according to the u. s. cdc: "most healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. children may pass the virus for longer than 7 days. symptoms start 1 to 4 days after the virus enters the body. that means that you may be able to pass on the flu to someone else before you know you are sick as well as while you are sick. some persons can be infected with the flu virus but have no symptoms. during this time those persons may still spread the virus to others. "
when is the flu no longer contagious?