24-hour coughs per hour was defined as the average hourly cough frequency based on 24-hour sound recordings using a digital recording device (cough monitor). A longitudinal analysis of covariance (ANCOVA) model was applied to log-transformed cough data to determine geometric mean (GM) 24-hour coughs per hour at baseline and week 24. The GMR (Week 24 GM 24-hour coughs per hour divided by Baseline GM 24-hour coughs per hour) is reported.

All China participants randomized to the gefapixant 45 mg BID or placebo groups who received at least 1 dose of study intervention. Participants needed to have baseline and at least 1 post-baseline measurement. Efficacy evaluation of the gefapixant 15 mg BID group was removed from the study objectives of the China cohort per protocol amendment 5. Participants were analyzed in the group as randomized.

Assessment of participants who have at least one AE during the main study period (24 weeks), the treatment extension period (28 weeks), and during 2 weeks of follow-up by telephone.

All randomized China participants who received at least 1 dose of study intervention. Participants were analyzed in the group as treated.

Assessment of participants who stop study treatment due to an AE during the main study period (24 weeks) or the treatment extension period (28 weeks).

All randomized China participants who received at least 1 dose of study intervention. Participants were analyzed in the group as treated.

Awake coughs per hour was defined as the average hourly cough frequency while the participant is awake, based on a 24-hour interval of sound recordings using a digital recording device (cough monitor). ANCOVA model was applied to log-transformed cough data to determine GM of awake coughs per hour at baseline and week 24. The GMR (Week 24 GM awake coughs per hour divided by Baseline GM awake coughs per hour) is reported.

All China participants randomized to the gefapixant 45 mg BID or placebo groups who received at least 1 dose of study intervention. Efficacy evaluation of the gefapixant 15 mg BID group was removed from the study objectives of the China cohort per protocol amendment 5. Participants needed to have awake 24-hour cough data at baseline and at least 1 post-baseline measurement. Participants were analyzed in the group as randomized.

The 19-item LCQ assessed the impact of chronic cough in three health-related quality of life (HRQoL) domains (physical, social and psychological). The LCQ is calculated as a mean score for each domain ranging from 1 to 7, with a total score ranging from 3 to 21. Higher scores indicate better HRQoL. A clinically meaningful improvement from baseline in HRQoL was defined as ≥1.3-point increase in the LCQ total score at Week 24. The percentage of participants (logistic regression model-based) with a ≥1.3-point increase in the LCQ total score at Week 24 is presented.

All China participants randomized to the gefapixant 45 mg BID or placebo groups who received at least 1 dose of study intervention. Efficacy evaluation of the gefapixant 15 mg BID group was removed from the study objectives of the China cohort per protocol amendment 5. Participants needed to have LCQ data at baseline and at least 1 post-baseline measurement. Participants were analyzed in the group as randomized.

24-hour coughs per hour was defined as the average hourly cough frequency based on 24-hour sound recordings using a digital recording device (cough monitor). A clinically meaningful improvement from baseline is defined as a ≥30% reduction in 24-hour coughs per hour at week 24. The percentage of participants (logistic regression model-based) with a ≥30% reduction from baseline in 24-hour coughs per hour at Week 24 (≥30% reduction from baseline) is presented.

All China participants randomized to the gefapixant 45 mg BID or placebo groups who received at least 1 dose of study intervention. Efficacy evaluation of the gefapixant 15 mg BID group was removed from the study objectives of the China cohort per protocol amendment 5. Participants needed to have 24-hour cough data at baseline and at least 1 post-baseline measurement. Participants were analyzed in the group as randomized.

The 7-item CSD was used to record participants' daily cough frequency, cough intensity, and disruption due to cough. Each item was rated on an 11-point scale ranging from 0 (best) to 10 (worst); the total daily CSD score was the sum of these seven item scores (Min=0, Max=70). Mean weekly CSD total score was defined as the average of the mean total daily scores collected during the week prior to each visit. The percentage of participants (logistic regression model-based) with a ≥1.3 point reduction from baseline in CSD at Week 24 is reported.

All China participants randomized to the gefapixant 45 mg BID or placebo groups who received at least 1 dose of study intervention. Efficacy evaluation of the gefapixant 15 mg BID group was removed from the study objectives of the China cohort per protocol amendment 5. Participants needed to have CSD data at baseline and at least 1 post-baseline measurement. Participants were analyzed in the group as randomized.

The 7-item CSD was used to record participants' daily cough frequency, cough intensity, and disruption due to cough. Each item was rated on an 11-point scale ranging from 0 (best) to 10 (worst); the total daily CSD score was the sum of these seven item scores (Min=0, Max=70). Mean weekly CSD total score was defined as the average of the mean total daily scores collected during the week prior to each visit. The percentage of participants (logistic regression model-based) with a ≥2.7 point reduction from baseline in CSD at Week 24 is reported.

All China participants randomized to the gefapixant 45 mg BID or placebo groups who received at least 1 dose of study intervention. Efficacy evaluation of the gefapixant 15 mg BID group was removed from the study objectives of the China cohort per protocol amendment 5. Participants needed to have CSD data at baseline and at least 1 post-baseline measurement. Participants were analyzed in the group as randomized.

The VAS is a single-item questionnaire with the response on a 100- point scale ranging from 0 ("No Cough") to 100 ("Extremely Severe Cough"). Mean weekly VAS score was defined as the average of the VAS scores collected during the week prior to each visit. The percentage of participants (logistic regression model-based) with a ≥30mm reduction from baseline in cough severity VAS score at Week 24 is reported.

All China participants randomized to the gefapixant 45 mg BID or placebo groups who received at least 1 dose of study intervention. Efficacy evaluation of the gefapixant 15 mg BID group was removed from the study objectives of the China cohort per protocol amendment 5. Participants needed to have CSD data at baseline and at least 1 post-baseline measurement. Participants were analyzed in the group as randomized.