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A fast-spreading mutated flu virus known as subclade K is fuelling a sharp rise in infections across England, with hospitals warning of mounting strain alongside COVID and RSV.
In the past week, an average of just under 2,700 hospital beds a day in England were occupied by patients with flu. There are concerns that figure could rise to somewhere between 5,000 and 8,000 by the end of this week, increasing pressure on the NHS at a time when a five-day strike by resident (junior) doctors is possible next week.
Why cases are rising so quickly
Subclade K is spreading rapidly because population immunity from previous infections and vaccinations is low. The virus is a variant of the H3N2 flu strain and is reported to have acquired seven new mutations in late summer.
Transmission is also higher than is typically seen with seasonal flu. Ordinarily, every 100 people infected with seasonal flu would be expected to pass the virus on to 120 others. With subclade K, that figure is 140, helping explain why cases are climbing quickly.
Current data suggests 18 in every 100,000 patients in England are consulting their GP with flu-like symptoms. That remains below the peak of around 50 in every 100,000 seen in 2017/18, which was described as the worst flu outbreak in recent years.
Children, Christmas and the risk to older relatives
Children are described as key spreaders of flu, with infections moving quickly through classrooms. Some schools have temporarily shut because of the impact.
With the Christmas holidays approaching, fewer school-based contacts may slow transmission among children. However, the season also brings increased mixing between families and elderly relatives, who are more likely to experience severe illness and may require hospital care. As a result, even if overall infections slow temporarily, the impact on hospitals could worsen.
The severity of flu and who is being urged to get vaccinated
Flu can be a severe illness rather than a mild cold, and while many people recover with a few days of rest and paracetamol to reduce fever, those who are vulnerable can become seriously unwell. During the 2017/18 outbreak, around 22,000 people died.
The NHS is urging people in certain groups to take up vaccination, including the over 65s, those with underlying health conditions, pregnant women, carers and children. The vaccine is not considered a strong match for subclade K, but it is still expected to reduce the chance of hospital admission by 30-40% in adults.
While it remains unclear when the outbreak will peak, the latest figures suggest the spread is far from over.
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