Washington: The global race for a COVID-19 vaccine boils down to some critical questions: How much must the shots rev up someone's immune system to really work?
And could revving it the wrong way cause harm? Even as companies recruit tens of thousands of people for larger vaccine studies this summer, behind the scenes scientists still are testing ferrets, monkeys and other animals in hopes of clues to those basic questions — steps that in a pre-pandemic era would have been finished first. "We are in essence doing a great experiment," said Ralph Baric, a coronavirus expert at the University of North Carolina, Chapel Hill, whose lab is testing several vaccine candidates in animals.