Why is flu so bad this year? Concern over ‘severe’ variant causing cases to spike this winter

A more severe type of flu is set to wreak havoc on the NHS this winter, with infections circulating at a rate not typically seen until early December.

Given that the virus has begun circulating five weeks early, experts fear that more vulnerable people, such as elderly pensioners, will not have received their vaccine.

Latest figures showed that the rate of hospital admissions for flu in England stood at 3.8 per 100,000 people last week, up from 2.4 the previous week, according to data published by the UK Health Security Agency (UKHSA).

While this is well below the peaks reached in recent years, it is a level of admissions usually not reached until next month and is further evidence that the current flu season has started “unusually early”, the UKHSA said.

Speaking at the NHS Providers conference in Manchester, Dr Antonia Ho, clinical senior lecturer and consultant in infectious diseases at the University of Glasgow, said: “Of the two seasonal influenza A viruses, the current dominant circulating virus (A/H3N2) tends to cause more severe illness than A/H1N1, particularly in older adults.

“For example, in 2022-23 winter season when A(H3N2) was the dominant virus, there were 16,000 influenza-associated deaths, compared to 8,000 last winter.

“It has arrived five weeks earlier than a ‘normal’ flu season, which means a smaller proportion of the vulnerable population may have received the flu vaccine.

“From previous experience, influenza waves that start early tend to affect a larger number of people in the population.”

Dr Ho added that the current circulating virus A(H3N2) had acquired seven new mutations over the summer, meaning it is quite different from the previous strain included in this year’s vaccine.

It also means that the virus could have changed sufficiently to escape the immunity that has been built up from previous infections and vaccinations.

“The R (reproduction) number is thought to have increased from 1.2 to 1.4, which means it is more transmissible. I.e. 100 people infected with this strain of flu can infect 140 people (rather than 110 to 120 people in other flu seasons),” she said.

The UKHSA estimates that deaths from flu in England stood at 7,757 last winter, compared with 3,555 the year before.

Child deaths involving flu also increased from 34 to 53.

The UK is braced for a spate of flu deaths this winter, with NHS leaders issuing a “flu jab SOS” urging people to get protected.

It follows the biggest flu season in Australia’s history, which is often seen as an accurate predictor of what the UK can expect.