A Study to Evaluate the Efficacy and Safety of Different Doses of Bimekizumab in Subjects With Active Ankylosing Spondylitis

The ASAS40 response was defined as relative improvements of at least 40% and absolute improvement of at least 2 units on a 0 to 10 Numeric Rating Scale (NRS), where 0 is not active and 10 is very active in at least 3 of the 4 domains: Patient's Global Assessment of Disease Activity (PGADA), Pain assessment (total spinal pain NRS score), Function (Bath Ankylosing Spondylitis Functional Index (BASFI)), Inflammation (mean of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) questions 5 and 6 concerning morning stiffness intensity and duration) and no worsening at all in the remaining domain. Note: Participants with missing data or who discontinue study treatment prior to Week 12 were counted as non-responders.

Time frame: Week 12

Population: The FAS consisted of all randomized participants who received at least 1 dose of investigational medicinal product (IMP) and had a valid measurement of the primary efficacy variable at Baseline.

The ASDAS was calculated as the sum of the following components: 0.121 x Back pain (BASDAI question 2 result) 0.058 x Duration of morning stiffness (BASDAI question 6 result) 0.110 x PGADA 0.073 x Peripheral pain/swelling (BASDAI question 3 result) 0.579 x (natural logarithm of the (hs-CRP \[mg/L\] + 1)) Back pain, PGADA, duration of morning stiffness, peripheral pain/swelling and fatigue are all assessed on a numerical scale (0 to 10 units). The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening. There is a minimum score of 0.636 for the total ASDAS score, but no defined upper score since CRP does not have a set upper limit. If one component for the ASDAS-CRP was missing at a given visit, that component was imputed by carrying the last observation forward, and the ASDAS-CRP was calculated accordingly. If the hs-CRP value was below 2 mg/L, then it was imputed as the constant value of 2 mg/L.

Time frame: From Baseline to Week 12

Population: The FAS consisted of all randomized participants who received at least 1 dose of IMP and had a valid measurement of the primary efficacy variable at Baseline.

The BASDAI is a validated self-reported instrument, which consists of six 10-unit horizontal Numeric Rating Scales (NRS) to measure severity of fatigue, spinal and peripheral joint pain and swelling, enthesitis, and morning stiffness (both severity and duration, respectively) over the last week. The final BASDAI score ranges from 0 to 10, with lower scores indicating lower disease activity. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening. Note: Missing data was imputed using multiple imputation based on the Markov-Chain Monte Carlo method for the intermittent missing data, followed by monotone regression for the monotone missing data assuming missing at random.

Time frame: From Baseline to Week 12

Population: The FAS consisted of all randomized participants who received at least 1 dose of IMP and had a valid measurement of the primary efficacy variable at Baseline.

The BASFI is a validated disease-specific instrument for assessing physical function. The BASFI comprises 10 items relating to the past week. The BASFI is the mean of the 10 scores such that the total score ranges from 0 (Easy) to 10 (Impossible), with lower scores indicating better physical function. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening. Note: Missing data was imputed using multiple imputation based on the Markov-Chain Monte Carlo method for the intermittent missing data, followed by monotone regression for the monotone missing data assuming missing at random.

Time frame: From Baseline to Week 12

Population: The FAS consisted of all randomized participants who received at least 1 dose of IMP and had a valid measurement of the primary efficacy variable at Baseline.

An AE is any untoward medical occurrence in a participant or trial subject that is administered a drug or biologic (medicinal product) or that is using a medical device. The event does not necessarily have a causal relationship with that treatment or usage. The results of this Secondary Outcome Measure were summarized from the adverse event pages of the Case Report Forms.

Time frame: From Screening until Safety Follow-Up Visit (up to Week 77)

Population: The SS consisted of all randomized participants who received at least 1 dose of IMP.

An adverse event (AE) is any untoward medical occurrence in a patient or clinical investigation participant administered a pharmaceutical product that does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign, symptom, or disease temporally associated with the use of a medicinal (investigational) product, whether or not related to the medicinal (investigational) product.

Time frame: From Screening until Safety Follow-Up Visit (up to Week 77)

Population: The SS consisted of all randomized participants who received at least 1 dose of IMP.

A serious adverse event (SAE) is any untoward medical occurrence that at any dose: * Results in death * Is life-threatening * Requires in patient hospitalisation or prolongation of existing hospitalisation * Is a congenital anomaly or birth defect * Is an infection that requires treatment parenteral antibiotics * Other important medical events which based on medical or scientific judgement may jeopardise the patients, or may require medical or surgical intervention to prevent any of the above.

Time frame: From Screening until Safety Follow-Up Visit (up to Week 77)

Population: The SS consisted of all randomized participants who received at least 1 dose of IMP.

The ASAS20 response was defined as an improvement of at least 20% and absolute improvement of at least 1 unit on a 0 to 10 NRS, where 0 is not active and 10 is very active in at least 3 of the 4 domains: PGADA, Pain assessment (total spinal pain NRS scores), Function (BASFI), Inflammation (mean of BASDAI questions 5 and 6 concerning morning stiffness intensity and duration) and absence of deterioration in the potential remaining domain \[deterioration was defined as a relative worsening of at least 20% and an absolute worsening of at least 1 unit\]. Note: Participants with missing data or who discontinue study treatment prior to Week 12 were counted as non-responders.

Time frame: Week 12

Population: The FAS consisted of all randomized participants who received at least 1 dose of IMP and had a valid measurement of the primary efficacy variable at Baseline.

The ASAS 5/6 response was defined as at least 20% improvement in at least 5 of the 6 domains: PGADA, Pain assessment (total spinal pain NRS scores), Function (BASFI), Inflammation (mean of BASDAI questions 5 and 6 concerning morning stiffness intensity and duration), spinal mobility (lateral spinal flexion) and high sensitivity C-reactive protein (hs-CRP). Note: Participants with missing data or who discontinue study treatment prior to Week 12 were counted as non-responders.

Time frame: Week 12

Population: The FAS consisted of all randomized participants who received at least 1 dose of IMP and had a valid measurement of the primary efficacy variable at Baseline.