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The dyamics of pandemics
What Are the Odds of Either Virus Becoming a Pandemic?
Here's something to keep in mind the next time you read stories about the next pandemic that is about to rid the earth of 90% of its population and fill the streets with carts of bloated bodies and flesh eating zombies: three conditions have to be met for there to be a pandemic.
1.The bacteria or virus in question must be readily able to mutate--to evolve around defenses. Thanks to the widespread and inappropriate use of antibiotics and antivirals both medically and agriculturally, that's not much of a problem for most pathogens now.
2.The bacteria or virus in question must not kill too high a percentage of people too quickly. At first glance, this might seem counterintuitive. After all, you'd think that the deadlier the better…from the virus' point of view. Not so. If a pathogen kills too many of its victims too quickly, it never has a chance to spread. If the infected person dies too quickly, they never get a chance to infect anyone else before they're cremated or buried. That's why diseases such as Ebola with up to a 90% mortality rate never get a lot of traction when it comes to infecting people outside of a local village. Malaria, on the other hand, which is far less lethal, nevertheless kills approximately 1.2 million people a year because it has such low lethality that it has a chance to infect many, many, many more people than Ebola.6 (Incidentally, H7N9 and MERS both fall in the high middle range--much more lethal than malaria, but nowhere near the self-nullifying threshold seen in Ebola.)
3.And the pathogen must be "easily" transmitted from human to human. This is where all the threats so far have failed the pandemic test. (Swine flu came the closest to qualifying.) There is no conclusive evidence that H7N9 transmits between humans at all, and even if they find that it can, the evidence at this point is that it certainly doesn't readily pass between people. Until such time as it mutates into a form where it can transmit sustainably from person to person, bird flu is not really a pandemic threat…among people. And as for MERS, no one knows how it transmits, although all evidence points to extended, intimate contact being required for transmission. In other words, it too fails the "sustainability" test. Again, unless the virus mutates into a form that transmits "readily," it likewise is not a pandemic threat.
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