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Even with vaccine, coronavirus variant spread may spiral out of control: Japanese expert

The main building at University of Tsukuba is seen in Tsukuba, Ibaraki Prefecture, in this March 26, 2020 file photo. (Mainichi/Takuya Yoshida)

TOKYO -- If coronavirus variants continue spreading, Tokyo infection numbers could outstrip previous surges even with vaccinations being administered, according to estimates by a disease modeling specialist at Japan's University of Tsukuba.

    "In addition to strengthening monitoring of the variant strains, people need to keep up anti-infection measures such as avoiding the 'three Cs' (confined spaces, crowded places and close contact settings), especially in the Tokyo metropolitan area," professor Setsuya Kurahashi told the Mainichi Shimbun.

    Virus variants are produced when, as a virus multiplies, its genetic code mutates. The frequency of these changes depends on the scale of an outbreak, and the coronavirus is thought to mutate about once every two weeks on average.

    Global authorities are at present primarily on alert for three variants, one each originating in Britain, South Africa, and Brazil. All three have an "N501Y" alteration to the 501 amino acids that make up the "spike proteins" on the virus's outer wall, which allow it to infect a host's cells. They are all also thought to be more infectious than the original version. The South African and Brazilian variants also have a change called "E484K," which some experts have said could reduce the immune response's efficacy against infection.

    If infections with these variants spread, what will happen? To shed some light on this question, professor Kurahashi ran estimates of changes in new daily case figures for the British and South African variants in Tokyo, taking inoculations into account.

    For the simulation, Kurahashi set the R rate -- the reproduction rate, or how many more people get the virus from one infected person -- at the same pace as seen from June 1, 2020 onward, after Japan's first coronavirus state of emergency was lifted. He also assumed Tokyo's population would move around at the same increased rate seen in the post-emergency declaration period.

    The simulation starts with 10 confirmed coronavirus variant cases in the Japanese capital as of March 21 this year. It also has limited vaccinations for regular people starting in March -- though in fact only medical workers were getting the shots at the time -- and inoculations for people of all ages beginning in June onwards, with around 70,000 people getting the vaccine each day. The simulation assumes 95% of those who get both vaccine shots will not be infected.

    Under the simulation for the British variant, Tokyo's overall coronavirus case numbers begin to increase from June, hitting more than 1,000 daily infections from just the variant in early September.

    For the South African variant, the simulation assumed the vaccine's efficacy would drop by half. In that scenario, daily infection numbers top 1,000 in early August, and continue to increase steadily after that. If the infection expanded continuously in the same way as the original coronavirus, numbers would be even higher.

    "If the variants spread, case numbers could rise at an accelerating pace," said Kurahashi. "Even with the vaccine, without severe measures like restricting people from going out, it may become difficult to get infections under control."

    (Japanese original by Ayumu Iwasaki, Science & Environment News Department)

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