2.5 Anaphylaxis Cases Reported Per Million COVID-19 Moderna Vaccine Shots
Nine of the 10 cases occurred in individuals with documented history of allergies, allergic reactions
MONDAY, Jan. 25, 2021 (HealthDay News) -- The rate of anaphylaxis is 2.5 cases per million Moderna COVID-19 vaccine doses administered as of Jan. 10, 2021, according to research published in the Jan. 22 issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.
Researchers from the CDC COVID-19 Response Team describe allergic reactions, including anaphylaxis, after receipt of the first dose of the Moderna COVID-19 vaccine in the United States as of Jan. 10, 2021.
The researchers found reports of 1,266 (0.03 percent) adverse events after receipt of the Moderna COVID-19 vaccine were submitted to the Vaccine Adverse Event Reporting System as of Jan. 10, 2021, when 4,041,396 first doses of Moderna COVID-19 vaccine had been administered in the United States. One hundred eight of these case reports were identified for further review as possible severe allergic reaction. Ten of these case reports were determined to be anaphylaxis (rate, 2.5 anaphylaxis cases per million Moderna COVID-19 vaccine doses administered). Nine occurred in individuals with a documented history of allergies or allergic reactions; five of these individuals had anaphylaxis history. All eight of the cases with follow-up information available had recovered and been discharged home. Of the remaining case reports, 47 were assessed to be nonanaphylaxis allergic reactions and 47 were nonallergic adverse events. For four case reports, insufficient data were available to assess the likelihood of anaphylaxis.
"Based on this early monitoring, anaphylaxis after receipt of Moderna COVID-19 vaccine appears to be a rare event," the authors write.
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Primary Care
Anaphylaxis and COVID-19 Vaccination
With the rollout of the vaccination program, anaphylaxis from the COVID-19 vaccine has come under scrutiny. Initially, it seemed to occur only in people who had anaphylaxis before; but, then, the unthinkable happened—a nurse who had no allergic history nor history of anaphylaxis had anaphylaxis after the shot.
How common is anaphylaxis and when does it happen after the shot? The vaccine studies cannot give guidance because they had excluded patients with anaphylaxis. So, we need to turn to the real-world data collected by the CDC.
On January 15, 2021, the CDC published in Morbidity and Mortality Weekly Report (MMWR) the anaphylaxis cases from 1,893,360 doses of Pfizer–BioNTech COVID-19 vaccine. The data were taken from the Vaccine Adverse Event Reporting System (VAERS). There were 175 cases of severe allergic reaction based on the signs and symptoms entered into the system. Only 21 met the Brighton Collaboration case definition for anaphylaxis. This works out to 11.1 cases per million doses administered. For comparison, the influenza vaccine anaphylaxis rate is 1.3 cases per million; so, there is a significant increase with this mRNA vaccine.
The median time of symptom onset was 13 minutes (range, 2–150 minutes), with 71% (15) of the patients having the reaction within 15 minutes and 14% (3) having it after 30 minutes. So, a 30-minute wait would capture 86% of the cases in this analysis.
Emergency department treatment was all that was needed in 81% (17) of the cases, and 19% (4) needed hospitalization, 3 of whom were admitted to the ICU. There were no deaths.
Only 33% (7) of the cases had a history of anaphylaxis and 81% (21) of the patients had a documented history of allergies. There were 83 cases of non-anaphylaxis allergic reactions, which included symptoms of pruritus, rash, itchy and scratchy sensations in the throat, and mild respiratory symptoms.
For the Moderna vaccine, the MMWR published on January 29, 2021 stated that, with 4,041,396 shots, there were 10 cases that were determined to be anaphylaxis, which comes to 2.5 anaphylaxis cases per million shots. A history of anaphylaxis was seen in 50% (5) of the cases, and 90% (9) had a history of allergies.
The MMWR stated that “Six patients were hospitalized (including five in intensive care, four of whom required endotracheal intubation).” The remaining 4 were treated in the emergency department, and there were no deaths.
One strange observation is that the anaphylaxis cases were predominantly in females. For the Pfizer vaccine, 90% (19) of the cases were in females. For Moderna, all 10 cases of anaphylaxis were in females. This could just be a play of chance due to the small number of cases and there were twice as many females vaccinated compared with males; so, we would expect more cases in females. Nonetheless, we should continue to monitor to see if there is a hormonal or gender bias to the anaphylaxis cases.
Now as to why people have these allergic reactions, the focus has turned to polyethylene glycol (PEG). That is the same PEG that we use in laxatives and in cosmetics and in PEGylated medications. The mRNA is protected by a sphere of lipids. PEG is put onto the lipid ball to make it stable. Some people are allergic to PEG just like some are allergic to penicillin or peanuts, and they will know they are allergic when they get the vaccine. That is why there will be individuals with no history of allergies or anaphylaxis who will still have anaphylaxis from this vaccination.
This concept needs to be explained to patients. We only find out you have a peanut allergy once you eat peanuts. So, even after we exclude patients with past anaphylaxis and allergies to components of the vaccine, we will still have patients who are just allergic to PEG, and when we vaccinate millions of people, we will find them.
On a practical note, my personal summary of the CDC recommendations reads as follows:
All normal-risk individuals need to wait 15 minutes after the shot; however, high-risk people need to wait 30 minutes (as 86% with the Pfizer vaccine cases had reactions within 30 minutes). We should all be prepared to deal with anaphylaxis because, even though it is rare, we don’t want to lose a patient this way.
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