WASHINGTON — The American biotechnology company Novavax announced Monday the initiation of PREVENT-19 Pivotal Phase 3 Efficacy Trial of COVID-19 Vaccine in the US and Mexico. The Phase 3 trial of another investigational COVID-19 vaccine developed by biotechnology company Novavax, Inc., has started enrolling adult volunteers, the US National Institutes of Health (NIH) announced. In a statement issued on Monday, the NIH said that the randomized, placebo-controlled trial will enroll approximately 30,000 people at some 115 sites in the US and Mexico. PREVENT-19 will assess the efficacy, safety and immunogenicity of NVX-CoV2373 in the prevention of COVID-19. The two-thirds of enrollees are to receive active vaccine. Volunteers will be asked to give informed consent prior to their participation in the trial, according to the NIH statement. 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, it said. 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, Inc., a late-stage biotechnology company developing next-generation vaccines for serious infectious diseases, is the fifth company to enter a late-stage trial in the US. The Novavax vaccine, which uses a more traditional vaccine technology than Pfizer & Moderna, also has the advantage of not requiring ultra-cold storage, making it easier to distribute. A trial has already begun in the United Kingdom. Novavax had intended to begin its US trial earlier, but delayed the start because of manufacturing problems. — Agencies