Mutations thought to be spreading flu faster and earlier, with vaccines less effective than hoped
The NHS is bracing for one of its worst winters on record as a surge in flu cases puts pressure on GP surgeries, hospitals and ambulance services. The flu season is well under way in continental Europe, too, where the same flu strain active in the UK is emerging as the force behind a new wave of infections.
In the northern hemisphere it normally runs from mid-November to mid-February, though it can start as early as October and run into May. Health officials call the start of the season when 10% of suspected cases test positive for flu. At the start of November, the figure in England was already at 11% compared with 3% at the same time last year. The season is thought to have started four to five weeks earlier than usual.
There are always multiple flu types in circulation. Seasonal flu is caused by influenza A and influenza B viruses. Common subtypes of influenza A are known as H1N1 and H3N2. In the UK, a form H3N2 is dominating the season so far. The virus is a descendant of a strain that this year caused Australia’s worst flu season on record. Since then, the strain acquired seven new mutations, producing what scientists call a drifted strain of H3N2, named subclade K. The mutations are thought to help it spread faster, although it does not seem to cause more severe disease.
