Glenn wrote:
Bill, several years ago I read somewhere that part of why the current H1N1 outbreak has resulted in considerably less mortality this time around is that there is a kind of residual immunity in the global population due to the extent of the 1918 pandemic. I am not convinced of the idea of a population immunity passed from generation to generation, but what are your thoughts on it?
Whoa there!!! You *totally* do not understand. So let's start from scratch.
Influenza is a series of viruses that live in man and beast. When not floating around in humans, it infects swine and poultry. These viruses mutate all the time, giving them renewed ability to infect their hosts.
The jump from beast to man usually doesn't "take." Every once in a while though it does, as it did on that pig farm in Kansas circa 1917. When it does, we have a brand new virus which is of great concern to organizations like the CDC, because you never really know what you're going to get.
Each strain of influenza has a unique level of virulence. Some are well tolerated by the majority of the population. Others do more harm, and can results in a significant number of hospital stays (from complications like pneumonia) and mortality.
Typically the risk by age of mortality from influenza follows a "U" graph pattern. The very young and the very old are at highest risk of mortality, while healthy adults in the primes of their lives are able to take the hit and get moving again in a week. The 1917 H1N1 was unique in that the risk by age plot was a "W" rather than a "U". Why? Because this virus caused the immune systems of its hosts to attack the lungs. The stronger the immune system, the stronger the attack. Thus strapping, healthy young males would go from healthy to cyanotic (turning blue-black) in a day or two, and perish from complete respiratory failure. When soldiers were training to go overseas for war in 1918, they were densely clustered and so gave ample opportunity for this virus to spread and further modify via random changes.
The infection was so widespread and so devastating that most folks born in my father's generation were likely eventually exposed to it. Consequently when a variant of H1N1 started appearing in 2008/2009 and making its way around the globe, there was no ready supply of elderly for it to spread in via nursing homes and hospitals. So back when it hit Virginia before a vaccine was available, my father with stage IV cancer was safe from it while my son contracted the disease and was sick for a week. The virus skipped me because I was one of a rare few who got "the swine flu vaccine" back in 1976. That vaccination program got canned shortly after it got started because the pandemic never happened and there was hype made over some cases of Guillain-Barr Syndrome. (The added risk that year was 1 in 100,000.) In any case, I was protected by vaccine, my father was protected by exposure a lifetime ago, and my son was vulnerable.
- Bill