A Study to Evaluate the Efficacy and Safety of Esketamine for Reduction of Symptoms of Major Depressive Disorder

Change from Baseline in CDRS-R Total Score at Day 25

The CDRS-R is a 17-item, clinician-reported outcome measure of children's depressive symptom severity. Out of the 17-item, 3 items were non-verbal behavior (listless speech, hypoactivity, and depressed affect) rated on a 5-point scale from 1 (no depression) to 5 (severe depression) and 14 items were rated on a 7-point scale from 1 (no depression) to 7 (severe depression), where higher score indicated more severe depression. The CDRS-R total score was the sum of the 17-tems score and it ranged from 17 (normal) to 113 (severe depression). Higher score indicated more severe depression and worse outcome.

Time frame: Baseline (predose on Day 1) and Day 25 (4 hours post dose)

Change from Baseline in Clinical Global Impression - Severity of Suicidality - Revised (CGI-SS-R) Score at 24 Hours Post First Dose

The CGI-SS-R is a single item clinician-rated measure of the severity of participants' suicidality. The CGI-SS-R asks clinicians to rate the severity of a participant's suicidality using a 7-point scale that ranges from 0 (normal, not at all suicidal) to 6 (among the most extremely suicidal patients). Higher scores indicate greater severity.

Time frame: Baseline (pre-dose on Day 1) and 24 hours post first dose (i.e., Day 2)

Change From Baseline in Symptoms of MDD During the Double-Blind (DB) Treatment Phase as Measured by CDRS-R Total Score

The CDRS-R is a 17-item, clinician-reported outcome measure of children's depressive symptom severity. Out of the 17-item, 3 items were non-verbal behavior (listless speech, hypoactivity, and depressed affect) rated on a 5-point scale from 1 (no depression) to 5 (severe depression) and 14 items were rated on a 7-point scale from 1 (no depression) to 7 (severe depression), where higher score indicated more severe depression. The CDRS-R total score was the sum of the 17-tems score and it ranged from 17 (normal) to 113 (severe depression). Higher score indicated more severe depression and worse outcome.

Time frame: From Baseline up to Day 25

Percentage of Participants with Remission of Depressive Symptoms During the DB Treatment Phase

Remission of depressive symptoms is defined as a CDRS-R total score of both less than or equal to (\<=) 28 and \<= 34 during the DB treatment phase. The CDRS-R is a 17-item, clinician-reported outcome measure of children's depressive symptom severity. Out of the 17-item, 3 items were non-verbal behavior (listless speech, hypoactivity, and depressed affect) rated on a 5 point scale from 1 (no depression) to 5 (severe depression) and 14 items were rated on a 7-point scale from 1 (no depression) to 7 (severe depression), where higher score indicated more severe depression. The CDRS-R total score was the sum of the 17-tems score and it ranged from 17 (normal) to 113 (severe depression). Higher score indicated more severe depression and worse outcome.

Time frame: Up to Day 25

Percentage of Responders on Depressive Symptoms During the DB Treatment Phase

Responders on depressive symptoms is defined as \>= 50 percent (%) improvement in CDRS-R total score from baseline during the DB treatment phase. The CDRS-R is a 17-item, clinician-reported outcome measure of children's depressive symptom severity. Out of the 17-item, 3 items were non-verbal behavior (listless speech, hypoactivity, and depressed affect) rated on a 5 point scale from 1 (no depression) to 5 (severe depression) and 14 items were rated on a 7-point scale from 1 (no depression) to 7 (severe depression), where higher score indicated more severe depression. The CDRS-R total score was the sum of the 17-tems score and it ranged from 17 (normal) to 113 (severe depression). Higher score indicated more severe depression and worse outcome.

Time frame: Up to Day 25

Percentage of Participants with Resolution of Suicidality During the DB Treatment Phase

Participants with resolution of suicidality is defined as a score of 0 (normal, not at all suicidal) or 1 (questionably suicidal) on CGI SS-R, during the DB treatment phase. The CGI-SS-R asks clinicians to rate the severity of a participant's suicidality using a 7-point scale that ranges from 0 (normal, not at all suicidal) to 6 (among the most extremely suicidal patients). Higher score indicate greater severity.

