewers also conclude that the clinical characteristics of anaphylaxis cases following both vaccines were similar and that there were no apparent clinical differences between anaphylaxis cases with symptom onset within 30 minutes and those with symptom onset after 30 minutes. A 15-minute postvaccination observation period is recommended for all vaccine recipients, and a 30-minute period is recommended for those with a history of certain allergic reactions.

According to the report, common signs and symptoms in anaphylaxis cases were generalized urticaria, diffuse erythematous rash, angioedema, respiratory and airway obstruction symptoms, and nausea. About a third of the 66 case reports noted a prior episode of anaphylaxis from other exposures, including vaccines (rabies, influenza A[H1N1], seasonal influenza, unspecified), contrast media (gadolinium-based, iodine-based, unspecified intravenous), unspecified infusions, sulfa drugs, penicillin, prochlorperazine, latex, walnuts, unspecified tree nuts, jellyfish stings, and unspecified exposures.

In nearly all anaphylaxis cases, 92%, patients received epinephrine as part of emergency treatment. About half were treated in an emergency department and slightly less than half were hospitalized. Overall, 18 of the recipients ended up in intensive care, with seven requiring endotracheal intubation, according to the CDC.

Medical record review and follow-up suggests that, of the 7 patients who required endotracheal intubation, median time to symptom onset was 6 minutes (range, <1-45 minutes), with all but one patient having onset within 11 minutes.

All 7 of the patients who were intubated received epinephrine, 6 received corticosteroids, and 5 received antihistamines. In 4 of those patients, facial, tongue, or laryngeal angioedema was present, and hospitalization ranged from 1 to 3 days.

At the same time, 61 recipients, 92%, with follow-up information available are known to have been discharged from care or had recovered at the time of report to VAERS. No deaths from anaphylaxis after vaccination with either product were reported.

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