By Vishwadha Chander

(Reuters) – Severe allergic reactions to Moderna Inc’s coronavirus vaccine appear to be quite rare, the U.S. Centers for Disease Control and Prevention (CDC) said on Friday, after over 4 million people had received their first dose.

Based on the data, the CDC said anaphylaxis, a life-threatening allergic reaction, occurred at a rate of 2.5 cases per 1 million shots administered.

The agency cautioned that the risk of anaphylaxis was difficult to compare to non–COVID-19 vaccines because it is still so early in the vaccination program.

As of Jan. 10, there were 10 cases of anaphylaxis reported among 4.04 million people who received their first doses of Moderna’s two-shot vaccine, according to the agency’s Morbidity and Mortality Weekly Report.

The CDC said the characteristics of severe allergic reactions to Moderna’s vaccine were similar to those reported with the COVID-19 vaccine from Pfizer Inc and partner BioNTech SE.

Earlier this month, the CDC reported severe allergic reactions to the Pfizer/BioNTech shot occurred at a rate of 11.1 per 1 million vaccinations.

For both vaccines, symptoms presented within minutes after vaccination and were more common among women. Many of those who suffered anaphylaxis after receiving either vaccine had a history of allergies or allergic reactions, and several had an anaphylaxis episode in the past, the CDC said.

The agency said locations administering COVID-19 vaccines should screen recipients, have necessary supplies and staff members to manage anaphylaxis, and immediately treat suspected cases with an epinephrine injection, the same drug in EpiPens.

(Reporting by Vishwadha Chander in Bengaluru and Julie Steenhuysen in Chicago; Editing by Caroline Humer and Bill Berkrot)