The NHS remains on high alert over flu, health bosses say, but there are clear signs the surge in the virus has come to an end for now at least.

Community spread appears to have stabilised, the UK Health Security Agency says.

Meanwhile, the rise in hospital cases has slowed. And with just over 3,000 patients in hospital in England with the virus, the dire prediction by NHS chief executive Sir Jim Mackay of “between 5,000 and 8,000” cases has not materialised.

How serious then is this flu season so far, and how does it really compare to previous outbreaks of the virus?

The major difference between the 2025 flu season and the last three years is that the virus started spreading a few weeks earlier than normal.

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

UKHSA then records the percentage of those tests that come back positive for flu.

Figures had been rising quickly over the autumn and at the start of winter.

But last week the spread of the virus appears to have stabilised at a medium level, UKHSA says.

It is too early to say whether this marks the start of the peak. Flu is unpredictable, a lull can be followed by another surge.

The picture across the four nations of the UK is similar.

Some virologists have linked the earlier flu season this year to the type of virus that is circulating – known as H3N2.

Historically, seasons dominated by that strain tend to be more severe, with larger numbers of hospitalisations in older people, in particular.

H3N2 has not been the main form of flu detected in the UK for three years, which may mean that less immunity has been built up in the population.

Scientists also spotted a further shift in the genetic makeup of the virus over the summer.

This might have given the virus a head-start in the autumn.

The name ‘super-flu’ has been used by the NHS to describe this latest outbreak.

But that is not a medical term, and it does not mean the virus itself has suddenly become more dangerous or harder to treat.

“It is misleading and a bit frightening to call it super flu; it’s just a flu variant that is clearly a little bit more infectious than normal,” says Prof Lawrence Young, professor of molecular oncology at the University of Warwick.

“What we’re seeing is a flu season that’s perhaps two to three weeks earlier than normal.”

Separately, the NHS also records the number of the sickest patients in hospital with flu over the winter. Trends in hospital data tends to lag behind community spread as it takes some time for people to get ill enough to seek hospital care.

Figures for last week showed the number hit 3,140 in England, an 18% rise on the week before. But that was after a 55% jump in the week before that.

Although the national figure masks what is happening across different regions with some areas seeing numbers fall and others still seeing steep rises.

Those over 85-years-old are five times more likely to be hospitalised than the general population.

Comparing outbreaks over the decades is difficult because testing has improved in recent years, so a rise in hospital admissions over time might also reflect better detection.

But estimated figures on flu deaths shows that some winters have been particularly serious over the past 20 years.

In 2017-18, for example, it’s thought 25,000 people died from the virus in England, with care homes and older adults most affected.

That year an unusual form of the influenza B virus started circulating and the ‘beast from the east’ cold snap bought freezing temperatures to the UK, creating the ideal environment for the disease to spread.

Just three years before that, in 2014-15, modelling by scientists at UKHSA estimated that 35,000 had died, making it one of the most lethal flu seasons in decades.

Again, that was blamed on an outbreak of the H3N2 form of the virus and a seasonal vaccine that was not well matched to the exact form of the disease circulating.

There is nothing in the data so far which suggests anything comparable in 2025, but we won’t know for sure until the first estimates for this season’s influenza deaths are published in the new year.

The message coming from doctors and the NHS is for millions of people to continue to come forward for a flu vaccine.

Even though the genetic make-up of the virus has shifted, the main jab is still thought to offer an effective level of protection, particularly against ending up in hospital with severe disease.

The flu vaccine is free on the NHS for those over 65-years-old, young children, pregnant women, those with certain health conditions, carers, and front-line health and social care workers.

All other adults can get the same vaccine for between £15 and £25 from high street pharmacists.

The latest data shows that more than 70% of older people and care home residents had taken up the offer of a free jab by 14 December.

But vaccination rates in some other groups are much lower.

Only 45% of all front-line NHS workers in England have been vaccinated so far this year.