I thought mass vaccines were more recent, like 1950's polio etc. Before that, soldiers in WWI era. This was very interesting. I just did a search to find out more, and saw this (10th century):
"The first attempts to control smallpox occurred in the 10th century and used variolation (so called because small pox virus is Variola). In variolation (figure 2E), material (scabs) was obtained from the pustules of an infected person who did not die of the disease. This person, therefore, had a milder form of smallpox as a result of a naturally occurring variant. This material was used to infect another person who usually also got a milder disease."
http://pathmicro.med.sc.edu/lecture/vaccines.htm
I does sure make me wonder though, about poverty, outbreaks, designated vaccine groups. The HPV vaccine, for instance, became
mandatory for new immigrants to the USA (even though cervical cancer is rare and preventable with proper health care).
Maybe a person just has to go "Jehovah Witness' re contents of vaccine
{exercising spiritual rights}