A suspected case of HZ is defined as a new unilateral rash accompanied by pain (broadly defined to include allodynia, pruritus or other sensations) and no alternative diagnosis. A suspected case of HZ was confirmed by an algorithm that included Polymerase Chain Reaction (PCR) and the HZ Ascertainment Committee (HZAC) determination. The incidence rate (n/T) of confirmed HZ cases, expressed in terms of 1000 person-years rate, was calculated as the number of participants reporting at least one confirmed HZ case (n) in a group, over the sum of follow-up period expressed in years (T) in the same group, and multiplied by 1000.

The analysis was performed on the modified Exposed Set (mES), which excluded participants from the Exposed Set who were not administered 2 doses of the study treatment per protocol, or who developed a confirmed case of HZ prior to 30 days after the second vaccination.

A suspected case of HZ is defined as a new unilateral rash accompanied by pain (broadly defined to include allodynia, pruritus or other sensations) and no alternative diagnosis. A suspected case of HZ was confirmed by an algorithm that included PCR and the HZAC determination. The incidence rate (n/T) of confirmed HZ cases, expressed in terms of 1000 person-years rate, was calculated as the number of participants reporting at least one confirmed HZ case (n) in a group, over the sum of follow-up period expressed in years (T) in the same group, and multiplied by 1000.

The analysis was performed on the Exposed Set, which included all participants with at least one dose of the study treatment administered.

Assessed solicited administration site events included erythema, pain, pruritus and swelling at the injection site. Any = occurrence of the event regardless of intensity grade. Grade 3 pain = significant pain at rest, which prevented normal, everyday activities. Grade 3 erythema, swelling = erythema, swelling with a surface diameter greater than (>) 100 millimeters (mm). Grade 3 pruritus = itchy sensation that prevented normal, everyday activities.

The analysis was performed on the Exposed Set, which included all participants with at least one dose of the study treatment administered and with the solicited administration site events diary card data available after the corresponding vaccination for the specified duration.

Duration is the number of days in which a participant experienced the symptom within the 7-day solicited follow-up period. Assessed solicited administration site events included erythema, pain, pruritus and swelling at the injection site.

The analysis was performed on the Exposed Set, which included all participants with at least one dose of the study treatment administered, with solicited diary data available after the corresponding vaccination and who experienced the specified solicited administration site event within 7 days following the respective study treatment dose. Here, 'number analyzed' = participants with available data for each specified category.

Assessed solicited systemic events included fatigue, fever (defined as axillary temperature greater than or equal to (>=) 38.0°C/100.4°F), gastrointestinal symptoms, headache, malaise, myalgia, and shivering. Any = occurrence of the event regardless of intensity grade or relation to the study vaccination. Grade 3 = event that prevented normal, everyday activities. Grade 3 fever = axillary temperature higher than (>) 39.0°C/102.2°F. Related = event assessed by the investigator as related to the study vaccination.

The analysis was performed on the Exposed Set, which included all participants with at least one dose of the study treatment administered and with the solicited systemic events diary card data available after the corresponding vaccination for the specified duration.

Duration is the number of days in which a participant experienced the symptom within the 7-day solicited follow-up period. Assessed solicited systemic events included fatigue, fever (defined as axillary temperature >=38.0°C/100.4°F), gastrointestinal symptoms, headache, malaise, myalgia and shivering.

The analysis was performed on the Exposed Set, which included all participants with at least one dose of the study treatment administered, with solicited diary data available after the corresponding vaccination and who experienced the specified solicited systemic event within 7 days following the respective study treatment dose. Here, 'number analyzed' = participants with available data for each specified category.

An unsolicited AE is defined as any AE reported in addition to those solicited during the clinical study. Also, any 'solicited' symptom with onset outside the specified period of follow-up for solicited symptoms was reported as an unsolicited adverse event. Any = occurrence the event regardless of intensity grade or relation to the study vaccination. Grade 3 = event that prevented normal, everyday activities. Related = event assessed by the investigator as related to the study vaccination.

