Drugmaker Moderna announced Wednesday that it has begun a clinical trial of a COVID-19 booster shot specifically tailored to the highly contagious omicron variant.

Moderna said that the first participant in its Phase 2 study of an omicron-specific booster candidate has been dosed with the shot. 

The company also announced the publication of a study in The New England Journal of Medicine which showed that antibodies generated by Moderna's existing booster shot dropped by roughly sixfold six months after getting boosted, but the protection remains durable against the highly contagious variant.

"We are reassured by the antibody persistence against Omicron at six months after the currently authorized 50 µg booster of mRNA-1273. Nonetheless, given the long-term threat demonstrated by Omicron's immune escape, we are advancing our Omicron-specific variant vaccine booster candidate and we are pleased to begin this part of our Phase 2 study," Stéphane Bancel, CEO of Moderna, said in a statement. "We are also evaluating whether to include this Omicron-specific candidate in our multivalent booster program. We will continue to share data with public health authorities to help them make evidence-based decisions on the best booster strategies against SARS-CoV-2."

According to data from the CDC, the omicron variant now accounts for roughly 99% of new COVID-19 cases in the United States.

The company is aiming to enroll 600 people in its study, split into two groups: In one group, participants will get a dose of the omicron-specific booster six months after receiving the two-dose regimen of Moderna's vaccine. In the other, participants will get a dose of the omicron-specific booster after receiving the two-dose regimen of Moderna's vaccine and the company's existing booster shot.

The news comes one day after Pfizer and BioNTech announced that they have begun a study comparing their original vaccine to one tailored to the omicron variant. Their study is enrolling up to 1,420 participants, ages 18 to 55, and they are expecting to have the shots ready by March.