U.S. athletes trying to make the Winter Olympics will have to be fully vaccinated for COVID-19 under a groundbreaking new policy announced Wednesday by the U.S. Olympic and Paralympic Committee.

CEO Sarah Hirshland wrote in a letter obtained by The Associated Press that, starting Nov. 1, the USOPC will require staff, athletes and others utilizing training centers and other USOPC facilities to be vaccinated.

The requirement, she said, “will also apply to our full Team USA delegation at future Olympic and Paralympic Games.”

According to the team website, athletes will have to show proof of vaccination by Dec. 1. The U.S. is expected to send around 240 athletes to the Winter Olympics, though the mandate will impact hundreds more.