Influenza (flu) – symptoms, causes & treatment (Australia)
Influenza (the flu) is a contagious respiratory infection caused by influenza viruses. It is a respiratory virus infection that spreads easily.
Influenza (the flu) is a contagious respiratory infection caused by influenza viruses. It is a respiratory virus infection that spreads easily. The influenza virus often causes sudden fever, cough, sore throat, body aches and fatigue. Many people recover at home, but some people develop complications such as pneumonia.
Emergency
Call triple zero (000) for an ambulance or go to your nearest emergency department if you have flu symptoms and:
- you are short of breath, breathing fast, or struggling to breathe
- you have chest pain or pressure that does not settle
- you are confused, very drowsy, or you collapse
- your lips or face look blue
- you cannot keep fluids down or you have signs of severe dehydration
Key points
- Influenza is a viral respiratory disease that is mainly caused by influenza A and influenza B.
- Flu symptoms often start suddenly and include fever, cough, sore throat, runny or blocked nose, headache, muscle aches and fatigue.
- Some people have a greater risk of severe flu, including children under 5 years, adults aged 65 years and over, pregnant people, Aboriginal and Torres Strait Islander people, and people with some chronic medical conditions.
- Most people manage flu at home with rest, fluids, and medicines for fever or pain. Antibiotics do not treat influenza virus infection.
- Antiviral medicines can treat influenza in some people, and antivirals work best when started early (often within 48 hours of symptoms starting).
- An annual influenza vaccine is recommended for people aged 6 months and over in Australia. Some people can get a free flu vaccine through the National Immunisation Program.
What is influenza?
Influenza is a contagious viral infection that affects the respiratory tract (nose, throat and lungs). It is different from many common colds because it often starts suddenly and can cause a higher fever and more body aches.
Seasonal flu in humans is mainly caused by influenza A and influenza B. Influenza C can infect humans but usually causes a mild disease. Influenza D mainly affects cattle and is not known to cause disease in humans.
Flu spreads in households, workplaces, schools, childcare and aged care. In Australia, laboratory-confirmed influenza is monitored through public health surveillance, including reporting to the National Notifiable Diseases Surveillance System (NNDSS).
Protection after a previous illness is incomplete. Flu strains change over time, so a previous illness does not guarantee protection in a later season.
Symptoms of influenza
Common symptoms include:
- fever or feeling feverish
- chills or sweats
- cough
- sore throat
- runny or blocked nose
- headache
- muscle aches and joint pain
- fatigue or weakness
Some people also have nausea, vomiting, or diarrhoea, especially children.
Symptoms and illness patterns vary by age and general health. Some children mainly have fever and tiredness. Some older adults may have less obvious fever but can become weak, confused, or dehydrated.
Many people feel unwell for several days. Fever often settles first, while cough and tiredness can last longer. If symptoms are not improving after a week, or you are getting worse, see a doctor.
How long flu lasts and when it spreads
Many adults have the worst effects in the first 2 to 3 days. Cough and tiredness can last longer than fever. Children can stay unwell for longer than adults.
You can spread the flu before you realise you are sick. An influenza virus can spread before symptoms start. If you live with someone who is older, pregnant, or has a chronic condition, keep your distance, wear a mask if you need to share indoor space, and clean hands before preparing food.
Symptoms that need urgent care
Call triple zero (000) or go to an emergency department if you develop:
- shortness of breath, rapid breathing, or trouble breathing
- chest pain or pressure
- confusion, collapse, or severe drowsiness
- a seizure
- signs of dehydration such as very little urine, dizziness when standing, or inability to drink
Such warning signs can occur with severe illness or complications such as pneumonia.
When to see a doctor
See a GP or telehealth doctor if:
- you are in a group with a greater risk of complications
- you are pregnant
- symptoms are getting worse, or you are not improving after a few days
- you have a chronic medical condition and the illness is affecting your breathing, blood sugar, or daily function
- you have repeated vomiting or you are worried about dehydration
- you want advice about antiviral treatment
Telehealth can be suitable when illness is mild to moderate and you do not have emergency warning signs. A telehealth doctor can review your symptom pattern, check risk factors, and discuss whether you need a test, an antiviral medicine, or an in-person exam.
An in-person assessment is usually needed if you have shortness of breath, chest pain, confusion, dehydration, or if your doctor needs to check your chest and oxygen levels.
If you are not sure what to do, you can call healthdirect (1800 022 222) for advice. This service is for people in Australia, including people who are unsure whether they need urgent care.
Causes & risk factors
What causes influenza?
