Twelve more people have died from confirmed flu in the past week, taking the death toll to 39, according to the latest UK figures.
Data from the Health Protection Agency (HPA) showed 39 people have died with flu since October, including 36 with swine flu and three with another strain, flu type B.
All except one case were under 65 years of age and four were under the age of five.
Today's figures come after it was announced yesterday that cases of flu rose by more than 40% last week.
The Royal College of General Practitioners (RCGP) reported that incidences of flu in England and Wales reached 124 per 100,000 of the population in the week ending December 26.
There were 86 per 100,000 cases in the previous week.
There has been a general increase across all age ranges apart from children, with the middle-aged being particularly badly hit.
Professor John Watson, head of the respiratory diseases department at the HPA, said: "We are seeing a large amount of flu circulating across the country and would urge those people in an at-risk group to have their seasonal flu vaccine as soon as possible as this is the best way to protect themselves from flu this winter.
"Anyone who has symptoms of flu-like illness should get medical advice as soon as possible and their GP will prescribe antivirals to reduce their symptoms and lessen the risk of them developing complications.
"Although there were reports of many people during the pandemic only experiencing mild disease we can't stress enough that flu can be an extremely serious illness for people in 'at risk' groups, including pregnant women, the elderly and those with other underlying conditions such as heart problems, diabetes, lung, liver or renal diseases and those who have weakened immune systems."
Prof Watson added: "Most people with flu can 'self care' by taking plenty of rest, drinking lots of fluids and taking over the counter pain relievers such as paracetamol. But anyone displaying severe symptoms, particularly those in vulnerable groups, should contact their GP or local out-of-hours service for medical advice.
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"It is important that people do all they can to reduce the spread of the virus and they can do this by maintaining good cough and hand hygiene, such as covering your nose and mouth with a tissue when you cough and sneeze, disposing of the tissue as soon as possible and cleaning your hands as soon you can. These are all important actions that can help prevent the spread of germs and reduce the risk of flu transmission."
Experts believe the number of schoolchildren catching flu could change when they return to school following the Christmas break.
The increase still falls short of epidemic levels, which experts define as 200 cases per 100,000.
The RCGP figures came as an NHS pressure group warned that the flu outbreak could expose a "desperate" shortage in intensive therapy capacity.
Health Emergency claimed there was a lack of capacity and specialist nurses which they said could put lives at risk if the flu outbreak gathered momentum in the New Year.
Geoff Martin, chairman of Health Emergency, said: "We are getting reports of intensive care units in London where up to a quarter of the beds are filled with swine flu cases and the crisis is getting worse by the day.
"Cuts in recent years to bed and staff numbers have left the NHS dangerously exposed and there is no doubt that many ITUs (intensive therapy units) will soon have to close to new admissions, putting hundreds of lives at risk.
But the Department of Health insisted the NHS was coping well with the flu outbreak.
A spokesman said: "Our latest data shows that the number of people with confirmed or suspected flu in critical care beds is 460. This represents less than one in seven of the total critical care beds available.
"The NHS is coping very well and only a small percentage of the intensive care capacity is being taken up with patients with flu."