Cold and flu

Influenza (flu)

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 to 25 percent of Canadians may get the flu each year. Although most of these people recover completely, an estimated 500–1500 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. Nearly ten million doses of flu vaccine were distributed in Canada during the 2002–2003 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 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, 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 chicken pox. 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:

• 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
• healthcare 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.

The health effects of flu shots

The benefits of flu shots far outweigh the risks. The flu vaccine cannot cause influenza because it does not contain any live virus. The most common side effect is soreness at the site of injection, which may last a couple of days. You might also notice fever, fatigue and muscle aches within six to 12 hours after your shot, and these effects may last a day or two. Some people develop a condition called "oculo-respiratory syndrome" after a flu shot. The symptoms include red eyes and respiratory effects such as cough, wheezing, chest tightness, difficulty breathing, or sore throat. In most cases, the symptoms are mild and disappear within 48 hours.

Severe allergic reactions to flu shots are rare. A rare but possible side effect of influenza vaccination is Guillain-Barré syndrome (GBS). This is an autoimmune disease that attacks the nervous system and results in weakness and abnormal sensations. But, most patients recover fully. Your chance of developing GBS as a result of a flu shot is one in a million.

The primary reason to get a flu shot is to protect yourself from health effects related to flu. However, by getting a flu shot, you will also help protect other Canadians and reduce the burden on the health care system.

Concerns about SARS

There are concerns that Severe Acute Respiratory Syndrome (SARS) might re-emerge during the fall and winter flu season. SARS, influenza and flu-like illnesses caused by other respiratory viruses all have similar symptoms. When people first have these symptoms, it may be difficult for health care providers to distinguish one type of infection from another. There is no quick test for SARS. If you have symptoms that could be SARS, your doctor or health care professional will decide how to manage your case, including whether you should be isolated, based on your specific symptoms and risk factors for contracting SARS. If necessary, your doctor will perform specific tests for the SARS virus.

A flu shot does not offer any protection against SARS or other respiratory viruses. If you experience flu-like symptoms and have been vaccinated against the flu, you may still have the flu or another common respiratory virus. Flu shots will help to reduce the number of severe cases of flu coming to emergency departments and may help to reduce the number of false alarms about SARS. By reducing the number of suspicious illnesses that need extensive investigation, flu shots could also help ensure that a true outbreak of SARS would be detected more quickly.