Influenza is caused by infection with an influenza virus. The virus infects cells lining the airways. The immune response contributes to fever, aches, fatigue and other symptoms.
Small genetic changes in influenza viruses happen over time. These changes affect how well the immune system recognises later strains. This is one reason seasonal flu returns each year and why influenza vaccines are updated.
Flu spreads through virus-containing droplets and airborne particles from the nose or throat (for example, when an infected person coughs or sneezes), which can be breathed in by other people. Droplets can also land on surfaces; someone can then become infected if they touch the surface and then touch their nose or mouth.
Who has a higher chance of severe illness?
Many people recover without complications, but some groups have a higher risk of serious disease:
- babies and children under 5 years
- adults aged 65 years and over
- Aboriginal and Torres Strait Islander people
- pregnant people (any stage of pregnancy)
- people with chronic health conditions such as chronic lung disease, heart disease, diabetes, kidney disease, liver disease, or an immunocompromising condition
- people living in residential aged care or other long-term care settings
If you are in one of these groups and you become unwell, contact a doctor early.
Influenza A vs influenza B
Influenza A and influenza B are the main types that cause seasonal influenza in humans.
Influenza A is an influenza virus that can infect humans and animals. Influenza B is an influenza virus that mainly infects humans.
- Influenza A can be divided into subtypes based on surface proteins.
- Influenza B is not divided into these subtypes.
Both influenza A and influenza B can cause typical symptoms and both can lead to complications. A test result that reports "influenza A detected" or "influenza B detected" confirms flu illness, but treatment decisions usually depend more on symptom severity, time since onset, pregnancy, and other risk factors.
How influenza is diagnosed
A doctor may diagnose influenza based on symptoms and whether influenza is circulating in your area.
A PCR test on a nose and throat swab can confirm influenza virus infection. Influenza can also be diagnosed with a rapid antigen test (RAT).
- Some over-the-counter self-tests can detect influenza A and B (and some combine influenza/COVID-19/RSV in one test).
- Some tests report influenza A and influenza B separately.
- Some multiplex tests also report other respiratory pathogens.
Testing is more likely if you have severe illness, you are in a higher-risk group, you live or work in a high-risk setting such as aged care, or the result is likely to change treatment decisions. Public health units may recommend testing during outbreaks in institutions.
Other respiratory infections can have similar signs, including COVID-19 and RSV.
Treatment for influenza
Treatment depends on symptom severity, how long you have been unwell, and your risk of complications.
Symptom relief at home
Many people with uncomplicated infection treat symptoms at home:
- rest
- fluids, taken regularly
- paracetamol or ibuprofen for fever or pain (follow label directions)
Do not give aspirin to children under 16 years because of the risk of Reye's syndrome.
If you cannot keep fluids down, you may need medical review for dehydration.
Antiviral medicines
Antiviral medicines can treat influenza infection in some people. In Australia, antivirals used for influenza include oseltamivir and zanamivir. Baloxavir (Xofluza) is another option for uncomplicated influenza in people aged 12 years and over when started within 48 hours of symptom onset (eligibility depends on clinical factors).
Antivirals work best when started early, often within 48 hours of symptoms starting. In hospital, antivirals may be used later for severe illness.
Guidance for antiviral treatment prioritises people at greater risk of complications, people with severe illness, and some outbreak settings. Your doctor will consider timing, pregnancy, other medical conditions, and possible medicine interactions.
When hospital care is needed
Some people need hospital care for influenza. Reasons include low oxygen levels, dehydration needing intravenous fluids, pneumonia, or worsening of chronic conditions such as asthma, COPD, heart failure, or diabetes.
In hospital, treatment can include oxygen, fluids, monitoring, antivirals, and antibiotics if a bacterial infection is suspected.
Antibiotics
Antibiotics do not treat influenza because influenza is caused by a virus. Antibiotics may be used if a doctor suspects a secondary bacterial infection such as bacterial pneumonia, sinusitis, or ear infection.
Self-care & living with influenza
Reducing spread
Influenza is contagious. Practical steps include:
- stay home while you are unwell
- avoid close contact with other people, especially older adults, babies, and people with chronic disease
- use tissues and dispose of them after use
- clean frequently touched surfaces
Returning to work or school
Stay home until fever has resolved for at least 24 hours and you feel well enough to return to usual activities.
Self-care for recovery
- drink fluids, especially if you have fever
- rest and sleep
- eat small meals if appetite is low
- avoid smoking, which can worsen respiratory symptoms
Seek urgent health care if you develop shortness of breath, chest pain, confusion, collapse, or persistent vomiting.
Complications & outlook
Most people recover from seasonal flu without complications. Complications are more common in babies, older adults, pregnant people, and people with chronic medical conditions.
