Sars-CoV-2, the virus that started a pandemic that has upended lives - and killed over two millions of them - all over the world, has been evolving steadily over the last few months. The genetic code of the virus continues to change as it is passed from person to person all over the world.
Initially, the variants did not worry scientists; the adaptations provided little information about how harmful the virus actually is. Some variations of the virus ended up being a weaker form.
This time, however, it is different, says a Vox report.
At the moment, there are three different variants of Sars-CoV-2 around the world - and all of them have caused researchers concern.
The variant called “B.1.1.7” was first discovered in the UK in September last year. It is said to be a lot more contagious compared to the earlier variants of the novel coronavirus. There are also some clues that it could be a lot more deadly as well.
Some less-understood variants are one of the pairs identified in South Africa and Brazil, in October and December respectively. These variants could possibly surpass the immune systems in our bodies, making them a lot more dangerous, the Vox report says.
The question that now arises is: Why have these variants started to appear now?
The virus has been evolving
The virus has been changing for a while, and is nothing new.
“We’ve had many, many variants in Sars-CoV-2 for a long time now, and scientists have even been tracking these in fairly detailed ways since the summer of 2020,” said Emma Hodcroft, a molecular epidemiologist at the University of Bern. “The big difference is that, before December, we hadn’t really seen any variants that seemed to be behaving any differently.”
The scientists studying the mutants of the virus do not have clear answers as to why the variants are receiving attention in this particular period of time.
A lot of questions remain unanswered, particularly about whether there may be more variants to come, or how the world will prepare to fight them.
Experts have narrowed down to four reasons, with one main concept that explains it all - evolution.
Reason 1: The virus is diversifying with time
Evolution is made up of two components: natural selection and individual differences. It’s an ongoing process where organisms mutate as time passes. The organisms that acculture themselves to the environment stay back in the population, and weaker ones become less present.
When viruses are mutating, they make numerous copies of themselves. They mutate in huge numbers, and this is an ongoing process that replicates itself billions of times across the world.
When Covid-19 first broke out, the forms of the viruses were almost the same, as they were all present around the same period of time during the outbreak. But as the disease spread over the world, the virus has had the opportunity to mutate over the past one year, leading to a lot of genetic changes in different locations.
“We have no evidence that the underlying mutation rate is changing,” Sarah Cobey, an epidemiologist who studies viral evolution at the University of Chicago, told Vox.
However, evolution and open opportunities for change still don’t explain why the mutations we see now are a lot more dangerous.
“We are seeing evidence of adaptive evolution,” Cobey said. These variants appear to be either getting better at infecting people, or possibly evading the immune system, and they are doing so in similar ways. Diversity isn’t the only factor that provides an explanation. Natural selection does as well.
Reason 2: The virus is evolving as a response to the human immune system
Some of Sars-Cov-2’s mutations have provided it with advantages. This has made some variants of the virus stronger than the older ones.
“Some of those [genetic] substitutions are actually helping the virus replicate better,” said Sarah Cobey. This can result in the variants affecting a lot more people, compared to their predecessors.
The P.1 variant from Brazil and the 501Y.V2 variant from South Africa have combined to form a mutation called E484K. This mutation changes the portion of the virus that attaches to human cells. This portion is also the part that our bodies recognize after we are vaccinated.
But this mutation may allow reinfection, said Emma Hodcroft. This means that everyone who has already been infected with Sars-CoV-2 could possibly be at risk of reinfection by the new variants, but it has yet to be confirmed.
Hodcroft feels that the variants may have changed as a response to human immunity.
At the beginning of the pandemic, everyone’s immune system was not prepared to recognize the Sars-CoV-2 virus, as no one was exposed to it in the beginning. If a variant that was good at avoiding the human immune system existed, it would not have become prevalent as it would not have an advantage over other viral variants.
Hodcroft explains: “Even if this [E484K] mutation popped up — which we know it did, we can see that it popped up a few times — it might not have been in a place where this was an advantage.”
However, over the past year, a lot of people around the world have been affected by the virus, and have developed some level of immunity to it.
This gives the virus variants that can avoid the human immune system some advantage. They can duplicate in places where other variants can’t, and can become dominant.
