Early Data Show Moderna’s Coronavirus Vaccine Is 94.5% Effective

Moderna Therapeutics in Cambridge, Mass.Credit...Tony Luong for The New York Times

Moderna is the second company to report preliminary results from a large trial testing a vaccine. But there are still months to go before it will be widely available to the public.

The drugmaker Moderna announced on Monday that its coronavirus vaccine was 94.5 percent effective, based on an early look at the results from its large, continuing study.

Researchers said the results were better than they had dared to imagine. But the vaccine will not be widely available for months, probably not until spring.

Moderna is the second company to report preliminary data on an apparently successful vaccine, offering hope in a surging pandemic that has infected more than 53 million people worldwide and killed more than 1.2 million. Pfizer, in collaboration with BioNTech, was the first, reporting one week ago that its vaccine was more than 90 percent effective.

Pfizer and Moderna were the first to announce early data on large studies, but 10 other companies are also conducting big Phase 3 trials in a global race to produce a vaccine, including efforts in Australia, Britain, China, India and Russia. More than 50 other candidates are in earlier stages of testing.

The Food and Drug Administration has said that coronavirus vaccines should be at least 50 percent effective to be approved.

Researchers test vaccines by inoculating some study participants and giving others placebos, and then watching the two groups to see how many people get sick. In Moderna’s study, 95 people contracted the coronavirus: five who were vaccinated, and 90 who received placebo shots of saltwater. Statistically, the difference between the two groups was highly significant. And of the 95 cases, 11 were severe — all in the placebo group.

The results were analyzed by an independent data safety monitoring board, appointed by the National Institutes of Health.

Moderna, based in Cambridge, Mass., developed its vaccine in collaboration with researchers from the Vaccine Research Center, part of the National Institute of Allergy and Infectious Diseases.

“I had been saying I would be satisfied with a 75 percent effective vaccine. Aspirationally, you would like to see 90, 95 percent, but I wasn’t expecting it. I thought we’d be good, but 94.5 percent is very impressive.”

Dr. Anthony S. Fauci, director of the institute, said in an interview.

Stéphane Bancel, the chief executive of Moderna, said in a statement that the results had provided “the first clinical validation that our vaccine can prevent Covid-19 disease, including severe disease.”

Pfizer and Moderna each announced the findings in news releases, not in peer-reviewed scientific journals, and the companies have not yet disclosed the detailed data that would allow outside experts to evaluate their claims. Therefore, the results cannot be considered conclusive. The studies are continuing, and the figures on effectiveness may change.

The companies’ products open the door to an entirely new way of creating vaccines — and creating them fast. Both use a synthetic version of coronavirus genetic material, called messenger RNA or mRNA, to program a person’s cells to churn out many copies of a fragment of the virus. That fragment sets off alarms in the immune system and stimulates it to attack, should the real virus try to invade. Although a number of vaccines using this technology are in development for other infections and cancers, none have yet been approved or marketed.

“The fact that two different vaccines made by two different companies with two different kinds of structures, in a new messenger RNA concept, both worked so effectively confirms the concept once and for all that this is a viable strategy not only for Covid but for future infectious disease threats.”

said Dr. Barry R. Bloom, a professor of public health at Harvard.

Natalie E. Dean, a biostatistician at the University of Florida, said an important finding was that the vaccine appeared to prevent severe disease. Pfizer did not release information about disease severity when reporting its results.

Researchers say the positive results from Pfizer and Moderna bode well for other vaccines, because all of the candidates being tested aim at the same target — the so-called spike protein on the coronavirus that it uses to invade human cells.

Dr. Bloom said that the success of the two vaccines meant that measures of immunity used in earlier phases of the studies—participants’ antibody levels—-were reliable, and that other companies could use those measures as proof of effectiveness to shorten the testing and approval process for their vaccines.

It will be important to determine whether the vaccines work equally well in older and younger people, experts say. Researchers also want to know if the vaccines prevent people from spreading the virus — an ideal result that could help quash the pandemic.

Another big unknown is how long the immunity provided by the vaccines will last.

An additional concern is that both vaccines must be stored and transported at low temperatures — minus 4 degrees Fahrenheit for Moderna, and minus 94 Fahrenheit for Pfizer — which could complicate their distribution, particularly to low-income areas in hot climates. Although both vaccines are made of mRNA, their temperature requirements differ because they use different, proprietary formulations of fat to encase and protect the mRNA, Ray Jordan, a Moderna spokesman, said.

Other coronavirus vaccines being developed will need only refrigeration. If handled improperly, vaccines can become inactive.

But on Monday, Moderna said researchers had found that its vaccine had a longer shelf life in the refrigerator than previously thought: 30 days, not seven. And it will last 12 hours at room temperature, the company said.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University, said the relative ease of handling the Moderna vaccine would give it a big advantage.

“This vaccine presents the opportunity of using doctors’ offices, clinics and pharmacies as vaccination sites.”

he said, adding that he would not be surprised, should both vaccines become available, if vaccination sites requested Moderna’s.