I just finished reading the book “Dissolving Illusions: Disease, Vaccines, and the Forgotten History” by Suzanne Humphries, MD and Roman Bystrianyk. If you haven’t read it I highly recommend you do so.
The book cover the past two hundred year history of the development of vaccines starting with Dr Jenner’s treatment using cowpox pus scraped from the belly of a cow, to treat patients for smallpox. Past epidemics are analysed in light of the introduction of the so-called vaccinations. The authors include the histories of many common diseases of a few centuries ago, and explain how and when the vaccines were introduced.
The diseases include smallpox, polio, diphtheria, whooping cough (pertussis) and measles. There is no doubt that these diseases were once very serious with very high death rates. But the evidence is that there were factors other than vaccines that primarily were the cause for their diminishing mortality as we approached the 20th century.