Influenza A is a highly contagious virus that causes the flu. It has caused pandemics and epidemics worldwide. There are different strains of influenza A including avian flu which mainly affects birds but can infect humans, and swine flu which originated in pigs but has caused pandemics in humans. Symptoms of influenza A include fever, headache, muscle aches, and respiratory symptoms. While most cases are mild and can be treated at home with rest, annual flu vaccination is recommended to prevent catching and spreading influenza A.

1. Influenza A
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.
Birdflu
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.

2. Swineflu
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:
 fever and chills
 headache and muscle aches
 feeling tired and weak
 sneezing, and stuffy or runny nose
 sore throat and cough
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).