Influenza A: What It Is, How It Spreads & When to Seek Care

A major strain of the flu virus and a leading cause of seasonal flu outbreaks in Australia. It spreads through respiratory droplets from coughing, sneezing, or touching contaminated surfaces. Symptoms often include sudden fever, chills, muscle aches, fatigue, sore throat, and cough. While most cases resolve within 7–10 days, it can lead to serious complications in vulnerable groups such as older adults, young children, and people with chronic illnesses. Medical review is advised if symptoms worsen, breathing becomes difficult, or recovery is delayed.

What Is Influenza A?

Key Facts About Influenza A

A flu virus that affects the nose, throat, and lungs. It doesn’t just infect humans, it can also spread among animals like birds and pigs, making it more likely to change over time. These changes (mutations) are why new flu strains appear each year.

Influenza A is more likely than other flu types to cause larger outbreaks and even pandemics. Because of how easily it spreads and evolves, it’s closely monitored by health experts. Annual flu vaccination remains the best protection against the most common and serious forms.

Subtypes and Mutation

Influenza A is grouped into subtypes based on two surface proteins H (haemagglutinin) and N (neuraminidase), such as H1N1 and H3N2.

These subtypes can shift and drift each year, which is why the flu vaccine is updated regularly.

Learn more about Types of Flu Viruses.

How Does It Spread?

It spreads easily from person to person through tiny droplets released when someone coughs, sneezes, or even talks. You can also catch it by touching surfaces or objects with the virus on them like door handles or phones and then touching your nose, mouth, or eyes.

Crowded indoor spaces, such as public transport or offices, make it easier for the virus to spread. While Influenza A can cause more severe symptoms, its transmission is similar to other flu types. Regular handwashing, staying home when sick, and getting vaccinated help reduce the risk of infection.

Influenza A Symptoms

It can cause a range of symptoms that usually appear suddenly. Common signs include high fever, dry cough, sore throat, body aches, fatigue, chills, and headache. Some people may also experience a runny or blocked nose, nausea, or loss of appetite. Children might have vomiting or diarrhoea as well.

Symptoms can vary depending on the person’s age, overall health, and the particular strain of Influenza A. While most people recover in about a week, tiredness and a lingering cough may last longer.

If symptoms become severe or persist beyond 7–10 days, it’s important to see a doctor especially for those at higher risk, such as older adults or people with chronic conditions.

Learn more about our Flu Symptoms.

How Long Does Influenza A Last?

Symptom Duration

Most people with Influenza A recover within 5 to 7 days, although a cough or mild fatigue can linger for a week or more. Recovery time can vary depending on the person’s age, overall health, and the strain of the virus. Rest and fluids help speed up recovery.

Contagious Period

People with Influenza A are usually contagious from about one day before symptoms appear and for up to 5 to 7 days after becoming sick. Children, older adults, and people with weakened immune systems may remain contagious for longer. Because you can spread the virus before feeling unwell, it's important to take extra care during flu season especially around vulnerable people.

Stay home if you’re sick, cover coughs and sneezes, and wash your hands often to help prevent spreading the virus to others. Returning to normal activities too soon increases the risk of passing the flu on.

How Is Influenza A Diagnosed?

This is usually diagnosed based on your symptoms, especially during flu season when cases are common. Common symptoms like sudden fever, cough, and body aches often guide doctors to suspect the flu. To confirm the diagnosis, your GP may perform a flu test. The most common tests include rapid antigen tests, which can provide results within minutes, and PCR tests, which are more accurate but may take longer.

Getting a confirmed diagnosis helps your doctor decide the best treatment and care plan, especially if you are at higher risk of complications. If you feel unwell with flu-like symptoms, it’s important to see a healthcare professional for advice, testing, and management. Early diagnosis can help reduce the severity of symptoms and prevent spreading the flu to others.

