New York, Jan 28 (IANS): US drug maker Moderna has started trial of a Covid booster vaccine that specifically targets the Omicron variant, the company has announced.

This is after Pfizer began an Omicron-specific trial early this week. The company expect to have the shots ready by March.

Moderna, in a statement, said that the first participant in the phase two trial has already received a dose of the omicron-specific booster shot.

The company expects to enroll about 600 adult participants ages 18 and over split equally between two groups.

Participants in the first group will have previously received two-doses of Moderna's original vaccine, and participants in the second group will have previously received the two-dose vaccine and the currently authorised booster shot.

Participants in both groups will receive a single dose of the omicron specific booster.

The US drug maker also announced the publication of neutralising antibody data against the Omicron variant six months following a booster dose in The New England Journal of Medicine.

While Omicron neutralisation had declined 6.3-fold from peak titers at day 29 post-boost, levels remained detectable in all participants. Neutralising titers against Omicron declined more rapidly than titers against the ancestral strain of the virus (D614G) which declined 2.3-fold over the same time period, the company said.

The company is reassured that the neutralising antibodies against Omicron remain detectable after half a year, said CEO Stephane Bancel, in the statement.

"Nonetheless, given the long-term threat demonstrated by Omicron's immune escape, we are advancing our Omicron-specific variant vaccine booster candidate and we are pleased to begin this part of our Phase 2 study," said Bancel.

Bancel said in early January that Moderna could have data on the Omicron booster ready by March.