Tokyo 2020 organisers will this autumn begin the task of devising safety protocols to allow the Games to take place if the coronavirus pandemic is still raging.
But Tokyo 2020, which had been due to start on Friday until it was postponed for a year, will not be the first Olympic Games to face a health crisis, although the scale of the challenge posed by COVID-19 is unprecedented.
AFP looks at previous Olympics that went ahead in the face of viral outbreaks.
Nagano 1998: Flu
There was an outbreak of influenza the last time Japan hosted the Games -- the Winter Olympics in the central city of Nagano in 1998.
Nearly 1,500 schoolchildren in the Nagano region came down with the flu and some 200 people connected with the Games were taken ill -- although officials stressed other illnesses were also to blame.
The virus prevented Norwegian 1,500 metre gold medal-winning speed skater Adne Sondral from going for a double in the 1,000 metres.
German figure skating medal hopeful Tanja Szewczenko pulled out over health fears and the International Olympic Committee (IOC) also got involved, warning competitors against the flu and advising them to take on plenty of fluids.
That outbreak of flu was unrelated to the killer bird flu hitting southern China at the time.
Rio 2016: Zika
Ahead of the 2016 Rio Olympics, the talk was dominated by Zika, a mosquito-borne virus that can cause pregnant women to give birth to babies with microcephaly -- a deformation that results in abnormally small brains and heads.
The Zika outbreak began in 2015 and infected around 1.5 million people, according to the World Health Organisation (WHO), mainly in Brazil.
There was concern that international visitors to the Games could spread the virus globally, even though the WHO assessed the risk as "minimal."
Some leading tennis players and golfers -- including golf's current world number one Rory McIlroy -- decided not to compete due to fears over the virus.
The stories proved more dramatic than the facts, with no new cases reported during the Games.