TOKYO • The Tokyo Summer Olympics has survived being postponed, a mountain of scandal and bad publicity. Now comes the real challenge: pulling off the world's biggest sporting event safely in the middle of a pandemic.

When the Games begin on July 23, Covid-19 will still be a global reality. Even with the call to exclude foreign spectators, over 60,000 athletes, coaches, national team staff, media and other essential workers from more than 200 nations will converge on the Japanese capital - each with different rates of transmission, vaccination and viral variants.

"Based on the number of people arriving and the prevalence of the disease around the globe, the Olympics absolutely could become a super-spreading event that leads to quite a number of infections, as well as spreading internationally as people return home," said Spencer Fox, a research associate at the University of Texas at Austin who specialises in infectious disease modelling.

Organisers are relying on six "playbooks" of rules that detail how Olympic and Paralympic participants can compete and move around to manage the risks of what will be the biggest Covid bubble.

While those involved in the Games will be somewhat isolated from the Japanese public, Tokyo has ruled out using two core tenets of containment: quarantines and vaccinations. Without those, experts say infections could spread.

If it does, not only could the Olympics become the site of a sizeable outbreak that spreads into Japan, it could also become a cauldron of novel variants gathered from around the world. The risk is that athletes could bring them home, potentially fuelling the pandemic.

There is still a possibility that more stringent measures will be adopted, with the final version of the playbooks due in June.

"The situation surrounding the coronavirus is constantly changing, and it's our hope that the efforts of the government, the city of Tokyo and other stakeholders will help to mitigate spread of infections," Tokyo 2020 said in an e-mailed statement.

BUILDING A SPORTING BUBBLE

Sporting events have gone on worldwide this past year with success stories and cautionary tales.

The Olympic organisers are set to emulate the National Basketball Association (NBA), which saw no infections during its three-month run last year. But the NBA bubble saw just a few hundred athletes cordoned off at the Walt Disney World Resort in Orlando, Florida. Including staff and coaches, there were fewer than 1,000 people involved.

Officials at tennis' Australian Open this year took infection control seriously, requiring tests for athletes and mandatory quarantines upon arrival. Still, some charter flights headed for Melbourne saw cases among athletes and support staff. Injuries blamed on limited practice times were rampant as well.

While the event did not lead to a local outbreak or transmissions among players, the challenges show what can happen even when stringent precautions are in place.

The extent of the risk also varies depending on the sport. A study of the National Football League's latest season in the US found that American football players did not transmit the virus during game play, while high school wrestling matches turned into super-spreading events. The Olympics will feature 33 sports across 42 venues.

SOCIAL SETTING

Complicating the task is the social nature of the Games. Places like the Athletes' Village were designed to have people socialise. Although long conversations and collective meals will be off limits, how those rules will be enforced is unclear.

Some of the athletes are teenagers and the average age of an Olympian is usually in the 20s - groups where virus spread has been harder to control.

"While the playbooks are written, it's not clear how strictly they will be implemented," said Alex Cook, an associate professor at the National University of Singapore's Saw Swee Hock School of Public Health.

It is not just the athletes. The Games will require volunteers. It is not clear how such staff - which the Olympic organising committee and Tokyo metropolitan government say will probably number more than 150,000 - will be handled, and the playbooks do not offer explicit instructions.

Even in normal times, disease outbreaks are common at the Olympics. The Rio Summer Games were held amid the spectre of Zika. More than 300 athletes caught respiratory illnesses out of 10,568 competing in the London Olympics in 2012.

COVID CONTROL

Those flying into Japan will be required to have a negative Covid test and undergo additional testing at least every four days.

Increasing the frequency of testing is likely the best way to prevent an outbreak, experts say.

Seiko Hashimoto, Japan's Olympics chief, has indicated that more frequent testing for athletes is being considered.

"Short of vaccinating everybody, a combination of serial testing and the bubble is the best way," said Amesh Adalja, a senior scholar at the Johns Hopkins Centre for Health Security and an infectious disease physician.

Several countries, such as Singapore, have started vaccinating athletes and some national teams may have stricter infection control rules than playbooks.

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