Shingrix In Recipients of Allogeneic Transplants

Inclusion Criteria:

* Allo-SCT recipients being age 18 - 79 years at time of allo-SCT.
* Written informed consent being obtained from the subject
* Two doses of RZV, separated by 2 to 6 months, administered at least 1 year after allo-SCT.
* Enrollment at \>/= 18 months after second dose of Shingrix.
* Female subjects of childbearing potential (FOCBP) enrolled in the study only if they:

  * have practiced adequate contraception for 30 days prior to vaccination with any dose of zoster vaccine and
  * have a negative pregnancy test on the day of each dose of zoster vaccine and
  * agree to continue adequate contraception during the vaccination period and for 2 months after receipt of the vaccine.
* Investigator belief that the participant will comply with the requirements of the protocol

Exclusion Criteria:

* Active Graft Versus Host Disease (aGVHD) at the time of enrollment and receipt of the third dose of RZV
* Having received ≥20 mg prednisone for more than 2 weeks (or equivalent) in the 8 weeks preceding enrollment.
* Receiving any significant immunosuppressive therapy other than for graft maintenance, in the opinion of the investigator.
* Having received a live attenuated vaccine within the last 4 weeks, or inactivated vaccine in the last 2 weeks, prior to enrollment.
* Having a history of HZ after the administration of the primary 2-dose RZV immunization regimen.
* Pregnancy or breastfeeding
* Receiving investigational drugs from 30 day before enrollment or planned during the study
* Inability of participants unable to comply with the study schedule in the opinion of the investigator