Answer:
These vaccines won't always last forever. Eventually you'll have to get them "renewed." Also, the viruses are always changing and advancing.
Step-by-step explanation:
Your body won't take certain vaccines and keep them forever! These vaccines weaken over time, so getting them repeatedly will help your body. Diseases such as the flu change with each "flu season" they mutate and grow stronger, so scientists develop new vaccines to hold them at bay. I hope this helps! :)