Question about natural immunity (sorry more flu stuff).

[JMS]

I've read a couple times something to the effect that senior citizens are not a targeted group for receiving the H1N1 vaccine b/c many show immunity relating to the 1917 strain. Or something like that. My question is did those who are showing immunity definitely have the 1917 flu or is it possible to not get the flu, but still get immunity from exposure?

Thanks to anyone who chimes in :)

[Sillygirl]

1) It's not the 1917 flu, it's the more recent strains like 1954 and 1967 that were similar to H1N1. Not too many people alive these days from 1917.
2) Your immune system had to encounter the virus for you to have some immunity. The virus enters cells who place small pieces of the virus in special molecules called MHCs on their outer membrane. Then B-cells, which are the cells that produce antibodies, interact with that MHC molecule. A small portion of them go on to become memory cells, which persist for decades. If your body encounters the same virus, or a similar one, the memory cells rapdily divide and crank out antibodies. (There's a LOT more that goes on, but that's how you get lasting immunity.) Anyway, none of that process works without exposure to the virus. The case may have been quite mild, though.

[JMS]

Thanks Katie, that answers my question. I hesitated before typing 1917, but I could have sworn that is what I read :)

eta: I just heard on the news (again, I'm sourceless) that 50% of babies born today (in more developed nations) will live to be 100. Think of all the immunity!! :)