The influenza virus is an RNA virus. There are three types: A, B and C, of which A and B are the most common. The A type has different H and N subtypes and you may hear about different strains, for example H1N1 (swine flu) and H5N1 (avian flu). Outbreaks typically occur during the winter.


Every year the vaccine is changed to target multiple strains of influenza that are likely to cause flu. It needs to be given yearly to keep the person protected.

It is given free on the NHS people at higher risk of developing flu:

  • Aged 65
  • Young children
  • Pregnant women
  • Chronic health conditions such as asthma, COPD, heart failure and diabetes
  • Healthcare workers and carers



  • Fever
  • Coryzal symptoms
  • Lethargy and fatigue
  • Anorexia (loss of appetite)
  • Muscle and joint aches
  • Headache
  • Dry cough
  • Sore throat



Treatment is usually started based on the history, risk factors and clinical presentation.

Viral nasal or throat swabs can be sent to the local virology lab for polymerase chain reaction (PCR) analysis. This will confirm the diagnosis and also provide data to public health so that they can monitor the number of cases of influenza.



Public health monitor the number of cases of flu and provide guidance on when there is enough flu in the area to justify treating patients with suspected flu.

Healthy patients that are not at risk of complications do not need treatment with antiviral medications. The infection will resolve with self care measures such as adequate fluid intake and rest.

There are two options for treatment in someone presenting with suspected influenza that is at risk of complications of influenza:

  • Oral oseltamivir 75mg twice daily for 5 days
  • Inhaled zanamivir 10mg twice daily for 5 days

Treatment needs to be started within 48 hours of the onset of symptoms to be effective.

Post-exposure prophylaxis can be given to higher risk patients such as those with chronic diseases or immunosuppression within 48 hours of close contact with influenza. This aims to minimise the risk of developing flu and complications.

  • Oral oseltamivir 75mg once daily for 10 days
  • Inhaled zanamivir 10mg once daily for 10 days



  • Otitis media, sinusitis and bronchitis
  • Viral pneumonia
  • Secondary bacteria pneumonia
  • Worsening of chronic health conditions such as COPD and heart failure
  • Febrile convulsions (young children)
  • Encephalitis


Last updated March 2019
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