Ten cases of anaphylaxis and over 100 cases of severe allergic reactions were reported following administration of the first dose of the Moderna COVID-19 vaccine, but nearly all were among those with a history of allergic reactions, researchers found.
Of the 10 cases of anaphylaxis, nine were among those with a history of allergies or allergic reactions, and five had a previous history of anaphylaxis unrelated to vaccines, reported the CDC COVID-19 Response Team along with FDA officials in an early edition of the Morbidity and Mortality Weekly Report.
Rate of anaphylaxis was 2.5 cases per million Moderna doses, or 10 cases following about 4 million doses, which is higher than the widely reported 1.3 cases per million following an influenza vaccine. A prior report focusing mostly on the Pfizer/BioNTech vaccine found 21 cases of anaphylaxis following about 1.9 doses, or a rate of 11.1 cases per million through December 23.
Six of 10 individuals reported prior allergies or allergic reactions to drugs, including penicillin, acetaminophen, azithromycin, morphine, and codeine; two reported allergies to gadolinium, iodine, and intravenous contrast dye. Two said they had “unspecified” allergies, and one had no history of allergic reaction. All 10 were women.
It is unclear how many total cases of anaphylaxis have been reported, as this report focused specifically on Moderna. However, the manufacturer has been in the news for allergic reactions stemming from a particular lot of Moderna vaccines in California. State health officials recommended pausing doses from that lot, though CDC and FDA disagreed, according to media reports.
Current interim CDC guidance states individuals with a history of allergic reaction to vaccines or any injectable therapies should consider deferral of vaccination or consult with an allergist/immunologist, and should be observed for 30 minutes. Any individual with a history of anaphylaxis unrelated to vaccines or injectable therapies should be observed for 30 minutes, while those with a history of unrelated allergies should be observed for 15 minutes.
Median interval from vaccine administration to symptom onset was 7.5 minutes, and while nine patients had symptom onset within 15 minutes, one had symptom onset after 30 minutes. Interestingly, the report focusing on the Pfizer/BioNTech vaccine found a median interval to symptom onset of about 13 minutes.
Researchers examined data from Dec. 21, 2020 to Jan. 10, 2021, prior to California’s reporting of allergic reactions. About 61% of those receiving doses were women.
Median age of anaphylaxis cases was 47, and all patients received epinephrine. Six patients were hospitalized, including five in intensive care and four requiring intubation. Four were treated in the emergency department, and eight patients with follow-up information available were discharged or recovered at home.
They noted that of the 108 case reports for the Moderna vaccine, four did not have enough information to assess likelihood of anaphylaxis.
Researchers continued to stress these events are infrequent, writing, “anaphylaxis after receipt of the COVID-19 vaccine appears to be a rare event.” They added that vaccine administration sites should have providers available to recognize signs of anaphylaxis, administer epinephrine, and transport patients to facilities where they can receive care.
The authors disclosed no conflicts of interest.