February 4, 2022 12:19 PM EST

Tokyo officials took a calculated risk in hosting the Olympic Games last July and August. While infections of the Delta variant were causing surges around the world, including in the host city, Japanese Olympic and government authorities felt that proper control measures, including vaccination, masking, testing, and isolation would quell any outbreaks and keep the world’s largest sporting event from becoming a super spreader conflagration.

That bet proved to be mostly right, according to recently published data in a Research Letter in JAMA. What it means for the just-started 2022 Winter Olympics in Beijing, which have begun as the Omicron variant of COVID-19 continues to spread around the world, will become clear as the Games play out over the next month.

The study, by members of the Bureau of International Health Cooperation, the National Center for Global Health and Medicine Tokyo, the Infectious Diseases Control Center and Tokyo Organizing Committee of the Olympic and Paralympic Games, focused on athletes, coaches, and support staff during both the Olympic and Paralympic Games who stayed in the Olympic Village. All were required to test negative twice in the days before boarding their flights to Tokyo, and were tested with a saliva test upon arriving at the airport. While in the Village, athletes, coaches, and support staff were tested daily.

Health officials at the airport conducted 54,520 SARS-CoV-2 saliva tests, and 55 people tested positive, which was confirmed by an additional PCR test using a nasopharyngeal swab. These individuals were isolated in a designated facility until they tested negative.

Read more: I’m a Health Writer Who Covers the Olympics. Here’s What I Thought of the Tokyo Games Bubble

Among the more than one million daily tests conducted during both the Olympics and Paralympics, 299 were confirmed positive, leading to a positive rate of 0.03%. Based on these positive tests, 3,426 additional PCR tests were conducted during the Olympics and Paralympics on those identified as close contacts, with 15 of these people testing positive.

Cases increased steadily during the Games; there were 70 positive tests on opening day, which increased to a peak of 142 on day five before decreasing in the following days.

That trend likely reflects the fact that the pseudo bubble created in Tokyo for athletes was effective; the higher number of cases early on could be attributed to exposures during training camps or flights into the city. But once in Tokyo, athletes were restricted to using only Olympic transportation and dining in Olympic venues with screened staff. The authors of the report note that “public health control measures at the Tokyo Olympics and Paralympics worked well to prevent COVID-19 clusters inside the Village, despite a surge in new COVID-19 cases recorded in Tokyo during that time.”

Will Tokyo’s experience translate to Beijing during the 2022 Winter Games, which start on Feb. 4? Beijing officials are dealing with a very different virus than the one that stalked the Tokyo Olympics. Omicron is several times more transmissible than Delta, which means the number of infections has skyrocketed in stunning fashion. Unlike in Tokyo, however, athletes, coaches, and delegations arriving in Beijing must be vaccinated, or provide an approved medical exemption that requires them to quarantine for 21 days upon arriving in the city.

Read more: What Happens if an Athlete Tests Positive at the Beijing Olympics

The 2022 Winter Games will also be conducted under a stricter “bubble” than the one implemented in Tokyo. Athletes and media in Tokyo were allowed to use public transportation and mingle with the public after 14 days. In Beijing, athletes will be required to remain in the so-called Closed Loop for their entire stay. If they test positive, athletes will be required to move to an isolation facility if they don’t have symptoms, and to a hospital if they do. They can only leave those facilities if they test negative twice with 24 hours in between; generally, it takes at least five days or so for infected people to start testing negative for the virus. For most athletes, that means that testing positive will likely prevent them from competing.

The Beijing Games also look starkly different than the Tokyo Olympics; all staff interacting with Olympic athletes are gowned head to toe in white disposal protective suits, and are wearing masks and face shields as well as gloves. In Tokyo, masks and gloves were the extent of protective gear that most volunteers wore.

Cases will be inevitable as people arrive from around the world for the Beijing Olympics; already nearly 3% of athletes and officials have tested positive at Capital International Airport. Since Jan. 23, 200 positive COVID-19 cases have been detected among Olympics-related personnel, which includes workers. But Beijing’s stricter policies will likely help in controlling cases from erupting into widespread clusters. At least that’s what Beijing Olympic authorities are fervently hoping is the case.

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