Study to Evaluate the Efficacy and Safety of Suptavumab (REGN2222) for the Prevention of Medically Attended RSV (Respiratory Syncytial Virus) Infection in Preterm Infants

This study occurred in two parts: Part A and Part B.

Part A of the study was an open-label, PK evaluation of intramuscular (IM) administered
suptavumab in preterm infants for whom palivizumab was not recommended to enable the
selection of dosing regimens for Part B.

Part B of the study was randomized, double-blind, and placebo-controlled, designed to
evaluate efficacy, safety, serum concentration and immunogenicity of IM administration of
suptavumab in preterm infants for whom palivizumab was not recommended. The total duration of
Part B was up to 265 days (includes a 28-day screening period, 57-day treatment period and
180-day follow-up period).

Up to 1515 subjects were planned to be included in Part B of the study. Participants were
randomly assigned to 1 of 3 different groups, each with 505 infants; one group received one
dose of suptavumab and one dose of placebo, the second group received two doses of
suptavumab, and the third group received two doses of placebo.

There was a separate genetic testing sub study.

Key Inclusion Criteria:

1. Preterm, otherwise healthy male or female infant who is ≤6 months of age at the time
of the first dose (i.e., infant must be treated on or before their 6 month birthday)

2. Gestational age is ≤35 weeks, 6 days at birth

3. Parent(s) or legal guardian(s) of the infant is able to understand the study
requirements and willing to provide informed consent

Key Exclusion Criteria:

1. Eligible, recommended and have access to receive palivizumab per AAP or other local
guidelines, standard practice, or by their healthcare provider

2. History of CLD defined as requirement of supplemental oxygen for 28 days after birth

3. Known hemodynamically significant congenital heart disease

4. Known immunodeficiency, neuromuscular disease, or congenital abnormalities of the
airway

5. Known renal or hepatic dysfunction

6. Major congenital malformations, including congenital cleft palate, cytogenetic
abnormalities, or serious chronic disorders

7. Known or suspected impairment of immunological functions or autoimmune diseases

8. History of anaphylaxis

9. Previously received palivizumab or any other investigational RSV prophylaxis or
vaccine product

10. Previous reaction to IV immunoglobulin, blood products or other foreign proteins,
including vaccines and monoclonal antibodies

Note: Other inclusion and exclusion criteria apply