There’s tons of suspicion out there when it comes to vaccines, from worries that they will infect recipients with the very diseases they are meant to inoculate against, to concerns that they cause autism in children. But there’s one vaccine that all medical workers agree on as a necessity for certain high-risk groups: the flu shot. In any given year, your chances of catching this nasty bug range from 1 in 20 to 1 in 5. And it lands more than 200,000 people in hospital bed—and kills about 36,000 folks. Here’s what you need to know to protect yourself.