Seasonal influenza (flu)

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.

Those defined as ‘at risk’ include:

  • pregnant women in all stages/ any trimester of pregnancy
  • anyone aged over 65 years, even if they feel fit and healthy at the moment
  • children and adults who have any of the following medical conditions:
    • a chronic chest condition such as asthma
    • a chronic heart condition
    • chronic liver disease
    • chronic kidney disease
    • diabetes
    • lowered immunity due to disease or treatment such as steroids or cancer therapy (people living in the same house as someone with lowered immunity may also need to be vaccinated)
    • a chronic neurological condition such as stroke, multiple sclerosis or a condition that affects your nervous system, such as cerebral palsy, or hereditary and degenerative diseases of the central nervous system or muscles
    • any other serious medical condition - check with your doctor if you are unsure
    • children who have previously been admitted to hospital with a chest infection
  • children attending schools for children with severe learning difficulties
  • anyone living in a residential or nursing home
  • main carers for older or disabled people

People defined as being ‘at risk’ are eligible and encouraged to receive the flu vaccination free of charge on the NHS through their local GP practice. Furthermore, the flu vaccination is being offered to all children aged 2-4 years old and primary school children as they may pass flu onto people at risk.

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.

Influenza weekly surveillance bulletins

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

Other key links 

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