TORONTO - Canadians who got a flu shot this year may have cut in half their risk of getting sick enough from flu to require medical care, new data suggests.

"It seems that this vaccine is cutting your risk of influenza in half, which ... is still important protection, especially if you're a high-risk person," said Dr. Danuta Skowronski, a flu expert with the British Columbia Centre for Disease Control who oversees the surveillance network from which the data was drawn.

Skowronski said an important message from the data relates to the care of people who are at high risk of the complications of influenza if they become infected.

Doctors caring for such patients shouldn't assume that because they got vaccinated they won't contract influenza this winter, she said. For these people, use of antiviral drugs may be warranted if they become ill.

The mid-season flu vaccine effectiveness estimate is drawn from a surveillance network of a couple of hundred family doctors and community physicians in the country's five most populous provinces: Alberta, British Columbia, Manitoba, Ontario and Quebec.

The network is funded by the Canadian Institutes of Health Research, with support from the involved provinces.

Skowronski and colleagues crunched data submitted by physicians in the network over the weekend.

This type of work studies people who seek care for influenza-like illness, looking to see if they are actually infected with flu and whether they had received a flu shot.

It is similar to a U.S. effort to measure the effectiveness of flu vaccine there which is funded by the U.S. Centers for Disease Control.

The U.S. CDC released interim vaccine effectiveness estimates late last week. In their analysis, this year's vaccine reduces the risk of requiring medical help for flu by 62 per cent overall, and by 55 per cent for influenza A viruses.

Flu vaccine offers protection against two subtypes of influenza A, H3N2 and H1N1, as well as one type of influenza B virus.

The U.S. figures were based on a sample of patients in which the breakdown of flu infections was 57 per cent for influenza A and 43 per cent for influenza B.

The B component of the vaccine appears to be offering better protection this year than the A, about 70 per cent. And because the U.S. sample had such a large proportion of B cases, that had the effect of raising the overall estimate, Skowronski said.

But the Canadian figures are a closer representation of the proportion of A versus B viruses that are causing illness this winter in this country, she said. So far this flu season H3N2 has been responsible for the lion's share of Canada's cases.

In the interim analysis, 90 per cent of the positive cases were infected with influenza A and 10 per cent were infected with influenza B.

The A component of the vaccine appears to reduce one's risk by between 45 and 50 per cent, Skowronski said. There were too few B cases to calculate a reliable estimate, and the overall estimate for the flu shot was 47 per cent.

Skowronski said an additional analysis will be generated at the end of the flu season.

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  • Myth: The Flu Shot Can Give You The Flu

    <strong>Fact:</strong> This myth just will not die. So let's clear this up: You <em>cannot</em> get the flu from your flu shot. Why? That vaccine is made from a dead or inactive virus that can no longer spread its fever-spiking properties. <a href="http://www.everydayhealth.com/cs-cold-flu-pictures-myths/colds-and-flu-whats-true.aspx#/slide-4">In rare cases, a person may experience a reaction to the shot</a> that includes a low-grade fever, but these reactions are not <em>The Flu</em>, Everyday Health reported. Note: Even though the flu shot cannot cause the flu, there are a number of other <a href="http://www.everydayhealth.com/cold-and-flu/flu-vaccines.aspx">reasons not to get the vaccine</a>, including for some people with an allergy to eggs or a history of Guillain-Barre Syndrome.

  • Myth: If You've Already Had Your Shot, You Are Guaranteed To Be Flu-Free

    <strong>Fact:</strong> Unfortunately, even after slapping a bandage on that injection site, you <a href="http://www.cdc.gov/flu/about/qa/vaccineeffect.htm">may only be about 60 percent protected</a>, according to the CDC. That means, yes, you <a href="http://www.npr.org/blogs/health/2013/01/08/168814935/can-you-get-a-flu-shot-and-still-get-the-flu">can still get the flu after your shot</a>. Some people may be exposed to the flu in the two weeks it takes for the vaccine to take effect, reports NPR. Others might be exposed to a strain not covered in the vaccine, which is made each year <a href="http://www.flu.gov/prevention-vaccination/vaccination/index.html">based on the viruses experts predict will be the most common</a>, according to Flu.gov. (This year's batch seems to have been matched well to what is actually going around, NPR reports.)

  • Myth: Antibiotics Can Fight The Flu

    <strong>Fact:</strong> Plain and simply, antibiotics fight <em>bacteria</em>, not viruses. The flu -- and colds, for that matter -- are caused by viruses. In fact, <a href="http://www.fda.gov/Drugs/ResourcesForYou/ucm078494.htm">antibiotics kill off the "good" bacteria</a> that help to fight off infections, so that viral flu may only get <em>worse</em>.

  • Myth: The Stomach Flu Is A Type Of Influenza

    <strong>Fact:</strong> Nausea, vomiting or diarrhea, while often dubbed the "stomach flu," are <a href="http://www.flu.gov/about_the_flu/seasonal/">not typically symptoms of seasonal influenza</a>, which, first and foremost, is a respiratory disease, according to Flu.gov. The flu can sometimes cause these issues, but they won't usually be the <em>main</em> symptoms -- and are more common signs of seasonal flu in children than adults.

  • Myth: If You're Young And Healthy, You Don't Need The Shot

    <strong>Fact:</strong> Younger, healthy adults aren't among the <a href="http://www.cdc.gov/flu/about/qa/flushot.htm#high-risk">people the CDC urges most strongly to get vaccinated</a>, like pregnant women, people over 65 and those with certain chronic medical conditions. The young and healthy will more often than not recover just fine from the flu, with or without the shot. But protecting yourself even if you don't think you need protecting can actually be an act of good. The <a href="http://healthland.time.com/2011/10/13/no-excuses-a-brief-guide-to-the-flu-shot/">more people are vaccinated, the fewer cases of flu we all pass around</a>, which in turn offers greater protection to those at-risk groups.

  • Myth: You Can Get The Flu From Being In The Cold Without A Coat (Or With Wet Hair)

    <strong>Fact:</strong> Mom or Grandma probably told you this one at some point, and while you might not feel so cozy if you head out the door straight from the shower, doing so doesn't exactly condemn you to bed. <a href="http://www.health.harvard.edu/flu-resource-center/10-flu-myths.htm">The <em>only</em> way to catch the flu is to come into contact with the virus</a> that causes it. That might happen <em>while</em> you are outside in the cold, and flu season does certainly happen during cold weather, but it's not because you're cold that you catch the bug.

  • Myth: There's No Treatment For The Flu

    <strong>Fact:</strong> It's not antibiotics that cure-seekers should be looking for. While the two antiviral drugs available to fight the flu aren't a quick fix, they <em>can</em> <a href="http://www.webmd.com/cold-and-flu/features/top-13-flu-myths?page=2">reduce the length of your bout of the flu and make you less contagious</a> to others, according to WebMD. This year's earlier-than-usual flu season has already led to <a href="http://www.huffingtonpost.com/2013/01/10/flu-vaccine-shortage-tamiflu-_n_2448519.html">shortages of one of the drugs, Tamiflu</a>, in the children's liquid formulation, according to the medication's manufacturers. However, a number of experts in countries around the world have questioned Tamiflu's efficacy in fighting the flu, and some have even <a href="http://www.huffingtonpost.com/2012/11/12/tamiflu-evidence-british-medical-journal-cochrane_n_2117287.html">suggested a boycott until further data is published</a>.