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 \