Influenza or 'flu' is a respiratory illness associated with infection by influenza virus. Symptoms frequently include headache, fever, cough, sore throat, aching muscles and joints.

Influenza occurs most often in winter and usually peaks between December and March in the northern hemisphere. There are two main types that cause infection: influenza A and influenza B. Influenza A usually causes a more severe illness. The influenza virus is unstable and new strains and variants are constantly emerging, which is one of the reasons why the flu vaccine should be given each year.

For most people, influenza infection is just a nasty experience, but for some it can lead to more serious illnesses. The most common complications of influenza are bronchitis and secondary bacterial pneumonia. These illnesses may require treatment in hospital and can be life threatening, especially in the elderly, asthmatics and those in poor health. It’s estimated that 8,000 people die every year in the UK due to influenza, although this number can be higher in a bad season.


Information for health professionals

Every year, front line healthcare workers should get vaccinated against flu to protect themselves, their families and their patients. In recent years, adults of working age have been particularly affected by influenza, including getting the most serious complications.

Frontline Health and Social Care Worker 2018/19 seasonal influenza vaccine campaign: Trust guidance on data collection of vaccine uptake

Download the 2017/18 flu immunisation programme factsheet for healthcare practitioners.

Green Book:

Flu presentation:

Flu presentation with speaker notes PDF AQ updated 030818.pdf

Influenza weekly surveillance bulletins

Please click here to view all recent surveillance bulletins from the PHA.


PHA guidance for nursing and residential homes

Download Public Health Agency advice for nursing and residential homes on the management of influenza.


Department of Health policy on influenza and influenza immunisation 2016/17

The Department of Health is responsible for developing strategy and policy on all issues to do with influenza, including immunisation. Details are communicated directly to the service by the Chief Medical Officer.

View policy letters.


Key links 

Public Health England: Seasonal influenza: guidance, data and analysis