Mutated Flu Virus May Bring the Worst Season in a Decade
Flu season comes every winter, but experts say this year looks different.
A common strain of the flu virus suddenly changed over the summer, making it harder for our immune systems to recognize. The mutation caused the flu season to start more than a month early and could make people sicker than usual.
The UK’s National Health Service (NHS) has issued a “flu jab SOS,” warning that this winter could be one of the toughest in years.
“It does concern me,” said Professor Nicola Lewis, head of the World Influenza Centre at the Francis Crick Institute. “We haven’t seen a virus like this for a while. I’m not panicking, but I am worried.”
What Changed?
Flu viruses are always mutating, so scientists track their changes closely. Usually, these are small “drifts” that happen gradually. But every so often, there’s a major “shift” — a sudden jump in the virus’s evolution.
That big change happened in June when scientists found seven new mutations in a type of flu called H3N2. Professor Derek Smith from the University of Cambridge said these changes helped the virus spread faster — even outside the usual flu season.
“It almost certainly will sweep the world,” he said.
By September, cases were rising as kids went back to school and temperatures dropped. The mutations seem to help the virus dodge some of the immunity we’ve built from past infections and vaccines, making it easier to spread.
Why It Matters
Because this new version of the flu spreads more easily, it doesn’t need to wait for cold weather to take off. “We’re miles ahead,” said Prof. Lewis. “I think it’s going to be a strong flu season.”
Experts estimate the virus’s R number — how many people one infected person spreads it to — is around 1.4 this year, compared to the usual 1.2. That means 100 people could infect 140 others instead of 120.
Professor Christophe Fraser from Oxford University said, “It’s highly likely it’s going to be a bad flu season and it’s going to happen quite soon.”
In a normal year, about one in five people get the flu. That number could be higher this time.
Who’s Most at Risk?
Children are spreading the virus quickly in schools, but the biggest concern is for older adults. History shows that H3N2 strains tend to be more severe for seniors.
“H3 is always a nastier virus,” said Prof. Lewis. “It’s more impactful on the population.”
Last winter, nearly 8,000 people in the UK died from flu. In the 2022–23 season, that number was close to 16,000.
What Can You Do?
Experts say the most important step is to get your flu shot as soon as possible. The NHS says 2.4 million vaccination appointments are available in the coming week.
“This is absolutely the most important year to get vaccinated,” said Prof. Lewis.
This year’s vaccine isn’t a perfect match for the new mutation because it was designed before the virus changed. Still, doctors say it offers valuable protection — especially against severe illness and hospitalisation.
Dr. Mary Ramsay from the UK Health Security Agency said, “Whatever strains circulate this winter, the vaccine will still help protect those most at risk.”
Doctors are also being reminded to give antiviral medicines early to reduce the risk of complications.
Japan, which is also facing an early flu season, has even closed some schools to slow outbreaks.
As Prof. Lewis puts it, “It might all go away by next week — but I don’t think it will.”
