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Savannah, Georgia CNN  — 

The first Phase 3 clinical trial of a coronavirus vaccine in the United States began Monday.

The investigational vaccine was developed by the biotechnology company Moderna and the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health. The trial is to be conducted at nearly 100 US research sites, according to Moderna. The first patient was dosed at a site in Savannah, Georgia.

The trial is expected to enroll about 30,000 adult volunteers and evaluates the safety of the Moderna/NIH vaccine and whether it can prevent symptomatic Covid-19 after two doses, among other outcomes. Volunteers will receive either two 100 microgram injections of the vaccine or a placebo about 28 days apart. Investigators and participants will not know who has received the vaccine.

Results from a Phase 1 trial of the vaccine published earlier this month in the New England Journal of Medicine found it induced immune responses in all of the volunteers and was generally safe. It had mild side effects, including fatigue, chills, headache, muscle pain, pain at the injection site.

A Phase 1 study typically studies a small number of people and focuses on whether a vaccine is safe and elicits an immune response. In Phase 2, the clinical study is expanded and the vaccine is given to people who have characteristics – such as age and physical health – similar to those for whom the new vaccine is intended, according to the US Centers for Disease Control and Prevention. In Phase 3, the vaccine is given to thousands of people and tested for efficacy and again for safety.

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The Moderna/NIH vaccine is one of 25 in clinical trials around the world, according to the World Health Organization.

Moderna is one of several companies that received support from Operation Warp Speed, the federal government’s Covid-19 vaccine program. On Sunday, Moderna announced it had received an additional $472 million from the Biomedical Advanced Research and Development Authority for Phase 3 study and development of its Covid-19 vaccine, bringing the total to $955 million.

According to Johns Hopkins University’s tally of cases in the United States, there are more than 4.2 million confirmed cases of coronavirus in the United States and at least 146,935 people have died.