Final answer:
Vaccination is a medical advance that has decreased the spread of communicable diseases by stimulating the immune system to produce antibodies and provide immunity against pathogens.
Step-by-step explanation:
An advance in medicine that has led to a decrease in the spread of communicable diseases is vaccination. Vaccinations work by introducing a weakened or inactive form of the pathogen into the body, stimulating the immune system to produce antibodies without causing the disease itself. These antibodies provide immunity, so if the person is exposed to the actual pathogen, their body can quickly recognize and fight it off, preventing the spread of disease.