Because the effectiveness of the shingles vaccine appears to decrease over time it is suggested that the vaccine be given once… after age 60.
This is based on the Long-term Persistence Study done by the pharmaceutical company Merck. The study found a gradual decrease in vaccine effectiveness 6-7 years after vaccination.
Other interested study numbers were that vaccinating with shingles vaccine in patients aged 50-59 would prevent 20,000 shingles cases annually. But, vaccinating in the patients 60s would prevent 26,000 cases and in the 70s, 21,000 cases.
I agree with their rationale and will suggest shingles vaccine after age 60.