CDC Finds One in 400,000 Had Anaphylaxis After Moderna Shot

(Bloomberg) -- About one in 400,000 recipients of the Moderna Inc. Covid-19 vaccine had a severe allergic reaction to the first shot, according to a study from the U.S. Centers for Disease Control and Prevention released on Friday.

The research, which tracked 10 cases of anaphylaxis among about 4 million doses administered through Jan. 10, concludes that such reactions to the vaccine still appear to be rare. Anaphylaxis to vaccines is uncommon but well-established -- with flu shots, for instance, it occurs about 1.3 times per million doses administered, according to CDC officials.

The CDC continues to emphasize the safety of Covid-19 vaccines. It recommends that only those who are allergic to a component of Covid-19 vaccines or who had a severe allergic reaction to an initial dose avoid receiving the shots. The risk of contracting Covid-19 outweighs that posed by the vaccines, officials and clinicians say.

“Early monitoring of both the Moderna and the Pfizer-BioNTech COVID-19 vaccines indicate that anaphylaxis following vaccination is a rare event, and although anaphylaxis is serious, it occurs shortly after vaccination (usually within minutes), is readily diagnosed, and effective treatments are available,” CDC spokeswoman Kristen Nordlund said in an email. “Patients experiencing anaphylaxis after vaccination do well and recover.”

The CDC’s Nordlund said that as of Jan. 19, there have been 15 cases of anaphylaxis with the Moderna shot and 45 with the Pfizer shot, rates of 2.1 cases per million doses and 6.2 cases per million doses, respectively. The rates could change as more people are immunized and the CDC obtains more data, Nordlund said.

A CDC study on the Pfizer Inc.-BioNTech SE vaccine released earlier this month found about 11.1 cases of anaphylaxis per one million doses administered, similar but somewhat higher than Moderna’s 2.5 cases per one million doses.

All 10 patients who experienced anaphylaxis after receiving the Moderna shot were treated with epinephrine. Six were hospitalized, including five patients who received intensive care. Four then went on to need intubation.

The CDC said there have been no deaths and the eight patients for which it had follow-up information had been sent home from the hospital or had recovered.