Does seasonal flu vaccine protect against swine flu or make it riskier?
Less then two weeks ago, Canadian researchers reported in a paper that has not been published in a journal yet that immunization with the seasonal flu vaccine increased the risk of contracting pandemic H1N1 influenza and of developing more severe complications. Although most experts pooh-poohed the findings, which are often referred to as the "Canadian problem," some provincial health authorities postponed their seasonal flu vaccination programs.
Now, Mexican researchers report today in the British Medical Journal that vaccination for seasonal flu actually protects against infection by swine flu. In a small study of only 240 patients, Dr. Jose Valdespino of the Laboratories de Biologicos y Reactivos de Mexico in Mexico City and his colleagues found that those who received the seasonal flu vaccine were significantly less likely to contract swine flu and that, even if they did contract it, they were less likely to develop severe complications.
The problem with both studies--aside from the fact that they directly contradict each other--is that they run counter to everything we already know about the two viruses. Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention, said recently that there is no plausible mechanism by which vaccination could increase the likelihood of contracting swine flu. Furthermore, researchers in the United States, Australia and elsewhere have scoured their data and find no similar effect.
As for protection, researchers had fervently hoped that seasonal flu vaccination would provide some, thereby limiting the fatalities that might be associated with the pandemic. But every laboratory experiment they have performed shows there is none. The two viruses are simply too different for antibodies raised against one to affect the other. And again, according to CDC spokesman Joe Quimby, researchers have scoured their data and found no support for the new findings.
So where does that leave us? Back where we started. The most likely scenario is that both the Canadian and Mexican results are wrong and that seasonal flu vaccination provides no benefit against swine flu and no harm. Bottom line: get both vaccines.
-- Thomas H. Maugh II