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Omicron BA.5 strain may be highly pathogenic: Japan univ. research team

The Yasuda Auditorium of the University of Tokyo is seen in Bunkyo Ward, Tokyo, on June 15, 2021. (Mainichi/Kimitaka Takeichi)

TOKYO -- A research team led by the University of Tokyo expressed its view that the coronavirus's omicron subvariant BA.5 spreading across Japan "tends to proliferate more in the lungs than the BA.2 strain, which is currently mainstream, and may be highly pathogenic as well as infectious, based on experiments using human cells and animals."

    According to sources including the preprint version of the paper published by the research team in May, it was confirmed in an experiment using epithelial cells of "alveoli" inside the human lung that the BA.5 subvariant increased 18.3 times more than BA.2 strain.

    In another experiment using hamsters, the amount of ribonucleic acid (RNA) derived from BA.5 in the "periphery" in the deep part of the lungs increased 5.7 times compared to that of BA.2 three days after the animals were infected.

    Hamsters infected with BA.5 lost significantly more weight than those infected with BA.2, and more were found to have developed alveolar damage and bronchitis. In humans, as BA.2 proliferates in the respiratory tract and rarely reaches the lungs, it is believed to be unlikely for symptoms to become severe. However, the experiment found that BA.5 may easily increase in the lungs,

    Meanwhile, the World Health Organization announced in a weekly report dated June 22 that there is no information that the susceptibility to severe COVID-19 from BA.5 has changed.

    Kei Sato, one of the researchers and a professor of system virology at the University of Tokyo's Institute of Medical Science, said, "We experimented with non-immune hamsters, so we don't know if the same thing will happen with immunized humans."

    However, as the nature of BA.5 has changed from that of BA.2, he explained, "People without immunity can develop severe symptoms. There are places that have relaxed (anti-infection measures) thinking the omicron variant does not cause serious symptoms, but it is necessary to once again review anti-infection measures."

    (Japanese original by Mayumi Nobuta, Science & Environment News Department)

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