The other day on the news I heard that people who had measles as a child are considered to have lifelong immunity and don’t need to rush out and get a vaccine. I’ve interweb searched and it seems this is correct. I also found a very interesting article about why Herpes zoster is a bit different, from the Indiana University.
This idea from that link is interesting:
>>The ability to enter a latent state may have given varicella-zoster a survival advantage. Ancient hunter-gatherers would have lived in small groups where an outbreak of chickenpox could have infected the whole population. A credible theory proposed by Charles Grose, a pediatric infectious disease specialist at the University of Iowa, holds that, since chickenpox conveys lifelong immunity, the survivors could not be reinfected. And without new hosts, the virus would die out. However, by persisting for years in survivors in its latent state, varicella-zoster could reappear after a new generation of children was born. Since the shingles blisters are infectious, these children would get chickenpox and a new cycle would begin.<<