Unlike medications, vaccines don't attack infections directly. Instead, you're basically being injected with a partial version of the disease, which allows your immune system to build up a resistance. The trouble with severe illnesses is that symptoms can progress too quickly for you to build up the antibodies to fight them. Vaccines train your immune system so that if it encounters the disease again, you'll be ready to fight it off.
Army doctors use vaccines to prevent troops from contracting common -- and some less common -- illnesses. Some vaccines are more general, like measles, mumps, rubella and tetanus, but if troops are headed somewhere with the risk of infectious diseases less common at home, doctors will use vaccines that most of us don't have to worry about. For example, if troops are going to South America or Africa, Army doctors will vaccinate them against yellow fever.
Vaccines can be incredibly helpful in preventing illness. Doctors do as much research as they can on location-specific diseases so they can prepare themselves and the rest of the medical staff for preventing and treating anything the troops might run across.
Knowing as much as they can about where the troops are going is also important. Next, we'll see how doctors educate themselves.