Flu in four charts: How this year’s winter outbreak is different

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

NHS England chief executive Sir Jim Mackey warned that between 5,000 and 8,000 hospital beds could be occupied with flu patients over the weekend.

Health experts at the King’s Fund think tank have said talk of a “relentless wave of flu” has become worryingly familiar in recent years. But Chris Streather, medical director of the NHS in London, said the situation was “well within the limits” of what the NHS could cope with.

So how is winter 2025 really different and which patients have been most affected by what the NHS now describes as “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 sign of this was seen in October in data published by the UK Health Security Agency (UKHSA).

When someone goes to their GP or hospital with flu-like symptoms, they can be tested for various viruses, including flu, Covid and RSV.

UKHSA records the percentage of those tests that come back positive for flu, which can then give a strong indication that rates in the community are rising or falling.

Virologists have linked the start of this year’s flu season to a subtle change in the genetic makeup of the main flu virus circulating, 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 has not encountered this exact version of the flu before, meaning there may be less immunity developed in society, allowing it to spread more easily.

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

The latest breakdown of UKHSA data shows that the proportion of positive tests is currently much higher in children and young people who are still at school or college.

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

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

But there is another concern: that younger people will return home and then spread the disease to older relatives who tend to be more vulnerable.

The NHS records the number of patients hospitalized each week with influenza and other types of respiratory illnesses.

The figure has risen sharply in England, with an average of 2,660 flu patients occupying a hospital bed last week, up from 1,717 the week before.

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

But patients coming in now would have been infected with the virus about a week ago, when infection rates were lower.

The biggest concern for the health service is what will happen in the coming weeks as new cases appear in A&E.

The NHS has approximately 105,000 hospital beds available in England and tends to “warm up” during the winter, with 95% of them occupied at any one time.

If the number of flu patients requiring overnight treatment rises to 5,000 or more, as Sir Jim Mackey predicts, then the entire hospital system could come under greater pressure.

The message from doctors and the NHS is for people from vulnerable groups to continue coming forward for the flu vaccine.

Although the genetic makeup of the virus has changed this winter, the main vaccine is still believed to offer effective protection, especially against serious illness.

The flu vaccine is free on the NHS for people over 65, 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 between £15 and £25 at leading pharmacists.

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

But vaccination rates in younger at-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 this year at around the same level: around 42%.