Tuesday, May 19, 2009

Back to birds and flu

A PLOS One article, looking at how our current practice of influenza vaccination leaves us vulnerable to an H5N1 pandemic...

Let's put aside the (current) H1N1 concern, and go back to the H5N1, or avian, influenza strain, and its potential for a bad pandemic, since its lethality is significantly higher than any other currently circulating strain. We know that our current seasonal influenza vaccine does not protect us against infection with the H1N1 strain currently being passed around the globe. But not protecting us and leaving us more vulnerable are two very different things, something that flummoxes a lot of public health experts. What this paper did, roughly, was the following: immunize some mice against the H3N2 influenza, one of the components of every seasonal flu vaccine; document protection, both by antibody levels and by experimental infection with that H3N2 virus; infect with H5N1, and see which mice do best. All of the mice initially became ill, but the ones that were previously infected with H3N2, but not previously vaccinated, recovered at about day 6. Both the mice that were vaccinated against H3N2 and the mice that weren't previously experimentally infected with H3N2 didn't do so well, almost all having to be euthanized.

What conclusions can be drawn? Vaccination against one strain of influenza does not always protect us against another strain. This we knew. When naturally infected, our bodies mount a broader and more powerful immune response than when vaccinated against specific antigens, which we know very well. Vaccination, and subsequent protection against natural infection with seasonal influenza, leaves mice more vulnerable to a different strain, ie avian flu.

We shouldn't reconsider the principle of universal seasonal influenza vaccination - it's benefits are very well documented - just for the fear of an impending avian flu pandemic. What we should do, however, is investigate other vaccine subtypes and see if this can be replicated, ie does H1N1 (another component of our current vaccine) vaccination leave us more vulnerable? Can we alter, or expand, the subtypes in our seasonal vaccine so that we wouldn't be left more vulnerable to a novel strain? And most importantly, can we find a way to speed up vaccine design and dissemination, so that we are more prepared for a quickly spreading pandemic?

While the current swine flu seems to be more alarm than threat, it has gotten the global public health cylinders in motion, and has brought these discussions back to the forefront.

Bodewes, R., Kreijtz, J., Baas, C., Geelhoed-Mieras, M., de Mutsert, G., van Amerongen, G., van den Brand, J., Fouchier, R., Osterhaus, A., & Rimmelzwaan, G. (2009). Vaccination against Human Influenza A/H3N2 Virus Prevents the Induction of Heterosubtypic Immunity against Lethal Infection with Avian Influenza A/H5N1 Virus PLoS ONE, 4 (5) DOI: 10.1371/journal.pone.0005538

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