If one were to research the history of vaccines what would immediately stand out is the fact that the diseases we vaccinate for were well on the way out before the introduction of the vaccines. Diseases can go through cycles which is why we don't have a bubonic plague epidemic even though there was no vaccine to get rid of it at its height. What makes the most difference anywhere is clean water, improved nutrition, transportation (for nutrient-rich food), education/medical care (knowing how to treat wounds as to avoid tetanus, for example). Also, since smallpox has been mentioned, I would suggest researching the topic thoroughly to find some very surprising facts.