Flu Spreads through the Air

The influenza virus (the flu) can spread through the air alone. Researchers have discovered that the tiny droplets of moisture from an infected person's breath are able to travel more quickly through cold, dry air. This makes flu easier to transmit between people in the winter months.

Mucus is Reduced During the Flu Season

Cold, dry air also dries up the mucus in people's nasal passages. This mucus is one of the body's defenses against infection. When it is thicker, or there is less of it, as in the winter months, people are less likely to fight off the flu and more likely to be infected.

Flu Spreads through Close Contact

The flu can spread through immediate contact between people. People are in closer contact in the cold months when they are more likely to be indoors.

The Flu Spreads Quickly

Because a person infected with the flu can spread the virus even before they have symptoms, it is not always easy to know when someone has been exposed. Once a few people have the flu, many more can catch it from them quickly. This creates waves of the flu that peak during the winter months.

Flu Can Happen Anytime

Though there is a flu season, people can catch the flu at any time of year. The virus itself lives year around; however, conditions in the warmer months prevent the rapid spread of the flu.

Source:

Newscientist.com: Cold Weather Really Does Spread the Flu

Centers for Disease Control and Prevention: How Flu Spreads