More people in Britain died after contracting swine flu last winter, with most deaths among young and middle-aged adults, than during the pandemic a year earlier, official figures showed on Wednesday.
In total, 602 people in Britain were reported as having died with an influenza infection in the 2010/11 season, according to data from the Health Protection Agency (HPA).
Where information was available on the strain of the infection, more than 90 percent of the deaths - 535 out of 582 - were associated with A(H1N1) swine flu, the agency said in its annual flu report.
The figures for last winter compare to 474 deaths reported between June 2009 and April last year as being associated with A(H1N1).
The agency said that 70 percent of fatal cases last winter were in people aged 15 to 64. In past years, seasonal flu has predominantly affected the elderly.
"Traditionally the elderly have been more seriously affected by winter flu but the picture is beginning to change as we are now seeing a higher proportion of young and middle-aged people taken seriously ill," said the HPA's Professor John Watson.
In winter 2010, almost 70 percent of all those who died were in a clinical "at risk" group, which means they would have been eligible for vaccination against influenza.
But, where figures were available, almost 75 percent of them had not received the vaccine.
A(H1N1) swine flu killed at least 18,449 people and affected some 214 countries and territories after it was uncovered in Mexico and the United States in April 2009.
The quick spread of the infectious new strain worldwide prompted the UN health agency to declare a pandemic on June 11, 2009 until August 10, 2010.
But the response was marred by doubts about the severity of the virus.