Time to pericarditis recurrence (from randomization to 1st recurrence). Kaplan-Meier. Clinical Events Committee (CEC)-confirmed recurrences used for primary analysis. Recurrence defined as recurrence typical pericarditis pain with supportive objective evidence. CEC-adjudicated recurrences defined as:1) Re-appearance/worsening pericarditis pain (1 NRS ≥ 4) AND elevated CRP (≥1.0 mg/dL) on same day/separated by ≤ 7 days OR 2) Re-appearance/worsening pericarditis pain (1 NRS ≥ 4) AND abnormal CRP (> 0.5 mg/dL) on same day/separated by ≤ 7 days AND 1 supportive evidence OR 3) Re-appearance/worsening pericarditis pain (no NRS ≥ 4) AND elevated CRP (≥ 1.0 mg/dL) not attributable to other causes AND 1 supportive evidence. Supportive evidence: White blood cell count > upper limit normal, fever > 38C, pericardial rub, electrocardiogram changes consistent with pericarditis, new/worsening pericardial effusion (echocardiogram), new/worsening pericardial inflammation (magnetic resonance imaging).

Intent-to-Treat (ITT) Analysis Set: all participants who were randomized in the RW period.

Participants were asked to select the score that best describes their average level of pericarditis pain over the previous 24 hours using an 11-point numerical rating scale (NRS), where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'. Clinical response was defined as a weekly average of daily pericarditis pain on the NRS ≤ 2.0 and C-reactive protein (CRP) level ≤ 0.5 mg/dL, and on monotherapy of randomized study drug at Week 16.

ITT Week 16 Analysis Set: All participants randomized at least 16 weeks before data cutoff.

Participants were asked to select the score that best describes their average level of pericarditis pain over the previous 24 hours using an 11-point numerical rating scale (NRS), where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'. No or minimal pain was defined as non-missing NRS ≤ 2.

The percentage of days with no or minimal pericarditis pain in the first 16 weeks was calculated for each participant using 16×7 as the denominator. Missing values in pain diary were counted as 0 day with no or minimal pain. Days of using oral rescue therapy or corticosteroid count as 0 day with no or minimal pain. If bailout rilonacept was used, each administration (loading dose or not) was counted as 7 days without qualifying no or minimal pain.

ITT Week 16 Analysis Set: All participants randomized at least 16 weeks before data cutoff.

Percentage of participants with no or minimal pericarditis symptoms at Week 16, based on the PGIPS, a single-item measure of the participant's impression of the overall severity of pericarditis symptoms at the time the questionnaire is administered using a 7-point rating scale ranging from absent (0=no recurrent pericarditis symptoms) to very severe (6=recurrent pericarditis symptoms that cannot be ignored and markedly limits daily activities).

The exact 95% CI is calculated with randomization strata pooled. Participants who had received bailout rilonacept or rescue medication before the time point were considered nonresponders.

ITT Week 16 Analysis Set: All participants randomized at least 16 weeks before data cutoff.

Participants were asked to select the score that best describes their average level of pericarditis pain over the previous 24 hours using an 11-point numerical rating scale (NRS), where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'. Clinical response was defined as a weekly average of daily pericarditis pain on the NRS ≤ 2.0 and C-reactive protein (CRP) level ≤ 0.5 mg/dL, and on monotherapy of randomized study drug at Week 24.

ITT Week 24 Analysis Set: All participants randomized at least 24 weeks before data cutoff.

Participants were asked to select the score that best describes their average level of pericarditis pain over the previous 24 hours using an 11-point numerical rating scale (NRS), where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'. Clinical response was defined as a weekly average of daily pericarditis pain on the NRS ≤ 2.0 and C-reactive protein (CRP) level ≤ 0.5 mg/dL, and on monotherapy of randomized study drug at Week 8.

ITT Week 8 Analysis Set: All participants randomized at least 8 weeks before data cutoff.

Participants were asked to select the score that best describes their average level of pericarditis pain over the previous 24 hours using an 11-point numerical rating scale (NRS), where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'. No or minimal pain was defined as non-missing NRS ≤ 2.

