Influenza B has the potential to cause transmission, but the likelihood of transmission is not as great as that of influenza A. Influenza viruses can be divided into three types: influenza A, B and C. Influenza A is the most likely to cause infection. Influenza A viruses often mutate, and the mutated viruses can cause clinical symptoms after infecting humans, and the surrounding people are likely to have not been infected with such mutated viruses before, so it is easier to cause infection and the clinical symptoms are heavier. However, influenza B virus rarely mutates, so influenza B virus is not as contagious as influenza A. Because a person who has influenza B is likely to be surrounded by people who have also been infected with the corresponding virus, and the immune system has some recognition of this virus, he or she will not generally be infected when exposed to this virus again. Therefore, although influenza B can cause transmission, it is less likely to cause infection and epidemic than influenza A.