The vaccine seems safe and able to prompt the body to produce antibodies against the coronavirus at levels comparable to a natural infection.
The biotech company Moderna announced Monday (May 18) that their experimental coronavirus vaccine showed promising results in an early trial, known as a phase I study.
After receiving a single dose of the vaccine, called mRNA-1273, all 45 of the participants in the trial developed detectable levels of antibodies within 15 days, according to a statement from Moderna, which is based in Cambridge, Massachusetts.
Those 45 participants were divided into three groups that received different doses of the vaccine: 25 micrograms (µg), 100 µg and 250 µg. The participants were then given a second dose about a month later. The higher the dose (or with a second dose in the first two groups), the more antibodies were produced, the researchers found.
Two weeks after the first group of 15 participants received their second dose of 25 µg of the vaccine, the level of antibodies in their blood was comparable to the level found in blood samples taken from people who had recovered from COVID-19. Those who received two 100 µg doses had levels that exceeded those found in blood samples from COVID-19 patients. Samples for the other participants aren’t yet available, according to the statement.
But this data just refers to the levels of “binding” antibody, or antibodies that can bind to the coronavirus but don’t necessarily attack it. But the researchers also gathered data on “neutralizing” antibodies, or those that can block infection, from eight of the participants (data for the remaining participants is also not yet available).
All eight of those participants (four receiving 25 µg and four receiving 100 µg) had neutralizing antibodies at or above levels seen in those who recovered from COVID-19. In a separate study conducted in mice, similar neutralizing antibodies were found to prevent viral replication in mice infected with SARS-CoV-2.
The vaccine “was generally safe and well tolerated,” and no participant had serious side effects, the company wrote in the statement. “All adverse events have been transient and self-resolving.” Some had side effects such as redness at the injection site and fever, headache or flu-like symptoms, according to NPR.
Moderna’s vaccine uses a new technology that hasn’t been used in any approved vaccines to date: It uses a molecule called messenger RNA (mRNA) to instruct cells to build viral proteins, specifically the coronavirus’ spike protein, which the virus uses to infect human cells. The idea is that the immune system will then create antibodies that will recognize that spike protein and stop the coronavirus from infecting cells.
The Food and Drug Administration (FDA) recently gave Moderna the go-ahead to begin phase 2 of testing its vaccine, which will involve testing on an additional 600 people, according to a previous Live Science report. The company’s goal is to start their phase 3 trial in which they recruit hundreds to thousands of additional people to further understand whether the vaccine is working and if participants have any adverse reactions to it, in July and will use this data to figure out the correct dose to give to participants.
“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 25 µg,” Dr. Tal Zaks, the chief medical officer at Moderna, said in the statement. When combined with data from the mouse study, these results “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.”