As vaccines to protect against COVID-19 continue to roll out across the United States, the Centers for Disease Control and Prevention has documented a small number of reports of severe allergic reactions from some recipients. A report from the CDC, published Wednesday (January 6) in the agency’s Morbidity and Mortality Weekly Report, finds that most of these rare events occurred in those with a history of allergic reactions.

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As of December 23, nearly 1.9 million doses of Pfizer-BioNTech’s vaccine had been administered across the country, according to the report, with 21 verified cases of anaphylaxis that followed, a rate of 11.1 per million doses. Four of the individuals did not have a medical history of severe allergic reactions. Among those who did, seven had experienced anaphylaxis in the past. Epinephrine, the drug used in Epi-Pens, was given to 19 of the patients, and four were admitted to the hospital. Follow-up information was available for 20 of the patients, all of whom have since been discharged from the hospital or have recovered from their reaction.

“The good news is how rare these allergic reactions are and how readily recognizable and treatable they are,” Paul Offit, who serves on an external vaccine advisory committee to the US Food and Drug Administration, tells The Washington Post. “Yes, there’s an extremely small risk, but not a single person has died from the allergic reaction, while plenty of people have died from the virus.”

Everyone who receives the vaccine is advised to stay put for 15 minutes to monitor any harmful side effects, while it is recommended that those with a history of allergic reactions wait half an hour. The report found that the median time to onset of symptoms was 13 minutes. Only one person went over an hour before the reaction occurred, having a delay of 150 minutes. The CDC advises that anyone who experiences anaphylaxis after the first dose refrain from getting the second dose.

“People have a higher chance of getting hurt driving to the clinic for a shot than from the shot itself,” Offit, who codeveloped the RotaTeq rotavirus vaccine, continues.

The median age of the patients was 40, with a range of 27–60. Nineteen of the patients were women, and women also make up 61% of vaccine recipients, according to the report. There was no common thread among the preexisting allergies listed, which included tropical fruit, nuts, penicillin, and sulfa drugs, among many others. 

The report acknowledges multiple limitations of the study, chief among them that the data came from reports posted to the Vaccine Adverse Event Reporting System (VAERS), which is often an incomplete source of information. There also could be a heightened response in suspecting anaphylaxis, as the vaccine is so new and has been covered extensively in the media. There also could be a lag between when reports show up in VAERS and an accurate count of how many doses have been administered. Finally, the Moderna vaccine was only available for two days before data collection, so very few of those vaccines had been given at the time of the report.

Representatives from the CDC say that the risk of an allergic reaction from the vaccine is worth taking, given how deadly COVID-19 continues to be, as the US surpasses 360,000 total deaths.

“Of course, we all would hope that any vaccine would have zero adverse events. But even at 11 cases per million doses administered, it’s a very safe vaccine,” Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases at the CDC, said at a Wednesday news conference, according to STAT. “We’re in the setting of 2,000 Covid deaths per day. . . . I would say it’s still a good value proposition for someone to get vaccinated.”