1 day agoShareSaveJames GallagherHealth and science correspondentShareSaveGetty ImagesListen to James read this articleFlu strikes every winter, but this year something seems to be different.A seasonal flu virus suddenly mutated in the summer. It appears to evade some of our immunity, has kick-started a flu season more than a month early, and is a type of flu that history suggests is more severe.The NHS has now issued a “flu jab SOS” as fears grow that this will add up to a brutal winter.There is a lot of nuance and uncertainty, but leading flu experts have told me they would not be shocked if this was the worst flu season for a decade.”We haven’t seen a virus like this for a while, these dynamics are unusual,” says Prof Nicola Lewis, the director of the World Influenza Centre at the Francis Crick Institute.”It does concern me, absolutely,” she adds. “I’m not panicking, but I am worried.” So what’s going on? And what can we do?Scientists track the evolution of influenza viruses because they mutate constantly and the seasonal flu vaccine has to be updated each year to keep up.This evolution happens in a rhythm known as “shift and drift”. Most of the time the virus drifts along making minor changes and then every so often there is a sudden abrupt shift as the virus mutates substantially.That happened in June this year. Seven mutations appeared in a strain of H3N2 seasonal flu and led to a “fast increase” in reports of the mutated virus, says Prof Derek Smith, director of the centre for pathogen evolution at the University of Cambridge.Getty ImagesUnusually, this happened outside flu season, in the middle of the northern hemisphere’s summer.”It almost certainly will sweep the world, so from that standpoint, it’s something that will come up quickly,” says Prof Smith.By September, as children went back to school, the nights drew in and the temperatures started to drop, there was an uptick in cases.Exactly what the mutations are doing is still being explored, but they are probably helping the virus to evade some of the immunity we have built up over years of flu infections and vaccines.The result is the virus is finding it easier to infect people and spread – that is why the flu season is so early in the UK and other countries, including Japan.If the virus can spread more easily then it does not have to wait for more favourable wintery conditions – when we spend more time indoors with the heating on and the windows shut – to start the flu season.”We’re miles ahead,” says Prof Lewis. “I think it’s going to be a strong flu season.”If you remember your R numbers from the pandemic (that is the number of people each infected person passes the virus onto), they suggest the new mutant has an edge.Seasonal flu usually has an R number of around 1.2, while the early estimate for this year is 1.4, says Prof Lewis.So very roughly, if 100 people had flu, they would pass it to 120 in a typical year, and 140 this year.Worst flu season for a decade?”It’s highly likely it’s going to be a bad flu season and it’s going to happen quite soon – we’re already well into it,” says Prof Christophe Fraser, from the Pandemic Sciences Institute at the University of Oxford.”There are indicators that this could be worse than some of the flu seasons we’ve seen in the last 10 years.”In a typical flu season, around one-in-five of us get infected, but that could be higher this year, he warns.But all these predictions are still clouded in uncertainty.Some look to Australia for clues as it had the worst flu season on record this year, although it did not face the same mutated H3N2 we have. We know the virus is spreading very well in children in the germ-fest that is the school playground.But the immunity a 10-year-old has developed will be very differen …
