Healthy Skepticism Library item: 7002

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Publication type: news

Gram K.
To take the shot . . . or not; Some people get vaccinated every year. Some choose not to. Who's right?
Vancouver Sun 2006 Dec 4

Abstract:

Jim Wright didn’t get a flu shot this year. Didn’t get one last year or the year before either. Neither did Alan Cassels.
And it’s not because of the recent scare that the flu shot can in rare circumstances cause a paralyzing condition known as Guillain-Barre syndrome.
Nor is it that they are unaware of the public health drive to immunize as many B.C. residents as possible, some through a free vaccine and some paid.
It’s not even that they are fearful of the mercury in the vaccine, though they have considered that.
Wright, a professor of pharmacology and the managing director of Therapeutics Initiative, a medical think-tank that provides physicians and pharmacists with information on drug therapy, and Cassels, a University of Victoria drug policy researcher, don’t get the flu shot because they haven’t seen any evidence that it works or that no harm will come of it.
“I am not convinced that the benefits are that great,” says Wright.
“I would say point blank that the evidence is not in yet,” says Cassels.
“The evidence we have is incomplete and doesn’t point definitively in one direction. In my opinion, the evidence is all that counts.”
Last year, according to the Public Health Agency of Canada, 817 B.C.
influenza cases were confirmed out of 5,268 cases tested. There were 357 pediatric cases throughout Canada and three deaths attributed to influenza.
Both Wright and Cassels preach the gospel of evidence-based research — research that adheres to the gold standard of randomized controlled studies.
The bigger the study, the better. Anything else has an inherent bias, they say. Many flu vaccine studies are what are called “cohort” studies which compare people who get vaccinated with the people who don’t.
“It creates an inherent bias because the people who get the vaccine tend to be more health conscious than those who don’t. So you are always going to have an inherent bias toward the vaccine,” says Wright.
“The magic of randomization is that it is random. You don’t select for anything and if it’s large enough you balance for all the things known and unknown.”
Wright used to get the shot until he searched for randomized controlled studies proving it works. He didn’t find them.
“I was shocked at how little evidence there was,” he says.
He found just one large double-blind randomized controlled study of the elderly, surprising since they are the targeted population. It concluded that 62 of every 63 vaccinated seniors still got the flu.
Then he searched the reports of the Cochrane Collaboration for a review of studies of the vaccine’s benefit for children older than age two concluded it is only 28 per cent effective in reducing the relative risk of influenza-like-illness. And a similar analysis of studies for adults found the vaccine reduced the absolute incidence by just six per cent.
Cochrane researchers concluded that much more research needs to be done before widespread immunization is conducted. Both Wright and Cassels say they don’t understand why the public health people don’t use the Cochrane research to set their policies.
“People throw stats all over the place, but the Cochrane tend to cut through all that and you can kind of get the straight goods,” says Cassels.
But Dr. Patricia Daly, a public health officer with Vancouver Coastal Health, says she has seen many good studies showing the value of the flu shot. She said public health officials don’t pay much attention to the Cochrane reviews.
“It doesn’t include some very good studies in its data and we know that if we get an outbreak in a long term care facility and the residents have been vaccinated, we see far fewer cases and deaths.
“You don’t need a randomized controlled study when we already know,” she says. “It would be unethical to do that if we already know it works. No one is changing practices due to the Cochrane review.”
But Wright says it would only be unethical to do randomized studies if you trust the other data.
“She is trusting the data and I say you can’t trust it. I don’t accept that information and neither does the Cochrane. The top statisticians in the world are working for the Cochrane.”
The type of studies is one problem with interpreting benefit. Another is that sometimes researchers report a “relative risk reduction” and sometimes an “absolute risk reduction.”
When you reduce a risk from two per cent to one per cent, the absolute risk reduction is one per cent, but the relative risk reduction is 50 per cent, because you have cut the risk in half. The pharmaceuticals tend to use relative risk numbers, says Wright. Most of the time, when you are looking at anything over 10-20 per cent, you are looking at relative risk reduction,” says Cassels. “It makes the reduction look much better, but it doesn’t tell you what the risk was to start with.”
