Except that there are these things called airplanes. And boats. And trains. While it’s true that in many wealthier countries, vaccine-preventable diseases are rarer, travelers can unwittingly spread diseases they bring back from abroad to their community, which could spread quickly through unprotected populations.

And, not everyone can be vaccinated. Pregnant women and people with certain medical conditions rely on the rest of us being vaccinated and minimizing the chance they will be exposed to deadly diseases. Check out coverage of the recent measles outbreaks in New York City and the UK, and a recent whooping cough outbreak in California. There’s also this handy map of all the outbreaks of preventable diseases around the world.