A very impactful exercise is to wander through an old section (pre 1920) of a cemetery. Note the very high proportion of headstones for infants and young children. Recognize that prior to 1920 or so, a very high a proportion of children died from childhood diseases. Now, very few do! What brought about the change? The answer is VACCINATION! Scrolling down on the following site will give you a list of diseases, which led to severe sickness and many deaths. Clicking on any disease will give you further information including is cause, which is in most cases a VIRUS. We and our children are now protected from these diseases by vaccination, assuming we and our kids get vaccinated.
Diseases prevented by vaccination https://www.vaccinateyourfamily.org/vaccines-diseases/?
The following site provides a time line for the history of vaccination. Clicking on any point will give you further information. Note many sever outbreaks of disease. Pursue it as you wish.
The following short video describes Edward Jenner’s breakthrough work that proved the efficacy of vaccination in protecting against smallpox (late 18th early 19th century): https://www.youtube.com/watch?v=E_PKQ_M7AtU
Note that the cause of small pox was still not known at the time. In fact, the ideas of spontaneous generation and disease being caused by “spirits” of one sort or another still held sway.