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Highly contagious coronavirus variant accounted for 75% of infections in Tokyo in early May

The Tokyo Metropolitan Government building (Mainichi/Makoto Ogawa)

TOKYO -- The highly contagious coronavirus variant known as N501Y accounted for some 75% of infections in Tokyo in early May, the Tokyo Metropolitan Government revealed on May 20 during its monitoring meeting analyzing infection trends in the capital.

    Experts take the view that the variant is now the dominant source of infections, replacing the original strain.

    While the flow of people is decreasing in Tokyo, the number of infections remains high. Experts at the metropolitan government think it will take time before the number of infections drops due to the spread of the variant, which is said to be highly transmissible.

    According to the metropolitan government, the N501Y variant accounted for 30% of infections in Tokyo between April 5 and 11 in screening tests by organizations including the Tokyo Metropolitan Institute of Public Health and private institutions. However, the ratio surged to 74.9% between May 3 and 9.

    According to the survey by the Tokyo Metropolitan Institute of Medical Science, meanwhile, the number of people in downtown areas in Tokyo during the "Golden Week" holidays from late April to early May was up to 40% lower in the daytime (from noon to 6 p.m.) and up to about 50% lower at night (from 6 p.m. to midnight), compared to before April 25 when the state of emergency was issued. But the daily number of new infections remains high, with 843 registered in Tokyo on May 20.

    According to Atsushi Nishida, director at the institute's Research Center for Social Science & Medicine, it took five weeks in Osaka Prefecture, where N501Y infections earlier spread, for the number of cases to drastically fall after the flow of people was reduced at the end of March. Nishida pointed out, "It takes a long time from when the flow of people is restricted to see a decline in the number of infections caused by the variant." As the flow of people in Tokyo began to decline in late April, multiple experts believe it will take more time before infections in Tokyo will fall.

    The number of people going out in Tokyo, however, turned upward after the Golden Week holidays. Mitsuo Kaku, head of an expert board at the Tokyo Center for Infectious Disease Control and Prevention, commented: "There is a possibility that the medical crunch will become harsher during the lag (between the fall in people's activity in society and the actual decline in the number of infections). To prevent the spread of infections, it is very important to keep urging restraints on the flow of people."

    (Japanese original by Shinji Kurokawa and Asako Takeuchi, Tokyo City News Department)

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