T Cell Responses to Varicella Zoster Virus (VZV) Vaccine SLVP020

Inclusion Criteria: * Otherwise healthy adult non-twins and twin pairs, 40-49 years of age (Cross-Sectional study) or 50 years of age and older (Vaccination study). If a volunteer cannot participate in the Vaccination study after screening, may be considered for Cross-Sectional study. * History of prior chicken pox infection or living within the continental U.S. for past 30 years * Willing to complete the informed consent process * Availability for follow-up for the planned duration of the study (Cross-Sectional study: 1 visit; Vaccination study: 5 visits within 4-5 weeks) * Acceptable medical history and vital signs Exclusion Criteria: * History of shingles within 5 years of enrollment * Prior vaccination with Zostavax vaccine for prevention of shingles * Vaccination Study only: History of severe allergic reactions to vaccine components, including gelatin and neomycin. * Vaccination Study only: Life-threatening reactions to previous vaccinations. * Vaccination Study only: Adults weighing less than 110 pounds. * Active systemic or serious concurrent illness, including febrile illness on the day of enrollment/vaccination * History of immunodeficiency disorder * Chronic HIV, Hepatitis B or Hepatitis C infection * Known or suspected impairment of immunologic function, including, but not limited to clinically significant liver disease, diabetes mellitus treated with insulin, moderate to severe renal disease or any other chronic disorder which, in the opinion of the investigator, might jeopardize volunteer safety or compliance with the protocol. * Recent or current use of immunosuppressive medication, or anticipated use during study period, including systemic corticosteroids (corticosteroid nasal sprays, inhaled steroids and topical steroids are permissible). * Blood pressure \>150 systolic or \> 95 diastolic at Visit 1 * History of chemotherapy treatment for cancer. * Malignancy, other than squamous cell or basal cell skin cancer (includes solid tumors such as breast cancer with recurrence in the past year and any hematologic cancer such as leukemia or lymphoma) which, in the opinion of the investigator, might jeopardize volunteer safety or compliance with the protocol. Prostate cancer may be acceptable if no metastases and not undergoing treatment with immunosuppressive medications. * Autoimmune disease, including rheumatoid arthritis, treated with immunosuppressive medication such as Plaquenil, methotrexate, prednisone, Enbrel, which in the opinion of the investigator, might jeopardize volunteer safety or compliance with the protocol (thyroid disease may be acceptable). * History of blood dyscrasias, renal disease, or hemoglobinopathies requiring regular medical follow up or hospitalization during the preceding year * Use of anti-coagulation medication such as Coumadin or Lovenox, or anti-platelet agents such as aspirin (except aspirin up to 325 mg. daily), Plavix or Aggrenox which may, in the opinion of the investigator, jeopardize volunteer safety or compliance with the protocol. * Receipt of blood or blood products within 6 months prior to enrollment and during the study period * Use of antiviral medications within 24 hrs. prior to enrollment, and for the Vaccination study, for the 14 days following study vaccination. * Inactivated vaccine within 14 days prior to enrollment and during study period(avoid non-study related immunization during the study period) * Live, attenuated vaccine within 60 days prior to enrollment and during study period (avoid non-study related immunization during the study period) * Pregnant or lactating woman, planning to become pregnant (pregnancy should be avoided for 3 months following administration of Zostavax vaccine). * Use of investigational agents within 30 days prior to enrollment and during study period * Donation of a unit of blood within 6 weeks prior to enrollment and during study period * Medical or psychiatric condition or occupational responsibilities that preclude subject compliance with the protocol * Any condition which, in the opinion of the investigator, might interfere with volunteer safety, study objectives or the ability of the participant to understand or comply with the study protocol.