“Delta is a warning”: WHO concerned new COVID-19 variants will emerge

As the Delta variant of SARS-CoV-2 continues to sweep the globe some countries are dropping pandemic restrictions despite having only moderate rates of vaccination. With the World Health Organization warning Delta could be just the beginning of the virus’s evolution a new modeling study indicates high levels of virus transmission in conjunction with middling vaccination rates may be the ideal scenario for new variants to emerge.

In the space of about six weeks the Delta variant went from accounting for around 10 percent of all COVID-19 cases in the United States, to a stunning 83 percent of new cases. The increasing predominance of the Delta variant in the US was not unexpected, but the rapid pace of its spread was recently described as “troubling” by Rochelle Walensky, director of the Centers of Disease Control and Prevention.

While there are an increasing number of breakthrough COVID-19 infections being reported in vaccinated people, the vaccines are still powerfully effective in preventing hospitalization and death. Francis Collins, director of the National Institutes of Health, says current vaccines offer a 25-fold reduction in the risk of severe COVID-19 and hospitalization against the Delta variant.

So vaccines still work, but not enough people are vaccinated yet according to infectious disease expert Anthony Fauci. Currently only around 50 percent of the US population is fully vaccinated, with rates varying dramatically from state to state. Alabama and Mississippi, for example, have only fully vaccinated around 35 percent of their population, while Massachusetts, Connecticut and Maine are all in the mid-60s.

As restrictions such as social distancing and mask-wearing return to a number of US states Fauci says he doesn’t believe lockdowns will be necessary to get on top of this current wave. But he does point out higher rates of vaccination are the only long-term solution.

"So we're looking, not, I believe, to lockdown, but we're looking to some pain and suffering in the future because we're seeing the cases go up, which is the reason why we keep saying over and over again, the solution to this is get vaccinated and this would not be happening," he said recently on ABC news.

And in the meantime, as vaccination rates in poorer countries remain worryingly low due to unequal distribution, the World Health Organization is issuing a warning to countries beginning to reduce restrictions.

"Delta is a warning: it's a warning that the virus is evolving but it is also a call to action that we need to move now before more dangerous variants emerge," says Michael Ryan, the WHO's director of emergencies. "The virus has got fitter, the virus has got faster. The game plan still works, but we need to implement and execute our game plan much more efficiently and much more effectively than we've ever done before."

Ryan stresses our 2020 prevention strategies – such as masking, social distancing and avoiding busy indoor unventilated spaces – are still effective against the Delta variant. And they must continue alongside vaccination in order to reduce transmission and limit the emergence of new variants.

A new study published in the journal Scientific Reports has modeled the likelihood of a vaccine-resistant strain of SARS-CoV-2 emerging. It found the optimal environment for such a variant to emerge is when there is a high level of viral transmission in a moderately vaccinated population. The models indicate the vaccination rate sweet spot for the emergence of a dangerous new variant would be around 60 percent.

Peter English, past chair of the British Medical Association's Public Health Medicine Committee, notes it is always wise to view modeling studies with caution. However, he also believes this new study to be robust and consistent with other research.

“… in a relatively unvaccinated population, vaccine escape variants will have little competitive advantage, and are unlikely to become prevalent,” explains English, who did not work on the new study. “In moderately- or highly-vaccinated populations, however, variants that can still be transmitted to and by fully vaccinated people will have a considerable competitive advantage.”

The problem with many regions in the world dropping pandemic restrictions before a greater amount of people are vaccinated, according to English, is simple. More virus in a community means more vaccinated individuals will be infected, and this means there's a greater opportunity for vaccine-escape variants to spread.

Nick Davies, an expert in mathematical modeling from the London School of Hygiene and Tropical Medicine, says despite there being much uncertainty in the modeling, these results make sense.

“Every country should do their part to avoid creating fertile grounds for viral evolution where possible, which, thankfully, is a goal largely in alignment with public health and economic goals, as they all involve controlling transmission,” says Davies, who did not work on this new study. “But ultimately, dealing with the emergence of a vaccine escape strain is really a global issue, not a national one; as soon as a vaccine escape mutant emerges somewhere, it becomes everybody’s problem.”

The new research does not advocate for lockdowns in vaccinated populations, but rather it presents a range of non-pharmaceutical measures that should be in place until transmission has been reduced in a given community. Alongside masking and social distancing the study recommends considering widespread testing and genomic surveillance, and rigorous contact tracing to help isolate infected subjects and restrict further transmission.

Ultimately, the researchers are in line with WHO statements reminding us the only solution is evenly dispersed vaccination across the entire world.

“Without global coordination, vaccine resistant strains may be eliminated in some populations but could persist in others,” the new research concludes. “Thus, a truly global vaccination effort may be necessary to reduce the chances of a global spread of a resistant strain.”

The new study was published in the journal Scientific Reports.