N501Y mutation accounts for 73% of new infections in Japan

A random sampling survey was conducted on 14,751 cases around the country during the week through May 2. A total of 10,780 patients, or 73%, were positive for the N501Y mutation, which is considered to be highly contagious.

The N501Y mutation was found in more than 70% of newly infected COVID-19 patients in 27 prefectures, but was confirmed in fewer than 50% of patients in 11 prefectures, mainly in the Tohoku region and the northern part of the Kanto region.

The N501Y mutation is replacing the original virus nationwide, said a COVID-19 advisory board of the Health, Labor and Welfare Ministry.

An estimate by the National Institute of Infectious Diseases on the risk of the N501Y mutation was presented at a Wednesday meeting of the advisory board. It said patients infected with the mutant virus are estimated to be at 40% greater risk of severe symptoms than those infected with the original virus. Among those aged 40-64, the risk was said to be 66% greater.

“The medical care system must be strengthened, given the possibility that the risk of severe disease due to the mutant virus is increasing,” the board said.

Infections have almost stopped rising or have leveled off, and are not spreading nationwide, according to the board. However, there are large regional differences. New cases continue to increase in prefectures such as Aichi and Fukuoka, which were recently added to the ongoing state of emergency, and the burden on the medical system is increasing.

■ Surge in Indian variant

Also Wednesday, the National Institute of Infectious Diseases raised the alert level for another variant, known as the Indian variant, to the same level as the N501Y mutation, which includes the British variant. The Indian variant is believed to be responsible for the outbreak in India. It is said to be more contagious than the original form of the virus and may reduce the effectiveness of vaccines and drugs.

The health ministry plans to strengthen its nationwide monitoring system by starting a random sampling survey for the Indian variant.

As of Monday, 66 Indian variant cases had been found at airports, and four elsewhere in the country, Health, Labor and Welfare Minister Norihisa Tamura told a House of Representatives committee on Wednesday. The number has tripled in the two weeks since April 26, when 20 people had been confirmed to be infected with the Indian variant at airports and one person elsewhere in the country.