The percentage of days with no or minimal pericarditis pain in the first 24 weeks was calculated for each participant using 24×7 as the denominator. Missing values in pain diary were counted as 0 day with no or minimal pain. Days of using oral rescue therapy or corticosteroid count as 0 day with no or minimal pain. If bailout rilonacept was used, each administration (loading dose or not) was counted as 7 days without qualifying no or minimal pain.

ITT Week 24 Analysis Set: All participants randomized at least 24 weeks before data cutoff.

Participants were asked to select the score that best describes their average level of pericarditis pain over the previous 24 hours using an 11-point numerical rating scale (NRS), where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'. No or minimal pain was defined as non-missing NRS ≤ 2.

The percentage of days with no or minimal pericarditis pain in the first 24 weeks was calculated for each participant using 8×7 as the denominator. Missing values in pain diary were counted as 0 day with no or minimal pain. Days of using oral rescue therapy or corticosteroid count as 0 day with no or minimal pain. If bailout rilonacept was used, each administration (loading dose or not) was counted as 7 days without qualifying no or minimal pain.

ITT Week 8 Analysis Set: All participants randomized at least 8 weeks before data cutoff.

Percentage of participants with no or minimal pericarditis symptoms at Week 24, based on the PGIPS, a single-item measure of the participant's impression of the overall severity of pericarditis symptoms at the time the questionnaire is administered using a 7-point rating scale ranging from absent (0=no recurrent pericarditis symptoms) to very severe (6=recurrent pericarditis symptoms cannot be ignored and markedly limits daily activities).

The exact 95% CI is calculated with randomization strata pooled. Participants who had received bailout rilonacept or rescue medication before the time point were considered nonresponders.

ITT Week 24 Analysis Set: All participants randomized at least 24 weeks before data cutoff.

Percentage of participants with no or minimal pericarditis symptoms at Week 16, based on the Patient Global Impression of Pericarditis Severity (PGI-PS). The PGI-PS is a single-item measure of the participant's impression of the overall severity of pericarditis symptoms at the time the questionnaire is administered, using a 7-point rating scale ranging from absent (no recurrent pericarditis symptoms) to very severe (recurrent pericarditis symptoms cannot be ignored).

The exact 95% CI is calculated with randomization strata pooled. Participants who had received bailout rilonacept or rescue medication before the time point were considered nonresponders.

ITT Week 8 Analysis Set: All participants randomized at least 8 weeks before data cutoff.

Pericarditis recurrence is defined as the recurrence of typical pericarditis pain associated with supportive objective evidence of pericarditis. At any time during the RW period, participants who experienced a suspected recurrence of pericarditis symptoms reported to the study site/clinic for a scheduled or unscheduled visit, during which clinical assessments were performed to gather all the necessary diagnostic data to confirm or rule out the presence of pericarditis recurrence. A pericarditis recurrence event adjudication package was then prepared for adjudication by CEC. Kaplan-Meier estimate.

ITT Analysis Set: all participants who were randomized in the RW period.

Participants were asked to select the score that best described their average level of pericarditis pain over the previous 24 hours using an 11-point numerical rating scale (NRS), where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'.

ITT Analysis Set: all participants who were randomized in the RW period.

Kaplan-Meier estimate.

ITT Analysis Set: all participants who were randomized in the RW period.

Kaplan-Meier estimate. A pericardial rub (also called a pericardial friction rub) is an audible medical sign used in the diagnosis of pericarditis.

ITT Analysis Set: all participants who were randomized in the RW period.

Kaplan-Meier estimate. ST-segment elevation and PR-segment depression are ECG changes in the evolution of acute pericarditis.

ITT Analysis Set: all participants who were randomized in the RW period.

Pericardial effusion based on ECHO was evaluated by the central laboratory during the RW period. Kaplan-Meier estimate.

ITT Analysis Set: all participants who were randomized in the RW period.

Pericardial effusion based on ECHO was evaluated by the central laboratory during the RW period. "None or trivial/physiologic" is considered to be normal. The "RW Worst Post-baseline" category denotes the largest size of pericardial effusion category in which a participant was reported at any time during the RW period (post-baseline).

