In this April 2014 photo provided by the Vaccine and Infectious Disease Organization-International Vaccine Centre at the University of Saskatchewan, a researcher holds a ferret at their facility in Saskatoon, Saskatchewan, Canada. In 2020, the lab is working with 300 ferrets developing a COVID-19 coronavirus vaccine candidate and testing other vaccine candidates and therapeutics. (VIDO-InterVac at the University of Saskatchewan via AP)

FILE - In this July 29, 2008, file photo, a rhesus macaque monkey grooms another on Cayo Santiago, known as Monkey Island, off the eastern coast of Puerto Rico. Since 1938, the 37-acre island has served as a research colony where the monkeys, originally from India, are studied. Even as companies recruit tens of thousands of people for larger COVID-19 coronavirus vaccine studies in the summer of 2020, 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. (AP Photo/Brennan Linsley, File)