What is Influenza

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 is it 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.


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 visit the FluSmart website.


More information for Clinicians

Currently in Australia, only quadrivalent influenza vaccines are available.

They contain:

  • A (H1N1) – an A/Michigan/45/2015 (H1N1)pdm09 like virus
  • A (H3N2) – an A/Singapore/INFIMH-16-0019/2016 (H3N2)*
  • B (Yamagata lineage) – a B/Phuket/3073/2013 like virus
  • B (Victoria lineage) – a B/Brisbane/60/2008 like virus


* This is a different strain of the H3N2 from 2017


To find more information on vaccine composition, click here.


Co-administration with other vaccines

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: April 2017)


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Page published:   8 March 2017

Page updated:      18 September 2017