From the CDC Science Blog:

As we enter another influenza season, one question continues to vex medical and public health professionals: How do you stop people from catching the flu? The best way to prevent the flu is by getting an influenza vaccine every year. However, in the event of a large-scale influenza outbreak of a new virus strain or a pandemic, when influenza vaccine may not be promptly available, we will see tremendous demands on the health care system and its workers. Thus, it’s critical to understand how influenza is transmitted from person to person so that we can determine the best ways to protect health care workers while still enabling them to do their jobs.

The typical incubation period for influenza is 1-4 days (average: 2 days). Adults shed influenza virus from the day before symptoms begin through 5-10 days after illness onset. However, the amount of virus shed, and presumably infectivity, decreases rapidly by 3-5 days after onset in an experimental human infection model. Young children also might shed virus several days before illness onset, and children can be infectious for 10 or more days after onset of symptoms. Severely immunocompromised persons can shed virus for weeks or months.

Experts think influenza may be spread to uninfected people in three ways: large-particle respiratory droplet transmission, airborne transmission, and contact (or fomite) transmission. Most experts think that influenza viruses are spread mainly by large-particle respiratory droplets produced when people infected with influenza cough, sneeze or talk. These droplets can land in the mouths or noses of people who are...Read more>>