US biotech firm Moderna said on Tuesday it would enter the final stage of human trials for its Covid-19 vaccine on July 27, after promising early results were published in an influential journal.

The announcement came as the results from an earlier trial intended to prove the vaccine was safe and triggered antibody production was published.

The first COVID-19 vaccine tested in the U.S. revved up people’s immune systems just the way scientists had hoped, researchers reported Tuesday — as the shots are poised to begin key final testing.

“No matter how you slice this, this is good news,” Dr. Anthony Fauci, the U.S. government’s top infectious disease expert, told The Associated Press.

The experimental vaccine, developed by Fauci’s colleagues at the National Institutes of Health and Moderna Inc., will start its most important step around July 27: A 30,000-person study to prove if the shots really are strong enough to protect against the coronavirus.

The trial will enroll 30,000 participants across 87 locations, according to the website. Participants in the experimental arm will receive a 100 microgram dose of the potential vaccine on the first day and another 29 days later. Some patients will also receive a placebo.

Moderna’s experimental vaccine contains genetic material called messenger RNA, or mRNA. The mRNA is a genetic code that tells cells what to build — in this case, an antigen that may induce an immune response to the virus. It became the first candidate to enter a phase one human trial in March.

In May, the company released data from its early-stage trial, which showed the vaccine produced neutralizing antibodies against Covid-19 in at least eight participants. The vaccine also made binding antibodies in all participants.

The effort by Moderna is one of several working on a potential vaccine for Covid-19, which has infected more than 13 million people and killed at least 573,200 across the globe as of Tuesday, according to data compiled by Johns Hopkins University. More than 100 vaccines are under development globally, according to the World Health Organization.

Earlier this month, pharmaceutical giant Pfizer released positive results from its closely watched early-stage human trial of a coronavirus vaccine.

The U.S. is aiming to deliver 300 million doses of a vaccine for Covid-19 by early 2021. 

Scientists are still learning about key aspects of the virus, including how immune systems respond once a person is exposed. The answers, they say, may have important implications for vaccine development, including how quickly it can be deployed to the public.