Let's have a little look at how science works.
1. Scientists observe something happening, and form a hypothesis about why.
2. Scientists test the hypothesis by trying to make the same thing happen under controlled conditions.
3. If the same thing happens again and again and again while testing the hypothesis, scientists can make predictions about it happening in the future.
4. If the predictions come true, the scientists are happy and the world has a tasty new morsel of knowledge.
Now, let's apply this to something real, like, say.... a vaccine.
1. Scientists observe that, when a high enough proportion of a population is vaccinated against measles, the disease virtually disappears from that population. Maybe the measles vaccine helps prevent measles?
2. Scientists test the hypothesis by measuring the incidence of measles in populations with a high percentage of vaccinated people compared to populations with a low percentage of vaccinated people.
3. Again and again, scientists find that, in highly vaccinated populations, measles outbreaks are small and rare, and in populations with low measles vaccination, lots of people get measles. They predict that in the future, when the percentage of vaccinated people drops below a certain amount, measles outbreaks will occur.
4. Late last year, a person infected with measles visited Disneyland in California - an area with a reasonably high proportion of vaccine refusers - and infected other people with measles. Quite soon after that, lots of people got the measles.
Something else scientists could have predicted: The usual suspects of vaccine denialism began bending all the available information about the Disneyland outbreak to fit their pre-conceived idea that unvaccinated people have nothing to do with outbreaks of disease, and that relating an outbreak of disease to unvaccinated people is UNCOOL and HURTS PEOPLE'S FEELINGS.
I totally understand that the feelings of people who go to great lengths to deny the effectiveness of vaccines might be hurting. And I totally don't give a rat's arse. If loads and loads and loads of studies have found that measles outbreaks occur more often in unvaccinated populations, and you continue to deny that the current US measles outbreak has anything to do with unvaccinated people, there's not much I can do to help you. If you're cranky because science disagrees with you, tough. If you're out of sorts because diseases don't comply to your special view of the world, too bad. If the well-supported theory of herd immunity gives you a frowny face, cry me a frikkin' river.
But cheer up a little bit, because I wrote you a pome.
You can’t bring a cat to a dog fight
To watch it get mauled
And then act all appalled
At the dogs disobeying your rules.
You can’t throw a fridge down a staircase
And protest when it breaks
Because gravity makes
No exceptions for self-absorbed fools.
You can’t stick your hand in a blender
Then demand some redress
For the blood-spattered mess
‘Cause you liked how it was at the start.
You can’t help your kids catch the measles
By refusing a vax
In the face of all facts
But deny that you played any part.
When scientists make a prediction
Like the tides of the seas
Or the spread of disease
They’ve seen it again and again.
But your pox-ridden family is special!
And although their afflictions
Comply with predictions
YOU’RE RIGHT, and you’re going to complain.