Influenza A is the type of influenza virus involved in all known influenza pandemics. This is because Influenza A viruses can undergo major changes, producing a completely new strain. As most people have not built up any immunity to new strains of influenza, large numbers of people will become infected as the new virus spreads. For a new influenza to be capable of causing a pandemic, it must be able to:
While the characteristics of the virus that will cause the next flu pandemic are unknown, some general assumptions can be made based on past pandemics. The virus will be highly contagious and will spread very quickly among people, particularly in crowded situations.
The influenza virus enters the body through the nose or throat when someone:
Once someone is infected with the influenza virus, it usually takes from one to three days to develop symptoms.
People with influenza can be contagious from the day before they develop symptoms to up to seven days afterwards (typically three to five days in healthy adults and up to seven days in children). This time frame may be longer in children and people with decreased immune systems.
Not everyone who comes in contact with the influenza virus will get sick, but they may still spread it to others.
Some people who get influenza also develop secondary bacterial infections, including pneumonia, which can result in prolonged illness or death.
During an influenza pandemic, much of the population will become infected, many will get sick and some will die. It is expected that there will be greater amounts of illness and death during a pandemic than during a regular flu season.
The Public Health Agency of Canada (PHAC) is predicting the arrival of the pandemic virus in Canada within three months of its appearance elsewhere, but it could be more rapid. Outbreaks will likely occur simultaneously in multiple locations, although different areas of the country may experience peak activity at different times. The first peak in illness is expected to happen two to four months after the arrival of the virus in Canada.
In a local community, a pandemic wave will generally last six to eight weeks, but this can vary. A pandemic may last 12 to 18 months and more than one wave may occur within a 12-month period.