CAMBRIDGE, Mass. – A candidate vaccine against COVID-19 developed by the federal government and Moderna appears to be safe and to trigger an immune response, according to data released Tuesday from an early phase trial.
Whether that immune response is enough to protect someone from the coronavirus that causes COVID-19 remains unclear, according to several experts who reviewed the results.
Moderna's chief medical officer Tal Zaks said although the protective effect of the vaccine can't technically be known yet, all indications are that mRNA-1273 will be safe and effective.
"It's a good day for us," Zaks said.
Zaks said the levels of protective antibodies produced by the trial participants were similar to those found in patients who had recovered from COVID-19, suggesting that the candidate vaccine provides the same protection as an infection. Animal studies show mRNA-1273 can protect mice against infection, he said, and trials in primates and Syrian hamsters are underway.
The mRNA-1273 candidate did not generate a kind of immune cell that in other diseases made vaccinated people worse off, Zaks said.
The clinical trial was led by Anthony Fauci’s Vaccine Research Center at the National Institutes of Health. The experimental vaccine is being created quickly. On March 16, two months after Chinese scientists revealed the virus’s genetic sequence, a volunteer in Seattle was injected. That set a record for getting a candidate vaccine into human trials.
In the trial, 45 participants were divided in three groups – one that received a high dose, one a medium dose and one a low dose. Each person got two shots, a month apart.
All the reactions in the two lower dose groups were mild: More than half suffered minor fatigue, chills, headache or muscle pain, as is typical with vaccines. Three of those who received the highest dose had a severe reaction after the second shot, according to the study, including one participant whose fever spiked to 103.
The highest dose, 250 micrograms, was dropped from later stage trials, and only the 100-microgram dose will be proposed for use in people.
All the participants showed evidence of an immune reaction, which is the goal of immunization. COVID-19 is so new it's not clear how much of an immune reaction will be needed to protect against infection.
"It looks like their vaccine was able to induce a virus neutralizing antibody, which is positive," said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston. "But it's hard to know if the level of virus neutralizing antibody will be sufficient to induce protective immunity, or if it compares favorably with other (vaccine) candidates."
"These are good results," said Dr. Nadine Rouphael, who helped lead the trial at Emory University School of Medicine.
She agreed with Hotez that it's too early to know whether the vaccine will be protective. Neutralizing antibodies are key for fighting other infections, she said, but there are a lot of questions about COVID-19.
"How long will they stay, what's the right level of protection remains to be determined," she said Tuesday.
Learning whether the vaccine is protective will require a much larger study. A so-called Phase 3 trial with 30,000 participants is slated to begin July 27, Zak confirmed.
One challenge, Rouphael said, will be to find trial participants who naturally catch COVID-19. In trials for a Zika vaccine, the disease was brought under control, and it was very difficult to determine whether the vaccine was protective, because no one was catching it, she said.
Thousands of people volunteered for the small Phase 1 trial, Rouphael said, and she hopes people will continue to sign up for the research.
The novel coronavirus works by invading human cells, then forcing them to reproduce the virus in high volumes. One way to stop the disease could be to get the body to produce antibodies in advance that would prevent the virus from penetrating cells. Though the results show people injected produce antibodies, it’s not known whether that protects them from getting sick.
Moderna relies on a technology the company compared to digitizing vaccines. Rather than injecting someone with a weakened or dead virus, Moderna uses genetic material to trick the body into producing the critical antibodies before a person gets infected. Moderna was founded in 2011, but it has not successfully produced a vaccine.
The company, which went public in 2018, will join the NASDAQ-100, which includes the 100 largest nonfinancial companies listed on the Nasdaq Stock Market, based on market capitalization, the company announced Tuesday.
Paul Offit, a pediatrician and vaccine specialist at the University of Pennsylvania, said it isn't easy to understand what's going on in the immune system after vaccinations. Offit helped develop a vaccine against rotavirus, testing it in 35,000 infants and getting blood samples from all of them.
The vaccine worked in most babies, he said, but even with so many blood samples, researchers never figured out what was different about the immune systems of the babies who didn't get protection. "You'd think we'd be able to say here's why they weren't protected," he said, but "we couldn't find an immune correlate."
The goal is to have a vaccine ready in limited batches by January, or at the latest next summer. There is no way to tell whether either of those timetables are feasible. Historically, vaccines take many years to develop.
Contact Weintraub at kweintraub@usatoday.
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This article originally appeared on USA TODAY: Moderna's COVID vaccine candidate appears safe, effective data shows