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Expect flu to surge next winter as lockdown has led to low levels, experts warn

Measures to combat Covid-19 have had a dramatic impact on flu transmission - Telegraph
Measures to combat Covid-19 have had a dramatic impact on flu transmission - Telegraph

Experts have warned the world may face a dramatic resurgence of flu next winter, after lockdown, masks. increased hygiene and social distancing measures cut the virus to levels not seen for over a century.

Scientists fear that falling immunity levels to influenza - normally sustained by seasonal circulation of the virus - could now pave the way for one of the worst flu outbreaks for years.

“If I had to gamble on it, then I would guess that we are likely to get a more severe epidemic in the coming winter - assuming restrictions are fully lifted by then,” said Prof John Edmunds, of the London School of Hygiene & Tropical Medicine and a member of the government’s Sage committee of scientific advisors.

“We have effectively missed out on flu this winter, so the levels of immunity are less than would be typical. In fact, it is not impossible that we will have an out-of-season epidemic perhaps in the autumn, rather than winter,” he told the Telegraph.

In most years in the UK, seasonal flu kills between 10,000 and 30,000 people, depending on the stain and effectiveness of the annual vaccine. But over the last 12 months, flu deaths have hardly registered.

According to weekly surveillance data reported by Public Health England no cases of flu have been reported all year.

This, say experts, not only makes a violent rebound of the disease likely but makes predicting which strain will hit us next and - crucially - deciding which vaccine to produce much more difficult.

Decision makers are also concerned that the current pressure on the flu virus could also see a more transmissible stain emerge.

Dr John McCauley, director of the Worldwide Influenza Centre at the Francis Crick Institute - one of five WHO collaborating centres that constantly track pandemic flu viruses and helps to update influenza vaccines - said the current situation is unprecedented.

“I don’t think we’ve been in a position with so little flu in circulation for over a century,” he said. “What that means is overall in the population there’s less experience and therefore there’s less boosting of immunity.”

Dr McCauley added that identifying which strains this year’s vaccine must protect against has proved tricky, as the number of samples taken from flu strains has fallen 20 fold globally. “Because we’re looking at fewer samples, we don’t really know how representative they are,” he said.

A WHO panel on influenza meets twice a year to tweak the flu jab to make sure it protects against circulating strains. The latest gathering took place via a “very long teleconference” on Friday and details of the adjusted vaccine were revealed in February.

The degree to which social distancing has suppressed flu and other infectious diseases has startled experts around the world. In a Twitter thread Nicola Oliver, a director and public health expert at Medical Intelligence, gathered data demonstrating the striking fall of flu.

Over the past five years the number of specimens the Global Influenza Surveillance and Response System has collected - a proxy measure of the spread of flu worldwide - has ranged from roughly 15,000 to 40,000. In the past 12 months, this has plunged to below 1,000 (see chart above).

The same is true for other infectious diseases. Public Health England reports show fewer than 20 cases of norovirus were detected each week this winter, for instance, while the five year seasonal average hovers at between 150 and 200.

“The social distance measures that we have been under for the last year have also resulted in low levels of circulation of many other viruses, such as RSV [respiratory syncytial virus], adenoviruses and even noroviruses,” said Prof Edmunds.

“Similarly high levels of these other viruses might also be expected after we lift restrictions. The combination could well mean that winter pressures on the NHS might be particularly bad next year,” he said.

Prof Mark Woolhouse, a professor of infectious disease epidemiology at the University of Edinburgh, added: “I don’t think we know whether or not there will be a bad flu season. It’s speculative and there are scenarios where it could be worse than average or better than average.

“But I do think that the NHS has to be considering the possibility of a strong resurgence [of influenza],” he said, adding the UK should plan to repeat last year’s expanded flu vaccination drive to mitigate the risk.

Spillover: the origins of Covid-19 and why the next pandemic may already have started
Spillover: the origins of Covid-19 and why the next pandemic may already have started

Experts say social distancing measures over the last 12 months may also have increased the pressure of flu viruses to mutate and become more transmissible. However, Dr McCauley said it was unlikely seasonal flu would mutate to become more deadly.

He added that the threat of a zoonotic influenza strain jumping from poultry (as seen this weekend in Russia) or pigs remains stable as social distancing has not affected our behaviours around animals.

“You could speculate that with lower overall immunity to influence that you may have a bit of a drop to cross species immunity. But I don't think that that would be as marked as the [drop] in immunity to seasonal flu”, he said.

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