Time frame: Up to Day 25

Change From Baseline in Severity of Suicidality As Measured by Clinical Global Impression - Severity of Suicidality - Revised (CGI-SS-R) During the DB Treatment Phase

The CGI-SS-R is a single item clinician-rated measure of the severity of participants' suicidality. The CGI-SS-R asks clinicians to rate the severity of a participant's suicidality using a 7-point scale that ranges from 0 (normal, not at all suicidal) to 6 (among the most extremely suicidal patients). Higher score indicate greater severity.

Time frame: From Baseline up to Day 25

Change From Baseline in Clinician-Reported Frequency of Suicidal Thinking (FoST-ClinRO) During the DB Treatment Phase

FoST-ClinRO is a clinician-rated measure used to assess a participant's frequency of suicidal thinking assessed during the DB treatment phase. The measure uses a 6-point Likert scale that ranges from 0=Never, to 5=All of the time to assess suicidal thinking frequency, where higher scores indicate a more severe condition.

Time frame: From Baseline up to Day 25

Change from baseline in Patient-Reported Frequency of Suicidal Thinking (FoST-PRO) During the DB Treatment Phase

FoST-PRO is a single item participant reported measure of the frequency of one's suicidal thinking right now. The single item asks participants to rate the frequency with which they have suicidal thoughts (0 = I have no suicidal thoughts, 1 = I have suicidal thoughts a little of the time, 2 = I have suicidal thoughts some of the time, 3 = I have suicidal thoughts most of the time, and 4 = I have suicidal thoughts all of the time). Higher scores indicate greater severity.

Time frame: From Baseline up to Day 25

Change from Baseline in Patient Health Questionnaire, 9-item Modified for Adolescents (PHQ-A) Total Score During the DB Treatment Phase

The PHQ-A is a modified version of the PHQ-9 scale, specifically designed to measure depressive symptom severity in adolescents. A 10-item version of the PHQ-A will be used in this study; the first 9 items assess depressive symptoms. Adolescents use a 4 point Likert scale to rate the severity of their symptoms over the past 2 weeks (range: 0 = not at all to 3 = nearly every day). The PHQ-A total score is the sum of all item responses. The total score can be used to classify adolescents based on the severity of their depressive symptoms: 0-4 (no or minimal depression), 5-9 (mild depression), 10-14 (moderate depression), 15-19 (moderately severe depression), and 20-27 (severe depression). The tenth PHQ-A item measures the degree to which adolescents experience functional difficulties due to their depressive symptoms. Higher scores indicate greater depressive symptoms.

Time frame: From Baseline up to Day 25

Change From Baseline in KIDSCREEN-10 Total Score During the DB Treatment Phase

KIDSCREEN-10 is a global patient-reported outcome (PRO) measure of well-being and health-related quality of life in children and adolescents aged 8-18 years. It includes 10 items that measure the subjective health and psychological, mental and social well-being experiences of children and adolescents over the past week. The scores for the 10 items are summed to produce a total score. This total score can then be transformed into a T-score or percentile rank, based on normative data, to facilitate interpretation. The higher the total score, the better the reported health-related quality of life (HRQoL).

Time frame: From Baseline up to Day 25

Change from Baseline in Patient Global Impression of Severity (PGI-S) Depressive Symptoms at 24 Hours Post First Dose

The PGI-S is a single PRO item that captures one's perceptions of the severity of his/her depressive symptoms over the past 24 hours. Participants will be asked to rate their disease severity using the following 5-point scale: 1 = None, 2 = Mild, 3 = Moderate, 4 = Severe, and 5 = Very severe. Higher scores indicate greater disease severity.

Time frame: Baseline (predose on Day 1) and 24 hours post first dose (i.e., Day 2)

Change from Baseline in Clinical Global Impression - Severity Scale (CGI-S) Depressive Symptoms at 24 Hours Post First Dose

The CGI-S provides an overall clinician-determined summary measure of the severity of the participant's illness that considers all available information, including knowledge of the participant's history, psychosocial circumstances, symptoms, behavior, and the impact of the symptoms on the participant's ability to function. The CGI-S will be used to rate the overall severity of illness on a scale of 1 to 7. Considering total clinical experience with the depression population, a participant is assessed on severity of illness at the time of rating according to the following scale: 1=normal (not at all ill); 2=borderline ill; 3=mildly ill; 4=moderately ill; 5=markedly ill; 6=severely ill; 7=among the most extremely ill patients. Higher scores indicate greater severity.

Time frame: Baseline (pre-dose on Day 1) and 24 hours post first dose (i.e., Day 2)