FILE - Defending men's champion Serbia's Novak Djokovic practices on Margaret Court Arena ahead of the Australian Open tennis championship in Melbourne, Australia, Thursday, Jan. 13, 2022. Athletes have been put at center court of arguments over COVID vaccines. The NFL's Aaron Rodgers, the NBA's Kyrie Irving, and tennis's Novak Djokovic, have each become cultural touchstones in the cultural controversy. (AP Photo/Mark Baker, File)