This is from the CDC's site:

In a clinical trial involving thousands of adults 60 years old or older, Zostavax reduced the risk of shingles by about half (51%) and the risk of post-herpetic neuralgia by 67%. While the vaccine was most effective in people 60-69 years old it also provided some protection for older groups.

Research suggests that the shingles vaccine is effective for at least six years, but may last much longer. Ongoing studies are being conducted to determine exactly how long the vaccine protects against shingles.
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Not very good stats in my opinion.