ITT Analysis Set: all participants who were randomized in the RW period. Participants with a non-missing value at given time point.

Estimated from ANCOVA models including treatment arm as fix effect, baseline value, baseline value by treatment interaction, randomization strata as covariates.

ITT Analysis Set: all participants who were randomized in the RW period. Participants with a non-missing value at given time point.

Participants were asked to select the score that best described their average level of pericarditis pain over the previous 24 hours using an 11-point numerical rating scale (NRS), where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'. Estimated from ANCOVA models including treatment arm as fix effect, baseline value, baseline value by treatment interaction, randomization strata as covariates.

ITT Analysis Set: all participants who were randomized in the RW period. Participants with a non-missing value at given time point.

The PGIPS, a single-item measure of the participant's impression of the overall severity of pericarditis symptoms at the time the questionnaire is administered using a 7-point rating scale ranging from absent (0=no recurrent pericarditis symptoms) to very severe (6=recurrent pericarditis symptoms cannot be ignored and markedly limits daily activities).

The exact 95% CI is calculated with randomization strata pooled. Participants who had received bailout rilonacept or rescue medication before the time point were considered nonresponders.

ITT Analysis Set: all participants who were randomized in the RW period. Participants with a non-missing value at given time point.

The PGA-PA is a single-item, clinician-reported outcome measure that Investigators use to rate their impression of the patient's overall pericarditis disease activity at the time the assessment is completed, using a rating scale ranging from absent to very severe. The Investigator selected the box that best described a participant's pericarditis activity at the time of occurrence of the assessment: Absent, Minimal, Mild, Moderate, Moderately Severe, Severe, Very Severe.

ITT Analysis Set: all participants who were randomized in the RW period. Participants with a non-missing value at given time point.

The SF-36 determines participants' overall quality of life by assessing 1) limitations in physical functioning due to health problems; 2) limitations in usual role because of physical health problems; 3) bodily pain; 4) general health perceptions; 5) vitality; 6) limitations in social functioning because of physical or emotional problems; 7) limitations in usual role due to emotional problems; and 8) general mental health. Items 1-4 primarily contribute to the physical component summary (PCS) score of the SF-36. Items 5-8 primarily contribute to the mental component summary (MCS) score of the SF-36. Scores on each item are summed and averaged (range: 0=worst to 100=best) with higher scores indicating better health. Increases from baseline indicate improvement.

ITT Analysis Set: all participants who were randomized in the RW period. Participants 18 years and older with a non-missing value at given time point.

The SF-36 determines participants' overall quality of life by assessing 1) limitations in physical functioning due to health problems; 2) limitations in usual role because of physical health problems; 3) bodily pain; 4) general health perceptions; 5) vitality; 6) limitations in social functioning because of physical or emotional problems; 7) limitations in usual role due to emotional problems; and 8) general mental health. Scores on each item are summed and averaged (range: 0=worst to 100=best) with higher scores indicating better health. Increases from baseline indicate improvement.

ITT Analysis Set: all participants who were randomized in the RW period. Participants 18 years and older with a non-missing value at given time point.

The SF-6D is calculated based on responses to 11 items on the SF-36, that correspond to 6 domains: physical functioning, role participation (combined role-physical and role-emotional), social functioning, bodily pain, mental health, and vitality. Individual respondents can be classified on any of 4 to 6 levels of functioning or limitations for each of 6 domains, thus allowing a respondent to be classified into any of 18,000 possible unique health states. Using a standard gamble technique, each of these health states were mapped onto the SF-6D index score, which ranges from 0.00 (worst possible health state/death) to 1.00 (best possible health state/perfect health).

ITT Analysis Set: all participants who were randomized in the RW period. Participants 18 years and older with a non-missing value at given time point.

