Most airlines use a system called Timatic, which has information for requirements to get into a country, as well as recommended (or required) vaccines. Delta has a page that relays that information for you, Visa & Passport Information

Before I went to Spain for a semester, I had to get a check-up. The nurse recommended that I get a Hepatitis A vaccine for food-borne illnesses, though I never did do that. In a country like Cambodia, I would give that a little more thought, though.