It is clear that we are now dealing with a virus that spreads much more easily – probably more than twice as easily – than the version that emerged in Wuhan at the end of 2019.
The Alpha variant, first identified in Kent, UK, made a big leap in its transmission capacity. Now the Delta, first found in India, took an even bigger leap.
This is evolution in action.
So are we doomed to an endless parade of new and improved variants that are becoming increasingly difficult to contain?
Or is there a limit to how much the coronavirus can get worse?
It is worth remembering the journey that this virus is on. It has made the leap from infecting a completely different species (its closest relatives are bats) to us.
It’s like you when you start a new job: you’re competent, but there’s room for improvement.
The first variant was good enough to start a devastating pandemic, but now it’s learning on the job.
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When viruses jump into humans, it would be “very rare for them to be perfect,” explains Wendy Barclay, a virologist at Imperial College London. “They settle in and then they have a great time.”
The clearest way to compare the pure biological spreading power of viruses is to look at their reproduction number. GETTY IMAGES
There are examples of viruses, he says, from flu pandemics to Ebola outbreaks, that make the leap and then accelerate.
So how far could it go?
The clearest way to compare the pure biological spreading power of viruses is to look at their R0 (the reproduction number).
That’s the average number of people to whom each infected person transmits a virus, if no one were immune and if no one took extra precautions to avoid getting infected.
That number was around 2.5 when the pandemic began in Wuhan and could reach 8.0 for the Delta variant, according to Imperial College disease modelers.
“This virus has surprised us a lot. It goes beyond what we feared,” says Aris Katzourakis, a researcher studying viral evolution at Oxford University.
“The fact that it’s happened twice in 18 months, two lineages (Alpha and then Delta) each 50% more transmissible is a phenomenal amount of change.”
He thinks it’s “silly” to try to put a number at how high it could go, but he can easily see more jumps in the broadcast over the next two years.
Other viruses have a much higher R0, and the record holder, measles, can cause explosive outbreaks.
The virus can still “improve”, i.e. become more efficient in its mode of transmission. GETTY IMAGES
“There’s still room for it to go up more,” Barclay says. “Measles is between 14 and 30, depending on who you ask, I don’t know how it will develop.”
So how are the variants doing it?
There are many tricks that the virus could use to improve its spread, such as:
improve the way it is introduced into the cells of our body
survive longer in the air
increase viral load for patients to breathe or cough up more viruses
change in the process of infecting another person
One of the ways in which the Alpha variant became more transmissible was by improving the way it bypassed the mechanism that alerts of its intrusion, called the interferon response, into the cells of our body.
But this does not mean that by the time we get to Omega in the Greek alphabet of the variants we will end up with an unstoppable beast.
“Ultimately, there are limits and there is no super-defining virus that has all combinations of negative mutations,” Katzourakis says.
There is also the concept of evolutionary trade-offs: to get better at one thing, you often have to get worse at another.
The new variants are more transmissible than the original. GETTY IMAGES
The fastest vaccination program in history will give the virus a different hurdle to overcome and push it in another evolutionary direction.
“It’s quite possible that changes in the virus that make it better to avoid vaccines may end up compromising its ability to transmit in an absolute sense,” Katzourakis says.
He thinks the Beta variant — which has a mutation called E484K that helps evade the immune system but hasn’t gotten off the ground — is an example of this.
However, Delta has mutations that help it spread and partially bypass immunity.
Intermediate phase
It is still difficult to predict what the optimal strategy for the choir will prove to be.navirus. Different viruses use different techniques to keep infecting.
Measles is explosive, but it leaves a lifelong immunity, so you always have to find someone new. Influenza has a much lower R0, just above 1, but constantly mutates to evade immunity.
“We’re in a really interesting, intermediate and somewhat unpredictable phase, it’s hard to predict how it will play out a year from now,” Barclay says.
One thing that is often claimed, but which attracts the scorn of scientists, is that the virus must become milder in order to spread more easily.
Increasingly transmissible variants are a nightmare for the poorest countries. GETTY IMAGES
There is very little evolutionary pressure on the virus for that to happen. The virus has already been transmitted to the next person long before it kills the infected person.
And the people who spread it the most (the youngest) are the ones who don’t get sick much.
In rich countries with good vaccination campaigns, it is expected that the next variants may not represent a major problem due to widespread immunity.
But these increasingly transmissible variants are a nightmare for the rest of the world, making it increasingly difficult to contain covid-19.