The EQ-5D-5L is a self-reported health status questionnaire that consists of 6 questions used to calculate a health utility score for use in health economic analysis. There are 2 components to the EQ-5D-5L: a 5-item health state profile that assesses mobility, self-care, usual activities, pain/discomfort, and anxiety/depression used to obtain an Index Utility Score, as well as a visual analogue scale (VAS) that measures health state. Individual and index scores range from 0 to 1, with low scores representing a higher level of dysfunction. The VAS is designed to rate the participant's current health state on a scale from 0 to 100, where 0 represents the worst imaginable health state and 100 represents the best imaginable health state.

ITT Analysis Set: all participants who were randomized in the RW period. Participants 18 years and older with a non-missing value at given time point.

Participant's sleep quality was assessed with the ISI survey questionnaire. The ISI is a 7-item survey, with each question having 5 possible answers (none, mild, moderate, severe, or very severe), scored as 0, 1, 2, 3, or 4, respectively. Scores are summed for a total score, which ranges from 0 to 28. Lower scores are considered good, better, or healthy, and increasingly higher scores are considered to indicate greater insomnia.

Clinical interpretation of the total score is as follows:

0 to 7 = no clinically significant insomnia; 8 to 14 = subthreshold insomnia; 15 to 21 = clinical insomnia (moderate severity); 22 to 28 = clinical insomnia (severe).

ITT Analysis Set: all participants who were randomized in the RW period. Participants 18 years and older with a non-missing value at given time point.

Participant's sleep quality was assessed with the ISI survey questionnaire. The ISI is a 7-item survey, with each question having 5 possible answers (none, mild, moderate, severe, or very severe), scored as 0, 1, 2, 3, or 4, respectively. Scores are summed for a total score, which ranges from 0 to 28. Lower scores are considered good, better, or healthy, and increasingly higher scores are considered to indicate greater insomnia.

Clinical interpretation of the total score is as follows:

0 to 7 = no clinically significant insomnia; 8 to 14 = subthreshold insomnia; 15 to 21 = clinical insomnia (moderate severity); 22 to 28 = clinical insomnia (severe).

ITT Week 24 Analysis Set: All participants randomized at least 24 weeks before data cutoff. Participants 18 years or older

ORT included analgesics, NSAIDs, and/or colchicine. ORT use while waiting for at least 5 days since previous administration of study drug before receiving bailout, or within 5 days before the assessment of pericarditis recurrence, was excluded.

ITT Analysis Set: all participants who were randomized in the RW period.

ORT included analgesics, NSAIDs, and/or colchicine.

ITT Analysis Set: all participants who were randomized in the RW period.

MRI assessments were performed in a subgroup of participants (MRI substudy) to assess the percentage of participants with:

• Pericardial delayed hyperenhancement
• Myocardial delayed hyperenhancement
• Pericardial effusion

ITT Week 24 Analysis Set: All participants randomized at least 24 weeks before data cutoff. Participants in the MRI substudy with nonmissing data.

Participants were asked to select the score that best described their average level of pericarditis pain over the previous 24 hours using an 11-point numerical rating scale (NRS), where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'. Time to pain response was defined as number of days from first dose to the first day a participant's daily pain NRS was ≤ 2 of the 3 days over which the rolling average daily pain NRS was ≤ 2.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with a baseline NRS measurement >= 3.

Time to CRP normalization, defined as CRP ≤ 0.5 mg/dL, was censored at treatment discontinuation, taking prohibited medication, or Week 12, whichever occurred first.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with a baseline CRP measurement >= 0.5 mg/dL.

Time to rilonacept monotherapy was defined as the number of weeks from first dose to the first day of achieving monotherapy.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with background therapies at RI Baseline.

Time to treatment response is defined as time from first dose to the first day of pain response, and CRP ≤ 0.5 mg/dL within 7 days before or after pain response. Treatment response day will be the first day that the above criterion is met. If pain response occurs before CRP ≤ 0.5 mg/dL, each 3-day rolling average of NRS should be ≤ 2.0 from the day of pain response to the day of CRP ≤ 0.5 mg/dL. The response day will be the day of pain response. If CRP ≤0.5 mg/dL occurs before pain response, the response day will also be the day of pain response.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with baseline measurements of CRP >0.5 mg/dL and NRS > 2.

