Japan-specific COVID strains release alongside Games

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Strains of the novel coronavirus ravaging Japan in the summer of last year, when the Tokyo 2020 Olympics were delayed, subsequently spread to at least 20 countries and regions, research has found.

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

The Summer Olympics were held from July 23 to August 8, followed by the Paralympic Games between August 24 and September 5.

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

Out of this figure, many were Japanese residents. Contractors responsible for event site management, security and other duties accounted for the largest share with 502 cases. Those directly involved in the Games accounted for 201. Athletes tested positive in 41 cases.

At that time, Tokyo was under a third COVID-19 state of emergency. Because the AY.29 subvariant of the Delta variant, which was unique to Japan, was often detected during the sports spectacle, its subsequent discovery abroad strongly indicates that the virus originated in Japan.

The research team analyzed the genome, or complete set of genetic information, of new coronaviruses confirmed overseas up to January 10, 2022. The results revealed that 118 of them were linked to the sub -variant AY.29.

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

The 118 samples were divided into 55 different strains based on tiny but distinctive differences in their genomes.

Among them were cases that had no connection to sporting events. One of the strains is said to have reached Hawaii from Japan before the Games. Another is thought to have been transmitted by personnel associated with the US military stationed in Okinawa prefecture, the southernmost in Japan.

After excluding these 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 area.

Although the team stated, “There remains a possibility that these 41 strains are associated with Olympic and Paralympic participants”, it could not be confirmed whether the AY.29 was actually carried by visitors to the Games when returned to their country of origin.

According to Seiya Imoto, a biology professor at IMSUT’s Human Genome Center who carried out the research, no information necessary for ancestral research of virus variants detected in athletes and staff during the Games has been disclosed.

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

People unrelated to the Olympics and Paralympics may have left Japan during these times, as data from Japan’s National Tourism Organization shows that 40,000 to 60,000 Japanese departed each month for overseas destinations between July and September 2021.

Few AY.29-derived strains have been reported globally since the winter of 2021. Then the Omicron variant appeared and quickly ravaged Japan and other parts of the world.

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

“Some infections inevitably go undetected even if people are screened upon arrival and departure,” Imoto said. “What is important is to compare the countermeasures of the Games with their results in order to provide lessons for future international events. I want our success to be used for this 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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