An interim analysis of a Phase I clinical trial assessing Moderna’s Covid-19 vaccine candidate, mRNA-1273, has found the product to be generally safe and well-tolerated.

The findings have been published in the New England Journal of Medicine.

The interim analysis involved data from a two-dose vaccination schedule of mRNA-1273 administered 28 days apart across 25, 100 and 250µg dose levels in 45 healthy adult participants aged 18-55 years. It provides results through day 57.

In May this year, Moderna reported that its Covid-19 vaccine candidate showed dose dependent increases in immunogenicity across the three dose levels in the Phase I study. The latest data are said to reaffirm these previous findings.

According to the new interim analysis, mRNA-1273 was generally safe and well-tolerated without any serious adverse events reported through day 57. Adverse events were said to be generally transient and mild to moderate in severity.

The most notable adverse events were reported at the 250µg dose level, with three of the 14 participants reporting one or more severe events.

Also, the vaccine candidate was able to generate binding antibodies to the full-length SARS-CoV-2 Spike protein following the first vaccination in all volunteers. It was observed that all participants seroconverted by day 15.

All the three dose levels showed dose dependent increases in binding titers, as well as between prime and boost vaccinations within the dose cohorts.

Upon evaluation for neutralisation activity, no live SARS-CoV-2 neutralisation or PsVNA responses before vaccination were detected in any participant.

Moderna chief medical officer Tal Zaks said: “These Phase I data demonstrate that vaccination with mRNA-1273 elicits a robust immune response across all dose levels and clearly support the choice of 100µg in a prime and boost regimen as the optimal dose for the Phase III study.

“We look forward to beginning our Phase III study of mRNA-1273 this month to demonstrate our vaccine’s ability to significantly reduce the risk of Covid-19 disease.”

The Phase I trial was led by the National Institute of Allergy and Infectious Diseases (NIAID).