Participants were asked to select the score that best described their average level of pericarditis pain over the previous 24 hours using an 11-point numerical rating scale (NRS), where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'. Clinical Response was defined as a weekly average of daily pericarditis pain of ≤ 2.0 on the 11-point NRS and CRP level ≤ 0.5 mg/dL and participants must have been able to stop background SOC pericarditis therapy by Week 10.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants achieving treatment response in the RI period.

CRP normalization was defined as CRP ≤ 0.5 mg/dL.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with a baseline CRP measurement ≥ 0.5 mg/dL.

Participants were asked to select the score that best described their average level of pericarditis pain over the previous 24 hours using an 11-point numerical rating scale (NRS), where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with an assessment at given time period.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with an assessment at given time period.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with ECHO and ECG abnormalities at RI Baseline.

No or minimal pain is defined as non-missing daily NRS ≤ 2, where participants were asked to select the score that best describes their average level of pericarditis pain over the previous 24 hours using an 11-point NRS, where zero (0) indicates 'no pain' and ten (10) indicates 'pain as bad as it could be'.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period.

The PGIPS, a single-item measure of the participant's impression of the overall severity of pericarditis symptoms at the time the questionnaire is administered using a 7-point rating scale ranging from absent (0=no recurrent pericarditis symptoms) to very severe (6=recurrent pericarditis symptoms cannot be ignored and markedly limits daily activities).

The exact 95% CI is calculated with randomization strata pooled. Participants who had received bailout rilonacept or rescue medication before the time point were considered nonresponders.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with an assessment at given time point.

The PGA-PA is a single-item, clinician-reported outcome measure that Investigators use to rate their impression of the patient's overall pericarditis disease activity at the time the assessment is completed, using a rating scale ranging from absent to very severe. The Investigator selected the box that best described a participant's pericarditis activity at the time of occurrence of the assessment: Absent, Minimal, Mild, Moderate, Moderately Severe, Severe, Very Severe.

The exact 95% CI is calculated with randomization strata pooled. Participants who had received bailout rilonacept or rescue medication before the time point were considered nonresponders.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with an assessment at given time point.

The SF-36 determines participants' overall quality of life by assessing 1) limitations in physical functioning due to health problems; 2) limitations in usual role because of physical health problems; 3) bodily pain; 4) general health perceptions; 5) vitality; 6) limitations in social functioning because of physical or emotional problems; 7) limitations in usual role due to emotional problems; and 8) general mental health. Scores on each item are summed and averaged (range: 0=worst to 100=best) with higher scores indicating better health. Increases from baseline indicate improvement.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with an assessment at given time point.

The SF-6D is calculated based on responses to 11 items on the SF-36, that correspond to 6 domains: physical functioning, role participation (combined role-physical and role-emotional), social functioning, bodily pain, mental health, and vitality. Individual respondents can be classified on any of 4 to 6 levels of functioning or limitations for each of 6 domains, thus allowing a respondent to be classified into any of 18,000 possible unique health states. Using a standard gamble technique, each of these health states were mapped onto the SF-6D index score, which ranges from 0.00 (worst possible health state/death) to 1.00 (best possible health state/perfect health).

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with an assessment.

The EQ-5D-5L is a self-reported health status questionnaire that consists of 6 questions used to calculate a health utility score for use in health economic analysis. There are 2 components to the EQ-5D-5L: a 5-item health state profile that assesses mobility, self-care, usual activities, pain/discomfort, and anxiety/depression used to obtain an Index Utility Score, as well as a visual analogue scale (VAS) that measures health state. Individual and index scores range from 0 to 1, with low scores representing a higher level of dysfunction. The VAS is designed to rate the participant's current health state on a scale from 0 to 100, where 0 represents the worst imaginable health state and 100 represents the best imaginable health state.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with an assessment.

Participant's sleep quality was assessed with the ISI survey questionnaire. The ISI is a 7-item survey, with each question having 5 possible answers (none, mild, moderate, severe, or very severe), scored as 0, 1, 2, 3, or 4, respectively. Scores are summed for a total score, which ranges from 0 to 28. Lower scores are considered good, better, or healthy, and increasingly higher scores are considered to indicate greater insomnia.

