Influenza (A.K.A. the flu) is a respiratory virus infection that spreads easily from person to person, usually by coughing, sneezing, or direct contact. There are two main types of flu viruses, A and B. Flu A and B viruses that routinely spread among people (human influenza viruses) cause yearly seasonal flu epidemics. Each year, flu vaccines are designed to protect against these types of flu. 更多
