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Moderna’s Covid-19 vaccine led patients to produce antibodies that can neutralize the novel coronavirus that causes the disease, though it caused minor side effects in many patients, according to the first published data from an early-stage trial of the experimental shot.

The results were published Tuesday in the New England Journal of Medicine. Moderna had previously released some results in a press release, but many experts said they were not sufficient to draw many conclusions. Even now, many are withholding judgment.


“It certainly is a good beginning,” said Betty Diamond, director at the Feinstein Institutes for Medical Research, who was not involved in the trial. “There are certainly lots of things we don’t know yet right now.”

The study, which was run by the National Institutes of Health, showed that volunteers who received the vaccine made more neutralizing antibodies than have been seen in most patients who have recovered from Covid-19. But a second injection, four weeks after the first, was required before the vaccine produced a dramatic immune response.

“The hallmark of a vaccine is one that can actually mimic natural infection and induce the kind of response that you would get with natural infection. And it looks like, at least in this limited, small number of individuals, that is exactly what’s happening,” said Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, the NIH branch that conducted the trial. “The data really look quite good,” he added. “There were no serious adverse events.”


The data roughly mirror the results from a similar vaccine being produced by Pfizer and BioNTech, which were released July 1.

Moderna posted a listing on, a government registry, that says it will start a Phase 3 study in 30,000 patients on July 27. Pfizer and BioNTech said they plan to start their own large study by the end of the month. There are 23 vaccines in human clinical trials against the virus, SARS-CoV-2, according to the World Health Organization, with more set to begin testing soon.

In a statement, Moderna CEO Stéphane Bancel called the data “encouraging,” saying they “represent an important step forward” in the development of the vaccine, called mRNA-1273. “We are committed to advancing the clinical development of mRNA-1273 as quickly and safely as possible while investing to scale up manufacturing so that we can help address this global health emergency,” Bancel said.

One big question is whether producing antibodies predicts protection against infection — and how much protection. Another is whether the antibodies will last.

“We don’t know how much [antibody] we need to be protected, so we can’t say” all the participants “achieved a protective level,” Kathryn Edwards, scientific director of the Vanderbilt Vaccine Research Program, said in an email to STAT. “What we can say is that they made antibody that neutralized the virus, which is good.”

The study enrolled 45 healthy volunteers ages 18 to 55, testing three dose levels of Moderna’s vaccine. The trial participants were split roughly 50-50 between men and women. The population was 89% white, 13% Hispanic, 4% Black, 2% Asian, and 2% Native American. More results are expected to be reported later for older patients, who often mount a weaker immune response.

Volunteers got a shot in the arm on day 1 followed by a booster shot four weeks later. At the 100-microgram dose, the one Moderna is advancing into larger trials, all 15 patients experienced side effects, including fatigue, chills, headache, muscle pain, and pain at the site of injection. All side effects were considered mild or moderate.

A higher, 250-microgram dose led to more serious reactions and has been set aside. Although no side effects were severe — meaning that they required hospitalization — they were unpleasant, as was made clear when one volunteer in the study, Ian Haydon, went public with his experience taking the 250-microgram dose.

Researchers and drug companies have been racing with unprecedented speed to create a vaccine against the coronavirus. Moderna began its Phase 1 trial just 66 days after scientists first decoded the genome of SARS-CoV-2.

“It’s amazing just how fast we’ve gotten to this point,” Penny Heaton, CEO of the Bill and Melinda Gates Research Institute in Cambridge, Mass., said in an interview. “It’s like six years of work has been compressed into six months.”

That very speed is a reason for caution, said Paul Offit, chief of the division of infectious diseases at the Children’s Hospital of Philadelphia. He advised companies to be humble. He noted that he had worked on rotavirus vaccines for 25 years, and still the first attempt at one turned out to have a side effect that sent researchers back to the drawing board.

Already, he said, SARS-CoV-2 has done things experts never would have expected, he said. It spreads in hot weather. It causes deadly blood clots. It rarely makes children sick, but sometimes causes a surprising immune disorder. “I can promise you that over the next two years, we’ll learn a lot of things that we wish we’d known now that we are going to learn as we move forward,” Offit said.

