#16,094
While many politicians are eager to declare victory over the SARS-CoV-2 virus - or at least settle for an truce - and a small (but vocal) minority of the public consider the pandemic overblown (at best) or a hoax, the reality is we are far from being out of the woods, and there are growing concerns we may be entering the most dangerous phase of this pandemic.
COVID, as we saw in my last blog, has not only become increasingly transmissible over the past year (see CNN report CDC document warns Delta variant appears to spread as easily as chickenpox), it has increased in its severity as new variants (Alpha & Delta) have emerged.
While the current vaccines still reduce (but don't eliminate) the risk of infection, they also do a very good job in attenuating the severity of the illness. At least for now, with the variants we've seen to date.
The SARS-CoV-2 virus evolves primarily due to random mistakes it makes as it replicates in a host. Most of the errors are inconsequential, offer no evolutionary advantage, or are even detrimental to the virus, and these variants generally fail to compete against more `biologically fit' viruses.
Only rarely does the `right' mutation happen to hit the`right spot' in the genome, conveying an evolutionary advantage.
While random, the more hosts infected with the virus, the greater the number of opportunities for the virus to `hit the genetic jackpot', and reinvent itself into something more transmissible, or more dangerous.
Now, with vaccination uptake slowing, and face mask and social distancing requirements in many localities being relaxed (or abolished), we are seeing the Delta variant surge across the United States, Europe, and many other regions.
Today we've a cautionary study published in Nature Scientific Reports that models what might occur as NPIs (Non-pharmaceutical Interventions) are relaxed in regions where vaccination rates are high.
The late George E. P. Box (18 October 1919 – 28 March 2013) - Professor Emeritus of Statistics at the University of Wisconsin - is often credited with coining the familiar adage:
“All models are wrong, but some models are useful.”Consequently, we must take these types of studies with a grain of salt. As I'm hardly qualified to comment on (or even substantially grasp) their statistical analysis, all I can say is their ideas seem plausible to me.
Below you'll find a link and some excerpts from the study, and a link to some expert reactions on the Science Media Centre website (Note: I've reformatted and bolded some of the passages for easier readability). Follow the link to read the open-access report in its entirety.
Rates of SARS-CoV-2 transmission and vaccination impact the fate of vaccine-resistant strains
Simon A. Rella, Yuliya A. Kulikova, Emmanouil T. Dermitzakis & Fyodor A. Kondrashov
Scientific Reports volume 11, Article number: 15729 (2021
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.(SNIP)
By contrast, a counterintuitive result of our analysis is that the highest risk of resistant strain establishment occurs when a large fraction of the population has already been vaccinated but the transmission is not controlled. Similar conclusions have been reached in a SIR model of the ongoing pandemic56 and a model of pathogen escape from host immunity57.
Furthermore, empirical data consistent with this result has been reported for influenza58. Indeed, it seems likely that when a large fraction of the population is vaccinated, especially the high-risk fraction of the population (aged individuals and those with specific underlying conditions) policy makers and individuals will be driven to return to pre-pandemic guidelines59 and behaviours conducive to a high rate of virus transmission60,61.
However, the establishment of a resistant strain at that time may lead to serial rounds of resistant strain evolution with vaccine development playing catch up in the evolutionary arms race against novel strains.
(SNIP)
One simple specific recommendation is to keep transmission low even when a large fraction of the population has been vaccinated by implementing acute non-pharmaceutical interventions (i.e. strict adherence to social distancing) for a reasonable period of time, to allow emergent lineages of resistant strains to go extinct through stochastic genetic drift. The implementation of non-pharmaceutical measures at a time of high vaccination can also help reduce infectivity when the efficacy of vaccines is not perfect69.
Additional factors that may make these measures even more effective are: (1) increased and widespread testing, (2) rigorous contact tracing, (3) high rate of viral sequencing of positive cases58,70 and (4) travel restrictions.Finally, while our model formally considers only one homogenous population, our data also suggest that delays in vaccination in some countries relative to others will make the global emergence of a vaccine-resistant strain more likely. Without global coordination, vaccine resistant strains may be eliminated in some populations but could persist in others. Thus, a truly global vaccination effort may be necessary to reduce the chances of a global spread of a resistant strain.
You'll find multiple expert reactions at the following link:
JULY 30, 2021
Viruses have been around for millions of years, mostly because they are able to adapt to an ever changing environment.
Which is why, if we continue to underestimate this virus - and the ones that will inevitably come after it - we do so at our own peril.
