One of the most common questions you'll hear from someone who doesn't want to get vaccinated is this: "But if everyone else is vaccinated, why does it matter if I'm not?"
And the answer isn't entirely straightforward, because both the reason this person needs to get vaccinated, and the reason they feel they don't have to, come down to the same thing - something called 'herd immunity'.
Thankfully, very talented Reddit user theotheredmund has created this animation that beautifully breaks down herd immunity in about 20 seconds.
And it's the perfect thing to share in response to anyone who ever asks you again why they or their kids need to get vaccinated.
The short answer: it's not about you, it's about vulnerable people that can't get vaccinated, like newborn babies, or people going through chemo.
In the animation above, red is an invading pathogen, and you can see that the more people vaccinated against it in a community, the harder it is for it to spread and get a foothold in the first place.
But as soon as vaccination rates drop below around 90 percent, the pathogen runs rampant. Which is why it's so important for everyone who can get vaccinated to do so.
Herd immunity is basically the idea that if enough people are immunised against a disease, they'll create protection for everyone who isn't vaccinated.
Most importantly, they'll create protection for people who can't get vaccinated, such as very young babies and anyone immunocompromised, such as people with HIV, or those going through chemotherapy.
"You can see in the image, low levels of vaccination lead to everyone getting infected," explains theotheredmund.
"Medium levels slow down the progression of the illness, but they don't offer robust protection to the unvaccinated. But once you read a high enough level of vaccination, the disease gets effectively road-blocked. It can't spread fast enough because it encounters too many vaccinated individuals, and so the majority of the population (even the unvaccinated people) are protected."
But if everyone who's read something negative about vaccines online also decides not to get vaccinated and cash in on this herd immunity, then there won't be enough people immunised in a community to keep anyone safe.
This awesome animation was created using a simulation in R - an open-source programming language and software environment that was specially created for statistical computing and modelling - and put together with ImageMagick GIF stitching.
To be clear, these aren't real data being modelled. But theotheredumund calibrated the percentages based on the effectiveness of real herd immunity in diseases presented in this 1993 paper published in Epidemiologic Reviews.
"The project was simulated data, not real, to demonstrate the concept of herd immunity," explains theotheredmund on Reddit.
And we think they nailed it. Herd immunity is something that affects all of us, but that very few people understand - hopefully this animation changes that.
At the end of the day, wiping out disease in a population is a numbers game, and once those numbers drop low enough, all of us are in trouble.
After all, much of the reason we're all so blasé about diseases such as measles and polio today is because we don't actually see them in our communities anymore - thanks to herd immunity.
So, yes, it does matter that you get vaccinated.
A version of this article was first published in February 2017.