Has pandemic confusion struck harder than swine flu? Here's a brief primer of what a pandemic is - and isn't:
What is it?
A flu pandemic occurs when an influenza virus that hasn't circulated before in humans emerges from nature - from birds or pigs, for instance. Since people have little or no immunity, literally billions of people could get sick over time.
How does it happen?
A pandemic flu strain can be created two ways. An existing strain in an animal - say a bird - can mutate and acquire the ability to infect people. Or an animal flu virus can reassort or swap genes with another animal virus or a human virus, in the process acquiring the ability to spread to and among people.
How often does it happen?
If there is a pattern, nature isn't telling. The intervals between past pandemics range from as few as three years to as many as 56. In the 20th century, there were three pandemics: the 1918-19 Spanish flu, the Asian flu of 1957-58 and the Hong Kong flu of 1968-69.
Who gets sick?
In regular years, the very young and very old are hardest hit. But that's not necessarily the case during pandemics. The death toll for the Spanish flu was highest among people aged 25 to 34. With swine flu, teenagers and young adults seem most susceptible so far.
How many lives could it claim?
That is pretty much impossible to say. The WHO estimates between 250,000-500,000 people a year die of seasonal flu. As a greater percentage of the world's population would be expected to fall ill from a new virus, even if the death rate is the same as that of seasonal flu, more people overall would die. The WHO has long predicted two to seven million, but that's an estimate.
If it's not more severe than seasonal flu, is it a pandemic?
Yes. The term pandemic in the context of flu means a new virus that spreads widely. That virus does not have to cause severe disease to qualify.
Will there be a vaccine?
Yes, but not for awhile. Vaccine manufacturers are already at work growing the viruses needed to make the vaccine, but they'll have to test it first for safety and to determine how much people need to be protected. Canada has a contract with GlaxoSmithKline, which will make the vaccine at a plant in Ste-Foy, Que. The government hopes vaccine will start to be ready by the end of October.