Seasonal flu (seasonal influenza)

What seasonal flu is

Seasonal flu is a common and highly contagious respiratory infection.

It is usually caused by influenza A or B viruses, but there are many subtypes and strains.

Seasonal flu can cause mild to severe illness. Most people recover within a few days, but some people are at greater risk of getting severely unwell from it.

Seasonal flu is caused by a different virus to COVID-19.

Seasonal flu vaccines are the best protection against severe illness from flu.

Why it matters to public health

Seasonal flu is a common cause of hospitalisation. Before the COVID-19 pandemic, it was the most common cause of notifiable disease deaths.

Flu infections can vary widely from year to year. During the COVID-19 pandemic, flu cases were lower than usual, as COVID-19 restrictions reduced the spread of flu.

On average, each year in Australia, seasonal flu results in an estimated:

3,500 deaths
300,000 general practitioner consultations
18,000 hospitalisations.

This has a major impact on:

individuals – through illness, missed school or work, complications like pneumonia, hospitalisation and death
our health system – through added demand on health professionals, clinics and hospitals
businesses and our economy – through lost work time and productivity.

Because of these major impacts, and the fact that new flu viruses can cause pandemics, we:

monitor and report on the patterns of flu infections in Australia
plan for how to manage major outbreaks and pandemics.

Symptoms

If you have serious symptoms – such as severe shortness of breath or chest pain – call 000 immediately.

Common symptoms include:

fever and chills
cough
sore throat
runny or stuffy nose
tiredness
headache
muscle and joint pain.

Symptoms might range from mild to severe, and you might not get all of those symptoms.

healthdirect’s symptom checker can help you:

work out whether you have the flu or another illness
decide whether to see a doctor.

Check your symptoms

Onset of symptoms

Symptoms will usually show about 2 days after getting infected, but this can range from 1 to 4 days.

How it spreads

Seasonal flu spreads easily through droplets from your respiratory tract. When you do things like talk, cough or sneeze, these droplets disperse through the air and may land on people and surfaces.

Other people can catch seasonal flu by:

their mouth, nose or eyes coming into contact with these droplets
breathing in these droplets
touching surfaces or objects that have been in contact with an infected person, then touching their mouth, nose or eyes.

Read more about how seasonal flu spreads.

Infectious period

The time people are usually most infectious are the first 3 days after symptoms appear. You can infect others from the day before you show symptoms until around 7 days after symptoms begin, sometimes longer.

Prevention

Get vaccinated

Flu vaccines are available to protect against the most common strains. Eligible people can get vaccines for free under the National Immunisation Program or state or territory programs. If you are not eligible for a free vaccine, you can buy one from your doctor or pharmacy.

The best ways to protect against seasonal flu are to:

get vaccinated each year, especially around April–May
if you are sick with cold and flu symptoms, stay home and if you need to leave home, wear a mask
put physical distance between yourself and others
maintain good hygiene, including by regularly washing your hands and maintaining respiratory hygiene
avoid touching your eyes, nose and mouth, particularly if you are around people who are unwell
regularly clean objects and surfaces you use often, such as mobile phones and door handles.

High-risk groups and settings

Some people are at greater risk of getting the flu or of getting very sick from it.

The flu can spread quickly in homes and other settings including:

residential aged care homes
other residential care facilities
childcare centres
schools.

If you are at greater risk, it is especially important to:

get your flu vaccination each year – it’s free for certain people in high-risk groups
take steps to protect yourself
avoid crowded places
avoid people who are sick with cold and flu symptoms
see your doctor as soon as symptoms start – medicine works best when taken in the first 2 days of illness.

People at greater risk may choose to wear a face mask in a public place, and when around others.

People at greater risk of severe disease

Seasonal flu poses a greater risk of severe illness for:

babies and young children (aged under 5 years)
people aged 65 years or older
people who are pregnant
Aboriginal and Torres Strait Islander people
people with some chronic conditions
people who are immunocompromised
people who smoke.

People at greater risk of becoming infected

People are at greater risk of becoming infected with seasonal flu if they:

are not up to date with their annual vaccination
have had contact with someone who has the flu – especially if they have been in close and prolonged contact (such as living in the same house).

Diagnosis and treatment

Your doctor can diagnose the flu with a flu test. The sample is usually collected from your nose or throat with a cotton swab and sent do a laboratory for testing.

You can test yourself with a rapid antigen test (RAT) that detects the flu. These tests are widely available in supermarkets and pharmacies. These are not as accurate as tests requested by your doctor.

Surveillance and reporting

Influenza is a nationally notifiable disease – these are diseases that present a risk to public health.

Health authorities in each state and territory report new laboratory confirmed cases to us daily through the National Notifiable Diseases Surveillance System.

We also track data on flu collected through other surveillance systems, including:

This helps us to:

monitor case numbers around the country
understand who is at risk of severe disease
know where to target public health actions
decide whether we need to take action.

We analyse the data, and report on flu case numbers through:

our influenza dataset
the Australian Respiratory Surveillance Report
our data visualisation tool, where you can filter and search the latest information.

For more information about our surveillance and reporting activities, see our:

Outbreaks

Seasonal flu outbreaks are common, especially in winter months. Their frequency and severity vary depending on:

the strains circulating
vaccination rate
public health measures.

State and territory health departments provide guidance and support for outbreaks of seasonal flu – for example, in aged care homes or hospitals.

We have a national plan for responding to flu in certain situations when it presents a serious threat to Australia, such as when:

a new flu virus with pandemic potential is circulating
a state or territory requests assistance with seasonal flu.

In these cases, we follow our action plans, to minimise the impact on the health of Australians and on our health system.

Read more about how we define and plan for outbreaks and pandemics.

Support

For information about seasonal flu in your state or territory see:

We regularly add new content to this website. This will include more topics and diseases. In the meantime, information about other diseases in Australia is on the Department of Health and Aged Care’s website.

Last updated:

19 December 2024

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