TORONTO - As influenza season hits its stride, blaring headlines declare that there is a mismatch between strains covered by this year's flu shot and the viruses actually confining people to their beds with fevers, chills and bone-aching fatigue.
Flu experts and public health officials don't like it when the strains in the flu vaccine aren't an optimal match to the circulating viruses. They know elevated rates of sickness and influenza-related deaths may result.
But they dislike the headlines almost as much, fearing the black-and-white nature of the reporting will undermine fragile public confidence in the value of flu shots.
"It is often portrayed as a kind of 'on' or 'off' kind of thing. There's a match or there's a mismatch. And in that kind of situation, it's a very discomforting presentation for the public health community," says Dr. Keiji Fukuda, co-ordinator of the World Health Organization's Global Influenza Program.
"There is always concern we're really setting up a situation where people would say: 'Oh, why should I get something which is worthless?' "
A mismatch doesn't mean a flu shot was a waste of time, Fukuda and others insist.
The vaccine may confer less protection than it would have if it was made from viruses identical to those being coughed around your office or your child's school. But less and useless are not synonymous.
"I think most people would agree that the vaccine efficacy would not be as good as it would be if there was an exact match," says Dr. John Treanor, director of the vaccine treatment and evaluation unit at the University of Rochester in upstate New York.
"But what there is not good data . . . on is: How much of an impact would there be on efficacy if there is a mismatch of X amount? That's a much more difficult question to answer."
"So other than broadly saying 'Yes, it's better to have an exact match' you can't say very much about what this is likely to mean in terms of vaccine efficacy," he said, noting that some years mismatched vaccines are later shown to have provided good protection against circulating viruses.
Part of the problem is the lead-time to get that type of answer.
Experts now know that two of the three strains in this season's flu vaccine don't match the predominant viruses spreading in North America. But data showing how much or how little protection the vaccine offers against the circulating viruses haven't typically been generated until after the end of flu season.
For the first time this year an early estimate of flu vaccine efficacy is being calculated, says Dr. Nancy Cox, head of the Influenza Division at the U.S. Centers for Disease Control in Atlanta.
The estimates - one for each of the three flu viruses covered by the flu shot - should be published within two weeks, Cox says.
Each year the flu shot protects against one influenza B virus and two influenza A subtypes, an H3N2 and an H1N1.
This year the H1N1 virus in the vaccine is well matched to the one making the rounds. That's good news for most parts of Canada, because to date H1N1 has been the predominant disease-causing subtype north of the border.
But the influenza B strain and the H3N2 vaccine viruses are not the ones spreading in North America. And in the U.S. in recent weeks, H3N2-caused cases of flu have soared.
Confidence in flu shots isn't all that high to begin with, at least not in some quarters.
Many health-care workers, for instance, forgo flu vaccine, seeing them either as unnecessary or ineffective. And virtually everyone has heard stories of friends, family members, or colleagues who got a shot and still fell ill with what they insisted was flu.
Few people sick with flu-like symptoms will ever be tested to see what is actually ailing them. So whether they really had flu or another of the myriad bugs that trigger respiratory infections during the winter will never be known.
Flu shots aren't designed to protect against these other ailments, which are even lumped under the heading "influenza-like illnesses." But because they can be indistinguishable from flu to the sufferer, a person who got a shot and later came down with one of these infections might well be tempted to skip a shot in future.
Given the complexity of the situation, some public health officials would prefer not to talk about mismatches and sub-optimal vaccine efficacy at all.
Dr. Michael Osterholm is director of the Center for Infectious Diseases Research and Policy at the University of Minnesota. CIDRAP, as it is better known, runs an infectious diseases news operation; its writers were among the first to report on the vaccine mismatch this year.
"I actually received a fair number of negative e-mails from colleagues and public health officials for the articles that we first published in CIDRAP on the lack of protection from this year's vaccine," Osterholm acknowledges.
"All we did is just told the truth. We just said what was happening."
He thinks public health officials need to be frank about the shortcomings of flu vaccine, which - because it takes months to produce - is made from strains selected nearly a year before flu season starts. (Experts met at the WHO two weeks ago to select the strains for the 2008-09 vaccine.)
"The bottom line is . . . it's a crapshoot situation year after year," Osterholm says.
"It's a crapshoot whether we can grow it and get it out there. It's a crapshoot how much the uptake will be and will we overshoot production. . . . And then finally, will it work that year, given the mismatch (potential)? "
"In good years, when it works, it's great. Years it doesn't work, it does call into question the credibility of the vaccine," says Osterholm, who may be in for another onslaught of e-mail.
"I want to be very clear. I'm a strong advocate of seasonal flu vaccine," he says, though he adds that research to produce more broadly protective flu vaccines is critical.
"We owe the public to find a better vaccine as soon as possible. And in the meantime, people like me say: Keep vaccinating. You do no harm. You may do good."
