Moderna has begun enrolment of participants for the highest dose arm of a Phase I clinical trial assessing its mRNA-1273 vaccine candidate against Covid-19.

Led by the US National Institutes of Health (NIH), the trial is designed to include arms for 25μg, 100μg and 250μg dose levels of mRNA-1273.

Initiated last month, the trial will recruit a total of 45 healthy adults aged 18 to 55.

Moderna also announced that the company is hosting its first Vaccine Day and reported positive interim data from Phase I study of its Zika vaccine candidate, mRNA-1893.

Dosing has been completed in all 10µg, 30µg, 100µg and 250µg cohorts in the Zika trial. An interim analysis reviewed safety and immunogenicity data from the 10µg and 30µg cohorts.

The 10µg and 30µg doses of mRNA-1893 were found to be generally well-tolerated, without any vaccine-related serious adverse events (SAEs) or adverse events of special interest (AESI), after two doses of vaccination given 28 days apart.

These dose levels also triggered a neutralising antibody response in participants who are flavivirus infection-naïve (seronegative) and those with pre-existing flavivirus antibodies (seropositive), said the company.

A single vaccination of the 30µg dose was observed to be enough to convert baseline flavivirus seronegative participants. The company further noted a clear benefit with a two-dose series given 28 days apart.

Moderna chief medical officer Tal Zaks said: “I am encouraged by these interim Phase I data showing the ability of mRNA-1893 to elicit a strong neutralising antibody response.

“Our Zika programme, along with our continued work on a vaccine candidate against the novel coronavirus, underscore our commitment to improving global public health through developing mRNA vaccines to prevent the spread of infectious diseases.”

According to the company, clinical data showed that its vaccine technology was generally well-tolerated and could induce durable immune responses against viral antigens.

Moderna CEO Stéphane Bancel added: “The totality of data from our vaccines platform gives us reason to be optimistic about the prospects for our vaccines to come, including our vaccine against the novel coronavirus.”

Currently, Moderna has nine prophylactic vaccine candidates in development.