Flu in five charts – how this year’s winter outbreak is different

The NHS says it is facing a “worst-case scenario” after the number of people in hospital with flu rose by 55% in a week in England.

NHS England chief executive Sir Jim McKee says between 5,000 and 8,000 hospital beds could be filled with flu patients by the weekend.

Health experts at the King's Fund think tank said talk of an “unrelenting wave of flu” had become alarmingly familiar in recent years. But Chris Streeter, medical director of the National Health Service in London, said the situation was “well within what the NHS can cope with”.

How, then, will the winter of 2025 really be different and which patients will be most affected by what the NHS is now calling a “super flu”?

The main difference between the 2025 flu season and the previous three years is that the virus began spreading about a month earlier.

The first signs of this emerged in October in data published by the UK Health Security Agency (UKHSA).

When someone goes to their GP or hospital with flu symptoms, they can be tested for a range of viruses, including flu, Covid and RSV.

The UKHSA records the percentage of those tests that come back positive for flu, which can then provide strong evidence that infection rates in a community are either rising or falling.

The picture elsewhere in the UK, from Scotland to Wales and Northern Ireland, is broadly similar, with more tests coming back positive for flu in recent weeks.

Virologists attribute the start of this year's flu season to a subtle shift in the genetic makeup of the main circulating flu virus, called H3N2.

The so-called “super flu” is not a medical term and does not mean that the virus is more serious or more difficult to treat.

But the general public hasn't been exposed to this exact version of the flu before, meaning there may be less immunity in the community, allowing it to spread more easily.

Children tend to be more susceptible to the flu than older people, partly because their immune systems are still developing and also because they tend to spread viruses more quickly through close contact.

The latest breakdown of UKHSA data shows the proportion of positive tests is now much higher for children and young people still at school or university.

Some schools have had to reintroduce Covid-like measures to prevent the spread of the virus, such as reducing singing at assemblies and introducing sanitizing stations. and one site in Caerphilly had to be temporarily closed.

Every year, thousands of healthy children end up in emergency departments with complications after contracting the flu.

But there is another problem: young people will return home and then pass the disease on to older relatives, who tend to be more vulnerable.

The National Health Service records the number of patients admitted to hospital each week with influenza and other types of respiratory illnesses.

The number has been rising sharply in England, with an average of 2,660 flu patients in hospital beds last week, up from 1,717 the previous week.

People over 85 are five times more likely to be hospitalized than the general population.

But patients hospitalized now would have been infected with the virus a week or so ago, when infection rates were lower.

Of greater concern to health services is what will happen in the coming weeks as new cases emerge in emergency departments.

The NHS has around 105,000 available hospital beds in England and tends to overheat in the winter, with 95% of them occupied at any one time.

If the number of flu patients requiring overnight treatment jumps to 5,000 or higher, as Sir Jim McKee predicts, it could put the entire hospital system under greater pressure.

Doctors and the NHS are urging vulnerable people to continue to advocate for the flu vaccine.

Although the genetic makeup of the virus has changed this winter, the brunt of the attack is still thought to provide effective protection, especially against severe disease.

The flu vaccine is free on the NHS for over 65s, young children, pregnant women, people with certain health conditions, carers and frontline health and social care workers.

People in other groups can get the same vaccine for £15-25 from regular pharmacies.

As of November 30, about 70% of seniors and nursing home residents had taken up the offer of a free flu shot.

But vaccination rates in younger risk groups such as the clinically vulnerable were lower, at just over 40%.

Rates among NHS workers in England, which have fallen since the Covid pandemic, appear to have stabilized at around the same level this year at around 42%.