A shingles shot contains a vaccine against herpes zoster, which causes a rash with blisters, according to WebMD. Herpes zoster, also known as shingles, occurs only in people who have had chickenpox at some point in their lives.
The varicella-zoster virus causes both chickenpox and shingles. After a case of chickenpox, the virus never fully leaves the body and can emerge from nerve tissues years later as shingles, explains WebMD.
The vaccine reduces the risk of developing shingles by about half and shortens the duration of the illness in people who do develop shingles, notes WebMD. The vaccine also helps stop the spread of the shingles virus, which is contagious. In a person who has never had chickenpox, the virus causes chickenpox rather than shingles. People over 60 are advised to get the shingles vaccine.