A flare is defined as Ankylosing Spondylitis Disease Activity Score (ASDAS ≥2.1) at 2 consecutive visits, or ASDAS >3.5 at any visit during Period 2.

ASDAS is a composite index to assess disease activity in AS. The parameters used for the ASDAS (with high sensitivity C-reactive protein (CRP) as acute phase reactant) are total back pain, patient global, peripheral pain/swelling, duration of morning stiffness and CRP in mg/L. The ASDAScrp is calculated with the following equation: 0.121×total back pain+0.110×patient global+0.073×peripheral pain/swelling+0.058×duration of morning stiffness+0.579×Ln(CRP+1). (CRP is in mg/liter, the range of other variables is from 0(normal) to 10(very severe); Ln represents the natural logarithm). Data from five variables combined to yield a score (0.6361 to no defined upper limit), where higher the score worse the disease activity.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the nonresponder imputation (NRI) method.

A flare is defined as Ankylosing Spondylitis Disease Activity Score (ASDAS ≥2.1) at 2 consecutive visits, or ASDAS >3.5 at any visit during Period 2.

ASDAS is a composite index to assess disease activity in AS. The parameters used for the ASDAS (with high sensitivity C-reactive protein (CRP) as acute phase reactant) are total back pain, patient global, peripheral pain/swelling, duration of morning stiffness and CRP in mg/L. The ASDAScrp is calculated with the following equation: 0.121×total back pain+0.110×patient global+0.073×peripheral pain/swelling+0.058×duration of morning stiffness+0.579×Ln(CRP+1). (CRP is in mg/liter, the range of other variables is from 0(normal) to 10(very severe); Ln represents the natural logarithm). Data from five variables combined to yield a score (0.6361 to no defined upper limit), where higher the score worse the disease activity.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the nonresponder imputation (NRI) method.

The mSASSS is a four-point scoring system for lateral radiographs of the lumbar and cervical spine and has been shown to reliably track disease progression over time, where: 0 = normal; 1 = sclerosis, squaring or erosion; 2 = syndesmophyte; 3 = bony bridge.

By the scoring system of mSASSS of the spinal x-rays, a total of 24 sites were scored on the lateral cervical and lumbar spine: the anterior corners of the vertebrae from lower border of C2 to upper border T1 (inclusive), and from lower border of T12 to upper border of S1 (inclusive). Each corner was scored from 0 to 3, resulting in a range from 0 [no change] to 72 [progression].

Ixekizumab structure population who have been treated with ixekizumab for at least 24 months.

ASAS20 response is defined as a ≥20% improvement and an absolute improvement from baseline of ≥1 units (range 0 to 10) in ≥3 of 4 domains, and no worsening of ≥20% and ≥1 unit (range 0 to 10) in the remaining domain.

The following ASAS domains are used:

Patient Global: How active was your spondylitis on average during the last week? score ranges 0 (not active) to 10 (very active).

Spinal Pain: How much Pain of your spine due to Ankylosing spondylitis? score ranges 0 (no pain) to 10 (severe pain).

Bath Ankylosing Spondylitis Functional Index (BASFI): Participant asked to rate the difficulty associated with 10 individual basic functional activities. Participant response was captured using Numeric Rating Scale (NRS) (range 0 to 10) with a higher score indicating worse function.

Inflammation based on mean of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) Q5 & Q6 (mean of intensity & duration of stiffness): Score ranges from "0" (none) and "10" (very severe).

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the nonresponder imputation (NRI) method.

ASAS40 is defined as a ≥40% improvement and an absolute improvement from baseline of ≥2 units (range of 0 to 10) in at least 3 of the following 4 domains without any worsening in the remaining domain. The following ASAS domains are used:

Patient Global: How active was your spondylitis on average during the last week? score ranges 0 (not active) to 10 (very active).

Spinal Pain: How much Pain of your spine due to Ankylosing spondylitis? score ranges 0 (no pain) to 10 (severe pain).

Bath Ankylosing Spondylitis Functional Index (BASFI): Participant asked to rate the difficulty associated with 10 individual basic functional activities. Participant response was captured using Numeric Rating Scale (NRS) (range 0 to 10) with a higher score indicating worse function.

Inflammation based on mean of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) Q5 & Q6 (mean of intensity & duration of stiffness): Score ranges from "0" (none) and "10" (very severe).

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the nonresponder imputation (NRI) method.

ASDAS is a composite index to assess disease activity in AS. The parameters used for the ASDAS (with CRP as acute phase reactant) are total back pain, patient global, peripheral pain/swelling, duration of morning stiffness and CRP in mg/L. The ASDAScrp is calculated with the following equation: 0.121×total back pain+0.110×patient global+0.073×peripheral pain/swelling+0.058×duration of morning stiffness

+0.579×Ln(CRP+1). (CRP is in mg/liter, the range of other variables is from 0(normal) to 10(very severe); Ln represents the natural logarithm). Data from five variables combined to yield a score (0.6361 to no defined upper limit), where higher the score worse the disease activity.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the nonresponder imputation (NRI) method.

