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Seasonal Influenza

Seasonal influenza, commonly known as the flu, is an infection in the airways caused by the influenza virus. It’s called ‘seasonal’ influenza because the virus circulates annually in the winter season in Canada. In addition to seasonal influenza, you have probably heard about avian influenza and pandemic influenza.

Seasonal influenza is a contagious respiratory illness caused by the influenza virus. It is easily caught and easily spread. Influenza typically starts with a headache, chills and cough, followed rapidly by fever, loss of appetite, muscle aches and fatigue, running nose, sneezing, watery eyes and throat irritation. Nausea, vomiting and diarrhea may also occur, especially in children.

Influenza also lowers the body’s ability to fight off other infections which can lead to pneumonia, bronchitis or other complications. In addition, influenza can worsen a current medical condition such as diabetes, lung disease, heart disease, kidney disease or cancer. Although the burden of influenza can vary from year to year, it is estimated that, in a given year, an average of 12,200 hospitalizations related to influenza and approximately 3,500 deaths attributable to influenza occur.


Public Health Agency of Canada. Canadian Immunization Guide. Evergreen edition. (external link)

Public Health Agency of Canada. National Advisory Committee on Immunization. Canadian Immunization Guide Chapter on Influenza and Statement on Seasonal Influenza Vaccine for 2016-2017. (external link)