Clinical interpretation of the total score is as follows:

0 to 7 = no clinically significant insomnia; 8 to 14 = subthreshold insomnia; 15 to 21 = clinical insomnia (moderate severity); 22 to 28 = clinical insomnia (severe).

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants with an assessment.

Participant's sleep quality was assessed with the ISI survey questionnaire. The ISI is a 7-item survey, with each question having 5 possible answers (none, mild, moderate, severe, or very severe), scored as 0, 1, 2, 3, or 4, respectively. Scores are summed for a total score, which ranges from 0 to 28. Lower scores are considered good, better, or healthy, and increasingly higher scores are considered to indicate greater insomnia.

Clinical interpretation of the total score is as follows:

0 to 7 = no clinically significant insomnia; 8 to 14 = subthreshold insomnia; 15 to 21 = clinical insomnia (moderate severity); 22 to 28 = clinical insomnia (severe).

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants 18 years or older with an assessment.

Run-in Analysis Set: All participants who received at least 1 dose of study drug in the RI period. Participants 18 years or older with an assessment at given time point.

Annualized Recurrence Rate is defined as the number of recurrences in LTE periods for all participants/Sum of participant years in LTE periods for all participants. Participant years in LTE period is defined as the time from 1st dose date of LTE period to the date of End of Study, or data cutoff date, whichever is earlier. The 95% CI was calculated using an exact method with Poisson distribution. Pericarditis recurrence is defined as the recurrence of typical pericarditis pain associated with supportive objective evidence of pericarditis.

LTE Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period.

Long term extension (LTE) Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period. Participants with an assessment at given time point.

Percentage of participants with no or minimal pericarditis symptoms in the LTE Period, based on the PGIPS, a single-item measure of the participant's impression of the overall severity of pericarditis symptoms at the time the questionnaire is administered using a 7-point rating scale ranging from absent (0=no recurrent pericarditis symptoms) to very severe (6=recurrent pericarditis symptoms that cannot be ignored and markedly limits daily activities).

Long term extension (LTE) Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period. Participants with an assessment at given time point.

The PGA-PA is a single-item, clinician-reported outcome measure that Investigators use to rate their impression of the patient's overall pericarditis disease activity at the time the assessment is completed, using a rating scale ranging from absent to very severe. The Investigator selected the box that best described a participant's pericarditis activity at the time of occurrence of the assessment: Absent, Minimal, Mild, Moderate, Moderately Severe, Severe, Very Severe.

Long term extension (LTE) Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period. Participants with an assessment at given time point.

The SF-36 determines participants' overall quality of life by assessing 1) limitations in physical functioning due to health problems; 2) limitations in usual role because of physical health problems; 3) bodily pain; 4) general health perceptions; 5) vitality; 6) limitations in social functioning because of physical or emotional problems; 7) limitations in usual role due to emotional problems; and 8) general mental health. Scores on each item are summed and averaged (range: 0=worst to 100=best) with higher scores indicating better health. Increases from baseline indicate improvement.

Long term extension (LTE) Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period. Participants with an assessment at given time point.

The SF-6D is calculated based on responses to 11 items on the SF-36, that correspond to 6 domains: physical functioning, role participation (combined role-physical and role-emotional), social functioning, bodily pain, mental health, and vitality. Individual respondents can be classified on any of 4 to 6 levels of functioning or limitations for each of six domains, thus allowing a respondent to be classified into any of 18,000 possible unique health states. Using a standard gamble technique, each of these health states were mapped onto the SF-6D index score, which ranges from 0.00 (worst possible health state/death) to 1.00 (best possible health state/perfect health).

Long term extension (LTE) Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period. Participants with an assessment at given time point.

