About this disease

Influenza, commonly known as ‘the flu’, is an illness caused by a group of viruses (the influenza viruses) that infect the respiratory tract. Influenza infection usually has different symptoms and causes a more severe illness than most other common viral respiratory infections and may be a life-threatening infection in certain people; it should not be confused with the common cold! In most parts of Australia, influenza outbreaks are seasonal, occurring between late autumn and early spring. Seasonal outbreaks occur every year and vary from mild sporadic outbreaks to serious epidemics; it is estimated that between 5 and 20% of the population may be infected annually. Occasionally severe worldwide outbreaks (pandemics) occur involving higher infection rates and more severe disease.


In adults, the symptoms of influenza can include fever, dry cough, muscle and joint pain, extreme tiredness, headache and sore throat. In children, influenza may present with a cough, high fever and listlessness. Children can also get diarrhoea and vomiting as a result of influenza infection.

How it is spread

Influenza viruses are mainly spread when infected people cough or sneeze, releasing small virus-containing droplets into the air which can be breathed in and infect the respiratory tract of the people around them. Contaminated respiratory secretions on hands and other surfaces can also transmit the infection by hand to mouth or eye infection. It has been found that influenza viruses can survive for up to an hour in the air of an enclosed environment, more than eight hours on hard surfaces such as stainless steel and plastic, and up to five minutes on hands after transfer from other surfaces. One very important factor in the spread of influenza is that early in infection, even before symptoms become evident, an infected person can be shedding influenza viruses and infecting the people around them. Good cough and sneeze etiquette and hand washing can contribute to limiting the spread of influenza and other respiratory virus infections. It is generally believed that young children are the greatest spreaders of influenza because they generate more viruses in their respiratory tract and are less likely to practice good hygiene.


Influenza can lead to complications, such as pneumonia, which can sometimes lead to death.


Influenza vaccines are available which offer a high degree of protection against seasonal illness and the severe consequences of influenza; however, these must be administered annually due to changes in the influenza viruses. Good hygiene is one of the most important ways to help prevent colds and flu.   Vaccinating pregnant women against influenza gives a 3 for 1 benefit:

  • protects the woman during pregnancy and in the early months of motherhood
  • protects the young infant by transplacental antibodies
  • protects the young infant by antibodies in breast milk.

The World Health Organization (WHO) Strategic Advisory Group of Experts (SAGE) has identified pregnant women as the most important risk group for seasonal influenza vaccination. (WHO.SAGE Meetings.2012 [cited 2018 20 February]; Available from: http://www.who.int/influenza/vaccines/ SAGE_information/en/)


Recently some effective antiviral medications for influenza have been developed, based on original Australian research, and these can be used to treat influenza infections provided that they are taken in the early stages of the illness. Antibiotics only work for bacterial infections so they won’t work for colds and flu which are caused by viruses. For more information on influenza see our FluSmart pages.

Info for Clinicians

Seasonal influenza vaccines available for use in Australia in 2019, by age:

(This table is based on the 2020 ATAGI advice on seasonal influenza vaccines in Australia)

  • Australian Technical Advisory Group on Immunisation (ATAGI) statement on the administration of seasonal influenza vaccines in 2020 is available here.

    The Australian Influenza Vaccine Committee (AIVC) met on Wednesday 9th October 2019 in Canberra to recommend influenza viruses to be used in the 2020 influenza vaccines. The expert committee reviewed and evaluated data relating to epidemiology, antigenic and genetic characteristics of recent influenza isolates circulating in Australia and the Southern Hemisphere, as well as the serological responses to 2018-2019 vaccines. It was therefore recommended that 2020 influenza vaccines for the southern hemisphere contain:

    Quadrivalent egg based vaccines:

    • an A/Brisbane/02/2018 (H1N1)pdm09-like virus;
    • an A/South Australia/34/2019 (H3N2)-like virus;
    • a B/Washington/02/2019-like (B/Victoria lineage) virus; and
    • a B/Phuket/3073/2013-like (B/Yamagata lineage) virus.

    Trivalent egg based vaccines:

    • an A/Brisbane/02/2018 (H1N1)pdm09-like virus;
    • an A/South Australia/34/2019 (H3N2)-like virus; and
    • a B/Washington/02/2019-like (B/Victoria lineage) virus.

    To view the WHO full report on the recommended influenza vaccines for the southern hemisphere in 2020, click here.

  • See the Immunisation Handbook here

    And information on vaccines, dosage and administration for children here

  • Influenza vaccine can be given at the same time as Zostavax and pneumococcal polysaccharide vaccines, using separate syringes and injection sites (Adult vaccination: vaccines for Australian adults, NCIRS Fact sheet: October 2017)


  • Visit the Influenza Specialist Group (ISG) website here.

Page published:   8 March 2017

Page updated:      4 March 2020

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