The number of people in critical care with confirmed or suspected flu in England has risen to 460 - more than double the figure a week ago.
Statistics released by the Department of Health (DoH) on December 15 showed 182 people were receiving intensive care or were in high dependency beds, and as of today there were 460 patients receiving the same level of care.
The new figures are in line with what is expected for this time of year, the DoH said.
Of the 460 patients receiving critical care for flu, 366 were aged between 16 and 64, 51 patients are aged 65 and over and 26 are under five. Another 17 were aged between five and 15.
The new figures follow Thursday's announcement that 27 people had died from flu this season, including nine children. Of those who died, 24 had swine flu and three suffered from another strain - flu type B.
The data, from the Health Protection Agency (HPA), related to the number of confirmed flu deaths across the UK since October. Almost half of those who died were in an "at-risk" group, such as those suffering from diabetes, heart disease or asthma.
Dr Alan McNally, a molecular biology expert at Nottingham Trent University, said he believed last year's pandemic virus, H1N1, otherwise known as swine flu, had returned as a normal seasonal flu.
"What you are now seeing is last year's pandemic virus, which was referred to as swine flu, is doing what it would be expected to do if you were an influenza biologist," he said.
"It's come back as what is now normal seasonal flu. It's a bit of a worry, the number of people in intensive care. I think it comes down to the fact that this time last year, the uptake of the vaccine wasn't as strong as it should have been."
Health Secretary Andrew Lansley acknowledged that the 43% take-up rate for the flu vaccine among the younger, at-risk groups - such as pregnant women - was lower than last year, but rejected suggestions that the fall was due to the Government's decision not to run an advertising campaign this year.