In each warm body it infects, the virus behind Covid-19 has the potential to change. It can become more deadly, more transmissible or more resistant to the vaccines on which we are all pinning so much hope. Mercifully, the biology of Sars-CoV-2 means that such changes happen slowly and almost always fail to catch on.
But mutations, like pandemics, are a numbers game. Every new person infected provides another opportunity for the virus to adopt a new form. So far, Sars-CoV-2 has infected at least 106 million people worldwide and taken on many thousands of mutations. Most of those changes are slow and inconsequential – evolutionary dead ends that nobody will ever realise existed. But, in some people, the virus hits the jackpot.
That is seemingly what happened in Kent in September 2020. Usually Sars-CoV-2 mutates slowly. We can watch this happen, with single letters changing one at a time in a viral genome that contains almost 30,000 letters. But, in one great leap, the UK variant picked up 17 of those changes. Eight of them happened in the gene that encodes the spike protein – the hook the virus uses to latch on to and enter human cells. If the genome of Sars-CoV-2 was a 30,000-character-long poem then the UK variant re-wrote its first line, drastically changing its meaning in the process.
The emergence of the UK variant presented scientists with an urgent question: how did the virus make this genetic leap, seemingly out of nowhere? The leading hypothesis is that the new variant evolved within just one person, infected with Sars-CoV-2 virus for so long that the virus was able to evolve into a new, more infectious, form. Out of this human pressure cooker, a new variant burst onto the scene and sent the world scrambling to react. Borders closed, countries locked down once more, vaccines were re-tested.
None of this was enough to halt the spread of B.1.1.7 – the scientific name given to the UK variant. The new variant has now been found in 75 countries and is spreading locally in Brazil, Canada, China, the United States and most of Europe. Up to 70 per cent more transmissible than other coronavirus variants, B.1.1.7 is now responsible for the vast majority of new cases in England. On January 22, the UK’s chief scientific officer, Patrick Vallance, added another worry to the list: preliminary data suggests that the new variant may be 30 per cent more deadly than others. [Continue reading…]