Patient Education: Diseases Conditions Treatments & Procedures

Influenza

Introduction

Influenza, or the flu, is a common respiratory infection caused by the influenza virus. Strains circulate every year, making people sick. In Canada, flu season usually runs from November to April.

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.

Each year, hundreds of thousands of Canadians receive an influenza vaccine (commonly called the "flu shot") to avoid contracting influenza viruses that routinely circulate in the community. The vaccine provides immunity by stimulating the human body to produce antibodies to fight off certain viruses. The antibodies are effective for four to six months. When an individual is exposed to the influenza virus, the antibodies will help either to prevent infection or to reduce the severity of the illness it causes. A vaccine is usually administered by injection and includes a form of the virus that is dead or weakened so as to be harmless to people.