Why it spreads

People with flu can spread it to others. Most experts think that influenza viruses spread mainly by droplets made when people with flu cough, sneeze, or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Putting physical distance between yourself and others can help lower the risk of spreading a respiratory virus. Less often, a person might get flu by touching a surface or object that has influenza virus on it and then touching their own mouth, nose, or possibly their eyes.

When Are People with Flu Contagious?

Influenza viruses can be detected in most infected persons beginning one day before symptoms develop and up to five to seven days after becoming sick. People with flu are most contagious during the first three days of their illness. Some people, including young children and people with weakened immune systems may be contagious for longer periods of time.

Symptoms typically begin about two days (but can range from one to four days) after influenza viruses infect a person’s respiratory tract. It is theoretically possible that before symptoms begin, an infected person can spread influenza viruses to their close contacts. Some people can be infected with influenza viruses and have no symptoms but may still be able to spread the virus to their close contacts.