About SARS: there have been two of people "in their prime" dying, out of 19 deaths so far, both in their forties. One of them may have had another issue, but one of them was just fine.

Also, it's possible the numbers are low; in Canada, if you have SARS and need a respirator you get one. If the cases numbered in the thousands instead of the dozens, that would no longer be true. Rumours out of China paint a very bleak picture indeed; it's entirely possible that the numbers are still fictitious, even as they are pumped up tenfold. I've read that reported cases in Shanghai are two, while the real number is over 600. According to my Chinese housemate (who can no longer go home, even if he wants to; his town is a hot zone) most people there think the state is still covering up true numbers... not out of instructions to do so out of the top but more as force of habit wrt reporting bad news to party bosses.

As for West Nile in Canada, it turned out that many people in their prime got it last year, and that most of them have not yet fully recovered. It looks more like a crap shoot than a matter of overall health as to whether you get the full-on encephalitis/meningitis trip that is the worst case scenario with West Nile.