Allergic reactions to Moderna’s COVID-19 vaccine extremely rare, report says

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A vial of Moderna vaccine.

Moderna’s COVID-19 vaccine rarely causes serious 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, life-threatening allergic reaction called anaphylaxis. This equates to 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 causes severe allergies, but nine out of 10 cases have occurred in patients with previously known allergies (five previously had anaphylaxis). Most had

allergies to various drugs such as penicillin, but one had environmental and food allergies and another had no previously known allergies, according to the report.

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Nine in 10 patients developed symptoms – such as vomiting, nausea, wheezing, swelling of the tongue, and rash – within 13 minutes of 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 auto-injectors; four were treated in an emergency department and six were hospitalized, four requiring intubation. But all 10 patients have recovered, according to the report.

“Based on this early surveillance, anaphylaxis after receiving the Moderna COVID-19 vaccine appears to be a rare event,” the authors wrote in the report. But since there is not yet widespread data on COVID-19 vaccines, it is difficult to compare the risk of anaphylaxis with non-COVID-19 vaccines, they wrote. In a previous Morbidity and Mortality Weekly Report, published Jan. 15, 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 early data.

Still, the anaphylaxis associated with Pfizer and Moderna’s COVID-19 vaccines appears to be greater than the average number of anaphylaxis cases found for previous vaccines. In 2015, researchers calculated that the risk of developing a severe allergic reaction to a vaccine was about 1.31 in 1 million, according to a 2015 study published in the Journal of Allergy Clinical Immunology. “True allergic reactions to vaccines are very rare,” Dr. Purvi Parikh, allergist and immunologist at NYU Langone Health, told Live Science. “Statistically, you are more likely to be struck by lightning than to have a true anaphylactic reaction to a vaccine.” While cases are extremely rare – and shouldn’t deter people from getting the vaccine – experts are working to identify the causes of allergies.

People who had an allergic reaction to the first dose of the vaccine should not receive the second dose, the authors wrote. Vaccination centers should have all the necessary supplies and staff trained to treat anaphylaxis, they wrote. The CDC also recommends that people who receive COVID-19 vaccines also be monitored for about 15 minutes or 30 minutes if they have a history of allergies or anaphylaxis.

Originally posted on Live Science.