Influenza B is a type of virus that causes seasonal flu, primarily affecting humans. Unlike Influenza A, which can infect various animals, Influenza B is more specific to humans and is generally less severe. It can lead to symptoms such as fever, cough, sore throat, 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 Influenza B, along with Influenza A. Preventive measures include vaccination, good hygiene practices, and staying home when sick to reduce the spread of the virus.