7 facts about vaccines that show why they’re one of the most important inventions in human history

There’s a disease spreading right now, a disease that until recently, we’d considered eliminated — something that wasn’t spreading anymore except in places where it was imported from outside the country. But as the measles outbreak that started in Disneyland, and has spread to at least 14 states shows, measles is something we have to worry about again. And while in most people this virus causes a rash and a fever, in some it does does more. In one out of 20 children who catch it, it causes pneumonia. In a smaller number, one in 1,000, it can cause a sort of encephalatis, a tragic brain illness that can leave its victims deaf, blind, or brain damaged — if they survive at all And when you are talking about one of the most infectious viruses known to humankind, one where every infected person spreads the virus to an average of 15 people,...