Biotechnology firm Moderna has concluded participant enrolment for both cohorts in the Phase II clinical trial of its Covid-19 vaccine candidate, mRNA-1273.

Last month, the company closed enrolment in the first cohort of healthy young adults aged 18-55, and the second cohort of older adults aged 55 and above.

The trial’s Data and Safety Monitoring Committee reviewed safety results from the older adults cohort and recommended that the remaining Phase II enrolment could be continued. The recruitment for the older adult cohort is now complete.

Moderna is conducting the placebo-controlled, dose-confirmation Phase II trial to assess the safety, reactogenicity and immunogenicity of two mRNA-1273 vaccinations administered 28 days apart.

Participants are given placebo, a 50μg or a 100μg dose at both vaccinations.

The company added that enrolment for the cohorts of older adults aged 56-70 and elderly adults aged 71 and above in the US National Institutes of Health (NIH)-led Phase I trial has been completed.

Moderna chief medical officer Tal Zaks said: “We are committed to helping address this ongoing public health emergency and continue to focus on our Phase III study, which remains on track to start in July, less than seven months from the sequencing of the virus.”

The company has already finalised the Phase III trial protocol based on the US Food and Drug Administration (FDA) feedback.

During the randomised, placebo-controlled Phase III trial, around 30,000 participants will be enrolled at the 100µg dose level in the US.

The study is set to be performed in alliance with the US National Institute of Allergy and Infectious Diseases (NIAID), subject to regulatory approval.

Moderna has completed manufacturing vaccine doses required for the Phase III trial.

With the Phase III dose at 100μg, the company expects to deliver approximately 500 million doses annually, and potentially up to one billion doses per year starting next year.