A Phase 3 Study to Assess the Efficacy, Safety, and Tolerability of Itepekimab (Anti-IL-33 mAb) in Participants With Inadequately-controlled Chronic Rhinosinusitis With Nasal Polyps

EFC18419 is a multinational, randomized, double-blind, placebo-controlled, parallel-group, Phase 3 study with 3 treatment groups. The purpose of the study is to evaluate the efficacy, safety and tolerability of 2 dosing regimens of itepekimab compared to placebo as add-on therapy to intranasal corticosteroids (INCS) in male and female participants with chronic rhinosinusitis with nasal polyps (CRSwNP) aged 18 years of age and older. Study details include: * The study duration per participant (4-week screening, 52-week treatment, 20-week safety follow-up) will be up to 76 weeks. For participants transitioning to the LTS18420 study, the study duration will be 56 weeks. * The treatment duration will be up to 52 weeks. * The number of visits will be 9 site visits and 20 phone/home visits.

Inclusion Criteria: * Participants must be 18 years of age or older. * Participants with a history of chronic rhinosinusitis with nasal polyps (CRSwNP) for at least 1 year prior to screening * Participants must have at least one of the following features: * Prior sinonasal surgery for nasal polyps (NP). * Worsening symptoms of chronic rhinosinusitis (CRS) requiring treatment with systemic corticosteroid(s) (SCS) within the prior 1 year before screening (Visit 1). * An endoscopic bilateral Nasal Polyp Score (NPS) of at least 5 out of maximum score of 8 (with a minimum score of 2 in each nasal cavity) at screening and randomization. * Ongoing symptoms (for at least 12 weeks before Visit 1) of: * Nasal congestion/blockade/obstruction with moderate or severe (symptom severity score 2 or 3) at Visit 1 and a weekly average severity of greater than 1 in the week before randomization (Visit 2), AND * At least one of the following two symptoms: loss of smell or rhinorrhea (anterior/posterior). * A female participant is eligible to participate if she is not pregnant or breastfeeding, and at least 1 of the following conditions applies: * Is not a women of childbearing potential (WOCBP), OR * Is a WOCBP and agrees to use a contraceptive method that is highly effective, with a failure rate of \<1% during the study (at a minimum until 20 weeks after the last dose of study intervention). Exclusion Criteria: Participants are excluded from the study if any of the following criteria apply: * Participants with a history of clinically significant renal, hepatic, metabolic, neurologic, hematologic, ophthalmologic, respiratory (excluding those with asthma and aspirin-exacerbated respiratory disease (AERD) which may be included in the study), gastrointestinal, cardiovascular, cerebrovascular, or other significant medical illness or disorder, which, in the judgment of the Investigator, could interfere with the study or require treatment that might interfere with the study. * Participants who are currently smoking tobacco and/or vaping, or participants in whom smoking/vaping cessation has occurred \<6 months prior to Screening (Visit 1). Nicotine replacement therapy and/or noninhaled tobacco product use are not considered current smoking of tobacco. * Participants meet any contraindications for mometasone furoate nasal spray (MFNS) such as hypersensitivity to MFNS or any of its components; or participants with uncontrolled opportunistic infections. * Participants with a history of a severe systemic hypersensitivity reaction to a mAb. * Participants with conditions/concomitant diseases making them non-evaluable at Visit 1 or for the primary efficacy endpoint. * Participants with nasal cavity malignant tumor and benign tumors (eg, papilloma, blood boil etc). * Participants with severe uncontrolled asthma with history of 2 and/or more exacerbations, requiring SCS or 1 hospitalization requiring SCS in the past year. * History of concomitant lung disease (other than asthma, eg, COPD, interstitial lung disease) which in the opinion of the Investigator could interfere with performance and interpretation of spirometry. * Participants treated with intranasal corticosteroid(s) (INCS) (MFNS is permitted), intranasal emitting devices/stents, nasal spray using exhalation delivery system such as XhanceTM during the screening period. In Japan and China INCS other than MFNS are permitted. * Participants who have undergone any sinus intranasal surgery (including polypectomy) within 6 months before Visit 1. * Participants who received SCS 1 month prior to Screening (Visit 1) or during the screening period (between Visit 1 and Visit 2). * Known allergy to itepekimab or its excipients, or any drug or other allergy that, in the opinion of the Investigator, contraindicates participation in this study. The above information is not intended to contain all considerations relevant to a participant's potential participation in a clinical trial.