Flu season may have arrived months ahead of schedule. Although it is only early October, official figures released last week show respiratory virus infections climbing across Britain, prompting health leaders to warn that the country could be heading into an unusually challenging winter.
Monthly Covid infections have reached their highest level since October last year and are accelerating sharply. Recorded cases rose from 1,374 in August to 4,589 in September.
Flu infections are running at three times last year’s level. Professor Frankie Swords, NHS England’s national medical director, said monthly flu-related hospital admissions were “the highest I can remember seeing at this time of year”.
“Something is afoot,” wrote leading epidemiologist Dr Caitlin Rivers in a recent edition of her widely read medical newsletter, Force Of Infection.
Dr Rivers, who is based at Johns Hopkins University in the US, said a comparable rise in respiratory viruses is under way there. She plans to receive her flu jab as soon as possible—several months earlier than she normally would.
What is driving the rise? Experts say the flu virus currently circulating appears to be more transmissible than last year’s strain, increasing the likelihood of an early surge in cases.
Early US data indicates that this year’s dominant strain carries mutations that may help it evade the immune system. A study published in the journal Nature therefore concluded that fewer people may already have protection against the current flu strain. Yet other specialists believe the unusually early season could point to wider changes in how respiratory viruses move through populations.
“We don’t usually see flu going up in that noticeable a way until December,” says Dr Adam Finn, emeritus professor of paediatrics at the University of Bristol. “So the visible increase in flu recorded in September really is quite early.”
Official figures released last week show respiratory virus infections rising across Britain
Dr John Tregoning says: “Getting vaccinated and reducing risk-taking behaviour is the best thing you can do to not get sick.”
One factor could be the reduced immunity created by Covid lockdowns, says Professor Finn. “Covid changed all respiratory infections because no one was really socialising for around two years, so no one caught flu those winters,” he explains. “As a result, many people—particularly younger adults and children—have far less immunity to flu than they did before.”
However, that explanation does not account for every recent development. A number of northern-hemisphere countries in Asia, which generally experience flu patterns similar to the UK, have reported an unusual trend in recent years.
Instead of peaking during winter, when people spend more time indoors and may have weaker immune systems because of lower vitamin D levels, flu has increasingly been spreading during the height of summer.
Japan declared a flu epidemic in early October last year after infections began climbing as early as July. Taiwan and Hong Kong also recorded a summer rise in cases, with infections reaching their highest point in a decade.
“It’s caused a lot of consternation,” says Professor Finn.
The reason for this shift remains uncertain, as does whether it represents a lasting change. Professor Finn suggests that hotter summers linked to climate change may be contributing, as people spend more time in air-conditioned and poorly ventilated indoor environments.
That pattern could also help explain Britain’s early flu season, which follows a summer marked by record temperatures.
Professor Finn says Asia’s earlier flu outbreaks may also reflect low population immunity, making substantial epidemics more likely. If the pattern continues, countries worldwide may need to rethink when flu vaccinations are delivered. “It’s a very big change that has lots of consequences,” he says.
“If the flu now begins in April and continues until September, vaccines being offered in October are useless,” he says. “Instead, they may need to roll them out considerably earlier. Experts are scratching their heads about what to do.”
For now, public health guidance has not changed: anyone eligible should get a flu vaccination and wash their hands regularly to reduce the risk of infection.
Dr John Tregoning, professor of vaccine immunology at Imperial College London, says: ‘We’re not sure why flu season started earlier – but getting vaccinated and reducing risk-taking behaviour is the best thing you can do to not get sick.’
