At least 30,000 volunteers are needed for each of the four companies that plan to launch Phase 3 trials in the U.S.
About 138,600 Americans have already volunteered to participate in clinical trials for a Covid-19 vaccine less than two weeks after the launch of a national effort to sign up a total of 120,000 participants to help test four vaccines beginning this fall, according to the National Institute of Allergy and Infectious Diseases.
According to the Coronavirus Prevention Network website, most studies will require volunteers to visit a research site at least 10 times over one or two years where they will be injected with either a potential vaccine or a placebo.
