Aug. 2, 2021 – Easing of pandemic-era restrictions on masking and social distancing may increase the chances a vaccine-resistant strain of the coronavirus emerges, according to a new study published in Scientific Reports.

Although vaccination is the best strategy to control viral spread, we must also change our behavior and mindset to stay ahead of vaccine-resistant strains, according to the four authors of the report.

"We have become accustomed to thinking of the pandemic from the point of view of epidemiology, and advised to reduce transmission and the number of people getting sick and the death rate,” co-author Fyodor Kondrashov, PhD, an evolutionary biologist at the Institute of Science and Technology in Austria, said at a press briefing Thursday. “As the pandemic spreads across years, there will be a new dimension to our thinking, both for policymakers and the public. And that's the evolutionary perspective."

The coming "change of mentality" that Kondrashov foresees should reassure people that masking and social distancing even after being vaccinated is vital.

"It decreases the possibility that a vaccine-resistant strain is running around. We're not just trying to prevent the spread, but the evolution of novel variants, which are so rare at this point that we haven't yet identified them," he said.

The researchers simulated the probability that a vaccine-resistant strain will emerge in a population of 10 million individuals over 3 years, with vaccinations beginning after the first year. For eight scenarios, rates of infection, recovery, death, vaccination, and mutation, 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 lockdowns.

Three Factors

The study showed that three factors increase the probability of a vaccine-resistant strain taking hold:

  • Slow rates of vaccination.
  • High number of infected individuals.
  • Faster mutation rate.

These factors, Rello said, are obvious to some degree.

"Every infected individual is like a mini-bioreactor, increasing the risk that mutations will appear that will endow the virus with the property of avoiding the immune system primed by a vaccine," he said.

Not as obvious, Rello added, is 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 at the time a vaccine campaign is close to finishing and nonpharmacological interventions are maintained, then there's a chance to completely remove the vaccine-resistant mutations from the virus population,” he said.

In scenarios where a resistant strain became established, resistance initially emerged after about 60% of the population had been vaccinated. That makes nonpharmaceutical 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 CDC.

A ‘Powerful Force’

"We hope for the best, that vaccine resistance has not developed, but caution that evolution is a very powerful force, and maintaining some precautions during vaccination may help to control that evolution," said Kondrashov.

He's pessimistic because many countries are still having difficulty accessing vaccines, and vaccine efficacy wanes slightly over time. The authors warn that "the emergence of a partially or fully vaccine-resistant strain and its eventual establishment appears inevitable."

The worst-case scenario is familiar to population biologists: rounds of "vaccine development playing catch up in the evolutionary arms race against novel strains," the authors write.