Influenza (often called flu) is a respiratory infection caused by the influenza virus of which there are 3 types; A, B and C. 

Types A and B cause most of the disease in humans and type A has 2 commonly occurring subtypes; H1 and H3. Influenza viruses are characterised by the way they mutate from year to year thereby forming new strains and evading the immune system. Because of this, vaccination is required annually to protect against the current influenza strains.

How it is spread

Influenza is spread from person to person through respiratory droplets produced during coughing and sneezing. It may also be spread when others touch surfaces contaminated by the droplets and then transfer the infection to their mouth and eyes, where the virus can enter the body. The incubation period is short, usually 1 to 3 days.


The presentation of influenza illness often has an abrupt onset with symptoms including; tiredness, fever, headache, chills, sore throat, loss of appetite and muscle aches. There may be an associated cough, nasal discharge and sneezing.

How serious is influenza

The severity of influenza depends on the strain, the patient’s age, previous exposure to the strain and the presence of other medical conditions. Those at increased risk for severe disease or dying from influenza are listed in the groups recommended for annual vaccination.

Infectious period

Adults are infectious from the day prior to and up to 7 days from the onset of symptoms while children may remain infectious for 10 days.

Immunosuppressed people may shed the virus for weeks. The ability to transmit the virus is higher when cough and fever are present. 


Treatment for influenza includes rest, increased fluids and pain relief. Anti-viral treatment can shorten the duration of illness if commenced within 48 hours of the onset of symptoms.


Annual vaccination is recommended especially for those most at risk. The influenza vaccine is a safe and effective vaccine that does not contain any live virus, so people cannot catch influenza from having the vaccine. However, it does take around 2 weeks before the body is fully protected after vaccination. If you are exposed to someone with influenza infection during this time you may still become sick because your body is not yet fully protected.

Read more about the flu vaccination.

To stop the spread of disease, people should cough into their upper arm or cover their mouths when coughing and wash their hands regularly.

Regular hand-washing and disposing of tissues into the bin immediately, even when not coughing, may also help to prevent influenza. People with flu symptoms should stay at home and seek medical treatment as needed.


For more information call your nearest Centre for Disease Control.

Last updated: 31 May 2016

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