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Is XE a new variant of the coronavirus? Britain’s health security agency calls it a recombinant lineage of Omicron strains of coronavirus. Omicron is a variant of the coronavirus SAR-CoV-2. That makes XE a subvariant.

Scientists say XE combines Omicron BA.1 and BA.2 sublineages. And it has been found in Britain since January 19. A similar recombinant strain was reported in March from several countries, including Israel, Thailand, Hong Kong, Cambodia, and India. Researchers in Hong Kong referred to it as the “BA.2.2” variant, although the name was not official. Both are combinations of Omicron variants BA.1 (the original Omicron) and BA.2 (Stealth Omicron) but XE is of X lineage.

The variants keep coming. Already we have XA, XB, XC, XD, XE, XF, XG, XH, XI, XJ, XK, XL and many more will come. That’s the nature of viruses and mutation.

Here’s what we know about XE and other recombinant strains.

What are the new variants reported from Britain?

The new variants reported are hybrid or recombinant viruses because they are combinations of existing strains. These are not mutated strains from a single variant.

Three recombinant viruses detected by the United Kingdom Health Security Agency are XD, XE and XF; virologists say they stem from the X lineage. (A lineage is a group of closely related viruses with a common ancestor. SARS-CoV-2 has many lineages; all of them cause COVID-19, according to the US Centers for Disease Control and Prevention).

XD and XF are combinations of Delta and Omicron variants. An earlier report of a similar variant, dubbed Deltacron, was dismissed by scientists as possible lab contamination. However, XD and XF are said to be genuine subvariants. XD refers to the hybrid of Delta and BA.1 lineage of Omicron.

XE is a combination of Omicron variants BA.1 and BA.2. A similar strain was reported more than a fortnight back in some countries, including Israel, Thailand, Hong Kong, Cambodia, and India. It was unofficially called BA.2.2, but XE is of X lineage, as the name indicates.

How does a recombinant variant occur?

A recombinant strain emerges when a person is infected with two or more variants at the same time. It leads to the mixing of genetic material during replication, and a new strain is created within the patient’s body, a paper published in British Medical Journal said.

Susan Hopkins, Britain’s chief medical adviser, said: “Recombinant variants are not an unusual occurrence, particularly when there are several variants in circulation, and several have been identified over the course of the pandemic to date. As with other kinds of variants, most will die off relatively quickly.”

What is the XE strain?

XE is a “recombinant”, a mutation of Omicron strains BA.1 and BA.2

“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,” UKHSA’s Hopkins said.

Where are the XE cases found?

Almost 800 cases of the XE variant (BA.1 + BA.2) have been identified in Britain. A UKHSA report said 763 cases have been reported across the country as of March 22. Out of that, 637 were detected in England: most cases were in the east of England, south-east of England and London.

The first case of Omicron XE in Thailand was reported Saturday by the Centre for Medical Genomics, Ramathibodi Hospital in Bangkok.

Is the XE variant more transmissible?

There’s no concrete evidence that XE is highly infectious, but preliminary studies indicate it’s more transmissible than BA.2 subvariant of Omicron.

The new mutant XE appears to be 10 per cent more transmissible than the BA.2, the World Health Organisation said. “Early-day estimates indicate a community growth rate advantage of 10 per cent compared to BA.2, however, this finding requires further confirmation,” the global health body added.

Britain’s health agency said they arrived at a conclusion that the XE is 9.8 per cent more transmissible, adding that more data is needed before a concrete estimate about its spread can be released.

What are the symptoms of an infection caused by XE?

No severe symptoms have been reported. An XE infection tends to start with fatigue and sometimes dizziness, followed by headaches, sore throat, and fever. Although loss of smell and taste haven’t been reported, diarrhoea, nausea, vomiting and stomach ache are common.

Should we be worried?

Not really. Around 650 XE cases in three months don’t indicate high transmissibility, particularly since they are confined to Britain. But the XD strain is a cause for worry. As virologist Tom Peacock tweeted, the presence of Delta in the hybrid and its discovery in other countries call for caution.

What the experts say

John Brownstein, an epidemiologist and chief innovation officer at Boston Children’s Hospital, told ABC News: “Right now, there’s really no public health concern. Recombinant variants happen over and over. In fact, the reason that this is the XE variant recombinant is that we’ve had XA, XB, XC, XD already, and none of those has turned out to be any real concern.”

Rakesh Mishra, director of the Tata Institute for Genetics and Society in India, told news agency ANI: “The new mutant XE emerged for the first time in mid-January, but I believe that there is no need to push a ‘panic button’. So far, only 600 cases have been reported across the world. But we need to keep a close watch on it.”

Hopkins told The Sun: “As with other kinds of variant, most will die off relatively quickly. This particular recombinant, XE, has shown a variable growth rate and we cannot confirm yet confirm whether it has a true growth advantage.”

Will the vaccines work against XE?

Generally, all COVID vaccines have helped reduce the severity of infections and prevented hospitalisations and deaths except in people with underlying health conditions. That should hold true for XE too.

“So far, there is not enough evidence to draw conclusions about transmissibility, severity or vaccine effectiveness,” Hopkins said.

What is the XF variant, and where is it found?

The XF strain is a hybrid of Delta and Omicron variants. The UK health agency said that XF caused a small cluster in Britain, but only 39 sequences have been detected. The strain hasn’t been found outside the United Kingdom.

The first case of XF was registered on January 7, and no XF samples have been found since February 14, the agency said, adding that the strain is unlikely to trigger sustained community growth.

What’s the XD strain, where has it spread?

XD, also a recombinant of Delta and Omicron variants, was mostly reported from France, Denmark, Germany, Netherlands and Belgium. It was first detected in December, and by March 22, 49 samples had been found in these countries.

The spread of XD to several countries, and its inclusion of the more severe Delta make it a strain to watch out for, according to virologist Tom Peacock from Imperial College London.

“The concern would be if there are non-structural changes in Delta that contribute to severity and/or cell replication,” he tweeted.

What are the other strains in X lineage?

Here are the latest coronavirus strains of X lineage, according to

■ XG — Potential BA.1-BA.2 lineage with 140 new sequence designations. (107 sequences in Denmark, UK, US and Germany as of March 2).

XH — Potential BA.1-BA.2 recombinant of new lineage with 42 new sequence designations. (43 sequences in Denmark).

XJ — New BA.1-BA.2 recombinant lineage with 17 new sequence designations found in Finland (66 sequences as of March 25).

XK — Potential recombined BA.2-BA.1.1 new lineage with 15 new sequence designations. (1.4% sequences in Roeselare, Belgium).

XL — Potential BA.1-BA.2 recombinant new lineage with 38 new sequence designations. (38 sequences in Britain as of March 16).

What are the new variants in China?

China, which has been experiencing its biggest COVID outbreak since Wuhan, reported two Omicron subvariants vastly different from the existing strains in the international database GISAID.

One infection with a BA.1 subvariant was reported from the eastern Chinese city Suzhou, about 110 km from Shanghai. The other caused by a BA.2 subvariant was found in the northeastern city of Dalian.

Most of the infections in China and Hong Kong stem from existing variants, Bloomberg quoted Stephen Goldstein, a virologist from the University of Utah, United States. They don’t currently represent a global health threat, he added.