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90% of Tokyo mid-April COVID-19 infections from mutant strains: gov't data

This Oct. 17, 2018 file photo taken from a Mainichi Shimbun helicopter shows Tokyo Skytree in the capital's Sumida Ward. (Mainichi)

TOKYO -- Ninety percent of new coronavirus cases recorded mid-April in the capital were variant infections, according to Tokyo Metropolitan Government estimates revealed during its April 22 monitoring conference.

    While COVID-19 cases from original coronavirus strain infections accounted for 50% to 60% of the February total, by mid-April its share had fallen to around 10%. Conversely, the proportion of infections with the N501Y coronavirus variant, which is thought to be highly transmissible, has seen a sudden increase, leading the metropolitan government to raise the alarm that mutant variants appear to be rapidly replacing original virus strains.

    The analysis is based on results from Tokyo Metropolitan Institute of Public Health screenings. Between Feb. 15 and 21, 58% of infections screened were identified as from the original strain, while 42% were from E484K virus variant infections, which is feared to reduce the efficacy of immune responses and vaccines. Two months later, between April 12 to 18, original strain cases had fallen to 10.7%, while E484K variant infection cases were at mostly the same level of 56.5%, and N501Y mutant strain cases, which weren't detected in February, had risen sharply to 32.8%.

    A Tokyo government estimate also showed that if all virus strains in the capital were replaced with the N501Y variant and the daily tally of coronavirus cases in Tokyo were at 700, then infections would increase by 1.7 times, meaning that in two weeks infection numbers would outstrip 2,000.

    It is also estimated that hospitalized patients would surpass 6,000, leading to even more strain on the health care system; a situation that risks grave consequences for regular medical services, too.

    Mitsuo Kaku, chairman of the expert board at the Tokyo iCDC committee, which works to improve coronavirus countermeasures, said, "Considering the threat from the N501Y strain, we must keep our guard up and going forward closely watch the movements of mutant strains."

    (Japanese original by Toshiki Koseki and Shinji Kurokawa, Tokyo City News Department)

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