Influenza (flu) is a contagious respiratory illness caused by influenza viruses. Most people recover after a few days but for some people it can be fatal. An influenza vaccination each year provides the best protection against influenza.​

Last updated: 01 July 2012
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What is Influenza?

Influenza, or flu, is a highly contagious respiratory illness caused by influenza viruses. There are three main types of influenza virus that cause infection in humans - types A, B and C - and many sub-types or strains. Influenza can occur throughout the year but influenza activity usually peaks in winter.
Influenza is a vaccine-preventable illness but a new vaccine needs to be given each year because influenza viruses change (mutate) constantly. A new influenza vaccine is prepared each year to best match the strains predicted for the coming influenza season.

What are the symptoms?

People with influenza typically experience some or all of the following symptoms:

  • fever and chills
  • cough, sore throat and runny or stuffy nose
  • muscle aches, joint pains , headaches and fatigue (feeling very tired)
  • nausea, vomiting and diarrhoea (more common in children than adults).

Some symptoms may last for more than a week. Some people may also experience very mild symptoms, particularly if they have some immunity from a previous infection or vaccination.
Seek immediate medical advice if the illness quickly becomes worse or if any of the following occurs:

  • shortness of breath or rapid breathing
  • chest pain
  • confusion or sudden dizziness
  • persistent vomiting.

How is it spread?

Influenza viruses are mainly spread by droplets made when an infected person coughs or sneezes. Influenza can also be spread through touching surfaces where infected droplets have landed.
People with influenza can be infectious from the day before their symptoms start. Adults are most infectious in the first 3-5 days of their illness, while children remain infectious for 7-10 days, and people with weakened immune systems may be infectious for longer.

Who is at risk?

While anyone can get influenza, the following people are at higher risk of complications from influenza infection (and are eligible for free annual influenza vaccine):

  • All individuals aged 65 years or older
  • All Aboriginal and Torres Strait islander peoples aged 15 years or older
  • Pregnant women
  • Individuals aged 6 months and over with medical conditions predisposing to severe influenza, namely:
    • Cardiac disease, including cyanotic congenital heart disease, coronary artery disease and congestive heart failure.
    • Chronic respiratory conditions, including suppurative lung disease, chronic obstructive pulmonary disease and severe asthma.
    • Other chronic illnesses requiring regular medical follow up or hospitalisation in the previous year, including diabetes mellitus, chronic metabolic diseases, chronic renal failure, and haemoglobinopathies.
    • Chronic neurological conditions that impact on respiratory function, including multiple sclerosis, spinal cord injuries, and seizure disorders.
    • Impaired immunity, including HIV, malignancy and chronic steroid use.
    • Children aged 6 months to 10 years on long term aspirin therapy.

How is it prevented?

Influenza vaccination each year before winter arrives is the best way to prevent influenza.

  • Seasonal influenza vaccination is available for anyone aged 6 months and over to protect against influenza, provided they do not have a medical reason that precludes them from receiving influenza vaccines.
  • People at higher risk of influenza complications (see Who is at risk) are strongly recommended to have an annual influenza vaccination, and are eligible for free influenza vaccine under the National Influenza Vaccination Program.
  • In addition to people eligible for free vaccine, annual influenza vaccination is also recommended for those who frequently come in to close contact with other people at higher risk of influenza complications (such as health care workers, and family members), to help protect vulnerable people from infection.

For more information on general influenza vaccine recommendations refer to latest edition of The Australian Immunisation Handbook.

Take action to stop the spread of influenza by remembering to:

  • Cover your face when you cough or sneeze and throw used tissues in a rubbish bin.
  • Wash your hands thoroughly and often. Wash hands for at least 10 seconds, especially after coughing, sneezing or blowing your nose, or use an alcohol-based hand rub.
  • Stay at home until you're well. Wait at least 24 hours after your fever resolves so you that you are unlikely to infect other people. Keep sick children away from school and other activities.
  • Call ahead to see a doctor. If you think you may have influenza and you need to see a doctor, call first so the clinic can take precautions to reduce the risk to other people.

How is it diagnosed?

Doctors usually diagnose influenza based on symptoms. The diagnosis can be confirmed by testing a sample of fluid taken from the back of the nose and throat or a blood sample. These tests are usually only needed if the illness is severe or if there is an increased risk of complications.

How is it treated?

  • The symptoms of influenza are usually managed by bed rest and taking simple analgesics for muscle aches and pains.
  • Children under 16 years of age must not be given aspirin-containing medications while ill with influenza. This is due to the increased risk of children developing Reye syndrome, a form of encephalitis and liver degeneration.
  • Specific influenza antiviral medicines can reduce the severity and the duration of influenza but need to be taken within 48 hours of the first symptoms. These medicines need to be prescribed by a doctor, and are usually considered for people at higher risk of complications from influenza infection.

What is the public health response?

  • Laboratories must notify cases of influenza to their local Public Health Unit. Individual cases are managed by their health care provider.
  • Public health action focuses on outbreaks in high-risk settings such as health care facilities, special schools, residential care facilities, and Aboriginal communities.

Futher information

For further information please call your local Public Health Unit on 1300 066 055