Complications can include:
- pneumonia (viral pneumonia or secondary bacterial pneumonia)
- worsening of asthma or COPD
- worsening of heart disease
- ear infections and sinus infections
- myocarditis
- encephalitis
If you develop new chest pain, persistent fever, worsening cough, or shortness of breath, seek medical review.
Can influenza be prevented?
Vaccination is the main preventive measure for flu season. In Australia, annual influenza vaccination is recommended for people aged 6 months and over.
What the flu vaccine targets
Most flu vaccines used in Australia are updated each year to match influenza viruses expected to circulate in the coming season. For the 2026 season, the Australian Influenza Vaccine Committee (AIVC) recommended trivalent influenza vaccines (two influenza A strains and one influenza B/Victoria strain) and supported moving away from including a B/Yamagata component due to its continued absence. Vaccine brands and availability can change from year to year, so check the current annual guidance and product information.
The flu vaccine does not protect against every influenza virus and no flu vaccine prevents every case, but vaccine reduces the chance of severe illness in many people.
Different vaccines are recommended for different age groups. Influenza viruses are grouped into types. In people, the main influenza viruses are influenza A and influenza B. Influenza C can infect humans and usually causes mild disease. The influenza virus changes over time, so seasonal influenza vaccination is recommended each year.
You can get a flu vaccine at GP clinics, pharmacies, and some workplace or community health services.
Who can get a free flu vaccine?
The flu vaccine is free under the National Immunisation Program for some groups. Funded groups commonly include these people:
- children aged 6 months to under 5 years
- pregnant people
- Aboriginal and Torres Strait Islander people aged 6 months and over
- adults aged 65 years and over
- people aged 6 months and over with medical conditions that increase the risk of severe disease
Vaccines are funded because these groups have a higher risk of complications.
Can I get influenza after a flu vaccine?
Yes. No flu vaccine prevents every influenza infection. Vaccine effectiveness varies by season, age group, and how well vaccines match circulating influenza viruses. Even if you get influenza after a flu vaccine, vaccination can reduce the risk of severe illness and complications.
If you are in a group at greater risk, protect yourself and the people around you during seasonal flu. The flu vaccine is one layer of protection. Flu vaccines reduce the chance of influenza infection in many people, and vaccines are updated because influenza viruses change over time. The vaccine does not stop every infection, but the flu vaccine can reduce severe illness. A doctor or pharmacist can advise on flu vaccine choice and timing based on your health and risk.
Respiratory viruses can spread in similar ways, so hand hygiene, staying home when sick, and good ventilation also reduce spread. Measures also reduce spread of other respiratory viruses.
Other prevention steps
Along with vaccination, the following steps reduce spread:
- stay home when you are sick
- wash hands often
- cover coughs and sneezes
- improve ventilation in indoor spaces when possible
Public health responses also include outbreak management in institutions, guidance for public health units, and advice for health services during seasonal influenza surges.
How Doccy doctors can help
Doccy doctors can assess how you feel, review risk factors, and advise on home care and warning signs. A doctor can discuss whether testing is useful and whether antiviral treatment is time-critical.
Telehealth is not suitable for emergencies. If you have shortness of breath, chest pain, confusion, collapse, blue lips, or you cannot keep fluids down, call triple zero (000) or go to an emergency department.
Resources & support
- healthdirect: flu information and the nurse advice line (1800 022 222) for health advice.
- Australian Government Department of Health: seasonal influenza vaccination advice.
- State and territory health departments publish influenza updates during the season, including advice for schools, aged care and health services.
- The Australian Immunisation Handbook: influenza vaccines and eligibility.
- RACGP: assessment of influenza-like illness in primary care.
References
- Australian Government Department of Health. Seasonal Influenza Infection (Flu): CDNA National Guidelines for Public Health Units. https://www.health.gov.au/resources/publications/seasonal-influenza-infection-flu-cdna-national-guidelines-for-public-health-units
- Immunisation Coalition. Antiviral treatments for influenza. https://www.immunisationcoalition.org.au/resources/antiviral-treatments-for-influenza/
- RACGP. Causes and diagnosis of influenza-like illness (PDF). https://www.racgp.org.au/getattachment/1de9794f-14a1-4666-87e6-9ce9cb010b08/attachment.aspx
- healthdirect. Influenza (flu). https://www.healthdirect.gov.au/flu
- Australian Government Department of Health. The Australian Immunisation Handbook: influenza (flu). https://immunisationhandbook.health.gov.au/contents/vaccine-preventable-diseases/influenza-flu