2 possible ways
Over 90% of adults who don't think they had chickenpox
have blood evidence they did.
These have the same frequency of shingles as those who remember. Those who received the vaccine starting in the 1990's can also get shingles, although the frequency has been lower than those with wild chickenpox. Otherwise you cannot get shingles. You never want to get chickenpox as an adult. It can be deadly.