The health ministry announced Monday that Japan had for the first time detected the XE “recombinant variant” of the omicron strain of the coronavirus during a routine check at an airport.

The XE variant was detected in a woman in her 30s who arrived at Narita Airport from the United States on March 26. The woman, whose nationality was not immediately identified, was asymptomatic, the ministry said.

The woman had received two shots of vaccine developed by Pfizer Inc., but she tested positive on arrival for the virus. The XE strain was detected through genetic sequencing tests taken using samples from the woman at the National Institute of Infectious Diseases.