Why it is “almost impossible” for a variant of the coronavirus capable of defeating vaccines to emerge

The accumulation of mutations detected in the omicron variant from coronavirus They are concerned about three aspects: that they make it more transmissible, that it produces a more serious disease or that it implies a loss of efficacy in vaccines. But this last point does not mean that omicron, if the worst omens are confirmed, will be able to completely evade the action of vaccines. Different voices have trusted in recent days that their protection against critical illness will remain robust. And, furthermore, the hypothesis that a new variant is able to evade them completely is “practically impossible”. These are the reasons:

The “arsenal” that vaccines create

The immune response generated by vaccines is much broader and stronger than is commonly believed. As reminds LD Marcos López Hoyos, president of the Spanish Society of Immunology, the vaccine stimulates on the one hand the production of antibodies. It is the humoral response, which can prevent infection. But, in addition, the vaccine generates another response, the cellular one, in which a more complex “antigen processing” takes place and which creates a “much more varied” response to the virus. The immunologist of the University Hospital of Santiago, Jose Gomez Rial, contributes to LD some figures on the defense “arsenal” that our body creates with the vaccine: “Protein S includes approximately 1,200 amino acids” against which the so-called CD8-T cells “will recognize approximately 52 epitopes”, the portions of the antigen against which the defenses act, and the CD4-T cells, another 23. “The fact that the virus changes several of those amino acids of the total protein S does not mean by any means that the vaccines cease to serve, since of all this arsenal that we have generated there will always be some way to deal with it, “he explains. López Hoyos agrees: this variety of the immune response is what guarantees that “there will always be some cell that will respond“against the virus.

Gómez Rial believes, on omicron, that “it is most likely that some” of the epitopes recognized by neutralizing antibodies will be lost, but that “is not serious, since the cellular part covers many more and the S protein” would have to change a lot more to have a vaccine escape. “In his opinion, this possible partial loss of efficacy will translate into higher transmissibility of the virus (as it happened with delta) but serious illness will continue to be avoided, the main objective of vaccines and the key to getting out of the pandemic. All vaccines “are designed to protect us against small variations of the virus,” he insists.

Our immune system also mutates

Not only does the coronavirus change in its adaptation process to humans: our immune system also has “the capacity to adapt to the natural variations of viruses.” As José Gómez Rial explains, the human immune response adapts “to these changes” through the mechanism of “somatic hypermutation”, which causes the antibodies that are generated to vary to adapt to new variants and “have greater affinity in recognition“For the immunologist,” we must rely much more on our response capacity and think that it is not only the virus that changes but also that our response adapts to the new changes. “

A virus that would “self-destruct”

Despite the ability of our immune system to respond to threats after vaccination or infection, is it possible for the virus to mutate so much that it completely evades defenses and returns us to the starting box? López Hoyos sees it as “practically impossible”: “The virus would have to mutate so much that in the end it would self-destruct. It would not be feasible. “

Gómez Rial emphasizes that the so-called “escape variants” to vaccines are not common and what may exist, “at most, it is more or less effective against a certain variant but that it is not clinically relevant.” “We also have to take into account that mutations are not always advantageous for the virus since there may be a time when it loses transmission capacity because the S protein (the “key” to enter human cells) has changed so much that it does not enter the lock (the ACE2 receptor), so with the changes make it much less pathogenic and therefore dangerous. “

The professor of Parasitology Rafael Toledo also uses the metaphor of the key to explain LD that the appearance of a variant that “evades all that network of antibodies” is “very difficult”. He explains that, with each change, the virus “is risking its viability to survive”, that is, its transmission capacity. It’s like when a new key for the lock goes a little hard and you “tweak it a bit” to make it open better, he explains. “If you go over, stop opening,” says Toledo, who points out that when we talk about variants, we move “in a limited band” of changes. “The mutations can never be infinite because they would affect the viability of the virus,” he insists.

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