Frequently Asked Questions – Influenza

• What is influenza ("the flu")?
• How is it spread?
• What are the symptoms of flu?
• What is the difference between a cold and influenza?
• How serious is the flu?
• What is the best way to avoid getting the flu?
• What ways to reduce the risk of catching or spreading the flu?
• Who should receive the seasonal flu shot?
• What is the difference between influenza A, B and C?
• What is H1N1 Flu Virus?
• Does the seasonal flu shot protect against the H1N1 Flu Virus?
• What is avian influenza ("bird flu")?
• What is the bird flu virus that has made some domestic birds and humans sick?
• What causes an influenza A virus to change?
• What is the difference between a vaccine and an antiviral?

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What is influenza ("the flu")?
Seasonal influenza, or "the flu," is a common infection of the airways and lungs that can spread easily among humans. There are two types of influenza viruses that cause outbreaks each year: Influenza A and B. Animals can also be infected with influenza A.

How is it spread?
The influenza virus spreads through droplets that have been coughed or sneezed by someone who has the flu. You can get the flu if droplets land on the surface of your eye. You can also get the flu by shaking hands with an infected person or by touching contaminated surfaces, and then touching your own eyes, nose or mouth.

What are the symptoms of flu?
Influenza usually starts with the sudden onset of a headache, sore throat and muscle aches. The onset is often abrupt enough that people can remember precisely when it started. Most people recover from the flu in about a week.

What is the difference between a cold and influenza?
A cold is a mild infection of the upper respiratory passages caused by a variety of viruses. A cold may last for a week and symptoms include a runny nose, stuffy nose, cough and sore throat. A cold is caused by a rhinovirus, which is much different than an influenza virus. A person with a cold will not usually have a headache, fever or muscle aches. Symptoms such as nausea, vomiting and diarrhea do not usually accompany a cold.

How serious is the flu?
Most people recover from the flu in about a week. However, influenza may be associated with serious complications such as pneumonia, especially in infants, the elderly and those with underlying medical conditions. On average, the flu and its complications send about 20,000 Canadians to hospital every year, and an average 2,000 to 4,000 Canadians die.

What is the best way to avoid getting the flu?
The best way protection against influenza is getting the flu shot every year and practising basic hygiene, especially frequent hand washing or hand hygiene with alcohol hand rubs. When you get the flu shot, your body's immune system develops protection (antibodies) against the strains of the virus in the vaccine. The antibodies help prevent infection or reduce the severity of the illness. Different flu viruses can affect people every year, so the vaccine needs to be updated annually. This is why it is important to be immunized each fall.

What are ways to reduce the risk of catching or spreading the flu?

• Wash hands often with soap and warm water for at least 20 seconds, or use hand sanitizer.
• Keep your hands away from your face.
• Cough and sneeze into your arm, not your hand. If you use a tissue, dispose of it as soon as possible and wash your hands.
• Get immunized.
• Keep common surface areas—for example, doorknobs, light switches, telephones and keyboards—clean and disinfected.
• Eat healthy foods and stay physically active to keep your immune system strong.
• Keep doing what you normally do, but if you get sick, stay home.

Encourage all members of your household, especially children, to follow these practices. And, if you do get the flu, stay at home and rest until you are feeling better.

Who should receive the seasonal flu shot?

The National Advisory Committee on Immunization recommends the seasonal flu shot for:

• Those at high risk of complications or hospitalization from the flu, including:
  • Children and adults with chronic medical conditions, such as cancer, cardiovascular disease and asthma
  • Residents of nursing homes or long-term care facilities
  • The elderly
  • Healthy children 6-23 months of age
  • Healthy pregnant women

• Those in close contact with individuals at high-risk for complications (e.g. health care workers and household contacts)
• People who provide essential community services
• People in direct contact with the avian influenza-infected poultry during culling operation
• Persons who are morbidly obese (BMI ≥ 40).
• Aboriginal peoples.
• Healthy children 2 to 4 years of age.

Healthy children and adults from ages 5-64 years are also encouraged to get the flu shot each year to protect themselves and others.

What is the difference between influenza A, B and C?

There are three main influenza viruses; influenza A, influenza B and influenza C.
Seasonal influenza is usually caused by influenza A and B viruses.  Seasonal influenza occurs in Canada every year, generally during late fall and throughout the winter months. 

