I simple example of this is chicken pox (Varicella Zoster). A large proportion of adults have had it as kids. The immune system fights it off but virus particl

I simple example of this is chicken pox (Varicella Zoster). A large proportion of adults have had it as kids. The immune system fights it off but virus particles can still 'hide' from it and lay dormant inside pheripheral nerve tissue. A proof of this is 'shingles' in adults. i.e. a virus which probably infected the host +50 years ago and went dormant in their nerves finds the host immune system weak enough to come out again and start replicating.