A tale of two studies
© 2009 Roy Benaroch, MD
I haven’t posted a whole lot about H1N1, AKA the “new flu”, AKA the “swine flu.” New information and guidelines seem to be developing every week, and I can’t promise to keep posts here up-to-date on a topic that’s changing so rapidly—my editing and research staff, you know, is already swamped answering fan mail and media requests. But two stories just came out that have caught my eye, and illustrate some of my favorite topics: shortcomings of science reporting in the mainstream media, and the power and limitations of good science.
The first story came out at the end of September. Researchers in Canada reported that people who had gotten a seasonal flu shot (the ordinary vaccine that’s given every year) seemed more susceptible to getting H1N1 flu. Based on this research, some Canadian provinces have suspended efforts to vaccinate against the seasonal flu, and are proceeding only with H1N1 immunizations.
But there is more to this story. The quoted research hasn’t actually been published yet—meaning very few people have actually seen the results, or how they were obtained (According to this very short UPI piece, and international panel is “scrutinizing the data.”) The story was “leaked” to the press, which ran with it. They couldn’t possibly know if the research was done well. Putting together what seems to be reported in blog posts (and I don’t know if these sources are true), the study involved looking retrospectively at flu diagnoses reported by medical providers in Canada, and comparing whether people who had presumed H1N1 flu were more or less likely than people who didn’t have H1N1 flu to have had a seasonal flu shot.
This kind of study can be rife with problems. The cases of H1N1 were presumably not confirmed in a laboratory; and whether or not a person was diagnosed depended on them going to the doctor. But as you can imagine, people who tend to get flu shots are the kinds of people who seek medical attention for their problems—to me, it could be that having had the seasonal flu immunization isn’t a risk factor for H1N1, but just a marker for someone who’s more likely to go to the doctor for flu symptoms. In any case, since the study hasn’t been published yet, doctors and epidemiologists and—yes—journalists can’t possibly scrutinize the methods to see what the limitations of this study were. Can we draw any useful conclusions? Of course not.
Contrast this to another new story, one that came out this week. On October 6, the British Medical Journal published a study from Mexico that came to an opposite conclusion—that the seasonal flu vaccine may offer some protection against H1N1 flu. A summary, the full text, and a well-informed editorial are all available for anyone to read. These researchers compared 60 people with laboratory confirmed H1N1 influenza to 180 people who did not have the new flu, looking at how many of the had had the seasonal flu vaccine in each group. They found that the seasonal flu vaccine seemed to offer at least modest protection. Among unvaccinated people in this study, about 29% came down with H1N1 influenza, compared with about 13% of people who had had a seasonal flu immunization. The study is small, the authors acknowledge, and should not imply that seasonal flu immunizations are a strong protector against H1N1 flu, but they provide some evidence that at least seasonal flu immunizations won’t make the H1N1 epidemic any worse, and may in fact make it better.
By the way, I’ve seen nothing about the Mexican study in any newspaper.
So: the press, especially in Canada, harps on an unpublished study with results that are difficult to understand in context, because the details are unknown. A few weeks later, a well-done, published study about the same issue draws a conclusion opposite from that of the Canadian study and is ignored in the media.
I’m eager to see the Canadian study when it’s published. For now, I see no compelling reason to thing there should be any hesitation for patients to get a seasonal flu vaccine—now—and an H1N1 vaccine as soon as they’re available. I’ll be getting them to protect myself, my family, and my patients. You should too.