Photo/Illutration The health ministry building in Tokyo (Asahi Shimbun file photo)

A woman who arrived at Narita Airport from the United States was confirmed as Japan’s first infection case with the Omicron XE derivative strain of the novel coronavirus, the health ministry said April 11.

The woman in her 30s tested positive on arrival on March 26, and the XE strain was confirmed through genetic sequencing of her sample by the National Institute of Infectious Diseases (NIID), the ministry said.

The BA.2 subvariant of the Omicron strain has become the dominant source of COVID-19 in the recent increase in cases around Japan.

The XE strain, reported for the first time in Britain in January, spreads about 13 percent faster than BA.2, according to an early British study.

The woman showed no symptoms when she landed in Japan. She left an accommodation facility after completing the required self-isolation period for arrivals who test positive, according to the ministry.

She had previously received two shots of Pfizer Inc.’s vaccine.

“The speed of the spread of the XE strain appears to be faster quantitatively, but we should take into consideration various possibilities now,” said Tomoya Saito, director of the Center for Emergency Preparedness and Response of the NIID. “I think that we should be on alert for not only the XE strain but also other ones.”

England had reported 1,125 cases of the XE strain, less than 1 percent of all analyzed infectious cases, as of April 5.

The XE strain has also been confirmed in the United States, Denmark and other nations.

The XE strain is believed to be a genetic combination of the BA.1 and BA.2 subtypes of the Omicron variant.

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