“I want to be really clear: We aren’t 100% sure, scientifically, that this is what’s happened,” Hodcroft says. “But these are the kinds of things to think about when we think about why we might be seeing different variants now. We’ve changed the rules of the game.”
Reason 3: The virus has spread far enough for rare occurrences to start happening
As the pandemic progresses, rare occurrences have greater chances of occurring.
The B.1.1.7 variant has changed significantly over a short period of time. The changes are so great in number that scientists feel that the variant might have appeared in an immunocompromised person.
In most situations, the virus is completely eliminated by our bodies in a few weeks. “In people that have compromised immune systems, though, there’s a very different dynamic,” says Hodcroft. “So, for one thing, the virus could be in them for months instead of weeks.”
This allows the virus to evolve over a longer period of time, creating mutations that are equipped to avoid the human immune system.
Many different processes have to happen for this to take place: an immunocompromised person has to become affected, the virus has to go through several mutations, and then the person would have to spread the virus to other people.
“These are all like ‘super-edge cases,’” Hodcroft says. But “by keeping cases so high, you increase the chance that sooner or later, you’re going to hit that jackpot ... we keep rolling the die when we keep the cases up so high.”
Reason 4: Some Covid-19 treatments might have instigated evolution
The variants might have risen due to the use of convalescent plasma, Michael Worobey, the head of the department of ecology and evolutionary biology at the University of Arizona, told Vox.
Convalescent plasma is extracted from the blood taken from people who have recovered from Covid-19. Antibodies are present in the plasma transfusion, which can aid another Covid-19 patient. However, there is a small problem where for certain recipients, the plasma can harness an environment where the stronger variant of the virus is favoured.
“So there are cases where the identical [mutations] that characterize the UK variant have also evolved in patients who are chronically infected with the virus and were then given convalescent plasma,” Worobey said.
The virus builds diversity in the patient, and the plasma becomes a factor of natural selection. It then chooses a variant that can avoid antibodies in the plasma. “It’s essentially a perfect storm.”
Worobey further stated that this could have possibly happened with the B 1.1.7 variant.
A similar process could have also happened with monoclonal antibodies - synthetic antibodies that are produced as a treatment for the virus.
Plasma treatments have helped save a lot of lives when treatments for the coronavirus were scarce. However, when it comes to using convalescent plasma on people that are immunocompromised, Worobey said that it was quite irresponsible.
Vaccination needed now more than ever
The virus will keep evolving, and a lot more variants will form. They won’t all be dangerous.
“I think one thing that we definitely have to keep in mind, particularly in the next few weeks and months, is that a lot of people are now very interested in doing [viral genetic] sequencing and looking for variants,” said Emma Hodcroft. “And that’s fantastic. This is exactly what I’ve been kind of begging for for a long time — for more countries to really dedicate resources to this.”
But with the increased vigilance, she says, “we’re going to see a lot of false alarm variants.”
The next selection pressure to come up are vaccines. This might create variants of more concern in the future. There may be a strain of the virus that forms due to random mutations. It could potentially spread quite a lot if it becomes efficient at avoiding the immunity vaccines provide.
This is why evolution experts are vying for prompt vaccination. Partial immunity can act as a pressure for evolution in a single person as well as for most of the population.
“What we don’t want is for there to be high levels of virus circulating and spending a lot of time with a partially vaccinated population,” Hodcroft said. “We want to keep case numbers while we’re vaccinating as low as we can.”
“Once you vaccinate hundreds of millions of people, the virus is going to be under really quite intense pressure to evolve [immune] escape variants,” Michael Worobey said. Some of these variants may already exist, but remain undetected. “And those variants, I think, we can expect to sweep up to much higher frequency once vaccination provides this huge selective force.”
Evolution takes place when a lot of diversity is present, combined with the pressure of selection. It is what’s happening during the pandemic, as vaccination campaigns continue to progress.
For now, vaccines look promising. They are set to be very effective against most variants. They can also be updated for any changes in the future.
But how do we stop more viral evolution from happening?
“The best way to avoid it is to go back in time and not allow the pandemic to spin so out of control,” Worobey said. “If we had done that, and then vaccinated, then we would have been in a much less dangerous situation.”
