The Delta variant was first detected a year ago and is now dominant across the globe. Scientists are concerned that a new strain could supersede it, reports The Guardian.
Dominance of Delta variant
“It’s like the weather report,” says William Hanage, an epidemiologist at the Harvard TH Chan School of Public Health. “It used to be, ‘We have a little bit of Gamma there, we’ve got Alpha coming up here.’ But now it’s just Delta.”
Since it was first detected in India in December 2020, the Delta variant of Sars-CoV-2 has become so ubiquitous that it would be easy to assume that the once-rapid evolution of the virus has been replaced by a state of quiescence.
According to the World Health Organization, 99.5% of all Covid-19 genomic sequences reported to public databases are now Delta.
Other new variants
While new strains have continued to emerge, such as the recent AY. 4.2 or the Delta Plus variant in the UK, which scientists estimate to be 10-15% more transmissible, although there is no exact data for this yet, they are almost identical to the Delta variant, apart from the odd minor mutation here and there. Hanage has taken to referring to them as Delta’s grandchildren.
“There’s been quite a few Delta Pluses,” he says. “I did a recent radio interview where I said that Delta Plus is code for whatever people are getting their knickers in a twist about at the moment. It’s not gigantically more transmissible.”
Future of delta variant
But the reason Hanage and colleagues still scan databases such as Pangolin and Nextstrain each week, and the purpose of their regular Zoom calls, is to try and predict what might come next.
One possibility is that after the initial dramatic jumps in its genetic sequence, which gave rise to first Alpha, then Delta, Sars-CoV-2 will now mutate slowly and steadily, eventually moving beyond reach of the current vaccines, but only over the course of many years.
“I anticipate that the kind of evolution we will see is more what we call antigenic drift, where the virus gradually evolves to escape the immune system,” says Francois Balloux, director of the UCL Genetics Institute.
But the alternative is the sudden appearance of a completely new strain, with game-changing transmissibility, virulence or immune-evasive properties.
Ravi Gupta, professor of clinical microbiology at the University of Cambridge, refers to these strains as “super variants” and says he is 80% sure that another one will emerge. The question is when.
“We’ve got a Delta pandemic at the moment,” says Gupta.
“This new Delta Plus variant is relatively wimpy compared to the kind of thing I’m talking about. It has two mutations from the Delta strain, I don’t think they are that worrisome and it hasn’t taken off in a big way in other countries. But it’s inevitable that there will be another significant variant in the next two years and it will compete with Delta and it may out-compete Delta.”
Will we see a super variant?
During the latter half of 2020, epidemiologists began to observe signs of a concerning phenomenon known as viral recombination, in which different versions of Sars-CoV-2 exchanged mutations and combined to form a totally new strain.
Thankfully, Gupta says recombination does not appear to be that common, but it remains one feasible source of a new super variant, particularly in parts of the world where sizable proportions of the population remain unvaccinated and viral strains can circulate freely.
The second is a series of major mutations, either resulting in a greatly enhanced version of Delta or something very different. It is thought there remains significant scope for this to happen.
“While recent variants are versions of Delta, the virus has huge potential to evolve in the future,” says Gideon Schreiber, professor of biomolecular sciences at the Weizmann Institute of Science in Israel.
Antiviral pill
In recent weeks, concerns have emerged that the use of new antiviral pills, in particular Merck’s molnupiravir, could contribute to this by actively encouraging Sars-CoV-2 to evolve.
Molnupiravir works by interfering with the virus’s ability to replicate, littering its genome with mutations until it can no longer reproduce. Some virologists have argued that if any of these viral mutants survive and spread to others, it could theoretically spur the rise of new variants.
The super variant
Epidemiologists are now trying to model what a new super variant might look like. So far, the major transformations in the virus have helped to increase its transmissibility. Hanage explains that one of the reasons why the Delta variant had such an impact is because it grows extremely rapidly within human cells, before the immune system kicks into gear.
As a result, people infected with Delta carry approximately 1,200 times more viral particles in their noses compared with the original Sars-CoV-2 strain and develop symptoms two to three days sooner.
This is a result of natural selection. Different copies of the virus are being created all the time, but the ones that have survived and become more dominant are ones that are more capable of infecting new people.
Strains that can sidestep antibodies are likely to become more dominant, making the next super variant far more likely to be able to evade at least some parts of the immune response.
Measures taken
The Covid-19 vaccines are designed with viral evolution in mind, epidemiologists do not expect any new super variant to render them completely useless and so it would be extremely unlikely to lead to large serious outbreaks, such as those of the past two years.
In addition, there is a second generation of Covid-19 vaccines that have been developed. Vaccine developer Novavax is hoping to obtain regulatory approval for its jabs in the next couple of months, while many more vaccines are expected to come on the market between now and 2023.
According to Karin Jooss, executive vice-president and head of R&D at US pharmaceutical company Gritstone, which has a second-generation Covid-19 vaccine in phase I clinical trials, companies are sequencing all existing strains of Sars-CoV-2 and aiming to generate neutralising antibody responses against areas of the virus that are conserved between all those strains.
But epidemiologists also believe that relying on vaccines alone is not enough. Gupta says that even as we attempt to find a way to live with Covid-19 in the UK, there should still be some restrictions in place to limit the spread of the virus and reduce the number of opportunities it gets to mutate.
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Source: The Guardian
