This is an ancillary study to a randomized controlled trial of high dose vitamin D in older long-term care residents (NCT01102374). In this study, a subset of trial subjects will receive the zoster vaccine and the investigators will determine the immunological response to the vaccine in this older, frail population, as well as the association between vitamin D and immunological outcomes.

Objectives

1. To determine the increase in Varicella-zoster virus (VZV)-specific cell-mediated immune response from pre-zoster vaccination to 3 weeks post-vaccination in nursing home residents after 4 months of high dose vs. standard dose vitamin D3 supplementation.
2. In the same participants as Aim 1, to measure the association between pre-zoster vaccination 25-hydroxyvitamin D [25(OH)D] levels and the increase in VZV-specific cell-mediated immune response from pre- vaccination to 3 weeks post-vaccination.
3. Characterize the phenotypic and functional VZV-specific T cell responses to Zostavax, including memory, effector, Th1/Th2, and homing receptor-bearing T cells in the high compared to low ELISPOT responders.

Hypotheses

1. At baseline, higher serum 25(OH)D levels will be associated with higher levels of VZV-specific cell-mediated immunity (cross-sectional).
2. At baseline, higher serum 25(OH)D levels, independent of vitamin D supplementation dose, will be associated with greater increases in VZV-specific cell-mediated immune responses to Zostavax, as measured by the interferon (IFN)-γ ELISPOT assay.
3. Compared to standard dose, high dose vitamin D3 supplementation will enhance VZV-specific cell-mediated immune response to vaccination independent of baseline serum 25(OH)D levels.

Inclusion Criteria:

1. Aged ≥ 60 years;
2. Residing in a long-term care facility;
3. Have not yet received VZV vaccine

Exclusion Criteria:

1. terminal illness (expected survival <6 months);
2. anticipated discharge within 12 months;
3. unable to take whole or crushed tablets;
4. active cancer, except squamous/basal cell carcinoma;
5. severe malnutrition (body mass index <18 kg/m2);
6. current immunosuppressive medications (including corticosteroids);
7. renal failure (eGFR<15 mL/min/1.73m2);
8. currently taking >800 IU/d vitamin D supplementation;
9. history (or strong family history) of kidney stones;
10. history of sarcoidosis or other granulomatous disorders associated with hypercalcemia;
11. elevated baseline hypercalcemia (albumin-adjusted serum calcium >10.5 mg/dL);
12. serum 25 (OH)D level ≥40 ngl/ml at baseline;
13. inability to provide informed consent and no available healthcare proxy;
14. inability of participant or proxy to speak/understand English.
15. previous receipt of the Zostavax (anticipate <10% of trial;
16. known allergy to gelatin, neomycin, or any other component of the vaccine.