Olympians from the United States who competed at the Tokyo Games this summer were encouraged, but not required, to be vaccinated against Covid-19. More than 80 percent of them ultimately got their shots.

But that option will not be available for athletes aiming to make the next round of Games.

On Wednesday, the United States Olympic & Paralympic Committee announced that all athletes and team staff members who use the organization’s training centers and facilities would need to be fully vaccinated by Nov. 1.

The organization also said that by Dec. 1 any athletes vying to represent the country at the Winter Games, which are scheduled to begin on Feb. 4 in Beijing with the Olympics followed by the start of the Paralympics on March 4, will need to show proof of vaccination to be able to join Team U.S.A.’s delegation.

The International Olympic Committee has not announced a vaccine requirement for the Beijing Games.

“The stark reality is that this pandemic is far from over,” Sarah Hirshland, the U.S.O.P.C.’s chief executive, wrote in a letter reviewed by The New York Times. “This step will increase our ability to create a safe and productive environment for Team USA athletes and staff, and allow us to restore consistency in planning, preparation and service to athletes.”

The new policy, first reported by The Associated Press, takes the U.S.O.P.C. one step farther than the major North American professional sports leagues, none of which has required athletes to be vaccinated to compete.

The decision reflects the severity of the ongoing global health crisis as well as the lingering uncertainty about the sort of health protocols and preventive measures that will be deployed by Olympic and Paralympic organizers in Beijing.

Vaccines were not required for this summer’s Tokyo Games, which were postponed by a year because of the pandemic. In July, Jonathan Finnoff, the U.S.O.P.C.’s chief medical officer, said that about 83 percent of American Olympians had been vaccinated for the Tokyo Olympics. And the I.O.C. estimated that more than 80 percent of all Olympians staying at the athletes’ village in Tokyo were fully vaccinated.

The U.S.O.P.C.’s new policy arrived amid swirling speculation about the rules that athletes, officials, team staff members and journalists will face in China, where widespread lockdowns and strict quarantines have been fairly common during the pandemic. Athletes and officials have been bracing for any number of countermeasures, including the possibility of long quarantines and the implementation of a so-called bubble around the Games.

As it did for the Tokyo Games, the I.O.C. will release a so-called playbook next month detailing its preliminary rules and plans for preventing the spread of the virus at the 2022 Olympics. Twenty-eight athletes tested positive in Tokyo in the lead-up to the Summer Olympics and during the competition.

The I.O.C. created a single set of rules for Olympic participants in Tokyo, operating the Games as if no one had been vaccinated. It remains to be seen whether vaccinated athletes will have different privileges in Beijing.