An experimental vaccine to treat COVID-19 manufactured by Moderna was able to induce an immune response in all of the volunteers in an early-stage trial, according to data published online in a medical journal.
The initial results, published in The New England Journal of Medicine on Tuesday, showed the vaccine was generally safe and well tolerated in 45 volunteers, with no serious adverse events.
The study, run by the National Institutes of Health, showed that some antibodies were produced after one dose of the vaccine, but a second dose four weeks later was needed before the volunteers showed a dramatic immune response.
The results were “encouraging, and represent an important step forward in the clinical development of mRNA-1273, our vaccine candidate against COVID-19,” Moderna Chief Executive Officer Stéphane Bancel said in a statement.
There are still many unknowns about immunity, including whether antibodies actually protect against infection and just how much protection would be gained.
Moderna is expected to begin a much larger-scale study of the vaccine on July 27, a stage three trial that will enroll 30,000 participants across 87 locations. The company’s stage two trial began enrollment in late May.
The primary goal of stage three will be the prevention of symptomatic COVID-19. Moderna said key secondary endpoints will include prevention of severe COVID-19 (as defined by the need for hospitalization) and prevention of infection by the coronavirus.
According to Moderna’s posting on a government website, one group will be injected with 100 micrograms of the vaccine on the first day and then again on day 29. A second group will be injected with two doses of a placebo for comparison.
The initial stage of the trial focused on making sure the vaccine was safe in a small population as well as narrowing down the dosage. The next phases will eventually prove efficacy in a large population.
According to the results released Tuesday, the most commonly reported systemic adverse events following second vaccination at the 100 microgram dose were fatigue, chills, headache and muscle soreness, all of which were transient and mild or moderate in severity.
The study enrolled 45 healthy volunteers ages 18 to 55 at sites in Seattle and at Emory University in Georgia. The trial participants were split roughly 50-50 between men and women and tested three dose levels of Moderna’s vaccine at 25, 100 and 250 micrograms.
In an editorial accompanying the article, Penny Heaton, CEO of the Bill & Melinda Gates Medical Research Institute, said the speed with which Moderna was able to get results was “remarkable” but urged caution.
“Many phase 3 studies fail because of incorrect identification of the dose that best balances safety and efficacy,” Heaton wrote. “The dosing regimen for this mRNA vaccine is still under study.”