Help me understand disease mortality rates

I have a good idea for a story (maybe even a novel?) but in order to begin writing it, I need to understand how mortality rates are figured (well, I also need to find out if it causes sterility in surviors, but I’ll keep trying to look that up.)

The disease I’m interested in is Smallpox. If you look on google or what have you, most sites that talk about it claim it has “a 30% mortality rate.”

Which of the following is the most correct assumption I’ve come up with?

A. That 30% of people in a given population will die from it(regardless of how many have been vacinated or not).

B. That 30% of all unvacinated people will die of it.

C. that 30% of people who get it will die of it.

D. or that if you get it your chances are 3 in 10 that you’ll die of it, and the 30% isn’t reflective of showing what precent of the population dies.

Or am I just wrong to think that there’s a difference between the last three?

Have you read ?

30% disease mortality means that 30% of people who are infected with the disease will die. There are some strains of smallpox that are worse than others. See if you can find Richard Preston’s article (New Yorker?) about smallpox for more info. I think he just wrote a book about it, too.
Also look in the archives here for a column by Cecil on smallpox and vaccination (search engine is slow right now)

No, thanks for the link. But while it helps me rule out A and perhaps B, as I suppected, nothing on here really helps me figure which of the other two possiblities it means. I’m leaning towards D, is that right?

" If used as a biological weapon, smallpox represents a serious threat to civilian populations because of its case-fatality rate of 30% or more among unvaccinated persons and the absence of specific therapy. Although smallpox has long been feared as the most devastating of all infectious diseases,2 its potential for devastation today is far greater than at any previous time. Routine vaccination throughout the United States ceased more than 25 years ago. In a now highly susceptible, mobile population, smallpox would be able to spread widely and rapidly throughout this country and the world."

The neat thing is the above paragraph summarizes part of the plot I have in mind (though I’m more interested in the social repercussions of this happening than the instance of disease itself) so at least I’m headed in the right direction!

A case fatality rate is the percentage of persons diagnosed with a specific disease who die as a result of that disease within a given period. I assume we’re posting at the same time here?

Thanks, Jillgat and Duskster, I think I understand now :slight_smile: Who would have thought the first possiblity I came up with, before overanalyzing it to death, would be the right one?

To answer your other question, smallpox by itself doesn’t impair fertility in survivors. Some of em were left pretty darned ugly, though.

Historically about 30% of those who contract the disease die of it. But that’s an average. Some outbreaks have killed “only” 10% or less. Other outbreaks have killed 50% or more in a given area.

That’s also prior to early 21st Century medicine. Remember that until last year, inhalation anthrax was considered between 95-100% fatal once symptoms appeared, but intensive supportive care allowed (if I recall correctly) 5 out of 11 to survive. (Although none have, apparently, recovered enough to resume full time employment)

With smallpox - remember, a lot of us folks over 35 have been vaccinated at some point in our lives. Granted, most of the immunity tends to fade after 10 years or so, but some might remain in some individuals (this is highly variable), and even if it doesn’t prevent the disease it might lessen the severity. So, assuming unvaccinated populations, those over 35 might contract the disease at the same rate as those younger, but they might have fewer deaths, less blindness, and so forth. Or maybe not. We really don’t know (and I hope we don’t ever have to find out). Some folks may have been vaccinated more than once - military personnel, those who immigrated or traveled oversease prior to the early 70’s. Those folks might have slightly better chances than those vaccinated only once.

Also - the vaccination is believe to lessen the effects of the disease if given within 4-5 days of exposure. Again, you’d still get sick, but you’d be less likely to die. (You’d still have lots of scars, though…)

As for the oogy symptoms and many ways to die from this disease… the New Yorker article was nicely graphic. You can also google-search for both smallpox and adverse reactions to the cowpox-based vaccine (the fatal version of vaccinia is, um, extremely gross).


Although the fact that it leaves horrible scars, can cause blindness, and other disabilities does make it less likely that survivors will reproduce, assuming there are unscarred folks about to chose from (if everyone has pox scars it levels the playing field). But, remember - those most likely to have any resistance at all at this point are either the recently-vaccinated military (which will be mostly men) or those over 35 (in which case the women will be nearly at the end of their reproductive years). Between the die-off and the shortage of fertile women, the world’s “overpopulation problem” will be solved.

I will point out, however, that a successful vaccination DOES render the person vaccinated immune to smallpox for up to 10 years. In other words, if you’ve been recently vaccinated you won’t catch it at all, even if massively exposed while, for example, taking care of the ill and dying.

Just for the heck of it, I’d like to point out that the fatality rate is higher among pregnant women. Also, anyone with a compromised immunue system is likely toast - that’s everyone with HIV, organ transplant recipients, cancer patients on chemo, the very old, the very young… and folks with eczema. At least with active eczema (I had eczema as a baby AND survived the smallpox vaccine - have to ask mom about that… did they get the skin problem under control, then vaccinate me?) Folks with problem immunue system can be killed by the vaccine alone, much less smallpox itself. (Please see above reference to adverse effects from vaccinia available through google)

As for social effects… imagine 3 billion corpses. :eek:

Have everyone around you count off by threes in random order. Then imagine every “1” is dead and gone. What effect will that have on society, do you think?

Now imagine all the “2”'s are horribly scarred with some lingering disability (often sight is effected, but there are other potential problems)

That leaves the “3”'s to carry on with burying the dead , food production and transportation, health care, and, oh yes, in many areas rebuilding the population. Not to mention all those orphans to care for…

Look up the social effects of the Black Death on Europe. MASSIVE social disruption. Now, consider that the plague took decades to travel across Europe. Imagine this new plague affecting everyone. everywhere within a year or two (or even less) thanks to modern ability to travel great distances swiftly.

Anyone else having nightmares yet?