Virus, Mutation, Variant: These words are ubiquitous in our daily lives since 2020 and the COVID-19 pandemic. However, the mechanisms linking these three concepts are not always easy to understand. science and the future Explains the mutation process of a virus and the presence of variants.

DNA and RNA: the genetic material of viruses

First you should know that like living beings, viruses contain genetic material (DNA or RNA). The full name of DNA is deoxyribonucleic acid (you probably had to remember it in SVT). It is a molecule carrying genetic information (genome), it is present in the nucleus of almost all cells, as well as in many viruses.

This molecule is essential for the functioning, growth and reproduction of living beings. As a genetic code, DNA enables protein synthesis via messenger RNA. In fact, the RNA (ribonucleic acid) molecule copies and delivers the DNA’s genetic message outside the cell’s nucleus to allow the creation of proteins necessary for the functioning of our cells. Ribonucleic acid takes its name from the ribose (sugar) and nucleotides (adenine, cytosine, guanine, uracil) that make up it.

When the virus replicates, it can be subject to modifications: these are mutations. When genetic material is exchanged between multiple viruses, we have to do what we call recombination. As specified by the WHO, a variant is therefore a virus that contains one or more new mutations of the initial virus..

Mutation: Essential for the survival of the virus

Since viruses multiply rapidly and in large numbers, they have a greater capacity than cellular organisms to produce mutations in a short period of time. In addition, RNA viruses, such as coronaviruses, are more likely to mutate than DNA viruses. “This is because when they multiply they replicate their genome, a process that generates errors.“, says Inserm. As for SARS-CoV-2, the virus that causes COVID-19, it is rather stable because it contains an enzyme called “exoribonuclease” that corrects these errors, Inserm adds.. Thus it mutates more slowly than other viruses such as HIV or the influenza virus.

The survival of these viruses depends on these mutations, they are what will allow microbes to adapt to their environment, ie the different hosts that they infect, to AFP Vincent Anouf, deputy head of the National Reference Center Explained. For Respiratory Viruses (Institut Pasteur). “Often without consequences, these mutations can give the virus an advantage or even a disadvantage for its survival.This is the principle of natural selection, that is, to say that the organism will be able to survive best adapted to its new environment.

Thus some mutations may allow the virus to replicate more quickly, attack the body more severely, or infect new organs (for example by infecting the lungs and not just the upper airways). In the influenza virus, mutation of a gene that controls the production of proteins on its surface may also allow it to more easily attach to the cells it is infected.

mutation, this area of ​​uncertainties

SARS-CoV-2, on the other hand, belongs to the coronavirus (CoV) family. Its name comes from the protein (spike) it sports and which forms a kind of crown. It is through these skip proteins that it succeeds in infecting humans: in fact, they are completely homing to the Ace2 receptors present on our cells. If we stick to the theory of zoonosis (transmission of virus from animals to humans), the coronavirus would have infected an animal first, so a route to humans was probably first facilitated by genetic modifications, which allowed it to By whom could he be recognized? Human Ace2 receptors.

Once the inter-species barrier is crossed, the virus often requires new mutations to adapt to its new host, allowing it to reach full infection potential. The risk is that it becomes more virulent and spreads more easily from person to person.

Certain mutations can also reduce the effectiveness of a vaccine: this is the case if the strain for which it was designed has evolved in the meantime. Without this, “They can also alter the characteristics of the virus, such as altered transmission (for example, it can spread more easily), or its severity (for example, it can cause a more severe form of the disease.), explains WHO. Similarly, “The more viruses that are circulating, the more they can change“, says WHO. Thus, mutations are difficult to predict because the resulting variants are.