[Jimbobeast]

Originally Posted by Stuart

My chemotherapy makes me more susceptible to shingles, so I take Acyclovir as well to prevent it.

Your chemotherapy makes you more susceptible to disseminated zoster - whole body shingles - because your immune system is compromised, also encephalitis, where the virus attacks the brain.
Viruses can do you a world of hurt.
Chronic acyclovir therapy is a good idea and may help prevent complications, but it does not replace the vaccine (if your immune system is OK).