What virus causes influenza B?

Influenza B, also known as type B influenza, is an acute respiratory infectious disease caused by the influenza B virus. This virus primarily spreads through respiratory droplets when infected individuals cough or sneeze in close proximity to others. The clinical symptoms of influenza B are similar to those of influenza A, with recurrent fever being the most common symptom. Fever often develops suddenly and may reach as high as 40°C, accompanied by chills, headache, generalized body aches, fatigue, sore throat, and cough. In young children, these symptoms can be more severe.