Influenza or commonly called “the flu” is a respiratory infection caused by the influenza virus affecting millions of people all over the world. In Canada, flu season usually runs from November to April and an estimated 10-25% of Canadians get the flu every year.
The flu vaccine provides immunity by stimulating the human body to produce antibodies that will prevent infection or reduce the severity of illness caused by the virus. The antibodies are effective for four to six months. It is administered by injection and it contains a form of the virus that is dead or weakened, so it is harmless to people. Generally the flu shot is effective against the virus within two weeks of the injection.
Each year, the influenza virus can change slightly, making the vaccine used in the previous year ineffective. The annual vaccine is changed every year to provide protection from the virus strains that are predicted to be most common. Since the influenza strains change every year and because the antibodies last for only a few months, the flu shot must be administered annually.
An annual flu shot reduces the risk of complications associated with influenza infection. Common symptoms include fever, headache, extreme tiredness, dry cough, sore throat, runny nose, muscle ache and stomach symptoms (more common in children than adults). Bacterial pneumonia, ear infection, sinus infection, dehydration and worsening of chronic medical conditions (heart disease, asthma, diabetes) are serious complications related to influenza infection.
Being vaccinated against influenza virus prevents you from getting the flu as well as spreading it to others around you. You are able to pass on the flu to someone else one day before symptoms develop and about five days after becoming sick. Ultimately, the best way to prevent the flu is by getting flu vaccination every year.