Influenza is notoriously mercurial, forcing even the experts to guess at which strain will dominate from one year to the next. As Canada is learning this winter, almost as unpredictable as the virus itself is whether the public will be willing to embrace flu vaccination.
Public Health officials regularly plead and cajole, but most years the majority of people pass on getting a shot. Canadian flu vaccination rates sit pretty squarely in the one-quarter to one-third range, Statistics Canada data show.
But occasionally we experience a phenomenon such as what has been happening in Western Canada where, undeterred by frigid temperatures, people embarked on sometimes desperate searches for flu shots — something they should have done weeks ago to get optimal protection.
"The psychology of influenza vaccination uptake is sometimes almost as complex as the disease itself," says Michael Osterholm, director of the Center for Infectious Diseases Research and Policy at the University of Minnesota.
"We want everyone to be vaccinated. But the question is: Why do we sometimes have these runs?"
So far this year the data collected by the Public Health Agency of Canada and the U.S. Centers for Disease Control suggest North America is experiencing a normal sort of flu season.
"I think that this year will assuredly end up less — as far as sheer numbers — than the 2009 pandemic," says Dr. Michael Jhung, a medical epidemiologist in the CDC's influenza division.
For years, flu saved its biggest wallop for the elderly. But since the new H1N1 strain emerged in the 2009 pandemic, you can't assume that grandma and grandpa are the folks most likely to end up in ICUs with flu.
"So if you're a 50-year-old, you would be sad if your father or your mother went into ICU. But when it's your spouse or your brother, it's different. The risk is a lot more proximal."
Jhung says as of last week the U.S. had seen 2,622 hospitalizations. Of those, 61 per cent were in the 18-to-64 demographic. "When we think about who gets hospitalized for flu, it's usually 60 per cent of those hospitalizations are in people 65 or older."
In both Canada and the U.S., there are reports of really sick young and middle-aged adults in ICUs. That was the pattern during the H1N1 pandemic, so public health folks who know influenza aren't surprised. That's the way this virus rolls.
"I do get the sense — and this is not substantiated by any data — that clinicians are being maybe taken aback a little bit by the number of severe illnesses they're seeing in younger adults."
"Every time a child or a youth dies, demand goes soaring up," says Kendall.