Moderna’s COVID-19 vaccine rarely causes severe allergic reactions, according to new data released by the Centers for Disease Control and Prevention (CDC).
Between December 21 and January 10, more than 4.04 million people received Moderna’s COVID-19 vaccine, but only 10 developed a serious and potentially fatal allergic reaction, called anaphylaxis. This results in about 2.5 cases of anaphylaxis per 1 million people vaccinated, according to the CDC’s Weekly morbidity and mortality report.
It is not yet clear what is causing the severe allergies, but nine out of 10 of these cases occurred among patients with previously known allergies (five have already had anaphylaxis). Most had
allergies to various medications, such as penicillin, but one had an environmental and food allergy and another had no previously known allergies, according to the report.
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Nine out of 10 patients developed symptoms – such as vomiting, nausea, wheezing, swelling of the tongue and skin rash – within 13 minutes after receiving the vaccine and one developed symptoms within 45 minutes.
All 10 patients were treated with epinephrine – a hormone also known as adrenaline which is the key ingredient in EpiPens and similar autoinjectors; four were seen in an emergency room and six were hospitalized, and four required intubation. But all 10 patients recovered, according to the report.
“Based on this early monitoring, anaphylaxis after receiving the vaccine Moderna COVID-19 appears to be a rare event,” wrote the authors in the report. But, as there is still no widely publicized data on COVID-19 vaccines, it is difficult to compare the risk of anaphylaxis with non-COVID-19 vaccines, they wrote. In a previous Weekly morbidity and mortality report, published on January 15, the researchers estimated that the Pfizer-BioNTech vaccine causes anaphylaxis in about 11.1 cases per million doses (0.001% chance); this estimate was based on previous data.
Still, both anaphylaxis associated with Pfizer and Moderna’s COVID-19 vaccines appear to be above the average number of anaphylaxis cases found for previous vaccines. In 2015, researchers calculated that the chance of developing a severe allergic reaction to a vaccine is about 1.31 in 1 million, according to a 2015 study published in Journal of Allergy Clinical Immunology. “True allergic reactions to vaccines are very rare,” Dr. Purvi Parikh, an allergist and immunologist at NYU Langone Health, previously told Live Science. “Statistically, you’re more likely to be struck by lightning than a real anaphylactic reaction to a vaccine.” Although cases are extremely rare – and should not dissuade people from getting the vaccine – experts are working to identify what may be causing the allergies.
People who had an allergic reaction to the first dose of the vaccine should not receive the second dose, the authors wrote. Vaccine centers must have all the necessary supplies and trained personnel to treat anaphylaxis, they wrote. The CDC also recommends that people receiving COVID-19 vaccines should also be monitored for about 15 minutes, or 30 minutes if they have a history of allergies or anaphylaxis.
Originally published on Live Science.