Moderna gave its omicron-specific COVID-19 vaccine to the first participant in a clinical trial, the company announced Wednesday. The report comes a few days after Pfizer / BioNTech launched a trial of its shot targeting the fast-spreading variant.

The announcement coincides with the release of data showing that the two-dose series of Moderna’s original vaccine struggled to block the omicron variant of the virus, which has mutations that help it dodge those antibodies. A booster shot restored much of its ability to neutralize the virus — and while that protection weakened over time, it still stuck around for at least six months.

Still, Moderna CEO Stéphane Bancel said in a statement that the omicron variant is enough of a threat that the company plans to move forward with the variant booster.

The company is testing its omicron booster in one group of people who received a two-dose series of the original vaccine only and a second group who had a two-dose series and booster of the original vaccine. There will be around 300 participants in each group.

Bancel said in early January that Moderna could have data on the omicron booster ready by March.