Then there are the problems with the contents of the flu shot. There are many strains of the illness and every year the World Health Organization must predict which ones to put in the vaccine. It got it wrong in 1997. A nasty strain, called the Sydney, showed up in the community and many people got sick and some of them died. Daly suggests that shows the flu shot works when they get it right, but Cassels says that is just an assumption.
Cassels focuses his energy on drug policy and he has been following the experience of Ontario where everyone can get a free flu shot.
He says it costs $50-$55 million per year to immunize the whole population, but the number of confirmed cases of the flu actually rose to 164 cases per 100,000 residents in 2004 from 109 per 100,000 in 2000 when the mass immunization began.
That data is not definitive, Cassels says. “And if you are going to spend all that money, I would argue, you’d want to know definitively.
“But suffice to say it didn’t drop from 109 to 50 after spending $55 million per year.”
Besides, he says, no long term studies have been conducted to prove it causes no harm.
“My wife’s grandmother died three days after she got the flu shot,” he says.
“It was probably a coincidence but are they tracking that? No.”
Cassels points out the flu is very unlikely to kill a healthy person. At best it will prevent lost work or school time, though that is debatable. And he argues people often need that sick time to recoup from a stressful job.
Daly says she would prefer 10 days of vacation to relieve stress. She says the flu shot is essential for infants, the elderly and the chronically ill who could die from complications and is a good investment for healthy adults too, even though they have to pay for it themselves.
In a typical flu season, one in six people gets the flu, she says. She doesn’t know how many of those die because deaths are often blamed on an underlying condition such as heart or lung disease.
But she says public health officials estimate about 4,500 people die every year in Canada of the flu. Almost all of them are elderly, the very young and the immune-compromised, the same population targeted for free vaccines.
Out of a population of 32 million people, that means one in every 7,000 Canadians dies of the flu every year.
Immunizing the elderly is only 30-40 per cent effective, she concedes. It just isn’t as effective for them. But according to her information, it works better in healthy adults and when you immunize the staff of nursing homes, you can protect the residents by a rate of 60-70 per cent, she said, quoting a study in the Journal of Infectious Disease that was published in 1997.
Those are relative risk numbers says Wright, not absolute risk.
Dr. Janet McElhaney, an immunologist and gerontologist at UBC who is conducting flu research with seniors, agrees the current vaccine isn’t that effective at preventing the illness in the elderly, but it is very effective at reducing the severity of symptoms.
As well, she says studies show that the vaccine stimulates what is called the cell-mediated immune response, which would otherwise be inactive a year after getting the flu.
“If you get the infection and you don’t get vaccinated the next year, you will be partially protected [with antibodies], but it’s not as good as with the vaccine because you get the antibody response and the cell-mediated response.”
McElhaney says epidemiological studies show that even though the relative risk reduction is only 30-40 per cent, it still saves the health system money by reducing hospitalizations.
But epidemiological studies aren’t randomized controlled studies, so for Wright and Cassels, the jury is still out.
FLU SHOT STUDIES:
A few of the studies that have looked at how well flu vaccinations work.
Efficacy and effectiveness of influenza vaccines in elderly people: a systematic review, Lancet 2005; 366: 1165-74 authors: T. Jefferson, D.
Rivetti, A. Rivetti, M. Rudin, C Di Pietrantonj, V. Demicheli.
Assessment of the efficacy and effectiveness of influenza vaccines in healthy children: systematic review, Lancet 2005; 365: 773-80 authors: T.
Jefferson, S. Smith, V. Demicheli, A. Harnden, A. Rivetti, C Di Pietrantonj.
The Efficacy of Influenza Vaccination in Elderly Individuals: A Randomized Double-blind Placebo-Controlled Trial. JAMA. 1994; 272: 1661-1665. authors:
Govaert, Thijs, N. Masurel.
Vaccines for preventing influenza in healthy adults. Cochrane Database of Systematic Reviews. Cochrane Library 2000 (Issue 4) authors: V. Demicheli, D. Rivetti, J.J. Deeks, T. O. Jefferson.
Source: Karen Gram