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 February 2023

What is influenza (flu)?

Influenza is a highly contagious respiratory illness caused by influenza virus. There are two main types of human influenza viruses: A and B. There are also many sub-types and strains. Flu can occur throughout the year but is most common in autumn and winter. In most flu seasons there is more than one strain circulating in the community.

What are the symptoms of flu?

People with flu often experience some or all 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 that don't last long, particularly if they have some immunity from a previous infection or vaccination.

Who is at higher risk of severe illness?

While anyone can get flu, some people are at higher risk of severe illness (more likely to get very sick from flu, and may be at higher risk of needing hospital care), including:

  • Babies and children under 5 years of age
  • People aged 65 years and older
  • Aboriginal and Torres Strait Islander people
  • Pregnant women, at any stage of pregnancy
  • People with certain medical conditions including:
    • cardiac disease
    • chronic respiratory conditions, including severe asthma
    • chronic neurological conditions
    • immunocompromising conditions
    • diabetes and other metabolic disorders
    • renal disease
    • obesity
    • haematological disorders
    • children under 10 years of age on long term aspirin therapy.

Those at higher risk should discuss treatment with their GP in case they get flu

People at higher risk of severe illness may be eligible for antiviral treatments such as oseltamivir (Tamiflu®). Antivirals reduce severe illness, hospitalisation and death from influenza if taken early in the illness. Speak with your GP to understand your options, so that you know what to do if you test positive for influenza. To be effective, antivirals must be provided within 48 hours of when symptoms first appear, so it's important to contact a GP as soon as possible.

If you can't contact a GP, call the National Coronavirus Helpline on 1800 020 080 who are able to check if you are eligible for antivirals.

How long are people infectious?

People with flu can be infectious from the day before their symptoms start.

  • Adults are most infectious in the first 3-5 days of their illness
  • Children remain infectious for 7-10 days
  • Young children and people with weakened immune systems may be infectious for longer.

How is flu prevented?

Get your annual flu vaccine

  • People aged 6 months and over should get a flu vaccine to protect themselves against the virus
  • People at higher risk of severe illness are strongly recommended to have an annual flu vaccine and are eligible for free flu vaccine under the National Influenza Vaccination Program
  • People who regularly come into close contact with other people at higher risk of serious illness from flu (such as health care workers and family members) are also strongly recommended to get vaccinated to help protect vulnerable people.
  • A flu vaccination is needed every year as influenza virus strains change (mutate) constantly. A new vaccine is prepared each year to best match the strains predicted for the coming flu season. Vaccination is very effective in preventing serious illness from influenza virus.

Practice good hygiene

  • Stay at home when sick
  • Cover coughs and sneezes
  • Clean hands regularly with hand sanitiser or soap and running water for 20 seconds
  • Meet people outdoors or in well-ventilated areas.

How is influenza diagnosed?

Some people are told they have flu when they have a PCR (nose and throat swab) test. You only need to test for flu if you are at high risk of severe illness, or the illness itself is severe.

If you had a test at a PCR test clinic you may receive a SMS confirming you have influenza. Some providers test for multiple respiratory viruses and you may receive results for flu, respiratory syncytial virus (RSV) and COVID-19 as well.

How can I manage flu safely?

Flu is mostly spread by droplets made when people with flu cough or sneeze. It can also spread by touching a surface or object that virus droplets have landed on. People with flu can spread it to others before they are sick as well as while they are sick.

Stay at home and reduce the risk to others

If you are sick with flu, stay at home and avoid close contact with other people. Keep sick children away from school and other activities. To avoid infecting others, stay at home for at least 24 hours after your fever has resolved and until you are feeling well. This is especially important if you visit people who are more likely to get really sick if they get the flu – including pregnant women, infants, older people or people in hospital or residential aged care.

Monitor your symptoms

Most symptoms can be managed with:

  • Bed rest
  • Regular paracetamol and ibuprofen to relieve pain and fevers (children under 16 years of age must not be given aspirin-containing medications)
  • Throat lozenges for a sore throat
  • Staying hydrated with regular sips of water.

Please contact your GP if you are considered to be at higher risk of severe illness.

If you have COVID-19 or flu and have health questions that are not a medical emergency, call your GP or Healthdirect 24/7 for free on 1800 022 222 for fast, expert health advice from registered nurses.

If your get any of the following symptoms call Triple Zero (000) immediately and tell the ambulance staff you could have flu.

  • Shortness of breath or rapid breathing
  • Chest pain or pressure lasting longer than ten minutes
  • Confusion or sudden dizziness
  • Persistent vomiting.

Further information

Current as at: Wednesday 1 February 2023
Contact page owner: Communicable Diseases