A , Administration, answered. The first symptoms of influenza (flu) virus B, including fever, chills, headache, and body aches, often begin to go away after about 2 or 3 days. In some cases, these symptoms will last 5 days or longer. The respiratory symptoms of influenza virus B, such as coughing, throat irritation, and congestion may last for days or weeks. However, most people are not contagious after about a week from the beginning of symptoms.