The Flu Season

Seasonal epidemics

Influenza epidemics occur yearly during autumn and winter in temperate regions. Illnesses result in hospitalizations and deaths mainly among high-risk groups (the very young, elderly or chronically ill). Worldwide, these annual epidemics result in about three to five million cases of severe illness, and about 250 000 to 500 000 deaths. Most deaths associated with influenza in industrialized countries occur among people age 65 or older. In some tropical countries, influenza viruses circulate throughout the year with one or two peaks during rainy seasons.

In the Northern hemisphere, winter is the time for flu. The timing and duration of flu seasons vary. While flu outbreaks can happen as early as October, most of the time influenza activity peaks in January or later. During the past 26 flu seasons, months with the heaviest flu activity (peak months) occurred in November one season, December four seasons, January five seasons, February 12 seasons, and March four seasons.

Monitoring Flu Activity

World Health Organization (W.H.O.)

The WHO, with its partners, monitors influenza globally, annually recommends a seasonal influenza vaccine composition, and supports Member States efforts to develop prevention and control strategies. WHO works to strengthen national and regional influenza diagnostic capacities, disease surveillance, outbreak responses, and increase vaccine coverage among high-risk groups.

Centers for Disease Control (C.D.C.)

The CDC collects, compiles and analyzes information on influenza activity year round in the United States and produces a weekly report from October through mid-May. The U.S. influenza surveillance system is a collaborative effort between CDC and its many partners in state and local health departments, public health and clinical laboratories, vital statistics offices, physicians, clinics and emergency departments, and the Departments of Defense and Veteran’s Affairs. Information in five categories is collected from 10 different data sources that allow CDC to:

• Find out when and where influenza activity is occurring

• Track influenza-related illness

• Determine what influenza viruses are circulating

• Detect changes in influenza viruses

• Measure the impact influenza is having on deaths in the United States