A Study to Examine the Efficacy and Safety of Anti-Fel d 1 Antibodies Injections in Cat-allergic Adolescent and Adult Patients With Allergic Rhinitis Who Live With a Cat

Key Inclusion Criteria:

1. Generally healthy males and females who are 12 years and older at the time ofscreening.

2. Weight must be ≥40 kg at the time of screening

3. Documented or patient reported history (for at least 2 years) of symptomatic catallergen-triggered allergic rhinitis with or without conjunctivitis and with orwithout asthma as defined by all of the following criteria:

4. Positive skin prick test (SPT) with cat hair extract (mean wheal diameter atleast 5 mm greater than a negative control) at screening

5. Positive allergen-specific IgE (sIgE) tests for cat and Fel d 1 (both ≥0.7kUa/L at screening)

6. Documented or patient reported history of nasal and/or ocular symptoms upon catexposure

7. Symptomatic despite the use of medications to treat their nasal and/or ocularsymptoms

8. At least 1 generally healthy cat (that is unlikely to die during the study) livingin the home resulting in regular exposure

9. A daily total rhinitis/conjunctivitis symptom score (total symptom score [TSS]) ofat least 8 of 18 during at least 8 days of the 15-day baseline assessment period anduse of standard, therapeutic doses of pharmacotherapy for the treatment of allergicrhinoconjunctivitis on at least 8 days of the 15-day baseline assessment period.

Key Exclusion Criteria:

1. History of significant multiple and/or severe allergies, as assessed by theinvestigator, that would potentially interfere with the assessments during thebaseline and 12-week efficacy assessment periods or confound results, perinvestigator discretion, including significant rhinitis or sinusitis due to dailycontact with other allergens causing symptoms that are expected to coincide with thebaseline period or any of the efficacy assessment periods

2. Received REGN1908-1909 in a prior REGN1908-1909 clinical trial (receipt of placeboin a previous trial is allowed)

3. Active lung disease other than asthma

4. FEV1 less than 70% of predicted at screening or randomization

5. Treatment with an investigational drug within 2 months or within 5 half-lives (ifknown), whichever is longer, prior to screening

6. Persistent chronic or recurring acute infection requiring treatment withantibiotics, antivirals, or antifungals, or any untreated respiratory infectionswithin 4 weeks prior to screening. Patients may be re-evaluated after resolution ofsymptoms and specified time duration

NOTE: Other protocol-defined Inclusion/ Exclusion Criteria apply