Organizers insist the Olympics can be held in a safe bubble: athletes will be regularly tested, contact traced and socially distanced. By the time the Games start, officials expect more than 80% of athletes to be vaccinated.
But public health experts say there are many ways for the bubble to be punctured, especially if tens of thousands of largely unvaccinated and untested volunteers are moving between Olympic venues.
"Even without spectators, it's not a bubble. There are too many leaks in it," said epidemiologist Mike Toole from the Burnet Institute in Melbourne, Australia.
"Having these 70,000 volunteers out in the community, moving from neighborhood to neighborhood, then going into the Games – where you have around 20% unvaccinated – then you're looking at a high-risk scenario," he said.
The third and final Olympic Playbook of Covid-19 measures says some "sport specific" volunteers will be tested regularly at the Games, without specifying how many that would include.
Opposition to the Games: Warnings from Japan's medical community continue to grow. The Tokyo Medical Practitioners Association, an organization representing 6,000 doctors in Tokyo, wrote a letter calling for the Games to be canceled.
"The most important priority now is to fight against COVID-19 and to secure people's lives and livelihoods," the letter said. "Japan will bear a big responsibility if the hosting of the Olympic and Paralympic Games contributes to the spread of COVID-19 and increases the number of sufferers and deaths."
The head of Japan's Covid-19 taskforce, Shigeru Omi, said in June it's "not normal" to host the Olympics during the pandemic, warning the Games would have an impact on infections in Japan.