The Influenza B Virus is one of the main types of viruses that cause the flu, primarily affecting humans. Unlike Influenza A, which can infect various animals, Influenza B is more specific to humans and is known to cause seasonal outbreaks. It typically leads to symptoms such as fever, cough, and body aches. There are two main lineages of Influenza B: B/Yamagata and B/Victoria. Vaccines are developed each year to protect against the most common strains of the virus, helping to reduce the severity and spread of the illness during flu season.