COVID-19 vaccines enter phase-three trials — what it means

A subject receives a shot
A subject receives a shot in the first-stage safety study clinical trial of a potential vaccine by Moderna for COVID-19 at the Kaiser Permanente Washington Health Research Institute in Seattle on March 16.
Ted S. Warren | AP Photo file

Oxford University and Astra-Zeneca are reporting promising results this week from a COVID-19 vaccine trial. It's enough to push the vaccine into a phase-three trial, and enough for cautious optimism from Dr. Anthony Fauci, who's recently come under fire from the White House for being too negative.

Two other vaccine candidates are also entering phase-three testing.

“This is a major step forward. It puts us a lot closer,” Richard Kennedy, a professor of medicine and member of Mayo Clinic's Vaccine Research Group, told MPR News host Tom Crann.

“A phase three trial is going to involve tens of thousands of people, and they are people who are actually exposed to the disease and at risk,” he said. “What we're doing is giving them the vaccine and then comparing them to an unvaccinated group to see if the vaccine works at preventing illness or making it a less severe disease if they get it.”

Kennedy joined Crann on All Things Considered to explain how vaccine development works. To hear more, click play on the audio player above.

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