Moderna has announced the dosing of the first subject in Phase II clinical trial of its Omicron-specific booster candidate, mRNA-1273.529. 

The trial will analyse the safety, reactogenicity and immunogenicity of a single booster shot of the vaccine in adult subjects aged 18 years and above.

To be carried out at up to 24 sites in the US, the company anticipates enrolling nearly 300 subjects into two cohorts of the trial to receive one mRNA-1273.529 booster dose. 

Cohort 1 of the trial will enrol people who have already received the initial two-dose vaccine regimen of mRNA-1273 with the second dose administered a minimum of six months ago. 

Individuals who received the preliminary two-dose series and a 50µg mRNA-1273 booster administered minimum three months back will be part of cohort 2.

Furthermore, Moderna plans to incorporate mRNA-1273.529 in its multivalent booster programme.

The company also reported neutralising antibody findings against the Omicron variant of the SARS-CoV-2 virus six months after a booster shot. 

At day 29 following boosting, Omicron neutralisation dropped 6.3-fold from peak titers while levels were still detectable in all subjects, data showed. 

Neutralising titers against this variant decreased faster than titers against the virus’ ancestral strain (D614G), which dropped 2.3-fold over the same time.

The latest results comprise sera from 20 subjects who received the booster doses of mRNA-1273 at the 50µg and 100µg dose levels; multivalent candidate mRNA-1273.211 at the same dose levels; and 100µg of multivalent candidate mRNA-1273.213. 

Moderna CEO Stéphane Bancel said: “We are reassured by the antibody persistence against Omicron at six months after the currently authorised 50µg booster of mRNA-1273. 

“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 II study.” 

During this month, the US Food and Drug Administration amended the emergency use authorization for Moderna’s Covid-19 vaccine to decrease the time between the conclusion of the preliminary vaccine series and a booster shot to a minimum of five months.