Moderna has started dosing the first participants in all age cohorts of the Phase II clinical trial of its Covid-19 vaccine candidate, mRNA-1273.

mRNA-1273 is an mRNA vaccine encoding for a prefusion stabilised form of the Spike (S) protein, which was chosen by the company in alliance with Vaccine Research Center (VRC) at the National Institute of Allergy and Infectious Diseases (NIAID).

The Phase II trial will assess the safety, reactogenicity and immunogenicity of two vaccinations of mRNA-1273 administered 28 days apart. It is set to involve 600 healthy participants across the age groups of 18-55 and 55 and above.

Participants will receive either a 50μg dose, a 100μg dose, or placebo at both vaccinations and will be followed for 12 months after the second vaccination.

In the Phase I trial of the vaccine candidate, 25μg and 100μg dose levels demonstrated neutralising antibody titers at or above convalescent sera and were observed to be generally well-tolerated.

Moderna has decided to drop the assessment of the 250μg dose in the Phase II trial.

The US Food and Drug Administration (FDA) completed a review of the company’s investigational new drug (IND) application for the vaccine candidate on 6 May and granted fast track designation on 12 May.

Moderna reported initial results from the Phase I trial of mRNA-1273 led by the NIAID on 18 May, where the 25µg and 100µg dose levels showed dose dependent increases in immunogenicity, as well as between prime and boost.

The company intends to work with the NIAID to launch a Phase III trial in July. The dose for the Phase III study is expected to be between 25µg and 100µg.

Moderna noted that the planning for these studies was supported by funding from the Biomedical Advanced Research and Development Authority (BARDA).