How can we know what is the limit of a Covid-19 variant?

 

The Alpha variant, first identified in Kent, UK, performed a large jump in its ability to transmit. Now Delta, seen first in India, leapt further still.

 

This is evolution in action

So are we doomed to a never-ending parade of new and improved variants that get harder and harder to contain? Or is there a limit to how much worse coronavirus can become?

 

It's worth remembering the journey this virus is on. It has made the jump from infecting a completely different species - its closest relatives are in bats - to us. It's like you, starting a new job: you're competent, but not the finished article. The first variant was good enough to start a devastating pandemic, but now it's learning on the job.

 

When viruses jump to humans it would be "very rare for them to be a perfect," said Prof Wendy Barclay, a virologist from Imperial College London. "They settle in and then they have a great time."

There are examples of viruses, she said, from flu pandemics to Ebola outbreaks, making the jump and then accelerating.

 

So how far could it go?

 

The cleanest way of comparing the pure biological spreading power of viruses is to look at their R0 (pronounced R-naught). It's the average number of people each infected person passes a virus on to if nobody were immune and nobody took extra precautions to avoid getting infected.

 

 

This virus has surprised us a lot. It is beyond anything we feared," said Dr Aris Katzourakis, who studies viral evolution at the University of Oxford. "The fact it has happened twice in 18 months, two lineages (Alpha and then Delta) each 50% more transmissible is a phenomenal amount of change."

 

 

It's "foolish", he thinks, to attempt to put a number on how high it could go, but he can easily see further jumps in transmission over the next couple of years. Other viruses have far higher R0s and the record holder, measles, can cause explosive outbreaks.

 

 

How are the variants doing it?

 

There are many tricks the virus could employ to get better at spreading, such as:

 

.- Improving how it opens the doorway to our body's cells.

.- Surviving longer in the air

.- Increasing the viral load so patients breathe or cough out more viruses.

.- Changing when in the course of an infection it spreads to another person.

 

One way the Alpha variant became more transmissible was by getting better at sneaking past the intruder alarm - called the interferon response - inside our body's cells. But this does not mean that by the time we work through the Greek alphabet of variants and reach Omega that we'll end up with an unstoppable beast.