What's behind the rapid disappearance of the delta variant in Japan? It could be self-extinction.
BY OSAMU TSUKIMORI
STAFF WRITER
Nov 18, 2021
Why did Japan’s fifth and biggest wave of the coronavirus pandemic, driven by the supercontagious delta variant, suddenly come to an abrupt end following a seemingly relentless rise in new infections? And what made Japan different from other developed countries that are now seeing a fresh surge in new cases?
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Many scholars point to a variety of possibilities, which include one of the highest vaccination rates among advanced countries with 75.7% of residents fully vaccinated as of Wednesday. Other potential factors are the social distancing and mask-wearing measures that are now deeply embedded in Japanese society.
But the chief reason may be related to the genetic changes that the coronavirus undergoes during reproduction, at a pace of around two mutations per month. According to a potentially revolutionary theory proposed by Ituro Inoue, a professor at the National Institute of Genetics, the delta variant in Japan accumulated too many mutations to the virus’s error-correcting, non-structural protein called nsp14. As a result, the virus struggled to repair the errors in time, ultimately leading to “self-destruction.”
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“We were literally shocked to see the findings,” Inoue told The Japan Times. “The delta variant in Japan was highly transmissible and keeping other variants out. But as the mutations piled up, we believe it eventually became a faulty virus and it was unable to make copies of itself. Considering that the cases haven’t been increasing, we think that at some point during such mutations it headed straight toward its natural extinction.”
Inoue’s theory, while innovative, would lend support to the mysterious disappearance of the delta variant’s spread in Japan. While much of the rest of the world with similarly high vaccination rates, including South Korea and some Western countries, are suffering from record waves of new infections, Japan appears to be a peculiar case in that COVID-19 cases have remained subdued despite trains and restaurants filling up following the end of the most recent state of emergency.
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A similar natural extinction of the coronavirus could possibly be observed overseas, Inoue says, adding that detecting that would be difficult as no other country seems to have accumulated as many mutations in the virus’s nsp14 as in Japan, though similar mutations at the A394V site have been discovered in at least 24 countries.
But Inoue’s theory may also help explain why the outbreak of severe acute respiratory syndrome (SARS) ended abruptly in 2003. An in vitro experiment in which the researchers caused mutations in nsp14 in the virus that causes SARS led to findings that the virus eventually could not replicate itself as mutations piled up.
“No genome data exists, so it’s just a hypothesis, but because it has disappeared, it will never see the light of day again,” he said.
So what are the chances that we could see a similar natural extinction overseas of the COVID-19-causing SARS-CoV-2 virus?
“The chances are not zero, but that seems too optimistic for now as we’re unable to get hold of any such evidence, though we have looked at various data of other countries,” he said.
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https://www.japantimes.co.jp/news/2021/11/18/national/delta-variant-self-destruction-theory/