Explained: How XE, XD and XF Recombinants of COVID-19 differ from each other? Is one more dangerous than the other?

The World Health Organization (WHO) recently warned against XE recombinant virus, stating that its rate of infection is about 10 percent higher than that of the BA.2 (sublineage of Omicron) variant.

A recent study by the UK Health Security Agency (UKHSA) had also confirmed the prevalence of three hybrid COVID-19 variants - first was XD, second XF and third was the XE variant.

Soumya Swaminathan, the Chief Scientist at the WHO recently took to twitter to state, "Recombinants are expected as #SARSCoV2 is widespread among humans and many animal species now. Testing, surveillance (including ILI & SARI), sequencing & data sharing still important to keep track of the pandemic & take early action when new variants emerge."

Also read: Coronavirus: India reports first case of new XE variant; what we know so far

A recombinant virus is a combination of two previously existing strains. It can be produced naturally or by combining pieces of DNA using recombinant DNA technology.

In case of the SARs-CoV-2 virus, the recombinant strain shares the genetic material of two strains, which in the case of currently circulating hybrid variants is Omicron and the Delta variant. Given that both the Delta and the Omicron were highly transmissible and concerning, experts around the world are keeping a close eye on the emerging recombinants.

The XE recombinant, which is a combination of BA.1 and BA.2 Omicron sublineage, was first detected in the UK on January 19 and less than 600 sequences have been reported and confirmed so far, as per the UK Health Security Agency report. It contains the spike and structural proteins from BA.2 but comprises a fifth of the genome of BA.1.

"Early-day estimates indicate a community growth rate advantage of 10% as compared to BA.2, however, this finding requires further confirmation," says the WHO.

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Susan Hopkins, Chief Medical Advisor, UK Health Security Agency says, "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."

The recombinant variants XD and XF share genetic material of the previous strains of Delta and BA.1 Omicron variant of COVID-19. Both contain several 10s of sequences currently. While XD has been detected in France, Denmark and Belgium, XF has been widely identified in the UK.

Initial reports by the UK Health Security Agency suggest the XE variant has a growth rate of 9.8 percent over that of BA.2 sublineage, which is said to have the ability to dodge tracking.

India reported its first case of XS in Maharashtra on Wednesday (6th April, 2022). Out of the 230 samples sent for genome sequencing, one was identified as the XE recombinant variant, while the one other as the Kappa variant. 228 samples were found to be the Omicron variant of COVID-19.

However, the Ministry of Health and Family Welfare (MoHFW) denied the claims. Health Ministry sources said, "FastQ files in respect of the sample, which is being said to be XE variant were analysed in detail by genomeic experts of insacog who have inferred that genomic constitution of this variant does not correlate with genomic picture of XE variant. Present evidence does not suggest that it is XE variant,"

Currently, experts have no confirmation on the severity of the hybrid variants. However, depending on one's vaccination status, established immunity and history of past infections, symptoms could vary from person to person.

The most common symptoms to look out for are fever, sore/scratchy throat, cough, runny nose, sneezing, fatigue, body pain, rashes and discoloration, gastrointestinal problems and in certain cases loss of sense of smell and taste, which was less prevalent during the Omicron wave.

Severe symptoms include shortness of breath, heart palpitations, chest pain, low blood oxygen levels. In light of these symptoms, call for medical assistance immediately.