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Disease experts wary after discovery of virus mutation in Japan in Dec. 2020

The Toyama Building that houses the National Institute of Infectious Diseases is seen in Shinjuku Ward, Tokyo, in this file photo. (Mainichi/Kazuo Motohashi)

TOKYO -- Following the discovery of a number of coronavirus strains in Japan including a mutation of unknown origin, a sense of caution is growing among infectious disease experts concerning the variants, some of which could be more infectious or weaken the body's immune response.

    On Feb. 19, the National Institute of Infectious Diseases announced that a separate mutant strain of unknown origin had already been confirmed to be in Japan at the start of December 2020. The government is entrusting genome analysis of the strain to a private testing firm, to help strengthen its surveillance system. One expert asserted, "We probably won't be able to avoid the spread of variant strains."

    Minister of Health, Labor and Welfare Norihisa Tamura emphasized at a Feb. 19 press conference, "We're seeing the number of screening areas in this country increase, allowing us to get a grasp of the actual situation gradually." Around 60 regional public health institutes in prefectures including Saitama, Shizuoka and Niigata are using polymerase chain reaction (PCR) tests that can easily detect the mutations of the coronavirus from the U.K. and South Africa.

    Between 5 and 10% of positive tests are being screened as potential mutant strains. Samples that have a high chance of containing mutations are dispatched to the National Institute for Infectious Diseases, where it has become possible to analyze them genetically.

    The government is also going ahead with efforts to entrust a private testing firm with genetic analysis. At the national institute, it's possible to investigate about 550 samples per week. For the time being, officials plan to have the private firm analyze between 100 to 200 samples weekly, which will hopefully speed up efforts to identify the strains.

    As of Feb. 19, 173 people in Japan had been infected with mutant strains of the coronavirus. Excluding cases found in airport quarantine, the figure stands at 130. Among that subset, 124 have the U.K. strain, four have the South African one, and two have the Brazilian variant.

    But it has emerged that another strain which may be capable of weakening the body's immune response had been spreading in Japan even before the government improved its monitoring system. The infectious disease institute announced that this variant, which differs from the three mutant strains from the U.K. and elsewhere, was found in a sample collected at the beginning of December 2020.

    Although it is dissimilar from the U.K. strain in that it's not thought to be more infectious, it has reportedly achieved a mutation which can possibly weaken the immune response to it. It appears to have entered Japan from abroad, but the variant's country of origin is unknown. By Feb. 2, 91 infections of this strain had been confirmed across east Japan's Kanto region, and two were found in airport quarantine.

    A specialist on an expert panel advising the Ministry of Health, Labor and Welfare on infectious disease prevention measures, commented, "It's been pointed out that variant strains with greater infectivity may be able to infect children more easily. We won't be able to avoid mutations spreading, and in future it's also possible the virus spreading around this country could be replaced by a mutation."

    The specialist added, "We must sufficiently heed the newly found variant, which could weaken the immune response."

    (Japanese original by Naomi Hayashi and Sooryeon Kim, Lifestyle and Medical News Department)

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