"To repeat these vaccinations" means to have the same vaccines again, usually after a certain period of time has passed since the initial round of vaccinations. Full definition
The most common cause of these tumors is thought to be repeated vaccinations with vaccines. (2ndchance.info)
If you have decided to use these vaccines, you need to be aware that the immunity they provide will not last, and you will need to repeat the vaccinations at certain intervals. (caberfeidh.com)
So repeating vaccinations doesn't «boost» your dog's immunity. (yourpurebredpuppy.com)