Here's a peculiar one.
"Vaccine: A preparation that is used
to stimulate the body’s immune response against diseases. Vaccines are usually administered through needle injections, but some can be administered by mouth or sprayed into the nose." - current CDC definition of 'Vaccine'
"Vaccine: A product that
stimulates a person’s immune system to produce immunity to a specific disease, protecting the person from that disease. Vaccines are usually administered through needle injections, but can also be administered by mouth or sprayed into the nose." - CDC definition of 'Vaccine' BEFORE 9/1/2021
Interesting choice of words/change.