Photo/Illutration The Institute of Medical Science of the University of Tokyo in the capital’s Minato Ward (Kenta Noguchi)

Strains of the novel coronavirus rampant in Japan in the summer of last year when the delayed 2020 Tokyo Olympics were held spread afterward to at least 20 countries and regions, research shows.

Researchers primarily from the Institute of Medical Science of the University of Tokyo (IMSUT) concluded they could not rule out the possibility that the Games were responsible for the spread of the AY.29, a Delta subvariant that originated in Japan.

The Summer Olympics were held from July 23 through Aug. 8, followed by the Paralympics between Aug. 24 and Sept. 5.

Referring to a document from the organizing committee for the Games, the researchers noted that 863 people associated with the event, including athletes and staff members, were diagnosed with COVID-19 during the sessions.

Off that figure, many were Japanese residents. Contractors responsible for event site management, security and other duties accounted for the largest portion with 502 cases. Those engaged directly in the Games made up 201. Athletes tested positive in 41 cases.

Around that time, Tokyo was under a third state of COVID-19 emergency. Because the AY.29 subvariant of the Delta variant, which was unique to Japan, was often detected while the sports extravaganza was on, its later discovery overseas strongly indicates the virus came from Japan.

The research team analyzed the genome, or the complete set of genetic information, of new coronaviruses confirmed overseas through Jan. 10, 2022. The results revealed that 118 of them were linked to the AY.29 subvariant.

The viruses were spotted in 20 countries and regions, including the United States, Britain, Canada, Germany and South Korea.

The 118 samples were divided into 55 differing strains based on their genome’s tiny but distinctive differences.

Among them were cases that had no links with the sports events. One of the strains is believed to have reached Hawaii from Japan before the Games. Another is thought to have been transmitted by personnel associated with the U.S. military stationed in Japan’s southernmost prefecture of Okinawa. 

After excluding those irrelevant cases, the researchers found that in the remaining 41 cases, their ancestral strains had been collected from domestic patients in the Japanese capital, neighboring Kanagawa Prefecture and elsewhere in the Tokyo metropolitan region.

Though the team said, “There remains a possibility that these 41 strains are associated with the Olympic and Paralympic participants,” whether the AY.29 was actually carried by visitors to the Games when they returned to their home countries could not be confirmed.

According to Seiya Imoto, a professor of biology at the IMSUT’s Human Genome Center who did the research, no information has been disclosed that is necessary for ancestral research of viruses’ variants detected from athletes and staff during the Games.

On top of that, the viruses’ genome analysis alone could not determine who actually was the unwitting carrier on leaving Japan.

Individuals with no ties to Olympic and Paralympic Games may have left Japan during these periods as data from the Japan National Tourism Organization shows that 40,000 to 60,000 Japanese departed each month for overseas destinations between July and September 2021.

Few strains deriving from the AY.29 have been reported anywhere in the world since winter 2021. The Omicron variant then emerged and quickly ravaged Japan and other parts of the world.

Imoto called the team’s findings important, noting that much tougher anti-virus approaches designed to reduce infections as much as possible can place a heavy burden on athletes, lowering their performance.

“Some infections inevitably go undetected even though people are screened at the time of their arrival and departure,” said Imoto. “What is significant is comparing the Games’ countermeasures with their outcomes to provide lessons for future international events. I want our achievement to be utilized for that purpose.

The team’s findings were published Aug. 3 in the Swiss academic journal Frontiers in Microbiology at (https://www.frontiersin.org/articles/10.3389/fmicb.2022.883849).

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