Its Flu Season
November 2001

Tips at-a-glance:

• The flu is caused by influenza viruses and is infectious 3 to 7 days from onset
  
• Transmitted through air (coughing, sneezing) and surface contact (doorknob or telephone)
  
• Sudden onset with headache, chills, cough, fever, runny nose, sneezing, throat irritation
  
• Flu season is commonly November through to May
  
• Frequent hand-washing helps prevent its spread
  
• Vaccination is only proven effective method of prevention
  
• Treat symptoms with fluids and rest
  

Part One: General Information

What are the symptoms typical of the "flu"?
The term "flu" is often applied to almost anything that makes us feel unwell. However, the "flu" is a specific infection caused by influenza viruses and is usually a more severe illness than the common cold, which is caused by other respiratory viruses. Influenza typically has a sudden onset with headache, chills and cough followed rapidly by a fever, appetite loss, muscle aches, and tiredness. On the other hand, cold symptoms are limited to the upper respiratory tract with runny nose, sneezing, watery eyes, and throat irritation. Gastrointestinal symptoms, such as nausea, vomiting or diarrhea, can sometimes accompany influenza, especially in children, but are rarely prominent. The term "stomach flu" is often incorrectly used to describe gastrointestinal illness that is due to other causes.

How long is a person infectious once he/she gets influenza?
The period of communicability or infectiousness is usually 3 to 5 days from the onset of symptoms in adults and up to 7 days in young children.

When does the influenza season begin in Canada?
There may be local outbreaks of influenza anytime during the fall with definite outbreaks being common from November or December through April and May.

Why is influenza a winter disease?
Technically, influenza is not bound by seasons, and can occur all year round in tropical climates. But in temperate climates, like those found in Canada, influenza is predominantly a winter disease. The reasons for winter predominance of influenza occurrence have not been positively identified; however, it is possible that the transmission of the viruses are facilitated by people congregating indoors more during the winter or drier indoor air which may help the viruses to survive longer. It is recognized that, in instances where many people from different parts of the world are confined together, like on a cruise ship or an airplane, the chances of being infected increase. An example of this was the out-of-season outbreak on Alaskan cruise ships last summer.

Are there any means of preventing infection?
Hygienic practices such as hand washing, especially after contact with persons who may have the flu and after handling soiled tissues may, to some degree, reduce the risk of being infected. However, the only proven effective method of prevention is vaccination, preferably 2 weeks before the beginning of the active "flu" season.

Are there other viruses that can cause similar illnesses?
Yes. Respiratory infections other than common cold viruses may occur. Viruses such as respiratory syncytial virus (RSV) and parainfluenza viruses can cause infections which may be mistaken for the "flu" with similar symptoms including fever, cough, and sore throat. These viruses primarily affect young children but can re-infect adults. They tend to be present in varying degrees every winter.

Is there anything you can do once you have the "flu"?
For most individuals, treating the symptoms is the only recourse, that is, fluids and rest for the 5 to 7 days that symptoms might last. Recently, new medications have become available in Canada, specifically designed to treat the "flu". These drugs may decrease the length of time that symptoms persist by an average of 1 to 1.5 days if started within 48 hours of illness onset.

How many types of influenza virus are there?
There are two main types: influenza A and influenza B. Influenza A usually causes more severe illness than influenza B and can result in pneumonia, hospitalization or even death, especially in the elderly and those with chronic illnesses.

How does influenza travel the world so quickly?
The "flu" virus is transmitted from person to person very efficiently through droplets of saliva or phlegm that travel through the air, usually propelled by the action of coughing or sneezing. This mode of transportation is especially effective in confined or enclosed environments, typically experienced by Canadians in the winter months. It can also be passed through surface contact, for example touching an object like a doorknob or telephone receiver that has been recently handled by an infectious person. Air travel can help the virus move quickly from country to country, and subsequently, around the world in a very efficient manner.

How do you know what will be the predominant strain?
The Laboratory Center for Disease Control (LCDC) Health Canada collaborates with a network of laboratories across the country to identify and characterize strains of influenza. This network can determine what are the prominent strains and use this information to predict future "up and coming" strains for inclusion into future vaccines.

How many deaths due to influenza occur in Canada each year?
The number of deaths due to influenza or its complications during the "flu" season will vary each year, but is estimated to be approximately 500 to 1,500 per season.

How many influenza infections might we have in Canada in one season?
In 1991-1992 it was estimated that half of those Canadians under age 15 years had been infected with influenza A virus during that season and that about 26% of Canadians of all ages (or about 7 million) had influenza A virus infections.

What was the most common influenza strain in the 1998-1999 season?
Of the 184 viruses isolated and submitted for strain characterization to the LCDC during the 1998-1999 influenza season, 85% were influenza type A. The predominant strain was A/Sydney/5/97-like (H3N2).

Is the influenza A strain expected in the winter of 1999-2000 likely to cause a severe epidemic and is this strain more potent than other influenza strains?
The influenza A virus expected to be active in the 1999-2000 influenza season is similar to the influenza A/Sydney/5/97-like strain that was active last winter. This strain is included in the vaccine for the 1999-2000 influenza season. The influenza A/Sydney/5/97-like strain is not expected to be any more potent than previous strains, and the usual amount of infection is expected to occur this winter in those not protected by vaccine.

