A week ago, I noted that being old enough to have experienced earlier forms of the H1N1 influenza strain that were circulating prior to 1958 seems to protect against the new, pandemic H1N1 strain. In that post, I mentioned evidence that even getting vaccinated for the garden-variety seasonal flu appears to reduce your likelihood of coming down with a case of H1N1 and, especially, to lower the risk of needing hospitalization if you do get it.
That's a big surprise, as seasonal shots have to be redesigned every year due to the influenza virus's notorious ability to change its stripes. Different viral strains have differently shaped outer coats, so exposure to those strains (or to vaccines against them) raise different sets of antibodies. (An antibody is a protein, secreted in abundance by particular immune cells, that recognizes the three-dimensional shape of a pathogen and binds to it, inactivating it and flagging it for heavyhanded "follow-up" -- a euphemism for getting the crap kicked out of it -- by "thug" cells we carry around in our blood and lymph for that purpose.) It's known that the seasonal shot doesn't cause you to produce antibodies with the correct shape to stop H1N1 in its tracks.
Yet, now this: A study of U.S. military personnel reported yesterday at the annual meeting of the American Society of Tropical Medicine and Hygiene found that vaccination for seasonal flu cut H1N1 infection rates by half or more among soldiers below age 25 or older than 39.
How can this be? Your immune system has another potent way of recognizing pathogens: In every infected cell, viral proteins (as well as our own normal ones) get routinely carved into little pieces called peptides that eventually find themselves on display on the cell's surface, where each peptide can be inspected by roving immune road-warriors called T-cells. If the peptide looks suspicious, the T-cells call in the big guns.
T-cells recognize chopped-up peptides' constituent amino-acid sequences, rather than whole, functioning proteins' outer hillocks and hollows. What's more, essentially every part of every viral protein -- inside or outside -- is subject to T-cell inspection, not just their outsides as antibodies do. So, one might imagine, there are a whole lot of common viral protein pieces that can be sussed out by T-cells, but would have been missed by antibodies.
But what about the poor 25- to 39-year olds that, in this study, got no H1N1 cross-protection from the seasonal vaccine? That's a bit of a mystery, although some speculate that it could be related to the dirth of circulating H1N1 strains back in these soldiers' immune-systems' formative years.
My take: You don't have to be old to keep from getting a nasty case of H1N1, although it helps. Get yourself vaccinated. If there's no H1N1 vaccine available, and you're over 40 or under 25, the seasonal vaccine may protect you against H1N1, too. (If you can, get both.)
