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The first case in Japan involving a new mutation of the highly contagious delta variant of the coronavirus — of which only eight cases have been reported so far worldwide — has been confirmed, according to researchers.

A research team from the Tokyo Medical and Dental University, headed by associate professor Hiroaki Takeuchi, announced Monday in a statement that the first case of this delta variant sublineage was confirmed in a COVID-19 patient in mid-August.

Based on genome analysis, “it is highly likely the latest case mutated domestically,” the researchers said, adding that the patient had no history of traveling abroad.

The latest case contains the N501S mutation, which is similar to the mutation in the alpha variant known as N501Y that was first identified in Britain last year. At least a dozen submutations of the delta variant have been confirmed worldwide so far, in countries such as India and Israel, according to media reports.

When a patient is infected with a coronavirus variant carrying the N501Y mutation, they have a higher risk of secondary infection as well as of developing severe symptoms and dying. Due to the similarities between N501Y and N501S, researchers believe patients infected with N501S could face a similar prognosis.

More research is needed to confirm how potent the new mutation is compared with the original delta variant, they said.

The mutation was confirmed through genome analysis collected from COVID-19 patients treated at the Tokyo Medical and Dental University.

The analysis also showed that patients with the delta variant rapidly increased between late June and late July due to community spread.

Commuters arrive at Shinagawa Station in Tokyo on Aug. 2. | REUTERS
Commuters arrive at Shinagawa Station in Tokyo on Aug. 2. | REUTERS

Currently, the delta variant is growing dominant in Japan. According to the health ministry’s latest data, 1,046 new cases of the delta variant were found in 17,701 COVID-19 cases picked for variant screening in the week from Aug. 16.

Separately, the researchers have also concluded that at least two sublineages of the delta variant — AY.4 and B.1.617.2 — may have existed in Japan in July. But now, they only detect the B.1.617.2 strain of the delta variant.

The first infection with the delta variant in Japan was found on April 20. Delta has been classified as one of four variants of concern by the World Health Organization, and it has quickly outpaced other versions in some parts of Japan — it is now estimated to account for 95% of all cases in Tokyo.

With the delta variant making up a growing share of cases in Japan, the number of patients age 19 and younger is on the rise, a health ministry panel on the coronavirus said last week, calling for schools to take appropriate measures to prevent the spread of infections.

The U.S. Centers for Disease Control and Prevention believes the delta variant is as transmissible as chickenpox and about twice as contagious as previous variants.

The study was jointly conducted by virology and infectious diseases experts from the Graduate School of Medical and Dental Sciences affiliated with the Tokyo Medical and Dental University, the Laboratory of Genome Analysis at the Research Institute for Intractable Diseases and the Tohoku University Hospital.

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