Moderna has begun a phase 2 study evaluating an Omicron-targeted COVID-19 booster dose of its messenger RNA (mRNA) vaccine in adults 18 years and older.

An estimated 300 participants will be divided into two cohorts — those who have already received a two-dose primary series of the mRNA-1273 vaccine and those who received a two-dose primary series as well as a regular Moderna booster.

Both groups will be given the Omicron-targeted booster jab, which will then be assessed for immunogenicity, safety and reactogenicity.

Moderna CEO Stéphane Bancel said the company is “reassured by the antibody persistence against Omicron at six months after the currently authorized 50 µg booster of mRNA-1273,” but given the “long-term threat demonstrated by Omicron’s immune escape,” the company is working on a targeted shot.