Recently there has been talk of a new series of Sars-Cov-2 variants whose name begins with the letter X: XD, XE and XF. These variants are recombinants of other strains already described above.
A bit about recombinant variants
When viruses replicate, they sometimes make mistakes in their genetic code leading to individual mutations. Often, these mutations do not cause any change in the structure of the virus, which is called “silent mutations. Some mutations, however, can confer an advantage. For example, mutations that occur in the spike protein (the part of SARS-CoV-2 responsible for infecting our cells). They can make the virus more transmissible than the previous variants.
We have seen repeated mutations in the spike protein that produce worrying variants.
The recombination it is a different process, whereby two different variants infect the same cell, in the same person, at the same time. From there, they can combine their genetic material. Which results in a virus that has a mix of genes from both viruses. “parents” that infect. This recombinant variant can then spread to other people, as has been the case with Omicron XE.
Indeed, PANGOLIN (SARS-CoV-2 lineage surveillance carried out by the UK COVID-19 genetics consortium). It has identified multiple recombinant variants worldwide. At least three of these XD, XE and XFhave been detected in the UK.
Some recombinant variants, such as XD and XF, are combinations of the delta variant with lineages Omicron. You may have heard of these hybrids, which have been called “deltacron”. However, one of the XE variants is a combination of two omicron strains: BA.1 and BA.2.
Why are different variants combined?
Genetic recombination of viruses is not a new phenomenon. Occurs regularly with viruses like influenza and HIV. In fact, one of the proposed origins of the Wuhan virus SARS-CoV-2 original is a recombination event in bats.
The ECDC differentiates three levels to organize the progressive intensity of monitoring of new viral variants: variants in monitoring (XD and omicron BA.3), variants of interest (the omicron strains BA.4 and BA.5) and variants of concern (the delta variant and strains omicron BA.1 and BA.2). variants XE and XF they have not reached the level of relevance, for the time being, to be classified as variants under monitoring.
For its part, the World Health Organization also includes only the XD variant among those classified as follow-up.
WHAT AWAITS US?
We can define the virulence of a pathogen as the number of serious or very serious cases with respect to the total number of infected people. With due precautions, in general the virulence of pathogens It usually decreases with the time of coexistence with the host.
This can be explained because the reproductive success of a pathogen is greater the less damage caused to the host and, therefore, more can this transmit the pathogen. A dead dog does not transmit rabies.
For this, the less virulent variants they tend to spread better than others that limit or eliminate the mobility of the sick animal or person and, over time, tend to prevail in the community.
On the other hand, the immune system learns to deal with this virus by controlling its multiplication and modulating the response (which, in the case of coronavirus infection, is essential in the aggravation of the disease).
Therefore, and to conclude, we must expect that they will continue to emerge new variants of the coronavirus whose prevalence makes them jump to the press and the special surveillance of international organizations. But one can reasonably expect that these new variants will tend to be less virulent. Thus, the successive waves of the pandemic should be smoother and hospital response, if any, would not be significantly affected.
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