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Pandemic Influenza (Flu)

What is a pandemic?

Merriam-Webster's on-line dictionary defines a pandemic as "occurring over a wide geographic area and affecting an exceptionally high proportion of the population". In terms of illness, it is an outbreak of any disease such as typhoid or influenza (the "flu"). In comparison, an epidemic is similar but the disease affects a large number of people within a population, community, or region at the same time where as a pandemic is the same disease on a much larger more global scale.

Why is there so much talk about a pandemic flu?

Pandemic influenzas are caused by a new strain of the influenza virus. Because the virus is new, humans do not have an immunity to it and the illness is usually more severe. There is also no vaccine available. Historically a new strain appears 3 or 4 times a century or about every 30 or 40 years. The last outbreaks were:

  • "Spanish Flu" in 1918-1919
  • "Asian Flu" in 1957-1958
  • "Hong Kong Flu" in 1968-1969

A pandemic flu was declared by the World Health Organization (WHO) in June 2009 due to the emergence and quick spread of the H1N1 (Swine) flu virus. This pandemic was declared as being in the post-pandemic phase by August 2010. In this period, the major spread is considered over, but localized outbreaks may still occur for many years. These outbreaks are difficult to predict and will vary in severity.

How does a flu become a pandemic flu?

Influenza is caused by three types of viruses called influenza A, B, and C. Influenza types A and B are responsible for the respiratory disease that occurs almost every winter. Influenza type C usually causes a very mild disease, often without symptoms. Only type A influenza causes pandemics in humans.

Certain conditions have to be met for a pandemic to occur:

  • A new influenza A virus (that is the result of a major change to the virus) is present. With a new virus, people will have little or no immunity.
  • A virus that is easily passed from human to human.
  • The virus is able to cause serious illness or death.

What will be the impact of a pandemic?

It is impossible to predict the impact or death rate of a new influenza virus. WHO has estimated that 2 to 7.4 million deaths may occur as based on the 1957 influenza characteristics. Both the Asian (2 million deaths) and Hong Kong (1 million deaths) flus were milder and caused by a combination of human and avian viruses. In comparison, the Spanish flu is considered "exceptional" and caused the highest number of known deaths (40 to 50 million) worldwide and was likely to have been only avian virus in origin.

In addition, pervious influenzas were able to spread around the world in 6 to 9 months but these events occurred when most travel was by boat. With international air flights, a "modern" pandemic is expected to spread to all parts of the world in less than 3 months.

A pandemic will not be a "one time" event and periods of illnesses may come in 2 or 3 "waves" anywhere from 3 to 12 months apart.

What steps can I take to avoid getting the flu?

The most important step you can take to reduce the chance of infection is to wash your hands regularly - always wash regularly with soap and warm water.

See the OSH Answers Hand Washing - Reducing the Risk of Common Infections for more details.

Other steps you can take for personal hygiene are listed in Good Hygiene Practices - Reducing the Spread of Infections and Viruses.

The Public Health Agency of Canada (PHAC) also recommends that all Canadians over the age of 6 months get the seasonal flu shot every year.

Individuals can also help reduce the spread of the virus by:

  • Keeping your hands away from your face.
  • Coughing and sneezing into your arm, not your hand.
  • Keeping common surface areas clean and disinfected.
  • If you get sick, stay home.

Should a business plan for a pandemic flu?

Yes. Workplaces should prepare a plan that allows for normal business operations to continue when many people will be sick or absent. Estimates of how many people may be sick or absent range from 15-35% (Public Health Agency of Canada) to a high of 50% during the peak of a significant pandemic (New Zealand Ministry of Health).

When planning for a pandemic flu, remember a pandemic is not like the regular flu season, nor is it like a natural disaster (such as a hurricane or serious ice or snow storm). Remember, a pandemic will last much longer than a "one time" event and periods of illnesses may come in 2 or 3 "waves" anywhere from 3 to 12 months apart.

What should the business plan include?

A business should plan for approximately one quarter to one third of employees being absent during a pandemic. While rare, some workplaces may need to close or be forced to close by order of a Medical or Public Health Office depending on the seriousness of the pandemic.

When creating a business plan, remember that:

  • Health care resources will be less available as there will be more patients to care for and many health care employees may be sick themselves or have to care for family members.
  • Other business will be similarly affected (less resources, sick employees, etc.). Supplies/ resources, and customers may not be available.
  • Employees who are not sick themselves may have to stay home and care for family members. Alternatively, schools may be closed forcing parents to stay home.

Please see the booklet Business Continuity Plan: Infectious Diseases for more information.

Where can I get more information?

As a pandemic "evolves", information may change quickly. The following web sites and telephone services are good sources for the most current information:

For public information about avian influenza or pandemic influenza,

  • In Canada, call the Public Health Agency of Canada at 1-800-454-8302.
  • In the USA, call the Center for Disease Control and Prevention (CDC) at 1-800-CDC-INFO (1-800-232-4636).

You can also contact your local Ministry of Health or Public Health department for addition and local information. Check the blue pages of your telephone directory for these numbers.

Web Sites


Flu (influenza) - Government of Canada

Pandemic Preparedness - Public Health Agency of Canada

United States of America

Seasonal Influenza (Flu) - Center for Disease Control and Prevention (CDC), USA

Flu.gov - U.S. Department of Health & Human Services


Disease Outbreak News - World Health Organization

Document last updated on January 21, 2014

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Although every effort is made to ensure the accuracy, currency and completeness of the information, CCOHS does not guarantee, warrant, represent or undertake that the information provided is correct, accurate or current. CCOHS is not liable for any loss, claim, or demand arising directly or indirectly from any use or reliance upon the information.