What You Need to Know About Influenza B

Sick woman lying in bed
What Influenza B means for you. Sarah Kastner / STOCK4B / Getty Images

Although most people call influenza "the flu," there are actually many subtypes of the influenza virus and mutations occur all the time. There are three main types of influenza: A, B and C. Influenza A and B cause outbreaks of seasonal flu, but influenza C does not.

Influenza A is the most common type of the virus and is further broken down into subtypes (such as H1N1) and individual strains.

Influenza B is less common but still causes outbreaks of seasonal flu. One or two strains of influenza B are included in the seasonal flu vaccine every year to protect people from the strain(s) that researchers believe are most likely to cause illness during the upcoming flu season. The quadrivalent flu vaccine contains two strains of influenza B but the traditional trivalent flu vaccine only contains one. 

Influenza B is not broken down into subtypes like influenza A is, but it is broken down into individual strains.

How Flu Viruses Are Named

Influenza viruses are named using the following formula: 

  1. The antigenic type (A, B, C)
  2. The host of origin (swine, equine, chicken - if the origin is human, none is listed)
  3. Location of origin (city where the virus was first identified)
  4. Strain number
  5. Year of origin
  6. For influenza A viruses, the subtype is listed

A (made up) influenza B virus would be listed as B/swine/Hong Kong/15/2010.

Symptoms of Influenza B

Symptoms of influenza B are the same as the symptoms of other types of the flu. Most people will experience symptoms such as coughing, fever, headache, body aches, exhaustion, and congestion. When you get the flu, the symptoms come on strong and fast, not gradually. They typically last between 3 and 7 days and you feel so bad that it is hard to do almost anything other than lay in bed.


Getting Diagnosed With Influenza B

If you think you might have the flu, you should see your health care provider within the first 48 hours of the onset of your symptoms. He can perform a flu test and diagnose you based on the test results, your symptoms, and a physical exam. If your health care provider diagnoses you with the flu, you may be able to take antiviral medications to shorten the duration of your illness and lessen the severity of your symptoms. Some flu tests can identify whether you have influenza A or B, but many rapid tests that are performed in the doctor's office do not -- they only tell you whether or not you have the flu. Unfortunately, even those tests are often inaccurate.

What Influenza B Means For You

There is not much difference between influenza A and B when it comes to how they affect you -- meaning one is not more or less severe than the other. The major difference comes down to how they are classified and their potential to cause epidemics. Influenza B can cause outbreaks of seasonal flu but they occur less frequently than outbreaks of influenza A. Typically, two strains of influenza A and one strain of influenza B are included in the seasonal flu vaccine.

If you come down with the flu -- whether it is influenza A or B -- take care of yourself, try to get plenty of rest, stay hydrated, and stay away from other people so you don't spread the virus. If you are at high risk for complications from the flu or you believe you may have developed a secondary infection, be sure to see your health care provider as soon as possible.


Frequently Asked Flu Questions 2016-2017 Influenza Season. Centers for Disease Control and Prevention. 2016. http://www.cdc.gov/flu/about/season/flu-season-2016-2017.htm

Types of Influenza Viruses. Seasonal Influenza (Flu) 22 Mar 12. US Centers for Disease Control and Prevention. 10 May 12.

Flu. PubMed Health 16 Sep 11. US National Library of Medicine. 10 May 12.

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