TORONTO - A new study suggests a strange phenomenon spotted at the start of the 2009 flu pandemic may well have been real.
Canadian researchers noticed in the early weeks of the pandemic that people who got a flu shot the previous winter seemed to be more likely to get infected with the pandemic virus than people who hadn't received a flu shot.
Five studies done in several provinces showed the same result, but initially research outside of Canada did not.
Some in the flu research community dubbed it "the Canadian problem" and dismissed it.
But a new study in ferrets shows the animals get sicker when exposed to the 2009 flu virus if they were previously vaccinated with the vaccine given for the 2008-2009 flu season.
Lead author Dr. Danuta Skowronski says the reason for the effect is unclear, but she hopes other research groups will now try to figure it out.
Skowronski is an influenza expert at the B.C. Centre for Disease Control in Vancouver. She is the researcher who first spotted the unexpected — and unwelcome — effect.
She presented the ferret study findings Sunday at a major international infectious diseases conference in San Francisco.