Hospitals are bracing for a once-a-decade flu season in which a mutated version of the virus spreads widely among young people and is expected to cause a wave of hospitalizations when it reaches older adults.
The threat prompted National Health Service managers to redouble efforts to vaccinate staff and the public, expand same-day emergency care and treat more patients in the community to reduce the need for hospital stays.
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“Last flu season was particularly bad and we are very concerned that this year could be even worse,” said Elaine Clancy, group chief nursing officer at St George, Epsom and St Helier University Hospitals. “We are preparing for a surge of influenza in our wards.”
Scientists first discovered a mutated version of the flu virus in June. Genetic analysis shows it is a descendant of the strain that caused Australia's worst flu season on record this year. The country has more than 400,000 laboratory-confirmed cases, and low vaccination rates are exacerbating the problem.
The mutated virus, which changed through a natural process called antigenic drift, quickly became the dominant strain in the UK, causing the flu season to start more than a month earlier than usual.
Dr Claire Beynon, chief executive of public health at Cardiff and Vale University Council, said: “We are seeing a rapid and early increase in flu rates this winter and expect an increase in hospital admissions.”
A spokesman for NHS Greater Glasgow and Clyde said the number of flu in its facilities was normal for this time of year, but that it was moving to reduce pressure on hospitals at a “rapid pace”.
The number of flu cases rises every winter, but health officials fear this season could be especially severe if new mutations in the dominant strain help it evade people's immune defenses.
The virus is a subtype of H3N2 influenza that tends to cause more severe illness than other subtypes in circulation, especially in older adults. Mutations can increase the transmissibility of the virus. It's too early to tell whether they make the infection worse.
In a typical flu season, the R value, which is the average number of people an infected person passes the virus to, is between 1.1 and 1.2. This season the rate is expected to be 1.4, meaning for every 100 people who get the flu, they are expected to infect 140 more.
“Whenever the season starts early, the peak tends to be larger,” said Antonia Ho, professor in the department of infectious diseases at the MRC Virus Research Center at the University of Glasgow. One reason is that fewer people were vaccinated when they came into contact with the virus.
Thursday UK Health The UKHSA said flu cases overall continued to rise despite a temporary slowdown due to the school break. The infection most often occurs in children, but spreads among older people. Health officials expect that number to rise further as colder weather leads to more people mixing indoors.
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“The new strain of flu is worrying because a big flu season was already predicted,” said Caroline Abrahams, director of the charity Age UK. “It is more important than ever that everyone who is eligible, including older adults, gets the flu vaccine and takes precautions to stay healthy this winter.”
Early UKHSA data shows that existing vaccines are less effective at blocking infections caused by mutated influenza viruses. but at the same time provide good protection against serious diseases. In England, vaccine effectiveness against hospital visits and hospitalizations is still within normal limits, at 70–75% in children and 30–40% in adults.
Although H3N2 can cause severe flu seasons, it is not inevitable. In the 2003–2024 season, the season began early due to the introduction of the H3N2 strain. This led to 12,000 flu deaths in England and Waleswhich is at the lower end of the typical range.
Ho encouraged everyone who is eligible to take up the offer of vaccination and encouraged others to consider paying for the shot and using lateral flow tests to check for flu infections. Less than a third of people with one or more chronic conditions have sought the vaccine, according to the UKHSA.
Ed Hutchinson, professor of molecular and cellular virology at the MRC Virus Research Center at the University of Glasgow, said it was “quite likely” the UK was on track for its worst flu season in a decade.
“This could mean that large numbers of people require hospital treatment, especially people at risk, especially older people, but also people with underlying health conditions, pregnant women and very young children,” he said.
