This is in the news a lot at the moment. Here are some places to find out more about what is happening:
For surveillance data, try PROMED-Mail or the WHO's FluNet. PROMED-Mail covers all infectious diseases, including outbreaks affecting animals and plants, and FluNet, as the name suggests, covers just influenza.
CIDRAP, from the University of Minnesota, is useful for information on outbreaks of influenza in the USA. It also has a more global list of literature.
Public Health England has a page about seasonal flu, with links to information from the four nations of the UK, Europe generally and the WHO. Health Protection Scotland, in addition to the link from PHE, has a page about seasonal influenza for this season. Public Health England produce Weekly national flu reports. They look like they might go beyond England.