(Bloomberg) -- Moderna Inc. said it had started a study of a booster shot that combines a formulation designed to fend off the omicron variant with the company’s current Covid-19 vaccine.

The company said in a statement Thursday that the first participant in the study had been given the experimental shot. Moderna plans to enroll about 375 people in the trial, which it said will be conducted at about 20 sites in the U.S. 

The shot will be studied in adults 18 and older who previously received the two-dose primary series of Moderna’s vaccine, as well as a Moderna booster shot at least three months ago.

Omicron cases have been in rapid decline across the country in recent weeks after the variant caused a spike in cases earlier in the year. Pfizer Inc. is also studying a vaccine that combines an omicron-targeting candidate with its approved vaccine.

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