ASDAS is a composite index to assess disease activity in AS. The parameters used for the ASDAS (with CRP as acute phase reactant) are total back pain, patient global, peripheral pain/swelling, duration of morning stiffness and CRP in mg/L. The ASDAScrp is calculated with the following equation: 0.121×total back pain+0.110×patient global+0.073×peripheral pain/swelling+0.058×duration of morning stiffness+0.579×Ln(CRP+1). (CRP is in mg/liter, the range of other variables is from 0(normal) to 10(very severe); Ln represents the natural logarithm). Data from five variables combined to yield a score (0.6361 to no defined upper limit), where higher the score worse the disease activity.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the nonresponder imputation (NRI) method.

Patient Global: How active was your spondylitis on average during the last week? score ranges 0 (not active) to 10 (very active).

Spinal Pain: How much Pain of your spine due to Ankylosing spondylitis? score ranges 0 (no pain) to 10 (severe pain).

Bath Ankylosing Spondylitis Functional Index (BASFI): Participant asked to rate the difficulty associated with 10 individual basic functional activities. Participant response was captured using Numeric Rating Scale (NRS) (range 0 to 10) with a higher score indicating worse function. Inflammation based on Q5 & Q6 mean of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) (mean of intensity & duration of stiffness): Score ranges from "0" (none) and "10" (very severe). LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The BASDAI is a participant-reported assessment consisting of 6 questions that relate to 5 major symptoms relevant to radiographic axial spondyloarthritis (rad-axSpA): 1) Fatigue, 2) Spinal pain, 3) Peripheral arthritis, 4) Enthesitis, 5) Intensity, and 6) Duration of morning stiffness. Participants need to score each item with a score from 0 to 10 (NRS). Total score is obtained from the average of symptom scores ranging 0 (no problem) to 10 (worst problem), with a higher score indicating more severe AS symptom. BASDAI50 represents an improvement of ≥50% of the BASDAI score from baseline.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the nonresponder imputation (NRI) method.

High sensitivity CRP is the measure of acute phase reactant. It was measured with a high sensitivity assay at the central laboratory to help assess the effect of ixekizumab on disease activity. High sensitivity CRP is a sensitive laboratory assay for serum levels of C-Reactive Protein, which is a biomarker of inflammation. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

BASMI is a combined index comprising of the following 5 clinical measurements of spinal mobility in participants with radiographic axial spondyloarthritis (rad-axSpA).

1. Lateral Spinal Flexion
2. Tragus-to-wall distance
3. Lumbar Flexion (modified Schober)
4. Maximal intermalleolar distance and
5. Cervical rotation.

The BASMI linear result is the average of the 5 assessments and ranges from 0 to 10. The higher the BASMI score the more severe the participant's limitation of movement due to their AS. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

Chest expansion is the difference, in centimeter (cm), between the circumference of the chest in maximal inspiration and maximal expiration. While participants have their hands resting on or behind the head, the assessor will measure the chest encircled length by centimeter (cm) at the fourth intercostal level anteriorly. Two tries were recorded. The better measurement (larger difference) of 2 tries (in centimeters) was used for analyses. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The participant is to make a maximum effort to touch the head against the wall when standing with heels and back against the wall (occiput). Then the distance from occiput to wall is measured. Two tries will be recorded. The better (smaller) measurement of 2 tries (in centimeters) will be used for analyses. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The MASES is an index used to measure the severity of enthesitis. The MASES assesses 13 sites for enthesitis using a score of "0" for no activity or "1" for activity. Sites assessed include costochondral 1 (right/left), costochondral 7 (right/left), spinal iliaca anterior superior (right/left), crista iliaca (right/left), spina iliaca posterior (right/left), processus spinosus L5, and Achilles tendon proximal insertion (right/left). The MASES is the sum of all site scores (range 0 to 13); higher scores indicate more severe enthesitis. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B), and with Baseline MASES score >0. Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The SPARCC enthesitis is an index used to measure the severity of enthesitis. The SPARCC assesses 16 sites for enthesitis using a score of "0" for no activity or "1" for activity. Sites assessed include Medial epicondyle (left/right [L/R]), Lateral epicondyle (L/R), Supraspinatus insertion into greater tuberosity of humerus (L/R), Greater trochanter (L/R), Quadriceps insertion into superior border of patella (L/R), Patellar ligament insertion into inferior pole of patella or tibial tubercle (L/R), Achilles tendon insertion into calcaneum (L/R), and Plantar fascia insertion into calcaneum (L/R). The SPARCC is the sum of all site scores (range 0 to 16). Higher scores indicate more severe enthesitis. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B), and with baseline SPARCC score >0. Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The number of tender and painful joints was determined by examination of 46 joints (23 joints on each side of the body). The 46 joints were assessed and classified as tender or not tender. Sum of all joints checked to be tender/painful divided by number of evaluable joints which was multiplied by 46 to obtain TJC score. The scores ranges from 0 (no tender/painful joints) to 46 (all joints tender/painful). LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B), and with baseline TJC >0. Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The number of swollen joints was determined by examination of 44 joints (22 joints on each side of the body). The 44 joints were assessed and classified as swollen or not swollen. Sum of all joints checked to be swollen divided by number of evaluable joints which was multiplied by 44 to obtain SJC score. The SJC score ranges from 0 (no swollen joints) to 44 (all joints swollen). LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B), and with baseline SJC >0. Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

Anterior uveitis is an inflammation of the middle layer of the eye. which includes the iris (colored part of the eye) and the adjacent tissue, known as the ciliary body.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B), and regardless of history of anterior uveitis.

