Positive interim results were announced from a phase 1 study evaluating the vaccine candidate mRNA-1273 (Moderna) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). 

The study, which is being led by the National Institute of Allergy and Infectious Diseases (NIAID), is assessing the safety and immunogenicity of mRNA-1273 in 45 healthy adults aged 18 to 55 years. Participants received 1 of 3 doses of mRNA-1273 (25, 100, or 250mcg) administered intramuscularly on a 2-dose vaccination schedule, given 28 days apart.

Early results from the study showed dose dependent increases in immunogenicity across all 3 dose levels and between prime and boost doses within the 25mcg and 100mcg dose cohorts. Moreover, seroconversion was observed across all 3 dose levels after a single dose. 

At Day 43, binding antibody levels were found to be at or above levels seen in convalescent sera following the second dose at the 25mcg (n=15) and 100mcg (n=10) dose levels, respectively. The vaccine also elicited neutralizing antibodies (as measured by plaque reduction neutralization assays against live SARS-CoV-2) in 8 participants; levels at Day 43 were at or above those seen in convalescent sera.

With regard to safety, 1 participant in the 100mcg cohort experienced a grade 3 adverse event, erythema around the injection site. In addition, 3 individuals dosed at the 250mcg level experienced grade 3 systemic symptoms following a second dose. In general, the vaccine candidate has been shown to be well tolerated, with adverse events being transient and self-resolving; no grade 4 events have been reported.

“These interim phase 1 data, while early, demonstrate that vaccination with mRNA-1273 elicits an immune response of the magnitude caused by natural infection starting with a dose as low as 25µg,” said Tal Zaks, MD, PhD, Chief Medical Officer at Moderna. “When combined with the success in preventing viral replication in the lungs of a pre-clinical challenge model at a dose that elicited similar levels of neutralizing antibodies, these data substantiate our belief that mRNA-1273 has the potential to prevent COVID-19 disease and advance our ability to select a dose for pivotal trials.”

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Based on the findings from the phase 1 trial, Moderna will include a 50mcg and 100mcg dose in its phase 2 study of the vaccine; the NIAID phase 1 study will also be amended to include a 50mcg dose cohort. A phase 3 trial of mRNA-1273 is expected to begin sometime in July.

For more information visit modernatx.com.