Earlier this month, the chief executive of the Tokyo Olympics said he could not guarantee the Games would go on next summer even after they were postponed by a year because of the novel coronavirus pandemic. On Monday, a Japanese professor of infectious disease went even further, saying he thought the Olympics would have to be put off in 2021 as well.

“To be honest with you, I don’t think the Olympics is likely to be held next year,” Kentaro Iwata, a professor of infectious disease at Kobe University, said Monday, per the Associated Press. “Holding the Olympics needs two conditions; one, controlling covid-19 in Japan, and controlling covid-19 everywhere.”

“I am very pessimistic about holding the Olympic Games next summer unless you hold the Olympic Games in a totally different structure such as no audience, or a very limited participation,” Iwata added.

Devi Sridhar, professor of Global Health at the University of Edinburgh, told the AP last week that next year’s Olympics — and the 2022 Winter Games in Beijing, which are scheduled to begin about six months later — depend on the development of a covid-19 vaccine.

“I think it all depends on whether we have a vaccine,” Sridhar said. “And so I think if you talk to some of the scientists, they’re saying we’ll have a vaccine by the fall and we can manufacture it quickly and we can get it out to people. If we do, then I’d say, actually, we have a great chance of going ahead with the Olympics.”

But as said repeatedly by Anthony S. Fauci, the United States’ leading infectious disease expert, the process of developing a vaccine could take a year to 18 months.

“If it looks in the next few months that a vaccine is proving difficult, that actually it has massive side effects or it’s not effective or we’re not actually building immunity in individuals, then I think [the Olympics will] have to be delayed,” Sridhar said.

Even though it was the second country after China to record a case of the coronavirus, Japan has been criticized for its response to the pandemic, with Prime Minister Shinzo Abe not instituting a nationwide state of emergency until last week amid a sharp spike in positive tests. The country, which has seen about 11,000 confirmed infections and about 240 deaths as of Monday, has seen its medical facilities overburdened, with emergency rooms unable to treat people with other serious health conditions.