Positive data is emerging on a potential coronavirus vaccine developed by Moderna in partnership with the National Institutes of Health.

Healthy adults who were given the vaccine tolerated it generally well and all created neutralizing antibodies in response, according to interim results published in the New England Journal of Medicine on Tuesday.

The study details findings from the vaccines’s phase 1 study, which included 45 participants who were aged 18 to 55 and enrolled at the study sites in Seattle and at Emory University in Atlanta. The volunteers received two vaccinations 28 days apart. They developed a “robust” immune response with more than half reporting mild to moderate side effects, including fatigue, chills, headache, muscle pain and pain at the injection site, according to Moderna.

It’s the first vaccine tested in the U.S. to publish results from its trials in a peer-reviewed journal. While the creation of antibodies doesn’t ensure a vaccine will be effective, it is a positive sign.

Stéphane Bancel, CEO of Moderna, called the developments “encouraging,” saying they “represent an important step forward in the clinical development” of the vaccine.

Following the announcement, the company’s stock rose more than 16% after the market closed.

Earlier on Tuesday, the company announced that the vaccine will begin its largest study, involving 30,000 people, on July 27. It is expected to be the first U.S. vaccine to enter phase 3 trials.

Phase 1 typically looks at a small number of people to see if the vaccine is safe and produces an immune response. Phase 2 looks at an expanded group of people. In Phase 3, the vaccine is tested in thousands of people.

If the vaccine remains on track, Moderna reports it will be able to deliver “approximately 500 million doses per year, and possibly up to 1 billion doses per year” starting in 2021.