LOS ANGELES (CBS/AP) — California’s state epidemiologist is urging a halt to more than 300,000 coronavirus vaccinations using a Moderna vaccine version because some people received medical treatment for possible severe allergic reactions.

Dr. Erica S. Pan on Sunday recommended providers stop using lot 41L20A of the Moderna vaccine pending completion of an investigation by state officials, Moderna, the U.S. Centers for Disease Control and the federal Food and Drug Administration.

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“Out of an extreme abundance of caution and also recognizing the extremely limited supply of vaccine, we are recommending that providers use other available vaccine inventory,” Pan said in a statement.

She said more than 330,000 doses from the lot arrived in California between Jan. 5 and Jan. 12 and were distributed to 287 providers.

Fewer than 10 people, who all received the vaccine at the same community site, needed medical attention over a 24-hour period, Pan said. No other similar clusters were found.

Pan did not specify the number of cases involved or where they occurred.

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However, six San Diego health care workers had allergic reactions to vaccines they received at a mass vaccination center on Jan. 14. The site was temporarily closed and is now using other vaccines, KTGV-TV reported.

Moderna in a statement said the Cambridge-based biotech company “is unaware of comparable adverse events from other vaccination centers which may have administered vaccines from the same lot.”

The CDC has said COVID-19 vaccines can cause side effects for a few days that include fever, chills, headache, swelling or tiredness, “which are normal signs that your body is building protection.”

However, severe reactions are extremely rare. Pan said in a vaccine similar to Moderna, the rate of anaphylaxis — in which an immune system reaction can block breathing and cause blood pressure to drop — was about 1 in 100,000.

Moderna’s vaccine received emergency use approval from the FDA in December. A panel of FDA advisers, in a 20-0 vote, ruled that the benefits of the vaccine outweighed the risks for those 18 years old and up. It has shipped more than 200,000 doses to Massachusetts so far.

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(© Copyright 2021 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)