Could an unknown patient with a chronic Covid-19 infection be the origin of the dangerous new UK strain?

Tom Clarke

Former Science Editor

ITV News Science Editor Tom Clarke on how the new strain of the virus has spread

Scientists are now almost certain we're now dealing with a variant of the Covid-19 virus more infectious than any seen before.

If their assumptions are correct this is a major moment in the pandemic. This is the first time that any of the thousands of variants of the virus that have cropped up around the world this year behaves in a different way - making it worthy of the title "strain" - and one which could now mean we're dealing with a very different disease than the Covid-19 we've struggled with until now.So where did it come from? In the first analysis of the new strain, published today there are important clues.

To understand them, it's important to understand that SARS-CoV-2 (the coronavirus that causes Covid-19) is mutating all the time - about once or twice a month. Most of these mutants die out. But some persist as new families, or lineages, of the virus with their own branches of a great viral family tree. The first thing about the family this new strain belongs to is that it's like nothing that has come before. Those documented so far have just one or two mutations distinguishing them from their viral ancestors. This one has a group of 14 mutations found together in no other family. And at least three of them could explain why the virus now has a deadly edge.

One, called N501Y, changes the shape of the "receptor binding domain" of the virus's spike protein. This is the molecular "key" that helps the virus break into our cells and wreak havoc. It's thought the change the mutation causes improves how well the key fits, helping it break in more easily.

Immune compromised patients are treated with convalescent plasma donated by Covid-19 survivors. Credit: PA

A second, deletion 69-70, is thought to change the shape of a different part of the spike protein that might help it evade our immune system - a possible "stealth" power.

The third, mutation PH681H, is worryingly close to a location on the virus's surface that might help it fuse with the membranes of our cells. Making its journey inside easier.Each of these mutations has been seen in other SARS-CoV-2 families before. But never all together. It's the combination of their effects that might have allowed this strain to get it's evolutionary edge and become more infectious.But how? Well it's only a hypothesis, but it could be that it evolved inside just one, unlucky patient.

The mutations found in B.1.1.5 have all been seen evolving separately in immune compromised patients (like those on cancer treatment) who became chronically infected with the virus. These patients are unable to fight off their infection, meaning SARS-CoV-2 has time, to survive in their bodies and mutate. Like a living laboratory for its evolution.What's more, in places like the UK, immune compromised patients are treated with convalescent plasma donated by Covid-19 survivors, chock full of antibodies against the virus. If these therapies fail, the don't just fail the patient - they allow the virus inside them to adapt mutations to avoid those antibodies.It's only a theory, and the experimental results that could stand it up will be a long time in coming. But it's a plausible explanation for how the UK may have found itself home to a newly virulent strain of Covid-19.Government scientists said today it may be up to 70% more infectious than existing variants of Covid. That means we're going to have to try 70% harder to keep it under control before a vaccine hopefully halts its spread.