How Flu Spreads

Person to Person

The main way that influenza viruses are spread is from person to person in respiratory droplets of coughs and sneezes. (This is called "droplet spread.") This can happen when droplets from a cough or sneeze of an infected person are propelled through the air and deposited on the mouth or nose of people nearby. Influenza viruses may also be spread when a person touches respiratory droplets on another person or an object and then touches their own mouth or nose (or someone else’s mouth or nose) before washing their hands.

The Flu Is Contagious

Most healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 days after becoming sick. Children may pass the virus for longer than seven days. Symptoms start one to four 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 can still spread the virus to others.