While not a popular decision by many of those working in health care, in our Province many restrictions are now being removed faster than it took for the ink to dry on their initial draft. I don't know what they are thinking, especially considering the results of papers such as this. Those that like numbers will appreciate the fact that a mathematical model was used to help predict the changes found in this study.
Rates of SARS-CoV-2 transmission and vaccination impact the fate of vaccine-resistant strains
Abstract
Vaccines are thought to be the best available solution for controlling the ongoing SARS-CoV-2 pandemic. However, the emergence of vaccine-resistant strains may come too rapidly for current vaccine developments to alleviate the health, economic and social consequences of the pandemic. To quantify and characterize the risk of such a scenario, we created a SIR-derived model with initial stochastic dynamics of the vaccine-resistant strain to study the probability of its emergence and establishment. Using parameters realistically resembling SARS-CoV-2 transmission, we model a wave-like pattern of the pandemic and consider the impact of the rate of vaccination and the strength of non-pharmaceutical intervention measures on the probability of emergence of a resistant strain. As expected, we found that a fast rate of vaccination decreases the probability of emergence of a resistant strain. Counterintuitively, when a relaxation of non-pharmaceutical interventions happened at a time when most individuals of the population have already been vaccinated the probability of emergence of a resistant strain was greatly increased. Consequently, we show that a period of transmission reduction close to the end of the vaccination campaign can substantially reduce the probability of resistant strain establishment. Our results suggest that policymakers and individuals should consider maintaining non-pharmaceutical interventions and transmission-reducing behaviours throughout the entire vaccination period.
"Counterintuitively, when a relaxation of non-pharmaceutical interventions happened at a time when most individuals of the population have already been vaccinated, the probability of emergence of a resistant strain was greatly increased," they added.
"Our results suggest that policymakers and individuals should consider maintaining non-pharmaceutical interventions and transmission-reducing behaviors throughout the entire vaccination period."
"When most people are vaccinated, the vaccine-resistant strain has an advantage over the original strain," Simon Rella of the Institute of Science and Technology Austria, who worked on the study, told reporters.
"This means the vaccine resistant strain spreads through the population faster at a time when most people are vaccinated."
But if so-called non pharmaceutical interventions are maintained -- such as mask use and social distancing -- the virus is less likely to spread and change. "There is a chance to remove the vaccine resistant mutations from the population," Rella said.
The team used a mathematical model to predict these changes, but their findings follow what is known about the epidemiology of viruses and what's known as selective pressure -- the force that drives any organism to evolve.
The findings suggest that policymakers should resist the temptation to lift restrictions to celebrate or reward vaccination efforts.
This is likely to be especially true with a more transmissible variant such as the Delta variant, said Fyodor Kondrashov, also of the Institute of Science and Technology Austria.
"Generally, the more people are infected, the more the chances for vaccine resistance to emerge. So the more Delta is infectious, the more reason for concern," Kondrashov told reporters.
"By having a situation where you vaccinate everybody, a vaccine-resistant mutant actually gains a selective advantage."
On Tuesday, the US CDC altered its guidance on mask use. The CDC said earlier this year that fully vaccinated people are very safe from infection and can take off their masks in most situations.
Now, it says even fully vaccinated people can sometimes catch the virus and if they catch the Delta variant, they are just as likely to infect someone else as an unvaccinated person would be. It advised everyone in areas of high or sustained virus transmission to wear masks when around others.