Moderna Inc said on Wednesday its COVID-19 vaccine booster targeting the BA.1 subvariant of omicron generated a strong immune response against that variant, with antibody levels staying high for at least three months.

Omicron-tailored shots by Pfizer Inc and Moderna are already authorized by regulators in several countries. The United States has given the go-ahead for booster vaccines that target the currently circulating BA.4 and BA.5 subvariants of omicron.

"Clinical trial data now indicates that the superior immune response produced by our bivalent booster has durability for at least three months," Moderna Chief Executive Officer Stephane Bancel said in a statement.

Moderna said it expects data from human trials of its BA.4/BA.5 targeted vaccine later this year.