Juan Casuso, right, research coordinator from the University of Miami Miller School of Medicine, speaks with volunteer Julio Li during the intake process for Li to participate in testing for the National Institutes of Health-funded Moderna COVID-19 vaccine, Wednesday, Sept. 2, 2020 in Miami. Miami is one of 89 cities around the U.S., that's testing the Moderna COVID-19 vaccine. Study participants do not know if they're getting the vaccine or a placebo. (AP Photo/Taimy Alvarez)

Blood samples from volunteers participating in the National Institutes of Health-funded Moderna COVID-19 vaccine third phase clinical trail wait to be processed in a lab at the University of Miami Miller School of Medicine in Miami, Fla., Wednesday, Sept. 2, 2020 in Miami. (AP Photo/Taimy Alvarez)

University of Miami Miller School of Medicine nurse Loreta Padron prepares to test a volunteer for COVID-19, Wednesday, Sept. 2, 2020 in Miami. Miami is one of 89 cities around the U.S. that's testing the Moderna COVID-19 vaccine. (AP Photo/Taimy Alvarez)

University of Miami Miller School of Medicine phlebotomist Mayra Fernandez takes a blood sample from study participant Julio Li, Wednesday, Sept. 2, 2020, in Miami. Miami is one of 89 cities around the U.S. that's testing the Moderna COVID-19 vaccine. (AP Photo/Taimy Alvarez)

University of Miami Miller School of Medicine phlebotomist Mayra Fernandez prepares to take a blood sample from study participant Julio Li, Wednesday, Sept. 2, 2020, in Miami. Miami is one of 89 cities around the U.S. that's testing the Moderna COVID-19 vaccine. (AP Photo/Taimy Alvarez)

A "promotora" (health promoter) from CASA, a Hispanic advocacy group, tries to enroll Latinos as volunteers to test a potential COVID-19 vaccine, at a farmers market in Takoma Park, Maryland on Sept. 9, 2020. Minority enrollment in studies of two shots has inched up in recent weeks, but even more is needed this fall as additional vaccine testing gets underway over the next two months. (AP Photo/Federica Narancio)

University of Miami Miller School of Medicine Infectious Diseases Dr. Susanne Doblecki-Lewis, stands inside an exam room in Miami, Fla., Wednesday, Sept. 2, 2020. Doblecki-Lewis is leading the research on the National Institutes of Health-funded Moderna COVID-19 vaccine third phase of a clinical trial. “It’s really important that this vaccine work for everyone, or if it doesn’t, that we understand why,” she says. (AP Photo/Taimy Alvarez)

A "promotora" (health promoter) from CASA, a Hispanic advocacy group, tries to enroll Latinos as volunteers to test a potential COVID-19 vaccine, at a farmers market in Takoma Park, Md., on Sept. 9, 2020. Minority enrollment in studies of two shots has inched up in recent weeks, but even more is needed this fall as additional vaccine testing gets underway over the next two months. (AP Photo/Federica Narancio)

Infectious diseases research assistant Irma Barreto Ojeda, right, holds a tray with a syringe containing either a placebo or the Moderna COVID-19 vaccine as she confers with University of Miami Miller School of Medicine nurse Inza Patton, left, and pharmacist Barbara Huang Wednesday, Sept. 2, 2020 in Miami, as part of the National Institutes of Health-funded third phase of a clinical trial. They go through a verification process to confirm the right study participant is receiving the correct injection of either a placebo or the vaccine, which is only known to the pharmacy team. (AP Photo/Taimy Alvarez)

National Institutes of Health-funded Moderna COVID-19 vaccine study participant William Webb, right, gets a COVID-19 nose swab test by University of Miami Miller School of Medicine nurse Loreta Padron, Wednesday, Sept. 2, 2020 in Miami. Miami is one of 89 cities around the U.S. that's testing the Moderna COVID-19 vaccine. (AP Photo/Taimy Alvarez)