How Long Does Type B Flu Usually Last?

Medically Reviewed on 11/9/2022
How Long Does Type B Flu Usually Last
In most cases, flu type B lasts about 5-7 days

Influenza, commonly known as flu, is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs (respiratory tract).

In most cases, flu type B lasts about 5-7 days. Symptoms may resolve sooner or be less severe in people who have had a flu shot.

What are different types of the flu?

Although seasonal flu viruses are detected in the U.S. throughout the year, flu viruses typically circulate during the fall and winter, also known as the “flu season.”

Influenza viruses are divided into four main types:

  • Type A
  • Type B
    • B/Yamagata
    • B/Victoria
  • Type C
  • Type D

Influenza A and B cause seasonal epidemics of disease. Influenza A viruses are the only viruses known to cause pandemics (global epidemics). Influenza C viruses generally cause mild illness, whereas influenza D viruses primarily affect cattle and are not known to infect or cause illness in humans.

What are common flu type B symptoms?

For most people, the flu is a short-term illness with symptoms that appear 1-4 days after exposure to the virus. Flu type B symptoms typically occur suddenly and may be mild to severe:

How does flu type B spread?

Experts believe that flu viruses are spread predominantly by tiny droplets expelled when someone with flu coughs, sneezes, or talks.

These droplets may reach the mouths or noses of people nearby (about 6 feet away). Less often, a person may get the flu by touching a contaminated surface or object and then touching their mouth, nose, or eyes.

Pregnant women, people older than 65 years, young children, and people with certain health conditions such as asthma, diabetes, or heart disease are at a higher risk of serious flu complications.

When is the flu contagious?

Flu viruses can be detected in infected people 1 day before symptoms begin and up to 5-7 days after getting sick.

The contagious period varies depending on age group and viral load:

  • Adults with the flu are most contagious in the first 3-4 days of the illness.
  • Healthy adults may be able to infect others one day before symptoms have developed and up to 5-7 days after symptom onset.
  • People with weakened immune systems and children (younger than 5 years) may be contagious for longer.


Which illness is known as a viral upper respiratory tract infection? See Answer

How is the flu diagnosed?

Flu type B is generally diagnosed based on typical symptoms. 

Reverse transcription-polymerase chain reactions or viral culture of nasopharyngeal or throat secretions are the gold standards for determining influenza virus infection. Tests may be ordered as well, such as:

  • Rapid influenza diagnostic tests: Detects the virus (antigens) that stimulates an immune response
  • Rapid molecular assays: Detects the genetic material of the flu virus

What are treatment options for the flu type B?

The best way to reduce your risk of getting the flu and its potentially serious complications is by getting vaccinated each year. According to the CDC, the flu vaccine helps reduce flu-related illnesses and the risk of serious complications that can result in hospitalization or even death.

Seasonal flu vaccines do not protect against influenza C or D viruses or animal-origin (zoonotic) flu viruses, such as avian flu viruses, which can cause human infections.

Treatment options for flu type B include:

What are potential complications of type B flu?

Potential flu complications include:

When should you call a doctor about the flu?

If you experience any of the following symptoms, seek immediate medical attention:



  • Rapid or troubled breathing
  • Bluish lips or face
  • Chest pain
  • Severe muscle pain 
  • Dehydration (inability to pass urine for 7 hours, dry mouth, and decreased tear production)
  • Decreased alertness
  • Seizures
  • Fever higher than 104 F
  • Worsening fever or cough
Medically Reviewed on 11/9/2022
Image Source: iStock image

About Flu. Centers for Disease Control and Prevention

How long does the flu last? Harvard Health Publishing

B Strain Dominating Early in the Flu Season. WebMD