Influenza A
In most years, influenza A viruses are the most common cause of annual influenza outbreaks. Influenza A may cause large pandemics with significant mortality in young persons.

Influenza B
Although less common, outbreaks of influenza B occasionally occur. Outbreaks of Influenza B are generally more localized and in any one year may be restricted to one region of the country. Influenza B typically produces milder symptoms than influenza A when it infects humans. Influenza B also mutates much more slowly than influenza A; however, it still mutates too quickly for a person to build a lasting immunity to it.

Influenza C
Influenza C causes mild disease in humans, and does not occur seasonally.

What is H1N1 Flu Virus?

In Spring 2009, a new strain of the influenza virus, the H1N1 virus, was identified as causing influenza infections in people in North America. As the H1N1 Flu Virus spread around the world, the World Health Organization (WHO) (External link) declared it a pandemic influenza virus. As it was a new strain of influenza and because humans had little to no natural immunity to this virus, it caused serious and widespread illness.

On August 10, the World Health Organization declared that the H1N1 pandemic had entered the post-pandemic period (External link) . This decision was informed by epidemiological evidence from around the world showing the H1N1 influenza virus was circulating at lower levels and behaving like a seasonal influenza virus.

Canada’s influenza monitoring system confirms that since the spring, the H1N1 influenza virus has been circulating in Canada in low to undetectable levels.

The Agency will continue to work with provinces, territories and international partners to monitor for the H1N1 influenza virus and will remain vigilant in preparing Canada for any future influenza outbreak.

Does the seasonal flu shot protect against the H1N1 Flu Virus?

This year’s flu shot protects against the H1N1 flu virus, as well as two other strains of flu that are expected to make people sick this winter.

Even if you got the H1N1 flu shot last year, you should still get this year’s flu shot for two reasons:

• We don’t know how long the immunity in last year’s shot will last, and
• This year’s shot will protect you from two other strains of the flu.

Almost 50 per cent of Canadians do not have any immunity to the H1N1 influenza virus. It is important for all Canadians, particularly those in high risk groups, to get immunized so they can protect themselves and their families.

What is avian influenza ("bird flu")?
Wild birds are natural carriers of influenza A viruses. Usually these "bird flu" viruses cause the wild birds little or no harm. Domestic poultry (like chickens and turkeys) and animals, including pigs, can also get these viruses from wild birds and pass them on to other poultry and animals.

What is the bird flu virus that has made some domestic birds and humans sick?
In recent years, there has been growing concern about a particular strain of avian influenza virus – an H5N1 virus – that has spread through birds from Southeast Asia through Asia to parts of Europe and Africa. This strain has caused illness in some wild birds, but it has resulted in a high rate of death in domestic poultry. Millions of birds have been killed in an effort to prevent the spread of the virus.

Like other bird flu viruses, the H5N1 virus is not easily transmitted to humans. A limited number of people have contracted the virus through close contact with sick or dead birds. The death rate in these human cases has been high. But there is still no evidence that it can spread easily from person to person.

What causes an influenza A virus to change?
One way a new strain can emerge is if a person is sick with a human flu virus and then also becomes infected with a bird flu virus. The two different viruses could then mix together, creating a new subtype of influenza A virus. Because it's a new virus, people would have little to no immunity to it. Another way a bird flu virus can change is if it undergoes a number of mutations which could result in a new virus that can infect people and be transmitted among humans.

What is the difference between a vaccine and an antiviral?
When you get a vaccine against an influenza virus (usually in the form of an injection or "shot"), it introduces a virus to your body that is either dead or in a weakened state and is harmless. Your body quickly produces antibodies against the vaccine virus. These antibodies provide you with immunity against the virus for about four to six months. If you are exposed to the influenza virus during that time, the antibodies you have created will either prevent you from getting sick or will help reduce the severity of your illness. Unlike vaccines, antivirals do not stop you from getting sick by providing immunity. An antiviral is a medicine that you take by swallowing a pill or liquid, or by breathing it in. The medicine works by either destroying the virus or interfering with its ability to grow and reproduce. It can be given to patients when they are sick to reduce symptoms, to shorten the length of illness and to minimize serious complications.