When flu season arrives, it can feel like you’re surrounded by coughs, sneezes, and runny noses. The flu is a highly contagious respiratory illness that can strike quickly, leaving you achy, exhausted, and curled up in bed. In some cases, the flu can even lead to serious complications and hospital visits, which is why knowing the difference between flu A vs flu B matters, especially when it comes to recognizing symptoms and knowing when to seek emergency care.
What’s the Difference Between Flu A and Flu B?
Doctors recognize four main types of influenza viruses, A, B, C, and D, but the ones that affect humans the most are flu type A and flu type B. Flu C usually causes mild illness, while flu D affects cattle and does not infect people. That’s why the focus in flu season is mainly on flu A and B.
Flu A: This is the most common strain and is often responsible for major outbreaks, including global pandemics like the 2009 H1N1 “swine flu.” It can infect both humans and animals, which increases its chances of spreading and mutating. Because it changes quickly, new subtypes appear often, making it harder for immunity and vaccines to keep up.
Flu B: This strain only spreads among humans and mutates much more slowly, so its makeup stays more stable from year to year. While less likely to cause worldwide outbreaks, flu B can still lead to serious illness, especially in children and older adults. It usually shows up later in the season, with peaks in late winter and spring.
Because flu A mutates so easily, it’s often considered the “worst” strain. Still, both flu A and flu B can cause severe illness and complications.
Flu A vs Flu B Symptoms
The tricky part? Flu A and flu B have very similar symptoms, which makes it hard to tell them apart without a test. Both strains attack the respiratory system and can leave you feeling run-down for days. The difference usually comes down to how severe the illness feels.
Most people with the flu experience:
- Fever: Often sudden and sometimes high, especially with flu A.
- Chills and sweats: Common as the body tries to fight the infection.
- Body aches: Aching muscles and joints that make it hard to move.
- Fatigue: Extreme tiredness that can last even after other symptoms ease.
- Headache: Ranging from mild pressure to intense pain.
- Sore throat or cough: Dry coughs are especially common with the flu.
Some may also develop nasal congestion, sneezing, nausea, or stomach pain, though these symptoms can vary. Children in particular may experience vomiting or diarrhea with the flu, which is not as typical in adults.
Is There a Test for the Flu?
Yes, there are reliable tests that confirm whether you have influenza A or B. Since flu symptoms often overlap with conditions like strep throat, RSV, or COVID-19, testing is the only way to know for sure. A proper diagnosis also helps doctors rule out other illnesses that may require different treatments, such as antibiotics for strep.
Multiple options for flu testing:
- At-home test kits: Some can detect flu A, flu B, COVID-19, and RSV at the same time. These are convenient but may be less accurate.
- Rapid flu tests: Performed in clinics, urgent care, or emergency centers, giving results in about 15–30 minutes.
- Advanced lab tests (PCR): More accurate and detailed, often used in hospitals or for high-risk patients.
Consider getting tested if you:
- Develop sudden flu-like symptoms with a high fever
- Are at higher risk of complications (children, older adults, pregnant women, or people with chronic conditions)
- Need to confirm flu quickly for work, school, or medical care decisions
Getting tested not only ensures you receive the right treatment but also helps prevent serious complications like pneumonia and limits the spread of flu to others.
Can You Get Flu A and Flu B at the Same Time?
It may surprise you, but the answer is yes. Since flu A and flu B are caused by different strains of the virus, your body’s immune response to one does not protect you from the other. This means it’s possible to catch flu A first and then develop flu B later in the same season.
Although rare, some people can even be infected with both strains at the same time. When this happens, symptoms may be more severe, and the risk of complications, like pneumonia or dehydration, can increase. Children, older adults, and people with weakened immune systems are more likely to experience this type of co-infection.
Treatment Options for Flu A and Flu B
Unfortunately, there isn’t a medicine that can make the flu disappear instantly. However, there are effective ways to reduce the severity of symptoms, shorten recovery time, and lower the risk of complications.
Treatment options include:
- Antiviral medication (like Tamiflu, Relenza, or Xofluza): These prescription drugs work best when started within the first 48 hours of symptoms. They don’t “cure” the flu but can make symptoms milder and shorten the illness by 1–2 days. Antivirals are especially important for high-risk patients, such as children, older adults, or those with chronic conditions.
- Over-the-counter medicine: Pain relievers such as acetaminophen (Tylenol) or ibuprofen (Motrin, Advil) can bring down fevers, ease headaches, and reduce body aches. They don’t fight the virus itself but make you feel more comfortable.
- Rest and hydration: Your body needs extra energy to fight the virus. Getting plenty of sleep and drinking water, herbal teas, or clear broths can help prevent dehydration and speed up recovery.
How Long Does the Flu Last & How to Protect Yourself
For most people, flu symptoms last about 3–7 days, though cough and congestion can linger for up to two weeks, and you may still be contagious during that time. While there’s no guaranteed way to avoid the flu, you can lower your risk by getting your annual flu vaccine (ideally in September, but it’s never too late), washing your hands often, avoiding face-touching, staying home when sick, and supporting your immune system with good sleep, healthy food, and proper hydration. The vaccine not only reduces your chance of getting sick but also lowers your risk of hospitalization and serious complications.
Fight the Flu With Exceptional Emergency Center
Knowing the difference between flu A and flu B can help you better understand your symptoms and make informed decisions about your care. While most people recover with rest, fluids, and over-the-counter medication, the flu can sometimes lead to serious complications, especially in young children, older adults, and those with underlying health conditions. If you or a loved one experiences high fever, difficulty breathing, chest pain, dehydration, or symptoms that suddenly worsen, don’t wait. Exceptional Emergency Center is open 24/7 with a skilled, compassionate team ready to provide prompt, expert care. We’re here to help you feel better, stay safe, and get back to life faster.