Copy and Paste but good explanation.
Revaccinating and boostering are often used interchangeably but technically are different. Clearing up the definitions will help everyone be on the same page. As a general rule, give vaccines three weeks apart, whether revaccinating or boostering.
Revaccination
A term used almost exclusively with MLV, revaccination is giving a vaccine more than once to try to reduce the total number of non-responders in a group. Not every animal mounts an immune response to every vaccination. To create a comfortably low proportion of non-responders in a group, give a MLV more than once.
Even in the best-managed herd, the percent responders in one round of vaccination are likely no more than 90%. This leaves 10% of the herd unprotected.
Revaccination with the same efficacy would then leave only 1% of the herd unprotected (10% first vac x 10% 2nd vac = 1% probability in the non-responder group both times).
Booster
This term refers to giving a vaccine more than once to create protective immunity that cannot be achieved with only one dose. With killed vaccines, the first dose presents the antigen to the immune system, resulting in a small immune response, but little to no memory. The second dose presents the antigen again, resulting in a more substantial response from the immune system. The second dose provides protective immunity through memory.