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Relaxing non-pharmaceutical interventions once vaccination of the population has reached a tipping point before herd immunity may increase the likelihood of a resistant strain emerging which natural selection then favors, according to new findings from ” a modeling study published online on July 30 in Scientific reports.
While vaccination is the best strategy to control viral spread, changes in our behavior and mindset will increasingly be needed to stay ahead of vaccine-resistant strains, according to the four authors of the report.
“We got used to thinking about the pandemic from an epidemiological perspective and advised reducing transmission, the number of people sick and the death rate. As the pandemic spreads over the years, there will be a new dimension to our thinking, both for policy makers and the public. And that’s the evolutionary perspective, ”said co-author Fyodor Kondrashov, PhD, an evolutionary biologist at the Institute of Science and Technology (IST), Klosterneuburg, Austria, during a press briefing Thursday.
Kondrashov’s upcoming “mindset shift” should reassure people that masking and social distancing even after being vaccinated is not in vain. “This decreases the possibility of a vaccine resistant strain circulating. We are not only trying to prevent the spread, but the evolution of new variants, which are so rare at this stage that we have not yet identified them, ”he said.
The study focused on evolution generically, rather than specific variants. “We took the classic model used to study the epidemiology of pandemics, the SIR [susceptible, infected, recovered] model, and we modified it to study the dynamics of rare mutations associated with the emergence of a vaccine resistant strain ”, explained Simon A. Rella, lead author of the study and doctoral student at IST, during of the briefing.
The researchers simulated the probability that a vaccine resistant strain would emerge in a population of 10,000,000 individuals over 3 years, with vaccinations starting after the first year. For eight scenarios, infection, cure, death, vaccination and mutation rates and the percentage of individuals with resistant viral strains were factors in the model.
The model also simulated waves of low and high transmission, similar to the effects of large-scale interventions such as blockages.
Three factors
The study showed that a trio of factors increase the likelihood that a vaccine-resistant strain will establish itself:
These factors, Rello said, are obvious to some extent. “Each infected individual is like a mini-bioreactor, increasing the risk of mutations appearing which will endow the virus with the property of avoiding the immune system initiated by a vaccine,” he said.
Not so obvious, Rello added, that when most people are vaccinated, a vaccine resistant strain has an advantage over the original strain and spreads faster.
But we can stop it, he said. “Our model shows that if, by the time a vaccination campaign is about to end and non-pharmacological interventions are maintained, then there is a chance of completely eliminating vaccine-resistant mutations from the viral population. “
In scenarios where a resistant strain became established, resistance initially appeared after approximately 60% of the population had been vaccinated. This makes non-pharmaceutical interventions such as masking and social distancing vitally important. Just under 50% of the U.S. population over the age of 12 has been fully vaccinated, according to the Centers for Disease Control and Prevention.
“Our results suggest that policymakers and individuals should consider maintaining non-pharmaceutical interventions and transmission reduction behaviors throughout the vaccination period,” the investigators conclude.
A “mighty force”
“We hope for the best that resistance to the vaccine has not developed, but beware that evolution is a very powerful force, and maintaining certain precautions during vaccination can help control this development,” said Kondrashov.
Investigators rely on epidemiologists to determine which measures are most effective.
“There is a need to vaccinate as many people as possible as quickly and comprehensively as possible and to maintain some level of non-pharmaceutical intervention to ensure that rare variants have a chance of being suppressed instead of spreading,” concluded Kondrashov.
He is pessimistic because many countries still have difficulty accessing vaccines and the effectiveness of vaccines decreases slightly over time. The authors warn that “the emergence of a strain partially or totally resistant to the vaccine and its eventual establishment seems inevitable”.
The worst-case scenario is familiar to population biologists: series of “vaccine development catching up with the evolutionary arms race against new strains,” the authors write.
The limitations of the study are that some parameters of the rate of evolution of vaccine-resistant strains are not known, and when creating the model, the effects of increased testing were not taken into account. rigorous contact tracing, viral genome sequencing rates and travel restrictions.
Rather, the model illustrates the general principles by which vaccine resistance can evolve, Kondrashov said.
Scientific representative. Published online July 30, 2021. Full text
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