Moderna said its new two-strain Covid-19 booster increases people’s immunity against the dominant Omicron variant, bolstering the company’s hopes to roll it out as a fourth dose in the late summer.   

The US biotech company is the first to report preliminary results from a clinical trial of a vaccine targeted to Omicron. It said on Wednesday that the trial showed the “bivalent booster” — which contains the genetic code of the Omicron variant and the original strain of the virus — was safe and well-tolerated.

The vaccine elicited eight times more antibodies to tackle the Omicron variant than a fourth dose of the original formulation when measured one month after it was administered, the company said. It tackled the original strain just as well, but it could not prove it was superior.