1. There is no scientific study to determine whether vaccines have really prevented diseases. Rather disease graphs show vaccines have been introduced at the end of epidemics when the disease was already in its last stages. In case of Small Pox the vaccine actually caused a great spurt in the incidence of disease before public outcry led to its withdrawal.
2. There are no long-term studies on vaccine safety. Very short-term tests are carried out where the vaccinated subjects are checked against another group