B.C. Industry News

Vancouver Sun – Op-ed: Little data to show benefit of flu vaccine for pregnant women

February 2, 2014

By Alan Cassels, Special to the sun

I often listen to the CBC in the car when I’m driving.

The other week, if I’d looked at myself in the rear-view mirror while CBC’s House Doc was talking about a study of flu vaccines and pregnant women, I am sure I would have seen myself wincing.

At least I didn’t drive off the road, but boy, was that a doozy. I like the CBC’s medical journalists and think they usually do an admirable job. But did the hired help ever miss the mark on interpreting that study. Why? They came to some pretty wild conclusions, saying that if a pregnant woman had a flu shot, the baby was more likely to be full term, normal birth weight. A success right? Not so fast.

In the research world we always remind ourselves that “association doesn’t equal causation,” and we are wrong when we say peanuts cause elephants or fire engines cause fires, even though we often see the two in the same place.

The issue here is what we call the “healthy user bias,” which is to say, healthy women and healthy babies are more likely seen in the same place. It is quite likely that the women in this study who had a flu shot were not representative of all women, and were likely part of a healthier group of women to start with. Any outcome of the health of their babies should be properly attributed to the overall health of the mothers, not some other “associated fact” such as whether the mother liked to jog, had blue eyes, or, in this case, received a flu vaccine.

The problem is that asserting flu vaccines benefit pregnant women can’t be concluded from such a study. We often see this kind of bias creeping in when interpreting non-randomized trials and such conclusions need to be independently verified by a better quality randomized controlled trial, preferably one whose researchers are not funded by the pharmaceutical industry (which this one had.)

I shouldn’t single out CBC’s House Doc, because you see this kind of error commonly reported in the media, where associations are reported as “facts.”

What was most funny was when the House Doc reminded us that “association is not causation,” criticizing those deluded people who think the flu shot caused people to get the flu. If you got the flu just after getting vaccinated, that was just chance, he assured us. Just chance. Hmmm.

I did a quick check to see if the vaccines themselves used in B.C. have even been tested in pregnant women and here’s what I found: Of the three main flu vaccines being given this year in B.C., Fluad, Agriflu and Fluviral, all their product monographs (which are essentially the operating manuals for the vaccines) say the same thing: The safety of the vaccines have “not been established in pregnant women.”

After a quick check of U.S. data, I found that as of November 2013, there have been more than 93,000 reports of reactions, hospitalizations, injuries and deaths following influenza vaccinations made to the federal Vaccine Adverse Events Reporting System in the United States.

These reports include 1,080 related deaths, 8,888 hospitalizations, 1,801 related disabilities and more than 1,700 cases of GBS (Guillain-Barre syndrome) and let me hasten to say they are all “associations.” If Alan Cassels was to go on national radio and say the flu vaccine was what definitively injured these people, I’d be laughed off the air.

Yet, very respectable medical journalists can go on air or write stories making the same sort of assertions about an “association” between the flu shot and the health of pregnant women and their babies.

The way you solve this is by collecting better data, not by trying to exaggerate and deceive people with low-quality research. We have to remember that “healthy user bias” is everywhere, and that the health of pregnant women and their babies is too important a subject to be exposed to dangerous pathogens, such as biased interpretations of health research.

Alan Cassels is a drug policy researcher at the University of Victoria.

He can be followed on twitter.com/note>@akecassels.

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