Moderna‘s shares soared after the company said its potential vaccine to prevent Covid-19 produced a “robust” immune response in all 45 patients in its early stage human trial, according to newly released data published Tuesday evening in the peer-reviewed New England Journal of Medicine.

Moderna’s stock rose more than 16% in after-hours trading on the news. 

All 45 patients produced neutralizing antibodies, which scientists believe is important for building immunity and provided more promising data that the vaccine may give some protection against the coronavirus. In the trial, each participant received a 25, 100 or 250 microgram dose, with 15 people in each dose group. Participants received two doses of the potential vaccine.

After two vaccinations, the vaccine elicited a “robust” immune response in all participants in all dose cohorts, Moderna said. The company said the levels of neutralizing antibodies in patients in the high dose group were fourfold higher than in recovered Covid-19 patients. 

“These Phase 1 data demonstrate that vaccination with mRNA-1273 elicits a robust immune response across all dose levels and clearly support the choice of 100 µg in a prime and boost regimen as the optimal dose for the Phase 3 study,” Moderna’s chief medical officer, Tal Zaks, said in a statement. “We look forward to beginning our Phase 3 study of mRNA-1273 this month to demonstrate our vaccine’s ability to significantly reduce the risk of COVID-19 disease.”

In May, the company had released preliminary information from its early stage trial, but it lacked all of its data and it hadn’t been peer-reviewed yet.

Moderna said the vaccine was generally well tolerated, but more than half of the participants reported mild or moderate symptoms such as fatigue, muscle aches or pain at the injection site.

Evaluation of the durability of immune responses is ongoing, Moderna said, and participants will be followed for one year after the second vaccination.

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 Tuesday, Moderna announced it would begin its late-stage trial for its vaccine on July 27. The trial will enroll 30,000 participants across 87 locations, according to ClinicalTrials.gov. 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 1 human trial in March.

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.

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

Dr. Anthony Fauci, the nation’s top infectious disease expert, has often touted Moderna’s potential vaccine.

On Monday, he said he’s “cautiously optimistic” scientists will be able to create at least one safe and effective vaccine by the end of the year or early 2021.