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Today in Canada we are in the midst of a "normal" flu season. That is the recurring message from public health officials across the country.

Bear in mind, though, that normal is deadly: Millions of Canadians will be sickened and thousands will die, courtesy of the annual winter visitor.

This paradox helps underscore one of the most difficult challenges in public health: Communicating risk, particularly when it comes to the flu.

Influenza has been around for time immemorial but the virus is constantly mutating, making it a moving target.

Yet the flu chronicles, passed down through the generations and at lightning speed on social media, are also imbued with larger-than-life mythology and a great deal of misunderstanding.

So here's a plain-language version of what you need to know to deal with the outbreak of influenza that has come (or will soon come) to a community near you.

The flu is a infectious respiratory disease that is highly contagious. The virus jumps from pigs and birds to humans, as we are seeing with the current emergence of bird flus H5N1 and H7N9. But these strains only become a real worry when they start spreading among humans. Once a new strain is established in humans, it mutates to remain infectious, making the flu a wily opponent.

At greatest risk of harm from influenza are those with compromised immune systems: The very young, pregnant women, the frail elderly and people with chronic health conditions like asthma, heart disease and COPD.

The virus (or viruses, to be more precise) travels around the world, and across the country, in a fairly predictable fashion: In the case of Canada, the bug moves from west to east, roughly between November and March, with the number of cases rising and falling roughly along the shape of a bell curve.

We are now approaching the peak of flu season, which is why it may seem like everyone has the flu. In reality, between 5 and 20 per cent of the population will contract the flu in any given year.

There are also many other bugs kicking around, especially in winter. "The flu" has become a catch-all term, leaving us confused about the fact that influenza is a very specific respiratory disease.

This year's most common flu strain is H1N1. Many will recall that being a "pandemic" strain back in 2009 and that seems to have created extra worry. "Pandemic" is the term given to a completely new strain in humans, meaning a lot more people are susceptible to the virus.

H1N1 is now considered a seasonal strain. Lots of people have been exposed or vaccinated, so they have full or partial immunity. But lots of people will still get sick and some will die. That is "normal."

Somewhere between 4,000 and 8,000 Canadians a year die of influenza and its related complications, according to the Public Health Agency of Canada. Those numbers are controversial because they are estimates.

In fact, influenza, by its very nature, requires a lot of guesswork.

Take the flu vaccine. Public health officials have to guess, about six months in advance, what strains will be circulating to create vaccines to protect against them. This year they did well. The flu shot protects against A/H1N1 A/H3N2 and B/Massachusetts, and those are the circulating strains. In fact, 90 per cent of cases seen so far this year in Canada have been H1N1.

The distinguishing feature of H1N1 is that it hits young adults hard. It is not more deadly than H3N2, which ruled the roost last year, but does not affect the usual demographic – the elderly. The inordinate amount of attention being paid to H1N1 by the media reflects the sad reality that we take deaths of seniors for granted.

There is also a fair bit of controversy over how well the vaccine works. The honest answer is: It depends. It depends on the characteristics of the individual, and the match between the circulating strain and the vaccine. But the bottom line is that getting a flu shot offers more protection than not getting one. And don't buy into all the scare-mongering: The flu vaccine is relatively safe, and certainly a lot less harmful than the flu.

We can't prevent the annual appearance, nor predict how deadly it will be, but we can lessen its impact with simple measures like hand-washing and vaccination.

We can also arm ourselves with knowledge, which is the best tool we have to assuage fears and keep risks in perspective.