Is Flu A Or B Worse?

Flu season brings the same question every year: is flu A or B worse? The short answer is that influenza A causes most severe flu seasons and most hospitalizations. But influenza B can hit certain groups just as hard. The strain matters less than your age, your health, and whether you get treated early.

What Is The Difference Between Flu A And Flu B?

Influenza A and influenza B are two different types of the flu virus. They cause the same illness with the same symptoms. The difference is in how they spread and who they affect.

Influenza A is the more common type. It infects humans and animals like birds and pigs. It changes quickly, which is why new strains appear almost every year. Influenza A caused the 1918, 1957, 1968, and 2009 pandemics.

Influenza B is different. It mostly infects humans. It changes more slowly than A. It splits into just two main lineages, Victoria and Yamagata. For these reasons, B is less likely to cause a pandemic.

Both types circulate during flu season. In most years, A dominates early in the season and B appears later. Some seasons see a second wave of B cases after A has faded.

Which Type Causes Worse Illness?

Studies have found that influenza A leads to more hospitalizations and more deaths overall. This is partly because A is more common. But it is also because A tends to cause more severe illness in adults.

Research published in medical journals has compared outcomes between the two types. Adults hospitalized with flu A generally have higher rates of pneumonia and need intensive care more often than those with flu B.

Flu B is not harmless. It can cause severe illness, especially in children. Some studies indicate that children hospitalized with flu B may have outcomes similar to or worse than those with flu A. Flu B also hits older adults hard.

The honest answer is that both types can be serious. The virus type matters less than your individual risk. A healthy adult with flu B may recover in a few days. An older adult with flu A may end up in the hospital.

Who Is At Highest Risk For Severe Flu?

Certain groups face higher risk of severe illness from either type. The Centers for Disease Control and Prevention lists these groups as high risk:

• Adults aged 65 and older
• Children under 5, especially under 2
• Pregnant women and women up to two weeks postpartum
• People with asthma, diabetes, heart disease, or lung disease
• People with weakened immune systems
• People living in nursing homes or long-term care facilities

Children under 2 are particularly vulnerable to flu B. Some research suggests flu B causes a higher proportion of severe illness in young children than in adults. Parents should not assume flu B is the milder flu.

Older adults face the highest risk of death from either type. The immune system weakens with age, and the flu vaccine response is less robust in older adults. This is why a high-dose flu vaccine exists for people 65 and older.

How Do Symptoms Compare?

Flu A and flu B produce identical symptoms. You cannot tell which type you have based on how you feel. The symptoms include:

• Fever or chills
• Cough and sore throat
• Runny or stuffy nose
• Muscle and body aches
• Headache
• Fatigue
• Vomiting and diarrhea, more common in children

Some people think flu B causes more stomach symptoms. This is not well supported. Gastrointestinal symptoms can occur with both types, and they are more common in children regardless of strain.

The severity of symptoms depends more on your immune system than the virus type. A person with underlying health conditions will likely feel worse with either type than a healthy person would.

Flu symptoms come on suddenly. A cold builds gradually. With flu, you often feel fine in the morning and miserable by afternoon. This sudden onset is a hallmark of both flu A and flu B.

How Is Flu Treated?

Antiviral drugs work against both flu A and flu B. These include oseltamivir, which is sold as Tamiflu. These drugs work best when started within 48 hours of symptom onset.

Antivirals do not cure the flu. They shorten the illness by about a day and can reduce the risk of complications. For people at high risk, antivirals can mean the difference between a mild illness and a hospital stay.

Doctors may prescribe antivirals without a positive flu test during flu season. Testing is not always needed to start treatment. If you are at high risk and have flu symptoms, call your doctor early.

Most healthy people recover from flu without antivirals. Rest, fluids, and fever reducers like acetaminophen or ibuprofen are the mainstays of care. Do not give aspirin to children or teenagers with flu symptoms due to the risk of Reye syndrome.

Does The Flu Vaccine Cover Both Types?

Yes. The seasonal flu vaccine protects against both influenza A and influenza B. Standard flu shots contain two influenza A strains and one or two influenza B strains.

Flu B has two lineages, Victoria and Yamagata. Some vaccines include both lineages, which is called a quadrivalent vaccine. This provides broader protection against B.

The vaccine does not guarantee you will not get the flu. It reduces your risk of infection and significantly reduces your risk of severe illness, hospitalization, and death. This protection applies to both flu A and flu B.

Flu vaccine effectiveness varies by season. Some years the vaccine matches circulating strains well. Other years it matches poorly. Even in poor match years, the vaccine still provides partial protection and reduces severe outcomes.

Is Flu A Or B Worse For Children?

Flu B is a serious concern for children. Some studies indicate that flu B causes a disproportionate share of severe illness in children compared to adults. Children with flu B can develop pneumonia, croup, and worsening of asthma.

Children under 2 have the highest risk of flu complications. Their immune systems have not fully developed. They also have smaller airways, which makes respiratory complications more dangerous.

Parents should treat both types with equal seriousness. If a child has flu symptoms and is under 5, or has an underlying condition, contact a doctor promptly. Antiviral treatment is recommended for children at high risk.

Emergency warning signs in children include trouble breathing, bluish lips, chest pain, dehydration, seizures, and fever with a rash. These require immediate medical attention.

How Long Does Flu Last?

Most people recover from flu A or flu B within 3 to 7 days. The cough and fatigue can linger for two weeks or more. This timeline applies to both types.

Complications can extend the illness. Pneumonia, sinus infections, and ear infections can develop after the initial flu illness. Bacterial pneumonia is a serious complication that can occur days after you start feeling better.

If your symptoms improve and then suddenly worsen, contact a doctor. This pattern can signal a secondary bacterial infection. This happens with both flu A and flu B.

Can You Get Flu Twice In One Season?

Yes. You can get flu A and flu B in the same season. Having one type does not protect you from the other.

Your immune system builds antibodies to the specific strain you had. If you had flu A, your body has some protection against that specific A strain. It does not protect you from flu B or from a different A strain.

This is why the flu vaccine matters even if you already had the flu. The vaccine protects against multiple strains. Getting vaccinated after recovering from flu can still protect you from the other type.

How Can You Prevent The Flu?

The flu vaccine is the best prevention for both flu A and flu B. Annual vaccination is recommended for everyone 6 months and older.

Hand washing reduces transmission. Flu viruses spread through droplets when an infected person coughs or sneezes. They can also survive on surfaces for hours.

Avoid touching your face. Flu viruses enter the body through the eyes, nose, and mouth. If you touch a contaminated surface and then touch your face, you can infect yourself.

Staying home when sick reduces spread. The CDC recommends staying home for at least 24 hours after your fever resolves without fever-reducing medication. This applies to both flu types.