Influenza (Seasonal Flu) and the Influenza Vaccine

Influenza and influenza vaccine fact sheet in other languages.

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What is influenza?

Influenza (the flu), is a virus that comes around each fall (making it seasonal) that causes fever, chills, muscle aches, headache, runny nose, cough, weakness and tiredness. These symptoms usually last two to seven days. The cough and weakness may last for up to six weeks. Elderly persons may have the flu without a fever, and children may have stomach symptoms such as nausea, vomiting and diarrhea.

Who is at risk?

Everyone is at risk of getting the flu. Although most people will not get seriously ill, some people may develop flu-related complications such as lung infections (pneumonia), ear infections, dehydration (loss of body fluids) and, in rare cases, death. People most at risk include: children less than two years of age; people 65 years of age and older; residents of long-term care homes or chronic-care facilities; people with chronic health conditions such as diabetes, cancer, lung, heart or kidney disease; pregnant women; aboriginal peoples; and people who are obese.

How is the flu spread?

You can get the flu if you are coughed or sneezed on by someone who has the flu. Touching hands, surfaces or objects that someone with the flu has touched and then touching your eyes, nose or mouth can all lead to getting the flu.

What can I do to prevent the spread of the flu? Get the flu shot each fall.

Also follow these simple steps to protect yourself:

  • wash your hands frequently
  • cover your cough and sneeze with something other than your hands
  • stay home when you are sick
  • drink plenty of fluids
  • be physically active
  • avoid touching your eyes, nose and mouth with unclean hands
  • avoid close contact with persons who are sick with the flu
  • stay well rested
  • eat nutritious food

What is the influenza vaccine and what does it do?

Each year, the influenza vaccine (flu shot) protects against the three types of influenza viruses that are most likely to cause the flu that year. The flu shot cannot give you the flu because it does not contain live influenza viruses. The body needs two weeks to build up protection against influenza after the shot is given. Protection lasts four months or longer. The flu shot does not protect against colds or other illnesses with flu-like symptoms.

When should I get the flu shot?

As the flu shot takes two weeks to provide full protection, the earlier you get the vaccine the better. The flu shot is available starting in October.

I got a flu shot last year. Do I have to get it again this year?

Yes. You should get the flu shot each fall. The viruses that cause the flu change frequently. Protection from last year's vaccine has likely worn off. You need to get another shot to be protected this year.

Who should get the influenza vaccine?

Everyone who is six months of age or older should get the flu shot, unless there is a medical reason that prevents you from getting the vaccine. If you are at high risk for flu-related complications (see Who is at risk?) or live or work with people who are at high risk (e.g. healthcare workers and essential community services staff), getting the flu shot is particularly important.

How many doses of the vaccine do I need?

Adults should receive one shot each year. Children between six months and eight years of age who never had a seasonal flu shot should receive two doses the first year they get vaccinated. These two doses should be received at least one month apart, and they need one shot each year after that.

What are the side effects of the flu shot?

The flu shot is very safe. The most common side effects are soreness or redness where the shot is given, fever, headache or tiredness and achiness. Side effects usually occur one to two days after vaccination.

Severe side effects and allergic reactions are rare. In past years, a small number of people who received the flu shot developed oculo-respiratory syndrome (ORS). ORS can cause red eyes, cough, chest tightness, difficulty breathing, hoarseness, sore throat and swelling of the face. Symptoms occur within 24 hours and resolve within 48 hours.

In very rare instances (about one in one million doses of vaccine), the flu shot has been associated with a temporary neurological condition causing muscle paralysis called Guillain-Barré Syndrome (GBS). Seek medical attention if you believe that you, or someone in your care, had a reaction to the shot.

Who should not get the flu shot?

  • People with a severe allergy to eggs or any component of the vaccine (e.g., neomycin, thimerosal) or who had a serious allergic reaction to a previous dose of influenza vaccine
  • Babies younger than six months of age
  • Any person who has had Guillain-Barré Syndrome (GBS) or who has an active neurological disorder should speak with a doctor before getting vaccinated.
  • Most people who have had oculo-respiratory syndrome (ORS) can be safely re-immunized with the flu shot but should discuss this with a doctor first.
  • Anyone who is ill with a fever should delay receiving the flu shot until they feel better

What should I do if I get the flu?

Get plenty of rest and drink lots of fluids. Wash your hands often. Stay at home and away from children, the elderly and anyone with a serious illness until you are feeling better. Ask your doctor about medication to reduce aches, pain and fever. Also ask about anti-influenza drugs that may ease your discomfort and shorten the length of your illness. Children should not be given medication that contains acetylsalicylic acid (e.g. aspirin) because it can cause Reye's Syndrome, a sickness that can lead to brain and liver damage.

Where can I find more information?

Talk to your doctor or call Toronto Public Health at 416-338-7600.

Last updated on October 2011