We’ve lived with covid-19 for more than half a decade, but it’s still evolving A seasonal rise in covid-19 cases in Europe and North America has focused attention on a group of variants called XFG, which have dominated worldwide over the past year. A string of covid-19 variants have arisen since the virus emerged in 2019, but do we need to be concerned every time we hear of a new strain? Or have our past covid-19 infections and vaccinations given us a baseline level of protection?
Six years on from the height of the covid-19 pandemic, “we’re in this weird, uncharted territory,” says Danny Altmann at Imperial College London. But it is not as bad as some of my colleagues feared, where we’re brewing the next disaster.” In lab tests, XFG (sometimes known as Stratus) is better at evading antibody protection than previous covid-19 variants, which is thought to be why it has become dominant globally. But for most people, existing immunity from previous vaccinations and infections appears to be enough to protect against serious illness, leaving researchers counselling both calm and caution.
All covid-19 variants circulating today are descendants of Omicron, the last major strain to be named, which emerged in 2021. The virus “continues to evolve”, says Ian Mellis at Columbia University in New York, creating a succession of new variants that outcompete previous ones, causing waves of infection. XFG was first detected in early 2025, and the World Health Organization started officially monitoring it that June.
It now makes up around 60 per cent of sequenced covid-19 cases worldwide. It emerged from an exchange of genetic material between two subvariants of an Omicron lineage called JN.1, says Mellis, perhaps when they both infected the same person. Earlier this year, Mellis and his colleagues reported the results of lab tests01211-2) where they tested a range of covid-19 viruses, including XFG and another variant nicknamed Nimbus, against antibodies found in human populations.
They found that although both variants bound to host cells slightly less well, this was more than offset by a greater ability to evade covid-19 antibodies, compared with past variants. That ability to evade the immune response, on top of how widespread XFG is, may mean that more people will be susceptible to serious infection, says Altmann. In the UK, for example, 1638 covid-19 cases were identified in hospital settings during the first week of October, a rise from 1328 cases the week before.
But that is part of an expected seasonal rise, and lower than at the same time last year. Even though the virus is gradually drifting further from the original form, and many people in the UK haven’t been vaccinated for several years, “we’re making do with the immunity that we’ve got on board,” Altmann says. There is also now far less monitoring that could provide early warning of such an event, he says.
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