PANDÈMIA

All the colours of the coronavirus: mutations, strains and variants

Many experiments are still needed to find out how the new variants affect the pandemic

Most mutations experienced by the coronavirus have no effect, but those that vary capsule proteins can make it more dangerous. / GETTY

Since the week before Christmas, when UK Prime Minister Boris Johnson announced at a press conference that a new version of SARS-CoV-2 had become predominant in the south of England, one of the main concerns has been how these changes in the virus will affect the management of the pandemic. Do we have to fear a worsening of covid-19?

To answer this question we must first distinguish between variant and strain. Although these terms are sometimes used interchangeably because there is no clear enough definition, most experts reserve the qualification of strain to a microorganism that has changed its genome quite substantially from its original form to present its own functional characteristics and provoke a different immune response. The variant, on the other hand, would only have some divergences and would be considered a subtype of the same strain, with similar, but not necessarily identical behaviour. These genetic changes, both those leading to a variant and those leading to a strain, are produced by mutations, random alterations at one point in the virus genome.

Mutants by nature

All viruses mutate, but some mutate more often than others. The flu virus, for example, does so significantly each year. HIV is worse, because it mutates constantly, and this is one of the reasons why a vaccine to stop it has not yet been designed, even though it has been known for decades. At the other extreme is the measles virus, which is one of the most stable viruses (which is why a vaccine only needs to be given once in a lifetime). SARS-CoV-2 is not as stable, but it's also one of the relatively unchanging viruses. Many of the mutations it undergoes do not cause any other changes in the virus, and only occasionally does it result in a small variation in the proteins that make up the capsule. It is these substances that can alter its properties and make it more dangerous.

The new version of the coronavirus is considered to be a variant. It has been named VOC-202012/01 and belongs to the type B genetic lineage. 1. 1. 7. It is best to use these labels rather than calling it "the English variant", since it has been found in thirty-five countries so far (and may well be even more widespread). Moreover, there is still no certainty that it emerged in the UK: it was the first country to detect it (it was discovered on September 20), but this may simply be because it is one of the countries that does the most genetic studies.

This is not the first SARS-CoV-2 variant to be detected: thousands are known (grouped into five main families, called clades), and some had become prevalent before. For example, the one with the mutation called D614G, which was first seen in Europe in February and is now dominant worldwide. Or the variant known as 20a.eu1, which brings the A222V mutation and spread rapidly throughout Europe in summer after first appearing in Spain. However, there have not been any variations that are important enough for any of these variations to be called a strain.

The N501Y mutation

VOC-202012/01 has about twenty new mutations, but the main change is in the protein that allows the virus to bind to the human cells it invades. One of these mutations, N501Y, could make the virus attach more easily to its target (the ACE-2 protein), and therefore more infectious. But N501Y is not exclusive to this variant, since it has also been seen in the 501Y.V2 variant detected these days in South Africa (a country that, like the United Kingdom, is at a critical point in the pandemic's spread). This mutation has also been detected in some other variants that have been circulating for months in Australia, the United States and Brazil.

All the information we have about VOC-202012/01 is preliminary. Epidemiological data from the UK suggest that it is transmitted more rapidly (estimated to be 50% more effective at infecting, with a 0.4 point higher infection rate), but this has not yet been seen in any of the other countries where it has been detected. There may, therefore, be other explanations for the increased prevalence. In fact, other variants have become predominant in an area without necessarily increasing its infectivity, such as the Spanish 20a.eu1 itself. It will probably take months of experiments to know for sure.

What seems certain is that the new variant does not cause more serious cases or more mortality, it is easily detected by the available tests and recent analyses indicate that the antibodies generated by the vaccines being given would also recognise it (fortunately, if a variant never appeared that escaped the vaccines, it would only take a few weeks to readapt them and start producing new ones).

The only problem, then, would be this possible increase in infectivity, which, if confirmed, could complicate the management of this final phase of the pandemic, since more restrictive and longer-term measures would have to be applied in order to smooth out the infection curves in the places where VOC-202012/01 was dominant, and thus avoid the feared saturation of hospitals.

Salvador Macip is a researcher at the University of Leicester and at the UOC (Universitat Oberta de Catalunya)

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