The fatigue severity NRS is a participant administered single-item 11-point horizontal scale anchored at 0 and 10, with 0 representing "no fatigue" and 10 representing "as bad as you can imagine". Participants rate their fatigue (feeling tired or worn out) by circling the 1 number that describes their worst level of fatigue during the previous 24 hours. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The 16-item QIDS-SR16 version is a widely used validated scale designed to assess the severity of depressive symptoms. The participant was asked to rate the severity and frequency of specific symptoms present over the last 7 days. The QIDS-SR16 total scores range from 0 to 27, where higher scores indicate higher severity of symptoms. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The SF-36 is a 36-item participant administered measure designed to be a short, multipurpose assessment of health in the areas of physical functioning, role - physical, role - emotional, bodily pain, vitality, social functioning, mental health, and general health. The 2 overarching domains of mental well- being and physical well-being are captured by the Mental Component Summary and Physical Component Summary scores. T-scores are used for analysis. The summary scores range from 0 to 100, with higher scores indicating better levels of function and/or better health. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The SF-36 is a 36-item participant administered measure designed to be a short, multipurpose assessment of health in the areas of physical functioning, role - physical, role - emotional, bodily pain, vitality, social functioning, mental health, and general health. The 2 overarching domains of mental well- being and physical well-being are captured by the Mental Component Summary and Physical Component Summary scores. T-scores are used for analysis. The summary scores range from 0 to 100, with higher scores indicating better levels of function and/or better health. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The ASAS Health Index (ASAS HI) is a disease specific health-index instrument designed to assess the impact of interventions for SpA, including axSpA. The 17 item instrument has scores ranging from 0 (good Health) to 17 (poor Health). Each item consists of 1 question that the participant needs to respond to with either "I agree" (score 1) or "I do not agree (score 0)." A score of "1" is given where the item is affirmed, indicating adverse health. All item scores are summed to give a total score or index. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The European Quality of Life - 5 Dimensions 5 Level (EQ-5D-5L) is a standardized measure of health status used to provide a simple, generic measure of health for clinical and economic appraisal. The EQ-5D-5L consists of 2 components: a descriptive system of the respondent's health and a rating of his/her current health state using a 0- to 100-mm visual analog scale (VAS). The descriptive system comprises the following 5 dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. Each dimension has 5 levels: no problems, slight problems, moderate problems, severe problems, and extreme problems. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The WPAI-SpA consists of 6 questions to determine employment status, hours missed from work because of SpA, hours missed from work for other reasons, hours actually worked, the degree to which SpA affected work productivity while at work, and the degree to which SpA affected activities outside of work. The WPAI-SpA has been validated in the rad-axSpA participant population. Four scores are derived: percentage of absenteeism, percentage of presenteeism (reduced productivity while at work), an overall work impairment score that combines absenteeism and presenteeism, and percentage of impairment in activities performed outside of work. The computed percentage range for each sub-scale was from 0-100, with higher scores indicating greater impairment and less productivity. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

The Jenkins Sleep Evaluation Questionnaire (JSEQ) is a 4 item scale designed to estimate sleep problems in clinical research. The JSEQ assesses the frequency of sleep disturbance in 4 categories: 1) trouble falling asleep, 2) waking up several times during the night, 3) having trouble staying asleep (including waking up far too early), and 4) waking up after the usual amount of sleep feeling tired and worn out. Participants report the numbers of days they experience each of these problems in the past month on a 6 point Likert Scale ranging from 0 = "no days" to 5 = "22-30 days. The total JSEQ score ranges from 0 to 20, with higher scores indicating greater sleep disturbance. LS mean was determined by ANCOVA with treatment, geographic region, originating study, baseline value and Week 24 value as fixed factors.

Participants who achieved a state of sustained remission and were randomized to 40-week double-blind placebo controlled RWR period (Group B). Missing data was imputed using the modified baseline observation carried forward (mBOCF) method.

Percentage of participants with no new syndesmophyte formation was measured using the average of 2 selected readers of 3 readers.

Ixekizumab structure population who have been treated with Ixekizumab for at least 24 months

A treatment emergent - antidrug antibody (TE-ADA) positive participant is defined as: a) a participant with a >= 4-fold increase over a positive baseline antibody titer; or b) for a negative baseline titer, a participant with an increase from the baseline to a level of >= 1:10. Percentage was calculated based on the number of evaluable participants and was calculated by number of participants with treatment-emergent positive anti-ixekizumab antibodies / number of evaluable participants * 100%.

All randomized participants from Group B, who received at least one dose of study drug.