Treatment for Influenza A

Managing Symptoms at Home

Most people with Influenza A recover well at home with simple care. Rest and drinking plenty of fluids help your body fight the virus. Over-the-counter medicines like paracetamol or ibuprofen can relieve fever, aches, and discomfort.

Avoid alcohol and smoking, which can slow recovery. Most cases do not require prescription medication and improve within a week. If symptoms worsen or you have risk factors like extremes of age or chronic illness, seek medical advice.

Prescription Antiviral Options

In some cases, doctors may prescribe antiviral medicines to reduce flu severity and duration. These work best when started within 48 hours of symptom onset. Antivirals are often recommended for people at higher risk of complications, such as the elderly, young children, or those with chronic health conditions. Not everyone with Influenza A will need antivirals. Your GP will assess your situation and advise accordingly.

Early treatment can help prevent serious illness and speed up recovery.

High-Risk Groups

Certain people are more at risk of severe illness from Influenza A. This includes older adults (especially over 65), infants and young children, pregnant people, and those with weakened immune systems or chronic health conditions like asthma, diabetes, or heart disease. These groups should be extra careful during flu season, get vaccinated yearly, and seek early medical advice if symptoms develop. Prompt treatment can reduce the risk of serious complications.

Potential Complications

While most people recover from Influenza A without issues, complications can occur especially in high-risk groups. These may include lung infections like pneumonia or worsening of existing conditions such as asthma or heart disease. Secondary bacterial infections might also develop.

It’s important to monitor your symptoms closely and seek medical advice if you notice persistent or worsening cough, chest discomfort, shortness of breath, or confusion. Early medical care can help manage complications and improve recovery outcomes.

Influenza A vs Influenza B

Here’s a simple comparison to help you understand the differences between Influenza A and Influenza B:

Both Influenza A and B cause seasonal flu in Australia and are covered by the yearly flu vaccine to protect you against the most common strains.

Learn more about Influenza B.

Is Influenza A More Serious Than B?

Influenza A is generally considered more serious than Influenza B because it mutates quickly and can cause pandemics, affecting large numbers of people worldwide. This fast change makes it harder to predict and control.

However, both Influenza A and B can cause severe illness and complications, especially in high-risk groups like young children, older adults, and those with chronic health conditions. Regardless of the type, it’s important to get vaccinated each year and seek medical advice if symptoms worsen.

Preventing Influenza A

Flu Vaccination

Getting the flu vaccine every year is the best way to protect yourself and others from Influenza A and B. The vaccine is updated annually to target the most common Influenza A strains circulating that season, along with Influenza B strains. This helps ensure you have the best possible protection against the flu each year.

Vaccination reduces the risk of severe illness, hospitalisation, and complications, especially for high-risk groups. Contact your local Myhealth clinic to book a flu vaccination. Flu vaccines are also widely available through GPs, pharmacies, and community clinics across Australia.

Vaccination for Australians at high-risk of flu is funded by the Australian Government. For more information about government funded flu vaccination, ask your nearest Myhealth clinic.

Learn more about Flu Vaccination Services.

Everyday Prevention Tips

Simple habits can help stop the spread of flu viruses. Wash your hands often with soap and water, cover your mouth and nose when coughing or sneezing, and use tissues to catch droplets. Avoid touching your face, and clean commonly touched surfaces regularly. If you’re feeling unwell, stay home to prevent spreading the flu to others. These everyday steps protect not just you but your family and community, especially those at higher risk of complications. Combining good hygiene with vaccination gives you the best protection against the flu.

When to Speak to a Doctor

If your flu symptoms suddenly worsen or don’t improve after several days, it’s important to get medical advice. People at higher risk like young children, older adults, pregnant people, or those with health conditions should be especially careful.

Watch for warning signs such as trouble breathing, chest tightness, confusion, or a very high fever that won’t go down. These warning signs require prompt medical review as they may be a sign of complications developing. If you’re concerned, contact your local Myhealth clinic to book an appointment and get the care you need.