The analysis was performed on the Exposed Set, which included all participants with at least one dose of the study treatment administered and for whom unsolicited AEs data were available for the specified duration after each vaccination.

An SAE is defined as any untoward medical occurrence that resulted in death, was life-threatening, required hospitalization or prolongation of existing hospitalization, resulted in disability/incapacity or was a congenital anomaly/birth defect in the offspring of a study participant. Any = occurrence of the SAE regardless of intensity grade or relation to the study vaccination. Related = SAE assessed by the investigator as related to the study vaccination.

The analysis was performed on the Exposed Set, which included all participants with at least one dose of the study treatment administered and for whom SAEs data were available for the specified duration.

pIMDs are defined as a subset of AEs that include autoimmune diseases and other inflammatory and/or neurologic disorders of interest which may or may not have an autoimmune aetiology. Any = occurrence of the pIMD regardless of intensity grade or relation to the study vaccination. Related = pIMD assessed by the investigator as related to the study vaccination.

The analysis was performed on the Exposed Set, which included all participants with at least one dose of the study treatment administered and for whom pIMDs data were available for the specified duration.

An SAE is defined as any untoward medical occurrence that resulted in death, was life-threatening, required hospitalization or prolongation of existing hospitalization, resulted in disability/incapacity or was a congenital anomaly/birth defect in the offspring of a study participant. Any = occurrence of the SAE regardless of intensity grade or relation to the study vaccination. Related = SAE assessed by the investigator as related to the study vaccination.

The analysis was performed on the Exposed Set, which included all participants with at least one dose of the study treatment administered and for whom SAEs data were available for the specified duration.

pIMDs are defined as a subset of AEs that include autoimmune diseases and other inflammatory and/or neurologic disorders of interest which may or may not have an autoimmune aetiology. Any = occurrence of the pIMD regardless of intensity grade or relation to the study vaccination. Related = pIMD assessed by the investigator as related to the study vaccination.

The analysis was performed on the Exposed Set, which included all participants with at least one dose of the study treatment administered and for whom pIMDs data were available for the specified duration.

An SAE is defined as any untoward medical occurrence that resulted in death, was life-threatening, required hospitalization or prolongation of existing hospitalization, resulted in disability/incapacity or was a congenital anomaly/birth defect in the offspring of a study participant. Any SAEs related to the investigational vaccine or related to study participation or to a GSK concomitant medication/vaccine as assessed by the investigator are reported.

The analysis was performed on the Exposed Set, which included all participants with at least one dose of the study treatment administered and for whom SAEs related to investigational vaccine/study participation/GSK concomitant medication/vaccine data were available for the specified duration.

Vaccine response for anti-gE antibodies is defined as:

• For initially seronegative participants, anti-gE antibody concentration at post-vaccination >= 4-fold the cut-off value for anti-gE [97 international units per liter (IU/L)].
• For initially seropositive participants, anti-gE antibody concentration at post-vaccination >= 4-fold the pre-vaccination anti-gE antibody concentration.

The analysis was performed on the Adapted Per Protocol Set for immunogenicity, which included all evaluable participants from the Exposed Set who met all eligibility criteria, received 2 doses of the HZ/su vaccine/placebo according to their random assignment, did not receive forbidden medications, had no intercurrent medical condition complied with the vaccination and blood sample schedules and for whom results were available for the specified analysis at the specified time points.

Anti-gE antibody concentrations were determined by ELISA and expressed as GMCs in IU/L.

The analysis was performed on the Adapted Per Protocol Set for immunogenicity, which included all evaluable participants from the Exposed Set who met all eligibility criteria, received 2 doses of the HZ/su vaccine/placebo according to their random assignment, did not receive forbidden medications, had no intercurrent medical condition complied with the vaccination and blood sample schedules and for whom results were available for the specified analysis at the specified time points.