Moderna has enrolled first participant in a clinical trial of its Omicron-specific booster vaccine. This marks another step towards fight against highly transmissible Covid-19 variant.

Moderna and rival Pfizer-BioNTech are bolstering the efforts to test for vaccines specific to Omicron if they are needed amid continuing spread of the variant around the globe.

On Tuesday, Pfizer announced of beginning a 1,400-person study of a messenger-RNA vaccine aimed at Omicron.

The Moderna study will be conducted on 600 adults to test its booster, called mRNA-1273.529. These adults have received Moderna’s existing vaccine, including 300 who have received only two doses and 300 who have also received a third dose of vaccine.

The trial is aimed to examine the safety and the immune response that is generated by the Omicron-specific vaccine.

Vaccine makers are studying what vaccine types may be most effective while the coronavirus continues to mutate. Omicron-specific booster vaccine dose is one possibility; another is a multivalent vaccine that can induce protection against multiple strains. Other strategies include broad-acting vaccines that work against greater number of mutations.

Moderna is testing the new booster because of “the long-term threat demonstrated by Omicron’s immune escape", chief executive Stephane Bancel said. “We are also evaluating whether to include this Omicron-specific candidate in our multivalent booster programme.”

The company has said of being reassured by a report in the New England Journal of Medicine that showed patients with three doses of Moderna’s existing vaccine still had antibodies against Omicron six months after receiving the third shot.

But after the booster, levels of antibodies fighting Omicron declined faster than against the original strain of virus.