Influenza B: What to Know About Symptoms, Duration, and Care

Influenza, commonly referred to as the “flu”, is a family of viruses that includes several types. Influenza B is a common seasonal flu virus that affects only humans and often spreads in winter. While its symptoms like fever, fatigue, and sore throat are usually milder than those of Influenza A, it can still cause serious illness, especially in children and older adults.

Influenza B doesn't cause pandemics but contributes to yearly flu outbreaks. This guide explores how it spreads, how it differs from Influenza A, and when to seek medical advice for symptoms that worsen or linger.

What Is Influenza B?

Key Facts About Influenza B

Influenza B is a type of flu virus that causes seasonal illness in humans. Along with Influenza A, it’s one of the two main strains responsible for most yearly flu outbreaks. Unlike Influenza A, which can also infect animals and trigger pandemics, Influenza B spreads only between people and is generally associated with milder symptoms, though it can still lead to serious illness, especially in children and older adults. Annual flu vaccines in Australia include protection against both A and B strains of the flu to reduce the risk of infection.

Lineages and Mutation

Influenza B has two main lineages: B/Yamagata and B/Victoria. Both can circulate in the same flu season. Influenza B tends to mutate more slowly than Influenza A. The seasonal flu vaccine is reviewed and updated to protect against the most likely strains.

Learn more in our Types of Flu Viruses guide.

How Does It Spread?

Influenza B spreads mainly through respiratory droplets released when an infected person coughs, sneezes, or talks. It can also be picked up from contaminated hands or surfaces, especially in shared spaces. Schools, offices, and public transport increase the risk of transmission.

Like Influenza A, it’s most contagious in the early days of illness. Practising good hygiene like handwashing and staying home when sick helps stop the spread. Vaccination also reduces the chance of infection and limits community outbreaks.

Influenza B Symptoms

Influenza B often presents with symptoms such as fever, dry cough, fatigue, muscle aches, sore throat, and occasionally headaches or chills. While these symptoms are similar to those caused by Influenza A, they may be slightly milder. However, the difference isn’t always noticeable, especially in vulnerable groups.

Children may also experience nausea, vomiting, or diarrhoea alongside typical flu signs. Symptoms usually begin suddenly and can last about a week, though fatigue may linger longer. Recognising symptoms early helps with timely care and prevents spreading the virus to others.

Learn more in our Flu Symptoms guide.

How Long Does Influenza B Last?

Symptom Duration

Most people start to feel better from Influenza B within 5 to 7 days. However, tiredness and a cough can hang around a little longer, especially in kids or older adults. Rest and plenty of fluids help with recovery.

Contagious Period

You can spread Influenza B to others from about one day before symptoms start and for around 5 to 7 days after. Children, older adults, and people with weaker immune systems might be contagious for even longer. It’s best to stay home while you have symptoms like fever, cough, or sore throat to avoid passing it on. Washing your hands often, covering your mouth when coughing or sneezing, and avoiding close contact can help protect others.

If you’re not getting better after a week or feel worse, it’s a good idea to see your doctor especially if you're in a higher-risk group.

How Is Influenza B Diagnosed?

It is often diagnosed based on your symptoms such as fever, cough, and fatigue, especially if they appear during flu season. However, your doctor may recommend a test to confirm the diagnosis, particularly for those at higher risk of complications. The two main testing methods are rapid antigen tests (which give quick results) and PCR tests (which are more accurate and done in a lab). If you're feeling unwell, it’s best to see your GP for personalised advice and care.

You might not need a test to confirm Influenza B, especially if symptoms appear during flu season. A myhealth GP can assess and advise on treatment based on your risk.

Treatment for Influenza B

Managing Symptoms at Home

If you have Influenza B, the best care usually involves plenty of rest, staying well hydrated, and using over-the-counter medicines like paracetamol or ibuprofen to reduce fever and ease aches. Most people recover fully without needing prescription drugs. Taking these simple steps helps your body fight the infection and reduces discomfort.

Prescription Antiviral Options

For people at higher risk of complications such as older adults, young children, or those with chronic health conditions, doctors may prescribe antiviral medications. These drugs help reduce flu symptoms and shorten illness duration if started within 48 hours of symptom onset and are most effective when started early.

Who Is Most at Risk from Influenza B?

High-Risk Groups

Some people are more likely to develop complications from Influenza B. This includes young children, older adults (65+), pregnant individuals, and those with weakened immune systems or chronic health conditions like asthma or diabetes. These groups should take extra care to avoid infection and seek early medical advice if symptoms appear. Annual flu vaccination is especially important for protecting high-risk groups and reducing the chance of severe illness. The Australian Government funds flu vaccination for high-risk groups who hold a valid Medicare card.

Potential Complications

Complications from Influenza B can include pneumonia, ear infections, or worsening of existing chronic illnesses such as heart or lung disease. In vulnerable people, the flu can lead to hospitalisation or more serious health issues. Monitoring symptoms closely and getting prompt medical care is vital to prevent complications and support recovery.

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 are covered in the seasonal flu vaccine, which is updated each year to target the most common circulating strains. Learn more in our Influenza A overview.

Is Influenza B Less Serious Than A?

While Influenza B is usually milder than Influenza A, it can still make you feel very unwell. Influenza B causes similar symptoms to Influenza A, like fever, cough, and fatigue. In high-risk groups such as young children, the elderly, and people with ongoing health issues, Influenza B can lead to serious complications, just like Influenza A. Even if you're generally healthy, it’s important to monitor symptoms and rest properly. Vaccination each year remains the best way to protect yourself and others from both flu types.

Preventing Influenza B

Flu Vaccination

Getting a flu shot every year is one of the best ways to protect yourself and others from serious illness. The seasonal flu vaccine is designed to protect against the most common strains of both Influenza A and Influenza B expected to circulate that year. It’s especially important for those at higher risk like children, older adults, pregnant individuals, and people with chronic conditions. Even if you’re healthy, getting vaccinated reduces the risk of spreading the flu to more vulnerable people around you. Speak to your GP or pharmacist about getting vaccinated early in the flu season.

Did you know? The flu vaccine is updated every year to protect against both Influenza A and B strains. Getting vaccinated helps protect your entire community.

Vaccination is funded by the Australian Government for medicare-eligible high risk individuals. High risk individuals include people between 6 months and less than 5 years old, ages 65 or older, Aboriginal and/or Torres Strait Islander people over 6 months of age, pregnant people, and individuals with at-risk health conditions (e.g., asthma, diabetes, heart disease).

Everyday Prevention Tips

Simple hygiene habits can help stop the spread of Influenza B. Wash your hands often with soap and water, especially after coughing, sneezing, or being in public places. Always cover your mouth and nose with a tissue or elbow when you cough or sneeze. Stay home if you feel unwell to avoid passing the virus to others—especially in busy places like schools, offices, or public transport. Regular cleaning of shared surfaces, like doorknobs and desks, also helps reduce the risk of infection.

When to Speak to a Doctor

Most cases of Influenza B can be managed at home, but you should see a doctor if your symptoms are severe or not improving after a few days. Seek medical care straight away if you have chest pain, difficulty breathing, a high fever that won’t go down, or if you feel unusually drowsy or confused. People at higher risk like children, the elderly, pregnant individuals, or those with underlying health conditions should not delay seeing their GP.

Worried about your symptoms? Book an appointment at your nearest Myhealth clinic for professional care.