Why? First off, Covid-19 was a failure and the vaccine is a failure. More people survived than they had anticipated. Now they need a more virulent and deadly version of the virus to get the job done, and watch out for the vaccine they come up with. Maintain a population of 500 million.......
Those mice aren't regular mice they're "humanized" mice. Mice genetically engineered to somewhat parallel our system. Ever see a human ear grown on a mouse?