Japanese researchers estimate that more than 30 percent of the coronavirus infections in Tokyo and its surrounding areas are caused by the highly contagious Delta variant.
Scientists at the National Institute of Infectious Diseases said at a meeting of the health ministry's expert panel on Wednesday that they made the estimate based on results from screenings for coronavirus variants.
The screenings use samples from people who tested positive to detect the variant. The L452R mutation was first observed in India.
The researchers say the number of samples containing the Delta variant began to increase in mid-June in Tokyo and the surrounding prefectures of Saitama, Chiba, and Kanagawa. They say the variant is estimated to account for 34 percent of all infections in the areas.
The scientists also estimate that the ratio will likely rise above 75 percent by the end of July, and that the variant will account for nearly all cases in August.
In three western prefectures -- Osaka, Kyoto, and Hyogo -- the variant is estimated to account for 12 percent of all cases, much lower than the figure in the Tokyo area. But the researchers warn that the variant has possibly been replacing the original strain as the rate has gradually increased.
They also estimate that the Delta variant is 1.4 times more transmissible than the Alpha variant, which was first detected in Britain.
The health ministry's panel has stressed the need to strengthen nationwide monitoring of the Delta variant and prevent it from spreading further by conducting screenings thoroughly.