There are four types of influenza virus. Influenza A is the most common, followed by influenza B. Both are highly contagious and have similar symptoms, including fever, chills, and body aches.

Influenza, also known as the flu, is a viral respiratory illness that is most common during the fall and winter months. These viruses can spread when someone with the infection sneezes or coughs and droplets travel to another person’s nose or mouth.

All types of flu are different from the common cold. The flu can cause severe illness and worsen some chronic medical conditions, such as asthma, heart disease, and diabetes. In some cases, it can lead to death.

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There are four types of influenza virus.

Influenza A

Influenza A viruses cause seasonal flu epidemics almost every year in the United States. They can infect humans and animals.

Influenza A is the only type that can cause a pandemic, which is a global spread of disease. Bird flu and swine flu pandemics were both due to influenza A viruses.

An influenza A virus has two surface proteins: hemagglutinin and neuraminidase. These help doctors with classification.

Influenza B

Influenza B viruses can also cause seasonal epidemics that typically only affect humans. There are two lineages of influenza B: Victoria and Yamagata.

Influenza B viruses mutate more slowly than influenza A viruses.

Influenza C viruses cause mild illnesses. They do not appear to cause epidemics.

Influenza D

Influenza D viruses mainly affect cattle and do not seem to infect humans.

Flu resources

For more information and resources to help keep you and your loved ones healthy this flu season, visit our dedicated hub.

Flu symptoms can range from mild to severe, and they vary from person to person.

Potential flu symptoms include:

Some people experience severe symptoms, which can include:

A person who experiences any severe symptoms should seek medical attention.

Below are some key similarities and differences between influenza types A and B.

Prevalence

A 2020 retrospective study of people in hospitals in Australia states that the annual rate of influenza A viruses between 2016 and 2019 was 74.9% to 95.1%. The prevalence of influenza type B in the same period was 4.9% to 25.1%.

Transmission

Both influenza A and B are highly transmissible.

When someone with the flu coughs, talks, or sneezes, droplets can enter another person’s nose or mouth, transmitting the illness.

Alternately, a person can catch the flu if they touch a surface that has droplets containing the flu virus, then touch their own mouth or nose.

People can transmit the flu virus before they show symptoms and up to seven days after infection.

Severity

For someone who is generally healthy, the flu is not typically dangerous, and they will recover in a few days. However, it can severely affect certain groups of people, who should seek medical attention as soon as they have flu symptoms.

Those most at risk of developing flu complications include:

  • people who are pregnant
  • people with health conditions that weaken their immune system
  • young children
  • older adults

Both influenza A and B can cause seasonal epidemics, or flu seasons. However, influenza A is the only type responsible for flu pandemics, which are global epidemics.

Many people believe that influenza A is more severe than influenza, but this is not always the case.

A 2020 study of the 2017 to 2018 influenza season found similar rates of mortality (death) between the two types of influenza after 30 and 90 days. Although the researchers associated influenza A with higher rates of pneumonia and hospital ventilation.

Doctors will typically recommend the same treatments whether someone has influenza A or influenza B.

Home remedies may relieve flu symptoms, but prescription antiviral treatments may be necessary for people with a high risk of complications or severe symptoms.

Home remedies

To reduce flu symptoms at home, people can try the following methods:

  • drink plenty of fluids
  • get plenty of rest
  • take over-the-counter medications such as ibuprofen or acetaminophen (Tylenol) to relieve any pain

Antiviral medications

Antiviral medications are available by prescription only. They can help treat or prevent influenza and its complications.

Antivirals can especially benefit people with a greater risk of flu complications, including young children, older adults, pregnant people, and people with certain chronic illnesses.

Antiviral medications work best when a person takes them within 1 to 2 days of symptoms starting.

There are a few different types of antivirals for the flu, including:

These can come in pill, liquid, inhalable powder, or intravenous forms.

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The following steps can help prevent a person from getting or spreading the flu:

  • limit contact with people that have an active infection
  • stay home when ill
  • cover the nose and mouth when sneezing or coughing
  • wash the hands often
  • disinfect surfaces that may contain flu germs
  • avoid touching the eyes, nose, and mouth
  • wear a mask when leaving the house

According to the Centers for Disease Control and Prevention, everyone six months or older should get the flu vaccination every year.

It can take around two weeks for flu antibodies to develop after getting the flu vaccination, so people should get the vaccine before flu season starts.

The flu vaccine can come as an injection or a nasal spray. People can speak with their doctor about the different available options to choose the most suitable one for them.

A 2024 study looked at influenza vaccination effectiveness in the United States from 2022 to 2023. It concluded that vaccination may substantially reduce mortality, morbidity, and healthcare resource strain due to influenza.

Influenza A is the most common type and usually causes seasonal flu outbreaks. Influenza B can also cause flu outbreaks, but it mutates more slowly.

Influenza A is a highly transmissible virus that causes seasonal flu epidemics in the United States.

Seasonal flu outbreaks in the United States can be due to influenza A or B.

A person may experience fatigue, fever, body aches, and cough due to influenza A and influenza B. Many people recover with home remedies. However, if symptoms are not improving, it is a good idea to seek medical attention.

There are four types of influenza virus, and influenza A and B are the most common.

While many people recover from the flu with home remedies, influenza A and B can each cause serious illness and death in people with a high risk of complications.

There is no cure for the flu, but rest and drinking fluids can help ease symptoms. Antiviral medications may also help shorten the duration of the illness.

The flu vaccination is available to most people ages 6 months and older. Getting this vaccine every year can help prevent serious illness and complications due to the flu.