The fifth wave of the Covid-19 pandemic in Japan has virtually disappeared so rapidly that some scientists are wondering how it happened. A research team estimates that the highly infectious Delta strain mutated to the point of extinction in the island nation, that is, it essentially self-destructed.
In mid-August, Japan peaked Covid-19 cases, recording more than 23,000 new cases a day. The count is now around 170, with deaths attributed to the disease remaining mostly single digits this month.
The decline has been attributed by many to high vaccination rates, public acceptance of mask use and other factors, but some researchers say the decline was unique, compared to other nations with similar cases.
Ituro Inoue, a geneticist at the National Institute of Genetics, believes that Japan was lucky enough to see the Delta strain mostly eradicate other variants of the SARS-CoV-2 virus before it disappears. He explained his team’s theory to the Japan Times this week. For some time now, Inoue and his colleagues have been researching mutations in SARS-CoV-2 and how they are affected by the nsp14 protein, which is vital for the virus to reproduce.
RNA viruses, such as the one that causes Covid-19, tend to have a very high rate of mutation, which helps them adapt quickly to changes in the environment. However, this opens the door to a so-called “error destruction” when bad mutations accumulate and eventually cause a strain to disappear completely.
Studies have shown that more people in Asia have a defense enzyme called APOBEC3A that attacks RNA viruses, including the SARS-CoV-2 virus that causes COVID-19, compared to people in Europe and Africa. Thus, researchers from the National Institute of Genetics and Niigata University studied how the APOBEC3A protein affects the nsp14 protein and whether it can inhibit coronavirus activity.
The nsp14 protein appears to provide a form of error correction that helps keep the virus genome below the threshold of “error destruction”. In the case of the fifth wave of Covid-19 in Japan, the nsp14 of the Delta variant failed in this task, Inoue believes, based on the genetic study of samples collected from June to October.
“We were literally shocked when we saw the findings,” the researcher told the Japan Times. “The Delta variant in Japan was extremely contagious [απέτρεπε] other variants. “But as the mutations accumulated, we believe he eventually became a defective virus and was unable to make copies of himself.”
japantimes.co.jp
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