Although Japan has seen just one case, the outbreak highlights the risk of contagion given the millions of visitors expected for the Summer Games.

“We have to be very careful about what kind of infectious diseases will appear at the Tokyo Olympics,” Kazuhiro Tateda, president of the Japanese Association for Infectious Diseases, told a briefing on Wednesday.

“At these kinds of mass gatherings, the risks increase that infectious diseases and resistant bacteria can be carried in.”

Organizers of the Summer Games said they were working with authorities.

“Countermeasures against infectious diseases constitute an important part of our plans to host a safe and secure games,” Tokyo 2020 said in a statement.

It would not be the first time that fears of disease have clouded Olympic preparations.

In 2016, the Zika virus prompted some health experts to call for the postponement or relocation of the games in Brazil. They went ahead as scheduled.

Japan on Thursday raised its infectious disease advisory level for Wuhan, urging citizens to avoid non-urgent trips.

PATCHWORK VACCINATION

Until recently, Japanese health authorities were more concerned about beefing up routine vaccinations before foreign visitors arrive this summer. A patchwork policy toward inoculation over the past few decades has left large portions of the Japanese population unprotected against common diseases.

Outbreaks of rubella, which can cause birth defects, prompted the CDC to warn pregnant women about traveling to Japan in 2018. Ahead of the Olympics, the health ministry has been conducting catch-up vaccinations of middle-aged men who were left out of rubella vaccinations in the 1970s and 1980s.

Japan has no mandatory vaccination for mumps, which in other parts of the world is usually bundled with measles and rubella in MMR shots. Japan is fourth in the world in mumps cases, after China, Nepal and Burkina Faso, according to WHO data.

As for the coronavirus, the dangers of public panic and the resulting economic fallout may be greater than the disease itself, said Ikuo Tsunoda, professor of microbiology at Kindai University.

He compared it to the mad cow disease scare in the early 2000s that prompted Japan to ban beef imports from the United States and other countries despite little evidence of human transmission.

“This coronavirus, of course it’s somewhat deadly, but uncertain or inaccurate information spreads so quickly,” Tsunoda said.

“Rather than the virus itself, rumors make the public panic, and that causes a mess.”