Re:California schools' risks rise as vaccinations drop
by endtime on Sunday March 29, 2009 @11:33AM
(#537421)
Thanks for explaining. The first reason makes sense. The second doesn't, though. I understand that if an entire generation wasn't immunized, then that generation is susceptible when they are old (as at any age), but I don't see why, in the general case, older people would be more vulnerable.
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Re:California schools' risks rise as vaccinations drop
by timr on Sunday March 29, 2009 @02:24PM
(#537613)
If you only immunize 50% of each generation against a virus, then you slow the transmission rate of the virus, but you also allow the number of susceptible individuals to grow over time. Eventually, the number of susceptible individuals reaches a critical threshold, and outbreaks occur.
Because this process takes years, by the time the outbreaks begin, the average age of the un-immunized population has increased. On the other hand, if nobody is immunized, most people will acquire the virus at a young age, become naturally immune (or die), and the average age of incidence will be low.
Here's a link to a slideshow that explains the concept in greater detail (I've started it at a slide that discusses the Greek rubella outbreak, but if you want the mathematical models, go back to slide 1):