Short answers, pulled from the story.
Edward Jenner created the first vaccine and developed the concept itself. In 1796 he scratched cowpox pus from a milkmaid's hand into the arm of an 8-year-old boy, James Phipps, then showed the boy did not catch smallpox when variolated six weeks later.
The words vaccine and vaccination derive from Variolae vaccinae, meaning smallpox of the cow, the term Edward Jenner devised to denote cowpox. In 1881 Louis Pasteur proposed extending the terms to cover the new protective inoculations then being developed.
The measles vaccine is estimated to prevent a million deaths every year. In 1958 the United States recorded 763,094 measles cases and 552 deaths, but after new vaccines were introduced cases fell to fewer than 150 per year with a median of 56.
Vaccine types include live attenuated, inactivated, toxoid, subunit, conjugate, and outer membrane vesicle vaccines, plus genetic vaccines such as viral vector, RNA, and DNA vaccines. Each represents a different strategy to reduce illness risk while still inducing an immune response.
An mRNA vaccine is composed of the nucleic acid RNA packaged within a vector such as lipid nanoparticles, so cells produce a pathogen protein that triggers an immune response. The Pfizer-BioNTech and Moderna mRNA vaccines were deployed against COVID-19, and BNT162b2 was developed in 2020 with the help of Operation Warp Speed.
The World Health Organization characterized vaccine hesitancy as one of the top ten global health threats in 2019 because it often results in disease outbreaks and deaths from vaccine-preventable diseases. This persists despite overwhelming scientific consensus that vaccines are generally safe and effective.