Influenza (the flu) Health Effects and Risks

by Health Canada

Influenza (or flu) is a common respiratory illness affecting millions of Canadians each year. Getting an influenza vaccination (or flu shot) every year can help prevent the infection or reduce the severity of the illness.

Influenza is a respiratory infection caused by the influenza virus. Various strains of the virus circulate throughout the world year-round, causing local outbreaks. In Canada, flu season usually runs from November to April and an estimated 10-25% of Canadians may get the flu each year. Although most of these people recover completely, an estimated 4,000 to 8,000 Canadians, mostly seniors, die every year from pneumonia related to flu and many others may die from other serious complications of flu.

The influenza virus spreads through droplets that have been coughed or sneezed into the air by someone who has the flu. You can get the flu by breathing in these droplets through your nose or mouth, or by the droplets landing directly on your eyes. The flu virus is also found on the hands of people with the flu and on surfaces they have touched. You can become infected if you shake hands with infected persons or touch contaminated surfaces and transfer the virus to your own eyes, nose or mouth.

Flu vaccines have been around since the 1940s. The vaccine is made from fragments of inactivated influenza viruses, grown in fertilized hens' eggs and then purified. The flu viruses are capable of changing from year to year, so the composition of the vaccine has to be updated annually. This is why it is necessary to be immunized each fall. About 10 million doses of influenza vaccine are distributed annually in Canada each year during the flu season.

After you get a flu shot, your immune system produces antibodies against the strains of virus in the vaccine. The antibodies are effective for four to six months. When you are exposed to the influenza virus, the antibodies will help to prevent infection or reduce the severity of the illness.

The Health Effects of Influenza

Many people use the terms "flu" or "stomach flu" to describe other illnesses that may actually be a common cold or a mild case of food poisoning. There is no such thing as "stomach flu." A true case of influenza typically starts with a headache, chills and cough, which are followed rapidly by fever, loss of appetite, muscle aches and fatigue, runny nose, sneezing, watery eyes and throat irritation. Children may have nausea, vomiting and diarrhea, but these symptoms are uncommon in adults.

Most people recover within a week or ten days. However, some are at greater risk for more severe and longer-lasting complications, such as pneumonia. The groups at greater risk include very young children, people over 65, and people who already have medical conditions, such as chronic respiratory disease, heart or kidney disease, diabetes or a depressed immune system because of cancer, HIV infection, or some other cause.

Another possible health effect related to the flu is Reye's syndrome, which can develop in children and teenagers who are given salicylates (aspirin) when they have the flu or chickenpox. Reye's syndrome affects the central nervous system and the liver, and can be fatal. Do not give aspirin to children or teenagers with the flu, unless it is specifically directed by a doctor.

Minimizing Your Risk

The most effective way to protect yourself from flu is to be vaccinated each year in the fall. Flu shots are especially important for:

• children ages 6 to 23 months;
• adults and children with chronic heart and lung disease;
• anyone living in a nursing home or chronic care facility;
• people 65 years of age and older;
• people with chronic conditions such as diabetes, anemia, cancer, immune suppression, HIV or kidney disease;
• children and adolescents on long term acetylsalicylic acid (ASA) therapy;
• health care workers, other caregivers and household contacts capable of transmitting influenza to the above at-risk groups;
• people at high risk of influenza complications who are traveling to areas where the flu virus is likely to be circulating.

Certain groups should not be vaccinated. These include children under six months of age and people who have had a severe allergic reaction to eggs or a previous dose of the vaccine.

Regular hand washing is another way to help minimize your risk. By washing your hands often, you will reduce your chance of becoming infected after touching contaminated surfaces.

If you get the flu, you should increase the amount of fluids you drink (water, juice, soups) and get plenty of rest for seven to ten days. There are also new medications to treat influenza. If you take them within 48 hours of the start of your symptoms, they may reduce the length of your illness by an average of one or two days.

About the Author

www.hc-sc.gc.ca
Health Canada is the Federal department responsible for helping Canadians maintain and improve their health, while respecting individual choices and circumstances.