What is Influenza B?

Influenza B is a type of flu virus that can cause fever and respiratory symptoms. It's different from influenza A, the seasonal flu that often goes around in early spring and early fall, because influenza B can occur at any time of year. Unlike other types of influenza, influenza B doesn't carry a high risk of becoming pandemic, because it only infects humans and seals. Influenza B doesn't usually cause serious illness in healthy adults, but some people may be at risk for flu complications and even death. In healthy patients, the disease typically runs its course in seven to ten days.

There are several types of influenza. Influenza A is a common type of flu that usually strikes twice a year, in the spring and fall. Vaccinations are distributed to combat the spread of this type of flu. H1N1, or swine flu, is a more severe type of influenza that can also be prevented by vaccine. The influenza B virus can cause infection at any time of the year, and may account for as many as one third of all flu cases. Conventional flu vaccines usually protect against this type of influenza, too.


The influenza B virus is generally an airborne virus, meaning it can spread through the air on the droplets expelled by a cough or a sneeze. The flu virus can also live on surfaces, such as door handles or telephone receivers. It also can spread through direct physical contact with an infected person.

Symptoms of influenza B can appear within one to seven days after exposure to the virus, though they usually begin two or three days later. The virus can spread quickly to others. It can cause fever, chills, body aches, dizziness, headache, flushing, and lethargy. Nausea and vomiting can also occur.

These symptoms usually begin to subside within two to four days, giving way to respiratory symptoms such as a dry cough, a runny nose, a sore throat, and a headache. The fever may go away, and then come back. All symptoms except cough and fatigue usually clear up within four to seven days. Fatigue and cough associated with influenza can last for several weeks.

Pregnant women, children under two years of age, and senior citizens over age 50 are at risk for serious complications from the flu, and could even die from it. These individuals are generally advised to see a doctor. Most healthy adults, however, don't need medical treatment for influenza B, which usually runs its course in about ten days.



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