Covid: Is UK now a breeding ground for new variants?

Are we in the danger zone for creating new variants that could weaken the ability of vaccines to shield us from Covid? And does it matter?

Scientists have warned that the UK has created the perfect conditions by relaxing restrictions - which could see cases reaching 100,000 a day this summer - while large numbers of people don't have protection from both doses of the vaccine.

So far, the problematic variants have been those that spread significantly faster. The Delta variant, which was first identified in India, may spread twice as fast as the original form of the virus that emerged in China.

But speed isn't the only useful trait a coronavirus can acquire.

As more of us become immune, through vaccination and catching Covid, the more beneficial it is for the virus to evolve ways of dodging that immunity - known as immune escape.

"We are probably at the evolutionary high point, at the worst combination for an escape to happen in the UK," said Prof Aris Katzourakis, who studies viral evolution at the University of Oxford.

"The UK is in a prone position, whether it will happen we don't know, but it's more likely to happen here, now, than ever before."

But why?

There are two things to think about - how much opportunity the virus has to mutate and how big an advantage it would get by dodging the immune system.

Opportunity is a numbers game. Mutations are just random typos the virus makes when it invades our body's cells and makes thousands of copies of itself. The more infections there are, the greater the chance of fluking a favourable mutation.

How advantageous they are depends on how much immunity people have.

At the start of the pandemic, there was lots of virus around and lots of opportunity to mutate, yet there was little advantage to evading immunity because not that many people had it.

In the future, when most people will have some immunity from past infection or vaccines, then such mutations would be immensely beneficial to the virus.

Yet all that immunity or protection should keep infections down, giving the virus few chances to mutate.

So the field of viral phylodynamics, which merges how the virus is spreading, our immunity and evolutionary biology, suggests the sweet spot is when there is partial immunity, and still enough virus spreading.

That moment could be now - only 70% of adults, and few children, have received both doses of the vaccine and data from the Office for National Statistics suggests one in 80 people is infected.

This doesn't mean a new variant is destined to arise in the UK in the coming weeks, just the evolutionary pressures on the virus are making it more likely than before.

"I hope it doesn't, but it is a big gamble, if we compromise the incredible vaccines we have now I don't even want to contemplate what that world would look like," said Prof Katzourakis.

Variants that are better at escaping immunity have already emerged. They don't completely nullify the effect of vaccines in one fell swoop, rather they chip away at that protection.

This is already seen with the Delta variant, which accounts for nearly every case in the UK, and is slighter better at causing reinfection as well as evading vaccine protection, particularly in people with only one jab.

Prof Jonathan Ball, a virologist at the University of Nottingham, said: "In a population with partial immunity - particularly if a virus is spreading in the background - that will encourage a virus towards immune escape, that is inevitable.

"But what that ultimately means is unclear."

Laboratory studies suggest the Beta variant, which emerged in South Africa, has the greatest ability to evade the immune system so far.

However, vaccines are still holding up in the real world with studies suggesting they are providing greater than 90% protection from needing hospital treatment.

Also viruses don't tend to be perfect at everything. Evolutionary trade-offs mean it may have to sacrifice something else in order to be better at evading the immune system.

The virus uses its "spike protein" as a key to unlock the doorway into our body's cells. But it is also how our immune systems learn to recognise the virus. So mutations that change the shape may help the virus hide from the immune system, but make it harder to infect our cells.

"Could there be a virus that emerges that not only escapes vaccines very well, but also transmits well and causes disease in fully immune people? It's not looking likely," Prof Ball said.

"I'm reassured in truth, I don't think things are too bad."

However, the emergence of new variants in the months to come will be monitored very closely.

Follow James on Twitter