The first injection was given at 6:45 a.m.
This is phase three for the experimental biotech company, Moderna, working along with the National Institutes of Health.
Over the next few months, they will be enrolling 30,000 volunteers in 89 locations, including one in Philadelphia.
The experimental vaccine has already been proven to be safe and to produce an immune response in earlier studies.
But phase three is where they determine if it truly works to protect against the virus. Half of the participants will get two shots of the vaccine about a month apart. The other half will get two placebo shots. So it is a blind study.
During a live Twitter and Facebook chat Monday, Moderna's president said while the vaccine was developed in record time, they have been working on the technology for more than a decade.
One of the study's first volunteers also spoke about why she signed up.
Interested in volunteering for a COVID-19 Prevention Clinical Study? CLICK HERE