The EQ-5D-5L is a self-reported health status questionnaire that consists of 6 questions used to calculate a health utility score for use in health economic analysis. There are 2 components to the EQ-5D-5L: a 5-item health state profile that assesses mobility, self-care, usual activities, pain/discomfort, and anxiety/depression used to obtain an Index Utility Score, as well as a visual analogue scale (VAS) that measures health state. Individual and index scores range from 0 to 1, with low scores representing a higher level of dysfunction. The VAS is designed to rate the participant's current health state on a scale from 0 to 100, where 0 represents the worst imaginable health state and 100 represents the best imaginable health state.

Long term extension (LTE) Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period. Participants with an assessment at given time point.

Participant's sleep quality was assessed with the ISI survey questionnaire. The ISI is a 7-item survey, with each question having 5 possible answers (none, mild, moderate, severe, or very severe), scored as 0, 1, 2, 3, or 4, respectively. Scores are summed for a total score, which ranges from 0 to 28. Lower scores are considered good, better, or healthy, and increasingly higher scores are considered to indicate greater insomnia.

Clinical interpretation of the total score is as follows:

0 to 7 = no clinically significant insomnia; 8 to 14 = subthreshold insomnia; 15 to 21 = clinical insomnia (moderate severity); 22 to 28 = clinical insomnia (severe).

Long term extension (LTE) Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period. Participants 18 years or older with an assessment at given time point.

Participant's sleep quality was assessed with the ISI survey questionnaire. The ISI is a 7-item survey, with each question having 5 possible answers (none, mild, moderate, severe, or very severe), scored as 0, 1, 2, 3, or 4, respectively. Scores are summed for a total score, which ranges from 0 to 28. Lower scores are considered good, better, or healthy, and increasingly higher scores are considered to indicate greater insomnia.

Clinical interpretation of the total score is as follows:

0 to 7 = no clinically significant insomnia; 8 to 14 = subthreshold insomnia; 15 to 21 = clinical insomnia (moderate severity); 22 to 28 = clinical insomnia (severe).

Long term extension (LTE) Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period. Participants 18 years or older with an assessment at given time point.

This analysis was not done because Standard of Care treatment was not initiated in the LTE period.

Long term extension (LTE) Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period. Participants 18 years or older with an assessment at given time point.

Long term extension (LTE) Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period. Participants with an assessment at given time point.

LTE Analysis Set - Participants in MRI Substudy. The number analyzed on each row pertains to the number of participants with a given baseline status.

Long term extension (LTE) Analysis Set - MRI Substudy: participants in MRI Substudy who consented to LTE period and took at least 1 dose of study drug in the LTE period. Participants 18 years or older with an assessment at given time point.

Annualized Recurrence Rate is defined as number of recurrences in LTE periods for all participants/Sum of participant years in LTE period for all participants. Participant years in LTE period is defined as the time from 1st dose date of LTE period to the date of End of Study, or data cutoff date, whichever is earlier. The 95% CI was calculated using an exact method with Poisson distribution.

Pericarditis recurrence was defined as the recurrence of typical pericarditis pain associated with supportive objective evidence of pericarditis. At any time during the RW period, participants who experienced a suspected recurrence of pericarditis symptoms reported to the study site/clinic for a scheduled or unscheduled visit, during which clinical assessments were performed to gather all the necessary diagnostic data to confirm or rule out the presence of pericarditis recurrence.

LTE Analysis Set: participants who consented to LTE period and took at least 1 dose of study drug in the LTE period.

Annualized Recurrence Rate is defined as the number of recurrences in RW period for all participants/Sum of participant years in RW period for all participants. Participant years in RW period is defined as the time from randomization date to the date of EORW or last dose date + 6 weeks, whichever is earlier. The 95% CI was calculated using an exact method with Poisson distribution.

Pericarditis recurrence was defined as the recurrence of typical pericarditis pain associated with supportive objective evidence of pericarditis. At any time during the RW period, participants who experienced a suspected recurrence of pericarditis symptoms reported to the study site/clinic for a scheduled or unscheduled visit, during which clinical assessments were performed to gather all the necessary diagnostic data to confirm or rule out the presence of pericarditis recurrence.

ITT Analysis Set: all participants who were randomized in the RW period. Participants who received rilonacept in the RW period only.