The number of patients thought to be infected with the omicron BA.5 subvariant of the COVID-19 virus fell below 50% of all COVID-19 patients in Tokyo, indicating that BA.5 is being replaced by new omicron subvariants, according to materials released on Thursday by the Tokyo metropolitan government.
The omicron variant became the mainstream form in the seventh wave of infections in Japan in the summer of 2022.
As the new omicron subvariants are believed to have a high ability to evade immunity acquired via COVID-19 vaccines and other means, the Tokyo government is increasing its level of alert against them.
According to the Tokyo government, more than 90% of all COVID-19 patients in Tokyo were thought to be infected with BA.5 during a period from mid-July to early October in 2022. But the rate gradually decreased and lowered to 44.9% during the week of Dec. 20-26.
In contrast, the rate of patients thought to be infected with new omicron subvariants gradually increased during the same week, with 22% of patients thought to have the BF.7 subvariant, while 9.3% had the BA.2.75 subvariant and 8.4% had BQ.1.1.
A nationwide estimate by the National Institute of Infectious Diseases last year showed that the rate of patients thought to be infected with BA.5 had decreased to 50% as of Dec. 20, suggesting that BA.5 could gradually be replaced by new omicron subvariants, such as BA.2.75 and BQ.1.
It has been noted that BQ.1 in particular has a high ability to evade the immune system's defenses.
More than 30 million
The cumulative total of people infected with the novel coronavirus in Japan topped 30 million on Friday, according to a tally compiled by The Yomiuri Shimbun.
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