The purpose of this study is to determine the optimal timing of zoster vaccination to induce both higher cell-mediated immunity and humoral immunity in adult patients aged over 50 with history of zoster within 5 years.

Zoster vaccination is recommended by FDA for adults aged 60 years or older, and is approved for people aged 50 through 59 years old. For patients who had shingles, there is no specific length of time they must wait before receiving shingles vaccine. It is generally recommended that patients should wait for 6 to 12 months after recovery.

The investigators plan to make scientific recommendation for optimal timing of zoster vaccine after zoster illness by comparing immune response between two groups (vaccination at 6 months to 2 years after shingles vs. 2 to 5 years after shingles). Primary outcome is ELISPOT response at week 6 after vaccination. Secondary outcome is gpELISA titer at week 6 after vaccination.

All the patients will be asked if they have any contraindications for zoster vaccine by a physician before vaccination. And they will be monitored for any adverse reaction of the vaccination after 6 weeks (visiting the hospital).

Inclusion Criteria:

• Adults aged 50 years or older who have had shingles in 5 years
• Adults who did not receive zoster vaccination yet
• Adults who can understand and agreed with the informed consents.

Exclusion Criteria:

• Adults who have conditions which is contraindication for zoster vaccine
• Adults who had zoster vaccination already
• Adults who take immunosuppressants
• Human Immunodeficiency Virus (HIV) patients whose CD4 T cell counts below 500/mm3
• Adults with autoimmune disease who are anticipated to have a problem with immunogenicity for vaccine
• Adults who had organ transplantation and receive immunosuppressants
• Adults who are suspected to have active infectious disease
• Adults who are not eligible for zoster vaccination by investigator's assessment