Do vaccines promote the emergence of resistant variants?

According to a study from August 2021, a high vaccination rate can paradoxically favor the emergence of resistant variants. This is explained by the phenomenon called ” pressure selection ”: the more the number of people vaccinated increases, the more the competitive advantage of strains resistant to the vaccine increases. We could therefore conclude … that it is better not to vaccinate the population. However, this is to advance on a false reasoning. On the one hand, this competitive advantage disappears when almost the entire population is vaccinated, because the virus then no longer circulates sufficiently to produce mutations. According to the same study, the peak probability ofemergence of new variants is around 60% of people vaccinated, well below the threshold ofcollective immunity estimated at 90% and the vaccination rate reached in France.

Each virus replication produces 3% random errors

Second, it is more the high number of infections than the vaccination that will produce mutant viruses. This is very easy to understand: every time the virus replicates, about 3% of new copies have a random error, according to a study published in the journal PNAS. However, each infection produces thousands of copies in the body, which increases the number of mutated viruses. Of course, most mutations either have no effect or are disadvantageous to the virus. In addition, in the same individual, the mutated virus will be overwhelmed by other “normal” viruses and will not survive. So even if you are vaccinated and infected with a strain that acquires resistance, you are unlikely to pass it on to other people.

The number of contaminations, a determining factor in the emergence of variants

But there is always the risk that a mutation provides an advantage and be passed to a new host. It is only then that a new variant will emerge, possibly having a competitive advantage over the original strain. However, the greater the circulation of the virus, the more this probability increases. ” The fact that only a very small number of viruses trigger the next infection is the critical factor limiting the likelihood of new variants appearing. », Explains Vaughn Cooper, professor of microbiology and molecular genetics at the University of Pittsburgh. ” Under these circumstances, the best way to limit the progression of the coronavirus is to reduce the number of infections. », He supports. The modest benefit the virus would derive from the vaccine breakout is overshadowed by the vast possibilities of infecting unvaccinated people. It is not by chance that the Alpha then Delta variant appeared in the midst of the epidemic outbreak in England and India. So far, no dangerous variant has yet emerged in a highly vaccinated population.