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Flu season is just around the corner, and that means it's time for the tiresome ritual of bickering about whether the flu shot is effective or not.

So let's be clear from the outset: The flu shot is far from perfect. You need to vaccinate somewhere between 33 and 100 people to prevent one case of influenza. But effectiveness is, in large part, an academic debate. The real issue for the public is whether the benefits of vaccination outweigh the risks – and clearly they do.

However flawed the flu shot is, it's still the best weapon we have against the flu – in addition to basic stuff such as washing our hands and covering our mouths when we cough.

That's why public-health officials recommend that everyone over the age of six months should get a flu shot, with few exceptions.(And, for children, a needle is not even necessary; they can get a nasal-spray vaccine.) Influenza is an infectious respiratory disease that is highly contagious. In any given year, 5 per cent to 20 per cent of the population will contract the flu. It can be nasty, even deadly.

On average, about 3,500 Canadians die and another 12,200 are hospitalized annually due to the flu. 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 such as asthma, heart disease and chronic obstructive pulmonary disease.

The principal reason to get a flu vaccination is to protect the vulnerable. It's an act of altruism. Or, in the case of health workers, it's an ethical issue, a way of reducing harm to those to whom you minister.

That being said, it's worth understanding why the flu shot does not work as well as we would like.

The influenza virus – or viruses, to be more precise – travel around the world, and across the country, in a fairly predictable fashion. In the case of Canada, flu bugs move from west to east, roughly between November and March.

As they circle the globe, influenza viruses mutate regularly – which is why you need to get a new flu shot each year. The biggest technical challenge for scientists is predicting ahead of time which strains will be circulating in winter, because manufacturing of the vaccine needs to begin six to nine months before vaccines are administered.

Sometimes the match isn't perfect, as happened last year, when the vaccine protected poorly against the principal circulating strain, known as H3N2, and a lot of people got sick and died. (This year, the vaccine protects against H3N2, H1N1 and B/Phuket, and the spray also protects against B/Brisbane.)

A common lament is that you can still get "the flu" even if you get a flu shot. But it's worth noting that there are about 200 respiratory infections that circulate in winter; most are not influenza. In addition, paradoxically, the influenza vaccine works the least well in people who most need it, precisely because they have weak immune systems.

This is not a reason to eschew vaccination. It is unreasonable to expect the flu vaccine to be 100-per-cent effective; very few drugs are.

In fact, one of the most compelling reasons to get a flu shot is – stating the case colloquially – to protect your granny, if not yourself. Studies show one of the most effective ways of reducing the harm of influenza in the elderly is to vaccinate children.

There are two other common complaints about the promotion of widespread flu vaccination: that it's a bonanza for Big Pharma and that vaccines are harmful.

Yes, pharmaceutical companies make money from vaccines. But the flu shot (and spray) is relatively cheap and the programs likely pay for themselves by attenuating symptoms and reducing hospitalizations.

The fear-mongering about the harm of vaccines is largely unscientific bunk. The flu shot is quite safe (the biggest danger is triggering Guillain-Barré syndrome, but that is rare).

Do we need better, more effective, flu vaccines? Absolutely. But until they come along, the answer is not to do nothing. As former U.S. secretary of defence Donald Rumsfeld once said, "You go to war with the army you have."