According to this article (and others on the web) It is precisely those with a healthy immune system who are most at risk because their immune response is so strong. The group most at risk is right in the middle - not the very young or the aged. ....
Quote from the URL: "However, the middle age group--roughly age 15 to 50, give or take--tend to have an active, vigorous immune response upon invasion by a pathogen. Most of the time, this keeps us relatively free of disease from microbes, but some organisms tend to trigger this type of hyper-response that actually ends up harming the host--in some cases, fatally. This is what we've seen in some cases of H5N1 infection, and what's been induced in mouse models with the 1918 H1N1 strain."
(emphasis mine) -- Um, that's what I was saying -- middle aged people -- people in their mid-40's to mid-50's -- are at less risk than those between 15 and mid-30's or so. I know I said "15 to 34 are most at risk," but I also said "middle aged people are least at risk." And I think we all can agree that 50 is considered by most people to be "middle age." And your citation says "15 to 50, give or take." Give or take -- 45 to 55 are least at risk. Give or take.
That article is referring to people in the middle of an age group, and not making it synonymous with the idiom "middle aged." In other words, it divided people into broad categories -- the young (under 15), the next group (the middle group) age 15 to 50, and the older (51 and up). The exact quote: "Children have immune responses that are still developing, while the elderly tend to lose some immune function with the aging process. However, the middle age group...." It does not say "middle aged people are most at risk." It says those between "15 to 50, give or take" are, only using the words "middle age" to refer to the second of the three broad categories that they used. Hope this helps!
-Dorothy (LadyZolt)