I was reading about this several years ago.
Vaccines were created largely in response to the fact there were too many doctors and too many healthy, happy people in the United States. There wasn't enough business to keep the doctors busy when the medical schools were generating a glut of them.
The single best way to put people into the revolving door of medicine, it was found, was to "vaccinate" them frequently with as many cultures of disease viruses as could be dreamed up or fabricated. Once you got a rube sufficiently vaccinated you were guaranteed a never-ending supply of repeat business because of the side effects and the general debilitating effect that they had on a person's entire physiology.
So to put events in correct order:
1. Improved nutrition and sanitation was really hurting the medical industry.
2. They responded by initiating programs to vaccinate people, often for "free."
3. They claimed vaccinations were responsible for the reduced mortality and better health in the United States that was clearly present long before they began vaccinating people.
4. Doctors began to experience record levels of customers pouring into their system from the side effects of vaccines.
You couldn't make this stuff up. This is the way it really happened.