An investigational COVID-19 vaccine, mRNA-1273, was generally well tolerated and prompted neutralizing antibody activity in healthy adults, according to interim results published online Tuesday in The New England Journal of Medicine.
The ongoing phase 1 trial is supported by the U.S. National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.
The experimental vaccine, co-developed by researchers at NIAID and U.S. biotech company Moderna, is designed to induce neutralizing antibodies directed at a portion of the coronavirus "spike" protein, which the virus uses to bind to and enter human cells.
The trial, led by Lisa Jackson of Kaiser Permanente Washington Health Research Institute in Seattle, was launched on March 16 when the first participant received the candidate vaccine.
The interim report detailed the initial findings from the first 45 participants aged 18-55 enrolled at the study sites in Seattle and at Emory University in Atlanta.
Three groups of 15 participants received two intramuscular injections, 28 days apart, of either 25, 100 or 250 micrograms of the investigational vaccine.
In April, the trial was expanded to enroll adults aged above 55, and it now has 120 participants.
No serious adverse events were reported, according to the study. More than half of the participants reported fatigue, headache, chills, myalgia or pain at the injection site. Systemic adverse events were more common following the second vaccination and in those who received the highest vaccine dose.
The interim analysis includes results of tests measuring levels of vaccine-induced neutralizing activity through day 43 after the second injection.
Two doses of the vaccine prompted high levels of neutralizing antibody activity that were above the average values seen in convalescent sera obtained from persons with confirmed COVID-19 disease, according to the study.
A Phase 2 clinical trial of mRNA-1273, sponsored by Moderna, began enrollment in late May.
Moderna plans to begin its final phase of testing for the vaccine on July 27.
