Pharmaceutical company Moderna is testing its Omicron-specific COVID-19 booster vaccine, dosing the first participant in a stage two trial.

The second stage of the trial will evaluate the effectiveness and safety of the shot as a single booster for people over the age of 18.

It will be broken into two cohorts, people who have had two mRNA doses with the second dose being at least six months ago, and people with two doses and a booster who received their last jab at least three months ago.

The company expects to use 300 people in each cohort and the trials will be conducted in up to two dozen sites in the US.

Early data revealed a 37-fold increase in antibody levels in its 50 microgram dose and 83-fold increase in its 100 microgram dose compared to pre-booster levels, the company says.

Other figures showed Omicron neutralisation was detected in only 55 per cent of participants seven months after the second dose.

But while Omicron neutralisation six months after a 50 microgram booster dose declined, it remained detectable in all participants.

The company says it can bring new vaccine candidates to a clinical stage within 60 to 90 days of a new variant of concern emerging.

– AAP