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H1N1 flu and the persistence of memory

People of a certain age have been known to complain that, while they lucidly recall the details of childhood events, they can't remember what they ate for breakfast.

As it is with brains, so it may be with immune systems. Older people's immune responses, while generally somewhat sluggish in revving up after, say, a vaccine against seasonal influenza, seem to retain a knack for fending off the current H1N1 flu onslaught. A large Canadian study published in the November 12 issue of the New England Journal of Medicine reports a much lower risk of H1N1 infection among those born before 1957. This, the authors suggest, is quite possibly as a result of having been exposed to one or another of the somewhat related strains that were making the rounds before the year the Russians launched Sputnik, the Milwaukee Braves beat the Yankees, Buddy Holly cut "That'll Be the Day," On the Road and Atlas Shrugged went into print, and the tiring viral variants were retired by leaner, hungier, less pandemic-H1N1-reminiscent strains.

But if there's a take-home lesson here for the young'uns among us, it's not that you should have been around when this new flu's grandpappy had to walk four miles in the snow to get to your respiratory tract. Far from it. In fact, there's reason to believe any previous influenza exposure -- including exposure to the seasonal flu vaccine -- helps.

As summarized in an editorial in the same issue of NEJM, people who have been vaccinated for seasonal influenza seem to hold up better against H1N1 infection than those eschewing a seasonal stick in the arm. In a Mexican case-control study, for example, patients who'd received a standard seasonal vaccine showed substantial signs of protection against H1N1 infection.

Or was it just that those who get seasonal flu shots are healthier to begin with?

A reasonable question. But there's good immunologic evidence that even the seasonal flu vaccine provides cross-protection against H1N1. The editorial notes a different Canadian study's finding: among adults 18-64 years of age, only 9% of those not vaccinated against seasonal flu showed significant levels of antibodies capable of fighting off the H1N1 strain; but of those who'd had the seasonal shot, a full 25% showed these robust antibody levels.

What until only yesterday were the prevailing strains of influenza are quickly being displaced by the new reigning heavyweight, the pandemic H1N1 flu virus, which now accounts for the great majority of influenza infections. Yet for all its punch-packing pugnacity, H1N1 may yet be vulnerable to a good, fast jab -- in this case, a jab in the arm -- even one that was aimed at the new champ's checked-out distant cousin.

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