Caesar's plan to keep all his vaccinations up to date will most likely help him avoid the polio virus. Vaccinations are specifically designed to prevent infectious diseases, and polio is one such disease that can be effectively prevented through vaccination.
Sickle cell disease and diabetes are genetic or chronic conditions that are not preventable through vaccination. AIDS, caused by the HIV virus, does not have a vaccine available to completely prevent infection, although there are preventive measures such as pre-exposure prophylaxis (PrEP).
So, keeping vaccinations up to date is primarily aimed at preventing diseases like polio.