Flu season is considered to be the time each year that is characterized by the prevalence of outbreaks. In the U.S., flu season is estimated to occur as early as October and as late as May. Seasonal flu activity usually peaks around January to February though.

The exact reason behind rash of outbreaks is still unclear, but some studies have suggested that during the fall and winter seasons, people tend to stay indoors more often, which promotes transmission from person to person. Other factors, such as a decline in the amount of ultraviolet radiation, colder temperature, and more arid air, are also being considered by many researchers to cause these seasonal outbreaks.

Whatever the reasons may be, recent studies suggest that 5% to 20% of U.S. residents are affected by the flu every year, usually around the autumn and fall seasons. Seniors, children, people with chronic health conditions, and even healthy people are all at risk of experiencing complications from the seasonal bug.