• Participant must be at least 18 (or the legal age of consent in the jurisdiction in which the study is taking place) years of age inclusive, at the time of signing the informed consent. - Participants with bilateral sino-nasal polyposis, that despite prior treatment with Systemic corticosteroids (SCS) anytime within the past 2 years; and/or medical contraindication/intolerance to SCS; and/or prior surgery for NP have: - An endoscopic bilateral NPS of at least 5 out of a maximum score of 8 (with a minimum score of 2 in each nasal cavity) at visit 1; AND - Ongoing symptoms of Nasal congestion/blockade/obstruction and loss of smell for at least 8 weeks before screening (Visit 1), AND - Nasal congestion/blockade/obstruction and a weekly average severity greater than 1 in the 7 days before randomization (Visit 2) AND - loss of smell symptom severity score 2 or 3 at screening (Visit 1) and a weekly average severity of greater than 1 in the 7 days before randomization (Visit 2). - Participants with a physician diagnosis of asthma based on the Global Initiative for Asthma (GINA) 2020 treated with low, medium or high dose inhaled corticosteroids (ICS) and a second controller (ie, LABA), a third controller is allowed but not mandatory. The dose regimen should be stable for at least 1 month before Visit 1 (screening visit) and during the screening and run-in period. - Asthma Control Questionnaire 5-question version (ACQ-5) score ≥1.5 at Visits 1 or 2. - Treatment with intranasal mometasone ≥200 μg once daily (QD) (or equivalent of another INCS) for 1 month prior to Visit 1 and during the run-in period (for CRSwNP). - Eligibility as per omalizumab drug-dosing table (serum IgE level ≥30 to ≤1500 IU/mL and body weight ≥30 to ≤150 kg) and ability to be dosed per the dosing table.

Participants are excluded from the study if any of the following criteria apply: - Participants who have undergone any sinus intranasal surgery (including polypectomy) within 6 months before Visit 1. - Participants who have had a sino-nasal surgery changing the lateral wall structure of the nose, making impossible the evaluation of NPS. - Participants with conditions/concomitant diseases making them non evaluable at Visit 1 or for the primary efficacy endpoint such as: Antrochoanal polyps, Nasal septal deviation that would occlude at least one nostril, Acute sinusitis, nasal infection, or upper respiratory infection. - Severe asthma exacerbation requiring treatment with SCS in the last 4 weeks prior to Visit 1 and during screening. - Severe concomitant illness(es) that, in the Investigator's judgment, would adversely affect the participant's participation in the study - Diagnosed with, suspected of, or at high risk of endoparasitic infection, and/or use of antiparasitic drugs within 2 weeks before Visit 1 (screening visit) or during the screening and run-in period. - History of human immunodeficiency virus (HIV) infection or positive HIV 1/2 serology at Visit 1 (screening visit). - Known or suspected immunodeficiency, including history of invasive opportunistic infections - Active malignancy or history of malignancy within 5 years before Visit 1 (screening visit), except completely treated in situ carcinoma of the cervix and completely treated and resolved non metastatic squamous or basal cell carcinoma of the skin. - History of systemic hypersensitivity or anaphylaxis to dupilumab and omalizumab, including any excipient - Treatment with a live (attenuated) vaccine within 4 weeks before Visit 1 (screening visit). The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.