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Vaccine resistant coronavirus mutants are more likely to emerge when a large portion of the population is vaccinated and viral transmission is high and no action is taken to stop the spread, suggests a new model. In other words, a situation that is very similar to the current one in the United States.
The mathematical model, published on July 30 in the journal Scientific reports, simulates how the vaccination rate and the viral transmission rate in a given population influence Variants of SARS-CoV-2 come to dominate the viral landscape. The best way to suffocate vaccine-resistant mutants before they spread is to get shot in the arms as quickly as possible, while keeping viral transmission low, the authors found; in their model, they assume that low transmission rates reflect the adoption of behavioral measures such as masking and social distancing.
This last point is crucial: if viral transmission is low, any vaccine-resistant mutants that emerge are less likely to spread and, therefore, they are more likely to die, said lead author Fyodor Kondrashov, who directs an evolutionary genomics laboratory. at the Austrian Institute of Science and Technology.
Related: Coronavirus Variants: Here’s How SARS-CoV-2 Mutants Stack Up
If viral transmission is high, vaccine-resistant mutants have the potential to infect many unvaccinated and vaccinated people. This means that these variants could easily compete with other versions of the virus and would soon become the dominant strains in circulation.
This worst-case scenario occurs when many, but not all, people in the population are vaccinated, transmission rates are high, and the virus spreads unchecked, the authors found. In this scenario, vaccine-resistant mutants are more likely to emerge when about 60% of the population is vaccinated; at this point, a large portion of the population is protected against the original virus, so infections with this viral strain begin to decline and vaccine-resistant mutants gain a competitive advantage. And if viral transmission remains high, these mutants will soon reign supreme, the model suggests.
These findings are “neither counterintuitive nor surprising,” said Michael Levy, associate professor of epidemiology in the departments of biostatistics and epidemiology at the Perelman School of Medicine at the University of Pennsylvania, who did not attend. in the study.
“Evolution needs pressure, and as more and more people are vaccinated there is more selective pressure on the virus” to change in order to escape vaccine-induced immune responses, Levy said to Live Science in an email. While not necessarily surprising, the new study draws attention to the “very real possibility” that emerging mutants may challenge the effectiveness of existing vaccines.
Dr Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, expressed similar concerns when discussing the generalization delta variant with the press agency Mcclatchy this week. Early data suggests that vaccines still protect against the delta variant, although they work best against the original virus, Previously reported live science. But Fauci said he was concerned that, given current infection rates, the virus now has “a lot of chance” of spawning an even more formidable mutant than delta.
Related: 20 of the worst epidemics and pandemics in history
“There could be a variant that persists that can sideline the delta,” Fauci said. Reducing viral transmission would help eradicate such a variant before it takes over, or prevent it from existing.
The new model highlights the risk of allowing SARS-CoV-2 to spread relentlessly, especially when a large portion of the population – but not everyone – is vaccinated. That said, the model doesn’t quite match reality and we still face some big unknowns, Kondrashov said.
For example, in the simplified model, the original and mutant strains are all equally transmissible, but different strains often vary in terms of transmissibility. For example, the delta variant, considered the most transmissible version of the virus to date, has so far surpassed all known variants of the coronavirus with some traits escaping the vaccine.
Being able to dodge vaccines helps a mutant gain the upper hand only once a population approaches herd immunity for other versions of the virus; Before that point, vaccine-resistant variants must compete with vaccine-vulnerable variants for bodies to infect, Kondrashov said. Because delta spreads so easily, delta has a competitive advantage over vaccine resistant, low transmissibility variants – for now.
It is also not known how many mutations a variant would need to detect to be both highly transmissible. and able to escape vaccines, or if this is likely with SARS-CoV-2; a mutant like this would be of concern if it could start to spread as the delta increases.
Highly transmissible strains may increase the rate of emergence of new vaccine-resistant mutants, as the high rate of spread gives the virus a greater chance of mutating, the authors wrote in their report. But overall, higher transmission rates do not change the overall pattern depicted in the model, primarily how often mutants appear and when they become established in the population, they wrote.
That said, the exact likelihood that an infected person will start producing vaccine-resistant mutants is a “very big unknown,” Kondrashov said. “This is probably the biggest unknown variable we have in our model.” Different individuals probably have slightly different chances of becoming hosts of troublesome mutants; for example, people who are immunocompromised can sometimes shed the virus for months, during which time the virus is very likely to mutate, studies to suggest.
Although the model does not precisely mimic reality, “I do not see any assumptions [the authors made] that would change the main point, which isn’t surprising, Levy said. At a fundamental level, when a large proportion of people are vaccinated but transmission rates are high, it paves the way for the emergence of vaccine-resistant variants, it “The fact that we don’t have a variant yet being able to fully escape mRNA vaccines doesn’t mean one won’t come. “
So what can we do to avoid this worst case scenario?
For Kondrashov, the main takeaway is that “it is very necessary to maintain non-pharmaceutical interventions”, such as masking, “throughout the vaccination campaign, until the very end”. However, in the idealized model, every imaginary person in the population has an equal probability of being vaccinated, it is only a matter of timing, he noted. This does not reflect a reality where children cannot yet be vaccinated and not all eligible adults are willing to be vaccinated.
Since we do not live in a model, the authors instead recommend that people maintain measures such as masking and distancing “for a reasonable period of time” even once the proportion of people vaccinated approaches the threshold of immunity. collective, they wrote in their report. This would help drive the resistant strains to extinction before they spread too far.
This aligns with new guidance from the Centers for Disease Control and Prevention (CDC), which states that fully vaccinated people must wear masks in indoor public spaces if there is “substantial” transmission of coronavirus in their area. (You can track your county’s transmission rate on the CDC website.) This is because vaccinated people who get delta can sometimes transmit the virus just as easily as those who don’t.
Originally posted on Live Science.
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