How likely are you to get a flu shot this year?

It was chalked up to a strange phenomenon seen only in Canada at the time: at the start of the 2008-2009 flu season, people who got a seasonal flu shot for the were more likely to get infected with the pandemic virus than people who hadn't received that shot.

The result was duplicated in five studies that took place in different provinces.

At first, research didn't show that the effect was duplicated outside of Canada.
Now, a new study by a group of Canadian researchers shows that the effect may have been real, by duplicating it in a group of ferrets.

The study, headed up by Dr. Danuta Skowronski from the B.C. Centre for Disease control, injected half of a group of 32 ferrets with the 2008-09 seasonal flu shot and the other half got a placebo. Then, all the ferrets were injected with the pandemic H1N1 virus. The ferrets that had received the vaccine were significantly sicker than the ones that did not. Skowronski noted that researchers in other countries have found similar results since the pandemic.

At this point, the reason for the effect is unclear, but there are two theories about why it happened. The first theory posits that the virus used in the vaccine was similar to the H1N1 virus, but not close enough for the body to produce antibodies that could combat the pandemic virus.

The other theory, known as the infection block hypothesis, is that people who get the flu shot are only protected against the kind of flu the shot contains. When people who got the shot in 2008 didn't get the flu, they may have been less able to fight off the pandemic virus.

Skowronski said the findings shouldn't deter people from getting seasonal flu shots, because the documented effect was solely linked to the pandemic virus.

"Pandemics are infrequent occurrences, but seasonal influenza recurs on an annual basis. It's a substantial cause of morbidity and mortality, and the seasonal vaccine substantially protects against that severe outcome due to seasonal influenza," she told The Canadian Press.

What do you think? Do the results of this study change your mind about getting a flu shot?