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Influenza A

4-minute read

Key facts

  • Influenza A is a type of virus that causes the flu. Most people who have flu are infected with the influenza type A virus.
  • Symptoms of Influenza A include fever and chills, sneezing, coughing and a sore throat.
  • As well as infecting people, the influenza A virus can infect animals, including birds and pigs.

What is influenza A?

Influenza A is a type of virus that causes influenza (the flu), a highly contagious respiratory illness. If you get it, you will need to rest at home and avoid infecting others. Vaccination can protect you against influenza A.

The other types of influenza virus are type B and type C.

Influenza types A and B are the most common causes of flu in Australia and can cause major outbreaks and severe disease. Influenza type C can cause an illness in children that is similar to the common cold.

Most people who have flu are infected with the influenza type A virus. This virus has caused flu pandemics — the worldwide spread of a new disease. Influenza A has also caused most epidemics — the widespread occurrence of an infectious disease within a community at a particular time.

Although coronavirus (COVID-19), is a viral illness that has developed into a pandemic, the virus that causes COVID-19 is different from the one that causes influenza.

Both the influenza A and influenza B viruses circulate in the community and change continually, with new strains coming out each winter. This is why yearly vaccination is recommended.

What are the types of influenza A?

As well as infecting people, the influenza A virus can infect animals, including birds (causing avian flu) and pigs (causing swine flu). In some cases, these types of influenza can be passed on to humans.

Bird flu

Avian influenza — also known as 'bird flu' — is a subtype of influenza virus A (H5N1) that mainly affects birds. The virus has caused serious infections and even deaths in humans but has not been found in Australia.

Although bird flu can be severe, the number of cases found in humans has been small. Most people diagnosed with bird flu have caught it from infected birds — so far, there is no evidence that bird flu can pass from human to human.

Swine flu

Swine flu is a type of influenza A virus found in pigs. In 2009, a strain of flu virus known as H1N1 caused a respiratory infection in humans which spread rapidly around the world and became a pandemic. The World Health Organisation (WHO) declared the swine flu pandemic over in August 2010.

The 1918 flu pandemic was also caused by an influenza A H1N1 virus.

Swine flu is mild in most people but can be severe for some high risk groups such as people with chronic conditions, pregnant people and Aboriginal or Torres Strait Islander people.

Symptoms, treatment and prevention

If you have influenza A, you will have some or all of these symptoms:

Children may also have abdominal pain, nausea and vomiting.

In most cases you can treat the symptoms of a mild flu yourself by resting at home. Medicines are available to treat pain and fever. Most people will get better within 7 to 10 days.

The best way to prevent catching the flu is to have a flu vaccination every year, and to practise good hygiene.

For more information on treating flu symptoms, prevention and when to see a doctor, see Flu (influenza).

CHECK YOUR SYMPTOMS — Use the colds and flu Symptom Checker and find out if you need to seek medical help.

Is it a cold or the flu?

View this infographic to identify cold or flu symptoms and debunk the most common myths.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: April 2021


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