WASHINGTON, Dec. 28 (Xinhua) -- The Phase 3 trial of another investigational COVID-19 vaccine has begun enrolling adult volunteers, the U.S. National Institutes of Health (NIH) announced on Monday.

The randomized, placebo-controlled trial will enroll approximately 30,000 people at approximately 115 sites in the United States and Mexico.

It will evaluate the safety and efficacy of NVX-CoV2373, a vaccine candidate developed by biotechnology company Novavax, Inc.

Volunteers will be asked to give informed consent prior to their participation in the trial. They will be grouped into two cohorts: individuals 18 through 64 years old and those aged 65 and older, with a goal of enrolling at least 25 percent of all volunteers who are 65 years old or older.

After providing a baseline nasopharyngeal and blood sample, participants will be assigned at random to receive an intramuscular injection of either the investigational vaccine or a saline placebo.

A second injection will be administered 21 days after the first.

Participants will be followed closely for potential vaccine side effects and will be asked to provide blood samples at specified time points after each injection and during the following two years, according to the NIH.

Scientists will analyze the blood samples to detect and quantify immune responses to SARS-CoV-2, the virus that causes COVID-19.

Novavax is leading the trial as the regulatory sponsor. The U.S. National Institute of Allergy and Infectious Diseases (NIAID), and the U.S. Biomedical Advanced Research and Development Authority, are funding the trial.

Trial organizers also are emphasizing recruitment of people who are at higher risk of severe COVID-19 disease, including those who are African Americans, Native Americans, or of Latino or Hispanic ethnicity, and people who have underlying health conditions such as obesity, chronic kidney disease or diabetes.

"Addressing the unprecedented health crisis of COVID-19 has required extraordinary efforts on the part of government, academia, industry and the community," said NIAID Director Anthony Fauci.

"The launch of this study -- the fifth investigational COVID-19 vaccine candidate to be tested in a Phase 3 trial in the United States -- demonstrates our resolve to end the pandemic through development of multiple safe and effective vaccines," Fauci said.

Novavax's investigational vaccine, NVX-CoV2373, is made from a stabilized form of the coronavirus spike protein using the company's recombinant protein nanoparticle technology.

Currently there are two COVID-19 vaccines authorized for emergency use in the country by the U.S. Food and Drug Administration, one developed by American drugmaker Pfizer in partnership with German company BioNTech, and the other developed by American drugmaker Moderna.

Phase 3 clinical trials of two COVID-19 vaccine candidates, developed by multinational pharmaceutical company AstraZeneca and U.S. pharmaceutical company Johnson & Johnson, respectively, are underway in the United States.