Although stimulating the production of neutralizing antibodies does not prove that a vaccine will be effective, it is considered an important early step in testing. Meanwhile, the reported side effects were not severe enough in the majority of patients to preclude further testing, according to the report from researchers at the National Institute of Allergies and Infectious Diseases.
More than half of those who received the middle of three doses suffered from mild to moderate fatigue, chills, headache and muscle pain. In addition, 40% of people in the mid-dose group had a fever after the second vaccination. Three of the 14 patients who received the highest dose of vaccine had serious side effects, but this dose is not used in larger trials.
“Man, that’s a lot of adverse events,” said Tony Moody, a doctor and researcher at the Duke Human Vaccine Institute. He said it would be “unusual” for a vaccine to have this rate of side effects. On the positive side, he said the levels of antibodies produced were “really encouraging”.
If researchers measure the right thing, the vaccine should work, he said, noting that this can only be proven in large trials.
The first results come from the first group of 45 patients who received the vaccine and evaluated three doses of the vaccine which were administered in two injections. The average dose from this initial trial will be used in a large final trial of the Moderna vaccine, called mRNA-1273, which is scheduled to start on July 27.
The final phase trial will compare the vaccine to placebo injections in 30,000 healthy people at high risk of contracting the coronavirus.
An important limitation of the data is that it only includes data from the first 45 patients in the study, all aged 18 to 55 years. Results from a second part of the phase 1 trial that included older people – a demographic key to any COVID-19 vaccine, given the high mortality rate in older patients – are not yet available.
William Haseltine, a former Harvard Medical School researcher who chairs Access Health International, said the levels of neutralizing antibodies produced were “respectable” and perhaps protective. But he said that “the jury is out” on the safety of the vaccine.
Unlike traditional vaccines, which inject a weakened or inactivated virus or a piece of virus to trigger an immune response, the Moderna product uses genetic material called messenger RNA to cause cells to produce the advanced protein of the coronavirus. The goal is to produce antibodies against the virus that protect against the disease when someone is subsequently exposed to the coronavirus.
The vaccine “clearly worked in that antibodies against the peak protein were generated, including antibodies that had a virus-neutralizing ability,” said Paula Cannon, professor of microbiology at the Keck School of Medicine at the ‘USC. A key question will be how long will the antibodies last before they start to decline, she said.
Initial results from the Phase 1 trial are largely consistent with Moderna’s first-line results published in a press release in May, but provide more detail on the levels of antibodies produced and the side effects seen.
Moderna was criticized at the time by some scientists for publishing a press release describing positive results that temporarily boosted the company’s stock price, but included some numbers that would allow scientists to interpret the data.
The government-sponsored trial was conducted by Lisa A. Jackson of the Kaiser Permanente Washington Health Research Institute in Seattle, NIAID said in its statement. Emory University of Atlanta also enrolled trial participants.