Flu Virus B Symptoms

Influenza type B is one of the two virus types that cause seasonal influenza. It belongs to the virus family Orthomyxoviridae along with influenza type A, the other cause of seasonal flu. The Centers for Disease Control and Prevention states that 5 percent to 20 percent of the U.S. population contracts the flu each season. Influenza type B generally causes a milder form of the flu than influenza type A. The seasonal influenza vaccines provide protection against influenza types A and B. Notably, influenza type B does not cause pandemic influenza outbreaks.


Sudden onset of fever is often the first symptom of flu. Fever rises rapidly during the initial hours of the illness. In adults, the temperature is typically 100 F to 102 F (37.7 C to 38.8 C). Children usually run higher fevers up to 105 F (40.5 C). In general, the younger the child, the higher the fever is. On average, the fever of flu lasts roughly 3 days. Once the fever breaks, other symptoms typically begin to wane.


Headache commonly appears along with the fever of influenza B. It is generally mild and eased by over-the-counter pain relievers. Flu-related headache often clears when the fever breaks.

Body Aches

Without seeking a medical diagnosis, many people informally distinguish the flu from other viral illness by the presence of body aches. There is some merit to this observation. Body aches are a hallmark characteristic of influenza–although not diagnostic since many other illnesses also cause body aches. Muscle aches typically predominate over joint achiness with influenza. The extremities and back muscles are commonly involved. Children may complain of calf muscle pain. Once the fever breaks, this symptom usually resolves quickly.


When you just don’t feel well, you have the symptom known as malaise. Influenza B causes malaise, which typically begins close to the time the body temperature spikes. Malaise is one of the slowest symptoms to resolve with the flu. Full resolution may take 2 weeks or more.

Runny Nose and Nasal Congestion

Influenza B virus infects the cells that line the nose and upper throat. The viral infection and immune response in the nasal passages cause a runny nose and congestion. These symptoms generally resolve approximately 4 days after the fever breaks.

Sore or Scratchy Throat

Invasion of the upper throat by the influenza B virus commonly causes a scratchy or sore throat. Mouth breathing because of nasal congestion can dry the throat and aggravate this symptom. The throat symptoms caused by influenza B usually resolve within a week of the onset of the illness.

Dry Cough

Direct irritation of the throat and drainage of nasal secretions down the back of the throat commonly cause dry cough. Cough often persists longer than the other symptoms of influenza B. It may take 2 weeks or more for the cough to completely clear.

About this Author

Tina Andrews has been a medical writer and editor since 2000. She has published in “Cancer,” “Ethnicity & Disease,” and “Liver Health Today,” and was formerly a medical officer with the Centers for Disease Control and Prevention. Andrews holds a Doctor of Medicine degree and a Bachelor of Arts in chemistry.