More rigorous departure screenings for the participants from the unvaccinated countries might have been necessary. Since samples in those unvaccinated countries are also undersampled with a longer lead time for data sharing, it will take longer to grasp the whole picture. However, propagation to unvaccinated regions might have caused unfathomable damages. Among the 20 countries, most European and North American countries have vaccination rates over 50% and sufficient genomic surveillances are conducted transmissions seem contained. Other countries or regions with multiple introductions were Canada, Germany, South Korea, Hong Kong, Thailand, and the Philippines.

The United States had 50 samples with 10 distinct introductions, and the United Kingdom had 13 distinct strains introduced in 18 samples. Phylogenetic analysis and ancestral searches identified 55 distinct introductions into those countries. As of January 10, 2022, 118 samples were identified in 20 countries. Simultaneously, ancestral searches were performed for the overseas AY.29 samples to identify their origins in Japan using the maximum variant approach. Phylogenetic analysis was performed to illustrate how AY.29 strains evolved and were introduced into countries abroad. Variants of SARS-CoV-2 genomes were performed to extract AY.29 Delta substrain samples with 5239C > T and 5514T > C. AY.4 substrain AY.29, which harbors two additional characteristic mutations of 5239C > T (NSP3 Y840Y) and 5514T > C (NSP3 V932A), emerged in Japan and became dominant in Tokyo by the time of the Olympic Games. Just before the games, the Alpha variant was being replaced with the more contagious Delta variant.

Tokyo Olympic and Paralympic Games, postponed for the COVID-19 pandemic, were finally held in the summer of 2021. 4Division of Health Medical Intelligence, Human Genome Center, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan.3Laboratory of Sequence Analysis, Human Genome Center, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan.Watson Research Center, Yorktown Heights, NY, United States Takahiko Koyama 1*, Reitaro Tokumasu 2, Kotoe Katayama 3, Ayumu Saito 4, Michiharu Kudo 2 and Seiya Imoto 3,4

Imoto boards