Moderna is aiming to begin its final phase of testing for its coronavirus vaccine July 27.
The Cambridge, Massachusetts-based biotech company is the first in the U.S. to announce an estimated start date for phase 3 trials.
Information about the trial, including guidance for vaccine volunteers, was posted on clinicaltrials.gov on Tuesday.
Moderna spokesperson Ray Jordan confirmed the estimated start date to CNBC. "We can add that we expect participants will be able to register with clinical sites beginning July 21," he said.
Moderna was the first company in the U.S. to begin testing coronavirus vaccines in humans, giving its first dose March 16.
The company aims to enroll 30,000 adults in the clinical trial, which is designed to test whether the vaccine works to prevent COVID-19. The trial will also look at the vaccine's safety.
Participants will either receive the vaccine or a placebo. They will be tracked for two years to see whether they get COVID-19 or have any adverse reactions to the vaccine.
The researchers will also periodically measure participants' antibody levels.
Also Tuesday, Moderna published data from its phase 1 clinical trial in the New England Journal of Medicine.
That trial, which involved 45 participants, was meant to test a new drug's safety, not its effectiveness. But the company said results from all 45 participants showed they developed antibodies key to fighting the virus at levels up to four times the amount found in patients who got sick and then recovered from the virus.
"These are the kinds of results that you want to see from an early trial," Dr. Iahn Gonsenhauser, chief quality and patient safety officer at the Ohio State University Wexner Medical Center in Columbus, said.
Gonsenhauser, who is not involved with any COVID-19 vaccine research, cautioned that while the findings are promising, scientists have not yet shown that COVID-19 antibodies lead to immunity, and if so, how long that immunity lasts.
Every person in the Moderna trial received two shots, 28 days apart. Participants were given one of three dosage levels: 25 micrograms, 100 micrograms and 250 micrograms. (In the phase 3 trial, the 100 microgram dosage will be used.)
The most common side effects were fatigue, chills, headache and weakness, the study found.
Moderna's chief executive officer, Stéphane Bancel, said in a statement that the company is "committed to advancing the clinical development" of the vaccine "as quickly and safely as possible while investing to scale up manufacturing so that we can help address this global health emergency."
The company estimates it could deliver 500 million doses per year, starting in 2021.
In an editorial published alongside the study, Dr. Penny Heaton, the chief executive officer of the Bill and Melinda Gates Research Institute in Cambridge, Massachusetts, wrote that the data are "promising."
However, Heaton added, "we must bear in mind the complexity of vaccine development and the work still to be done before COVID-19 vaccines are widely available."
It usually takes years to develop a vaccine. Researchers worldwide are working at a record pace to get one for COVID-19 within a year and a half.
Globally, at least 150 vaccines are in development, but the vast majority are in the earliest stages of study.
Including Moderna's vaccine candidate, just four potential vaccines have advanced to phase 3 trials so far. The other three are being tested in Brazil and the U.K., according to the World Health Organization.
The Food and Drug Administration has said that any COVID-19 vaccine would need to prevent illness or decrease the severity of the disease in 50 percent of people who receive it in order to be approved.