Massive measles outbreak - thank you, Andrew Fucking Wakefield

[Andy_L]

@WhyNot

No, you still don’t got it.

You get a vaccination. Yay! It will reduce the chances that you’ll get the disease. Reduce. Not eliminate. Reduce.

So then I get vaccinated. Yay! It will reduce the chances that I’ll get the disease or that I’ll pass it to you. Reduce, not eliminate.

So now **curlcoat **doesn’t get vaccinated. She goes to Germany and gets measles, but before she gets symptoms, we pass her in the produce section and she coughs on us.

Ooops! We’ve only reduced, not eliminated, our risk of catching it from her. Like most people that have been vaccinated, I don’t get it, nor do I pass it on to you.

You aren’t so lucky. Your vaccine reduced, but didn’t eliminate your chances of catching it. You got it, and you’re dead. Or meningitis or pneumonia or hepatitis (all potential complications of measles, more common in adults than children) or if you’re really lucky, you just miss two weeks of work and income feeling like crap.

That’s herd immunity in a nutshell. Vaccines are effective, but not quite 100% effective. Add up a bunch of not-quite-100% effectives, and some of us who were vaccinated *will *get sick, just like some number of people will get pregnant each year despite using 98% effective birth control pills.

Yeah. When you get vaccinated, you directly reduce your chance of catching a disease if you’re exposed to it. When other people get vaccinated, it indirectly reduces your chance of getting a disease because it reduces the chance that you get exposed. Obviously, reducing your chance of getting exposed and reducing the chance of catching the disease if exposed, is really good news.

While we’re dealing with common vaccine misconceptions, here’s an interesting one. Suppose there’s a vaccine that is 90% effective in preventing disease, and 50% of the population gets the vaccine. In a population of 1000 people in which everyone is exposed, 500 people get the vaccine, and of those only 50 people get the disease, while all 500 of the unvaccinated people get the disease. So in the 1000 person population, only 550 get the disease.

Now raise the percentage of people who get the vaccine to 90%. 900 people get the vaccine, and out of them 90 people get the disease, while all 100 unvaccinated people get the disease. Only 190 people get the disease, but notice that almost half of them are vaccinated. This doesn’t mean that the vaccine isn’t working - it means that most people are vaccinated.

It can get even more confusing - when vaccine uptake gets to 95%, 950 people get vaccinated, and of them, 95 people get the disease; meanwhile only 50 unvaccinated people get the disease. Now the majority of 145 people who got the disease were vaccinated - but again this is because the vast majority of everybody was vaccinated. A clearer way to express this is that even though the unvaccinated make up only 5% of the population, they made up over 30% of the people who caught the disease.