No, but there's been an oddity in this year's flu patterns:
One of the mantras of global public health is that infectious diseases know no borders. But this year's flu season continues to thumb its nose at that notion, rolling out in distinctly different patterns on either side of the 49th parallel.Maps generated by the Public Health Agency of Canada and the U.S. Centers for Disease Control show widespread flu activity in 49 U.S. states, but in only one province, British Columbia. Other parts of Canada are experiencing localized or even sporadic outbreaks; some may be past the peak of their flu seasons.
What explains the differences? Experts shake their heads and marvel at the enduring ability of the famously unpredictable influenza virus to confound explanation and prediction.
Ask Dr. Nancy Cox, head of the CDC's Influenza Division, if she's surprised to see distinctly different seasons playing out on the upper and lower part of the continent, and her response reflects her many years of study of this virus.
"Yes and no," says Cox, who is credited with having coined the oft-repeated expression, "If you've seen one flu season, you've seen one flu season."
"It surprises me because influenza viruses really do not respect boundaries. It doesn't surprise me because we've seen these very striking differences between influenza season in the U.S. and the influenza season in Canada in the past - and haven't been able to explain the differences."
For ease of discussion, people talk about influenza as if it were an entity. But in fact, there are three types that cause human disease - influenza A, B and to a lesser degree C. There are two subtypes of A viruses, H3N2 and H1N1.
And because the viruses mutate constantly, there are families of viruses within each of those types.
In Canada this year, two families of H3N2 viruses, one H1N1 virus, and two influenza B virus groups are circulating and causing disease. The flu shot gives people who get it protection against one H1N1, one H3N2 and one B virus.
But the main viruses causing disease so far this year in Canada are H1N1s that are closely matched to the one included in this year's flu shot. So people who got a flu shot - and as many as about a third of Canadians do - would be well positioned to ward off assault from those viruses.
In the United States, a recent surge in H3N2 activity has made those viruses the most predominant cause of illness there this year.