Three mutant strains of coronavirus have been causing concern among leading virologists. Known as XD, XE and XF, each so-called "recombinant" is being closely monitored for its severity and spread across Europe.
In the UK, coronavirus infection rates have been increasing for more than a week, and one of the main reasons behind this spike is thought to be the emergence of more sub-variants. In Wales the number of daily cases being reported is on the rise and has now reached close to 300 cases per 100,000 population, but it remains to be seen what is causing the increase here.
Imperial College of London virologist Tom Peacock has produced a useful twitter thread on these new lineages and how concerned the public should be about each one. Here, we look at his analysis in more detail.
Read more: What latest lateral flow tests results are telling us about the spread of Covid in Wales
What is a recombinant?
First of all, it's useful to understand some of the language Tom Peacock uses in his thread. A recombinant virus occurs when more than one variant of Covid infects and replicates in the same person, in the same cells. In other words, if someone is infected with both Delta and Omicron at the same time, for example, a hybrid is created.
"When two related viruses infect the same cell (ie. during a co-infection) the viral replication machinery can accidentally switch from one genome to the other resulting in a mixed genome - this is viral recombination," Tom said. He explained there was a reason why more recombinants were being identified now than at any other point during the pandemic.
"SARS2 has been doing this all of the way through the pandemic - however, it's only easy to see when the two parental viruses are distantly related. Therefore the reason we are seeing lots of recombinants is, until recently, we had lots of genetically distinct viruses circulating - Delta, BA.1 and BA.2. When recombinants occur between these lineages it is possible to identify, even if the switched part of the genome is small. The other reason we are seeing a lot now is because when BA.1 [Omicron] took off (at least in Europe and the USA) there were very high levels of Delta already circulating, therefore there were lots of opportunities to co-infect, recombine and transmit onwards."
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What is the XD lineage?
The XD lineage is the name given to the combination of French Delta and Omicron BA.1, more commonly known as Deltacron in the media. Experts say the "backbone" of Deltacron is derived from Delta, but its spike protein - which allows the virus to gain entry to human cells - originates from Omicron.
Dr Meng Khaw, national director for health protection and screening services at Public Health Wales, said there were currently no reported cases of this mutant sub-variant in Wales. However, he said he expected to see cases "eventually".
"There is no evidence of vaccine escape issues relating to Deltacron, and the best thing you can do to protect yourself against this and other variants is to take up the offer of coronavirus vaccine. You can also protect yourself and others by maintaining a social distance where possible, washing hands regularly, keeping homes well-ventilated, using a face covering, and working from home if you can."
What is the XE lineage?
Sequenced and verified by the UK Health Security Agency and Wellcome Sanger Institute, XE is the combination of BA.1, what we know to be Omicron, and the highly-transmissible BA.2, which has been frequently described in the media as 'Stealth Omicron'.
Experts claim the BA.2 sub-variant may have the ability to dodge tracking. According to the UKHSA, Covid's Omicron variant contains a genetic deletion in the "S" spike gene that makes it easier to track. However, in the stealth Omicron, there is no such gene drop out which makes it harder to detect.
What is the XF lineage?
Another form of Deltacron, XF is a UK Delta and BA.1 lineage which was once again sequenced and verified by the UK Health Security Agency and Wellcome Sanger Institute.
"So how concerned should we be about these (and other) recombinants? Recombinants that contain the spike and structural proteins from a single virus (like XE or XF) are fairly likely to act similarly to their parental virus. XD is maybe a little more concerning. It has been found in Germany, Netherlands and Denmark and it contains the structural proteins from Delta - if any of these recombinants were to act much differently than its parent it might be XD."
He concluded: "All these recombinants (including the smaller clusters that have not been assigned) should clearly be closely monitored for signs of growth and attempts should be made to isolate and characterise where possible."
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