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Influenza A

8-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 infection include fever, chills, muscle pains, coughing and a sore throat.
  • Influenza A is diagnosed through a PCR test, which can tell influenza A apart from influenza B and other similar viruses.
  • The best way to prevent influenza is to have a flu vaccination every year. It is recommended for everyone aged 6 months or older, especially those at high-risk.

What is influenza A?

Influenza A is a type of virus that causes influenza (the flu), a highly contagious respiratory illness. The flu can also be caused by influenza B and, rarely, influenza C.

The flu is the most common vaccine-preventable disease in Australia. Most people who have the flu are infected with the influenza type A virus.

Influenza A infection is more serious than the common cold. It can cause major outbreaks and severe disease.

The virus that causes COVID-19 is different from the virus that causes influenza.

Influenza A infections are most common in winter. This is when different subtypes or strains of Influenza A can be found the community.

What are the symptoms of influenza A infection?

If you have influenza A infection, you may have symptoms such as:

If you child has an influenza A infection, they may also have:

Influenza A infection can also cause serious complications, such as:

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

What causes influenza A infection?

Influenza A is a virus. It is spread through droplets from the nose or throat of an infected person, usually through coughing and sneezing. You can catch influenza A:

  • from contact with an infected person
  • by touching something that an infected person has coughed or sneezed on

The proteins on the surface of the influenza A virus are called hemagglutinin (H) and neuraminidase (N). Different virus subtypes have differences in their surface proteins.

Some influenza A subtypes can infect animals, including:

  • birds (causing avian flu)
  • pigs (causing swine flu)

In some cases, these types of influenza can be passed on to humans.

Bird flu

Avian influenza is also known as ‘bird flu’. Bird flu is caused by different subtypes of influenza A.

The most well-known subtype is called H5N1. This virus mainly affects birds. It has caused serious infections and even deaths in humans, but the number of cases has been few.

Bird flu usually spreads to humans through contact with an infected bird. So far, there is no evidence that bird flu can pass from human to human.

Swine flu

Influenza in pigs is caused by different subtypes of influenza A, such as H1N1.

In 2009, H1N1 caused a human pandemic. In Australia, this pandemic mostly affected humans.

Swine flu is mild in most people. However, it can be severe for some high-risk groups, even causing death. Swine flu does not spread through eating cooked pork.

How is influenza A diagnosed?

To find out if you have the flu, your doctor may order a flu test.

A nose or throat swab is usually taken and tested using a polymerase chain reaction (PCR) test. A PCR test can detect the genes of the virus or bacteria causing your symptoms.

You can also buy over-the-counter rapid antigen tests (RAT) to diagnose the flu at home. Usually, these tests can tell you if you have:

  • influenza A
  • influenza B
  • COVID-19

How is influenza A infection treated?

In most cases you can treat the symptoms of a mild flu yourself by staying at home and resting. It’s important to stay hydrated by drinking lots of fluids.

You can take paracetamol or ibuprofen to treat any pain or fever. Most people will get better within 7 to 10 days.

Your doctor may suggest anti-viral treatment:

  • if you are at high risk of severe influenza
  • to prevent influenza from spreading

Anti-viral treatments are most effective when given early. So, if you think you have the flu, visit your doctor as soon as possible.

Can influenza A infection be prevented?

The best way to prevent the flu is to have a flu vaccination every year. Influenza vaccines prevent against different types of influenza A and influenza B.

Who should get the influenza vaccine?

The Australian Immunisation Handbook recommends the influenza vaccine for everyone over 6 months of age, particularly people who:

  • are homeless
  • work with birds or pigs
  • travel during flu season
  • work in essential services
  • live or work with people at high risk of influenza

People who are at high risk of severe influenza should also get vaccinated. The flu vaccine is free for some people at high-risk.

People at high risk of influenza include:

  • people under 5 years old or over 65 years old
  • Aboriginal and Torres Strait Islander people
  • people with a condition that affects their immune system
  • people who are pregnant
  • people who are obese
  • people receiving cancer treatment, a stem cell transplant or organ transplant
  • people with Down Syndrome
  • people with a chronic illness

There are different types of influenza vaccines. Speak with your doctor about the best vaccine for you.

When should I get the influenza vaccine?

The following table shows when you should get the influenza vaccine.

When Who
1 dose, every year
  • Most people
2 doses, every year, 4 weeks apart
  • Children aged 6 months to 9 years getting the vaccine for the first time
  • People getting the vaccine for the first time after stem cell or organ transplant

Why do I need to get a new influenza vaccine every year?

Your body’s immune system detects influenza A based on the H and N proteins on its surface.

New subtypes of influenza A usually appear every winter.

In different subtypes, the H and N proteins are different. This means your body needs to make new antibodies to fight the infection.

This is why a new flu vaccine is offered every year.

Resources and Support

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

For more information on influenza vaccines, you can visit the Immunisation Handbook website.

You can find out more about the National Immunisation Program on the Department of Health website.

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

Last reviewed: July 2023

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