What is the H3N2 flu strain? Symptoms you need to look out for as UK cases surge
We are approaching the time of year when coughs and colds become common and everyone gets sick.
But health experts warn this winter could see the worst flu outbreak in years as a new strain threatens to devastate the NHS.
The H3N2 strain has been labeled “unsavory” by health bosses who have warned that flu hospital admissions are already rising.
Although not yet at its peak, admissions are growing at a rate not seen until December; Experts worry that many of the most vulnerable people may not yet receive their vaccines.
With the increase in cases Independent General practitioner and medical consultant Dr. He spoke with Giuseppe Aragona. Prescription Doctor, About how worried we should be about H3N2 and how we can prevent it.
What is the H3N2 strain?
H3N2 is a strain of the influenza virus that is recognized as one of two widely circulating strains. This strain, also known as subclade K, is currently the most dominant strain in the UK, according to the UK Health Safety Agency (UKHSA).
Dr Aragona explained that the letters and numbers refer to the surface proteins of the virus, hemagglutinin (H) and neuraminidase (N).
This particular combination can sometimes cause more serious illness, especially in older people or those with underlying health problems, he said.
“H3N2 changes regularly, so the version of the virus circulating this year may be different from previous years or the version in the seasonal vaccine, which could make people more susceptible,” he added.
What are the symptoms?
According to the UKHSA, flu signs and symptoms develop very quickly and extreme fatigue is common; This is different from cold symptoms that appear gradually.
The symptoms and severity of H3N2 disease are similar to seasonal flu, including fever, cough, runny nose, and possibly other symptoms such as body aches, vomiting, or diarrhea.
People considered to be at high risk for developing flu-related complications include: children under five (especially children under two), adults age 65 and older, pregnant women, and people with certain chronic medical conditions such as asthma, diabetes, heart disease, weakened immune system, and neurological conditions.
If you develop flu symptoms after direct or close contact with pigs, contact your doctor and tell them about your symptoms and contact with pigs.
How high are flu rates right now?
Latest figures showed the rate of flu hospital admissions in England rose to 3.8 per 100,000 people, from 2.4 last week, according to data published by the UKHSA.
While this is well below the peaks reached in recent years, it is a level of acceptance that is not typically reached until the following month. Experts say this is evidence that the current flu season has started “unusually early” and we could be bracing for a particularly tough winter.
This also follows the biggest flu season in Australian history, which is generally seen as an accurate prediction of what the UK can expect.
Why is H3N2 so bad this winter?
Dr Aragona said there were a number of different reasons why flu was expected to be particularly bad this winter.
First, he explained, the flu season started earlier than usual, which gave the virus more time to spread.
He also added that it had “evolved” from last year’s strain, meaning previous immunity and even the vaccine may provide less protection than usual.
“In recent years, fewer people, especially children, have been exposed to flu, leaving more people vulnerable,” he said. “Furthermore, colder weather, indoor mixing and social habits contribute to faster transmission, creating the perfect storm for higher flu rates.”
Earlier this week, experts warned that the strain had developed seven new mutations over the summer; This means it is quite different from the previous strain included in this year’s vaccine.
The UK is bracing for a flood of flu deaths this winter, with NHS leaders issuing a “flu vaccine SOS” urging people to stay protected.
There were nearly 8,000 deaths from flu last winter, according to the UKHSA. This figure is higher than the nearly 3,500 deaths recorded the previous year, but lower than the 2022-2023 season, when approximately 16,000 deaths occurred.
How can you prevent getting the flu?
Dr Aragona said the “most effective” way to protect yourself from H3N2 was to get a flu vaccine – especially if you were in a “higher risk group” such as being over 65, pregnant, very young or living with a long-term health condition.
“The vaccine may not prevent every infection, but it significantly reduces the risk of serious illness and hospitalization,” he said.
Dr Aragona added that protection can be increased by practicing good hand hygiene, covering your mouth and nose when coughing or sneezing, avoiding close contact with sick people and keeping your home well ventilated.
New data published by the UKHSA this week shows the 2025-2026 vaccine is now 70 to 75 per cent effective at preventing hospital admission in children aged 2 to 17 and 30 to 40 per cent effective in adults.
Dr said, consultant epidemiologist on vaccination at UKHSA. Jamie Lopez Bernal said the results provided “reassuring evidence” that the season’s flu vaccines could provide significant protection despite concerns about the new subclass.
He “strongly encouraged” anyone eligible to get the flu vaccine “as soon as possible,” calling it the “best defense” against serious illness.
Deputy chief medical officer Dr Thomas Waite said: “Flu can be an unpleasant infection for many and life-threatening for some; vaccination is the best form of defence.
“Early data from the UKHSA shows that this year’s vaccine continues to provide good protection against the flu strains circulating this year. Flu season started earlier this year. If you are eligible, now is the time to get vaccinated.”
Last year’s flu vaccine had a significant impact on reducing serious illness; They ranged from an almost 40% reduction in the number of people aged 65 and over hospitalized to a 75% reduction in the number of those aged 2 to 17.
How concerned should we really be about H3N2?
Dr Aragona said flu could be “unpleasant” for most healthy adults and children, but cautioned against panic as it was generally “manageable”.
“But for the elderly, those with chronic diseases and other vulnerable groups, H3N2 can be serious and this season may put extra pressure on health services due to the early onset and characteristics of the strain,” he said.
“The important thing is to be careful: get vaccinated, take reasonable precautions, and seek help early if symptoms become severe. With these steps, the risk can be managed effectively, even in a year when flu is more common.”
