Northern hemisphere countries are being told by health experts to brace themselves for flu outbreaks.
There has been a well-publicised surge of cases in the UK during December with swine flu appearing to be the dominant of the three strains circulating.
But the European Centre for Disease Prevention and Control warned much of the rest of Europe was also beginning to see increases too.
Meanwhile, parts of the US and Canada have reported higher levels.
Many of those being infected are younger age groups. This is because elderly people have some immunity to swine flu, most probably because of exposure to a similar strain many years ago.
In the UK, the number of people who have died with all types of flu this winter hit 27 this week after another 10 deaths.
The volume of patients going to their doctor with flu-like illnesses also rose, more than doubling to 87.1 per 100,000 in the past week.
Cases have been highest in children aged between five and 14, followed by children under four and then those aged between 15 and 44.
But the UK's Health Protection Agency (HPA) said a very large outbreak was "not likely".
The situation has led to a rise in patients in intensive care beds and also in those using the NHS's phone hotline, NHS Direct.
Health experts said most people with flu would be able to "self-care" by taking plenty of rest, drinking fluids and taking pain relief.
However, those with severe symptoms are being advised to consult their doctor.
Professor John Watson, an expert in respiratory disease at the HPA, said: "The level of flu activity we are currently seeing is at levels often seen during the winter flu seasons.
"Recent research conducted by the HPA has suggested that a very substantial wave of activity associated with the pandemic strain is not likely."
In the UK at-risk groups are being urged to come forward for vaccinations. The numbers getting immunised are still too low, doctors have said.
The rates being seen elsewhere in Europe are not as high as in the UK, but the European Centre for Disease Prevention and Control said there was evidence that the winter flu epidemics were "starting".
Russia and the Ukraine are thought to be the worst hit outside the UK.