TOKYO (Reuters) -When Japan won the bid to host the Olympic Games eight years ago, it billed Tokyo as a reliable and secure location, contrasting it with rivals struggling with finances and political instability. But 100 days before the start of the Olympics, the organisers face a deluge of challenges and growing uncertainty as the pandemic rages around the world, affecting decisions on everything from athlete safety to spectator numbers to ticket sales. The biggest headache is the resurgent coronavirus, with countries like India and Brazil battling new variants and a fresh rise in cases. In Japan, vaccinations have been the slowest among developed economies, as Tokyo has lurched in and out of soft lockdowns. Infections are on the rise, and experts worry here the city is on the cusp of an "explosive" jump in cases. As a result, foreign spectators have been barred, parts of the torch relay have been re-routed, and the organizers are yet to decide what to do with the domestic audience. This has caused major challenges for sports venues and travel agencies, already grappling with restrictions to block the virus. “The situation is constantly shifting. Even in the last few months the coronavirus situation has changed massively, and it will continue to do so, and it’s very challenging to continue preparations when we don’t know what the situation will be in the future,” said Hidemasa Nakamura, the top organising committee official overseeing logistical preparations for the Games. His team has created the first “playbook” with COVID countermeasures, including rules banning visits to shops and restaurants. If visiting athletes break protocol, it could result in their being barred from competing. But Nakamura pledged to overcome the challenges as “one team” and told Reuters it was “important to show what we have now, receive feedback, and finalise the playbook step by step, not to have these discussions behind closed doors.” The next update to the rules is expected this month, he said.