New COVID-19 Variant XE Is A 'Recombinant' Strain: What Does That Mean?

Cases of a new COVID-19 variant first detected at the start of the year continue to be reported across the globe, but health officials claim there is still not enough evidence to conclude whether or not it is more transmissible or severe than other variants.

Omicron XE, which was first identified in the U.K. in January, has been detected in Japan, the Japanese health ministry announced Monday, according to a CNBC report.

The variant was found in an asymptomatic woman in her 30s who arrived at Narita International Airport from the U.S. on March 26. Her nationality was not disclosed.

Aside from Japan and the U.K., the latter of which has reported around 1,125 XE cases as of April 5, the variant has also been detected in Thailand, India and Israel. A handful of cases have also been reported in the U.S.

XE is a recombinant variant of Omicron's original BA.1 strain and its so-called "stealth" strain, BA.2, the U.K. Health Security Agency (UKHSA) said in its latest COVID-19 variants report.

"A recombinant variant occurs when an individual becomes infected with 2 or more variants at the same time, resulting in a mixing of their genetic material within the patient’s body," the agency explained.

Recombinants "are not an unusual occurrence" and "several have been identified over the course of the pandemic," according to UKHSA's chief medical advisor, Dr. Susan Hopkins.

"As with other kinds of variant, most will die off relatively quickly," the doctor said.

XE's growth rate surpassed that of BA.2 by up to 20.9%, but the former made up less than 1% of total sequenced cases in England, while the latter accounted for 93.7% of cases, according to the UKHSA.

"This particular recombinant, XE, has shown a variable growth rate and we cannot yet confirm whether it has a true growth advantage. So far there is not enough evidence to draw conclusions about transmissibility, severity or vaccine effectiveness," Hopkins noted.

The UKHSA "will continue to monitor the situation closely," she said.

The World Health Organization, for its part, will continue to study recombinants and provide updates as further evidence becomes available.

Epidemiologists in the U.S. are currently not monitoring XE, and it has not been labeled either as a "variant of interest" or "variant of concern," the Centers for Disease and Control Prevention said on its website.

Overall, the U.K. has reported a total of 21,679,280 COVID-19 cases and 188,991 virus-related deaths, publicly available government data showed.