What is Reye's syndrome?
Reye's syndrome is a rare complication in children who have taken salicylates (aspirin) and are infected with influenza virus, or the virus that causes chickenpox. It specifically affects the central nervous system and the liver and can result in death. Children and teenagers with the "flu" should avoid aspirin unless specifically directed by a physician.

Are all new influenza strains isolated in China?
Some new strains come from China, however, they may also arise in different countries. For example, the predominant strain during the 1997-1998 and 1998-1999 seasons was influenza A/Sydney/5/97 (H3N2)-like, which means that it was first isolated in Sydney (Australia) in 1997.

Part Two: Influenza Vaccination

How do they decide what "flu" strains to put into a vaccine?
A global network of laboratories isolates and identifies specific influenza viruses as they appear. In Canada, this network involves regional, provincial/territorial and federal laboratories. The viruses identified are reported to the three World Health Organization (WHO) Collaborating Centers on Influenza. The vaccines are then updated to include the most current influenza virus strains that have the greatest likelihood of causing widespread and severe illness.

What are influenza vaccines made of?
Current influenza vaccines are made of dead influenza virus, which has been further treated to break up the virus into purified components.

How is it made?
Every year, the WHO makes a recommendation regarding which strains should be included in the influenza vaccination. Based on that recommendation, the global network of laboratories provide vaccine manufacturers with the seed strains they need to produce the vaccine. Influenza vaccine viruses are initially grown in fertilized hens eggs. The virus is then extracted from the egg, inactivated and "split" into parts, that are then used to make the vaccine.

What are the components of the influenza vaccine for 1999-2000?
The National Advisory Committee on Immunization (NACI) has recommended that the vaccine contain the following three components: A/Sydney/5/97 (H3N2)-like strain, an A/Beijing/262/95 (H1N1)-like strain, and a B/Yamanashi/166/98-like strain.

How does vaccination protect you?
After vaccination, the body's immune system produces antibodies against the inactivated virus in the vaccine. If you are exposed to the real virus, the antibodies prevent the infection or reduce the likelihood of severe illness should infection occur.

Who should receive the influenza vaccine?
Influenza vaccine is recommended for people who are at high risk for developing serious complications as a result of influenza, including:

• adults and children with chronic heart and lung disease,
  
• persons of any age resident in nursing homes or chronic care facilities,
  
• persons over the age of 65 years,
  
• persons with chronic conditions such as diabetes, cancer, immun suppression, kidney disease,
  
• children and adolescents on long term acetylsalicylic acid (ASA) therapy, and
  
• persons with HIV.

The vaccine is also recommended for people who are capable of transmitting influenza to those at high risk (health care workers and household contacts) and those providing essential community services. Anyone older than 6 months who wish to protect themselves against influenza should also consider vaccination even if they are not in a high risk group.

Why is it recommended that influenza vaccine be taken every year?
The antibodies produced in response to an influenza vaccine decline over time and may be too low to offer adequate protection for the following year. In general, influenza antibodies from vaccination only lasts 4-6 months. As well, influenza viruses continually undergo changes, as a result of a mutation in their genes and immunity acquired as a result of previous influenza infections or the previous year's vaccination would not necessarily protect against subsequent infections. As the influenza viruses change, the vaccine has to be updated on a yearly basis to include the most current strains.

Is it too late to get an influenza vaccination in January?
No. Active "flu" season begins in November and ends in May. Getting vaccinated at anytime between these months would still be useful to protect against infection; however, you should consult with your physician or local public health authority.

Is it useful to get a vaccination if you are already coming down with the "flu"?
Yes. The vaccine will not help with the current infection but could help protect against other influenza strains which may also be present in a given year.

Is it possible to become infected even if you have been vaccinated?
Yes. It is possible to become infected after vaccination, particularly in older adults whose immune systems may be less effective in responding to the vaccine. However, for those who still get infected after vaccination, the disease is likely to be less severe and less likely to result in hospitalization or death.

What factors affect the success of influenza vaccine?

• Whether an individual has experienced the types of influenza in the vaccine.
  
• The age of the person being vaccinated.
  
• The health of the person's immune system.
  
• The length of time from vaccination to exposure to a "flu" virus.
  
• The similarity between the virus they are exposed to and the vaccine they received.

How many vaccine doses have been distributed in Canada in recent years?
The number of vaccine doses distributed in Canada by manufacturers is estimated to be:

1998 - 5.1 million
1997 - 5.3 million
1996 - 4.3 million
1995 - 4.2 million
1994 - 4.0 million

Is there anything other than vaccine that can be used to control influenza?
Amantadine, an antiviral medication, can be used to protect people who have been in contact with an infected person or for individuals who may respond poorly to influenza vaccination (for example, the elderly). Amantadine is most useful in certain situations, such as outbreaks of influenza in nursing homes. It is not effective against influenza B virus. A new class of antiviral medications, the neuraminidase inhibitors, is able to inhibit both influenza A and B. One neuraminidase inhibitor, zanamivir (Relenza), has recently been given a Notice of Compliance with Conditions, allowing it to be sold in Canada for the treatment of influenza. Zanamivir, an inhaled medication, has been shown to reduce the duration (by an average of 1 to 1.5 days) and severity of "flu" symptoms when taken within 48 hours of the onset of symptoms. Zanamivir is not currently licensed in Canada, for the prevention of influenza. Antiviral medications should not replace influenza vaccine for the prevention of influenza.

Need help in balancing your work and family demands? WS Family Matters™ can help. Call your EAP at 1-800-387-4765 for service in English or 1-800-361-5676 for service in French.