Researchers measured the efficacy of Moderna’s vaccine in multiple ways, all of which showed higher average antibody levels than were seen in patients who had recovered from Covid-19. It took time for antibody levels to rise. Only after the booster shot did volunteers compare favorably with recovered patients.

In an editorial in NEJM, Heaton noted that it needs to be confirmed that measurements of such antibodies predict efficacy. “They are the best tools available,” she wrote, “and are supported by findings in nonhuman primates.”

At the 100-microgram dose, patients had neutralizing antibody levels, measured in what are called geometric mean titers, of 231.8 at day 57, compared to 109.2 in patients who recovered from Covid-19.

Experts said that given the multiple types of tests, it is impossible to compare vaccines based on laboratory results between different vaccines. For its vaccine, Pfizer had said that neutralizing antibody levels were 267 at 28 days, but they were 94 (a lower level than Moderna reported) in recovered patients, apparently using a different test. Pfizer has not disclosed data beyond 28 days.

Asked to compare the Moderna and Pfizer vaccine data, Fauci said, “I don’t think you could say anything about one being better than the other. They both induce good responses. Let’s see what happens in the real world.”

Several researchers said that seeing the results increased their hope not so much in Moderna’s vaccine, but in arriving at one or more vaccines that will help reduce the impact of the virus.

“I am cautiously optimistic, based on the data that we’ve seen so far, that amongst the several different vaccine platforms that are being tested, there seem to be encouraging Phase 1 data to suggest that at least one of them is going to work,” said Francis Collins, director of the National Institutes of Health. “And maybe several of them.”

But he warned that such science is not predictable. “Hence the word cautiously is attached to the word optimistic in this situation,” Collins said.

This story has been updated with comments from Anthony Fauci.

Helen Branswell contributed reporting.

  • Moderna’s data is solid. If it is producing neutralizing antibodies, the vaccine is doing the job that it is designed to do. There is at least 90% chance it will work!! Let’s keep our fingers crossed!!

  • The population was 89% white, 13% Hispanic, 4% Black, 2% Asian, and 2% Native American

    I think it is advisable the writer first takes a grade 1 math class. Otherwise all is great . 😂😂😂

    • Hispanic is an ethnic group not a race, so don’t add that percentage to the total. The numbers reported by the article author are correct. There was also 2% Unknown race. The percentages add up to 99% (it’s a very small sample of 45 and the study authors rounded to the nearest whole number, so it’s not 100%).

    • What side effects? At the dose they are producing (100mcg) they were mild and the most prevalent complaint was mild pain at the site of injection.

      It’s a shot so that’s expected.

      As for prevalence, not sure why this is important. Those who get vaccinated would be protected from those who don’t. So what’s the issue?

  • Being a type one diabetic obviously considered a pre-existing condition which a large part of the world’s population has,what’s the foreseeable statistical projection as to the above treatment?

    • This IS pharma technology and work, no different than what Big Pharma does. Biopharma is essentially all one industry. BioNtech has the parallel technology like Moderna’s, and they partnered it with Pfizer to scale it up.
      No one in “Big Pharma” benefits if the covid vaccines fail. Get a grip on yourself and stop with the paranoia.

    • You are absolutely right and I have been wondering why nobody has done a report or an article about STAT news obvious negative bias against Moderna, I don’t see them say they were wrong about the implied covering up of phase one results that they made up in previous articles. Everyte Moderna comes out with good news Stay news has to come out with something negative, never a middle of the ground post but always leaning negative. Need further investigation both from the people and the SEC IMO…

  • Since transporting the vaccine is a huge problem, why aren’t we seeing testing done that would mimic real world use. Let the vaccine sit around for a few hours at room temperature and lets see what happens to the results.

    • to understand results, i.e. cause and effect, it is necessary to minimize the number of degrees of freedom in the experiment, which requires that the process implement controls

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