Study D5290C00008 is a Phase 2, open-label, uncontrolled, single-dose study to evaluate the safety and tolerability, pharmacokinetic(s) (PK), occurrence of antidrug antibody (ADA), and efficacy of nirsevimab in immunocompromised children who are ≤ 24 months of age at the time of dose administration. Approximately 100 subjects will be enrolled. Subjects will be followed for approximately 1 year after dose administration.

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infection (LRTI) among infants and young children, resulting in annual epidemics in Japan. Children with congenital or acquired immunodeficiencies, transplant recipients, and those receiving immunosuppressive therapy are at increased risk for severe RSV-associated LRTI with prolonged viral shedding and higher viral loads, resulting in prolonged hospitalizations, admissions to the intensive care unit (ICU), and the need for mechanical ventilation. Palivizumab (Synagis®) is the only approved agent for RSV prophylaxis, and its half-life (t1/2) is approximately 1 month, infants and young children need to receive monthly intramuscular doses of palivizumab throughout the RSV season to maintain protection. This constitutes a significant burden on healthcare providers as well as the infants/children and their families.

Nirsevimab may provide a cost-effective opportunity to protect all infants from RSV disease based on an improvement in potency and the extended t1/2 that is expected to support once-per-RSV-season dosing.

Inclusion Criteria:

• Neonate, infant, or young child ≤ 24 months of age at the time of dose administration who, per investigator judgement, are:

  1. In their first year of life AND entering their first RSV season at the time of dose administration OR
  2. In their second year of life AND entering their second RSV season at the time of dose administration

• The subject must meet at least 1 of the following conditions at the time of informed consent.

  1. Diagnosed with combined immunodeficiency (severe combined immunodeficiency, X-linked hyper-immunoglobulin M [IgM] syndrome, etc); antibody deficiency (X linked agammaglobulinemia, common variable immunodeficiency, non-X-linked hyper-IgM syndromes, etc); or other immunodeficiency (Wiskott-Aldrich syndrome, DiGeorge syndrome, etc), or
  2. Diagnosed with human immunodeficiency virus infection, or
  3. History of organ or bone marrow transplantation, or
  4. Subject is receiving immunosuppressive chemotherapy, or
  5. Subject is receiving systemic high-dose corticosteroid therapy (prednisone equivalents ≥ 0.5 mg/kg every other day, other than inhaler or topical use), or
  6. Subject is receiving other immunosuppressive therapy (eg, azathioprine, methotrexate, mizoribine, mycophenolate mofetil, cyclophosphamide, cyclosporine, tacrolimus, cytokine inhibitors, etc)

• Written informed consent and any locally required authorization obtained from the subject's parent(s)/legal representative(s) prior to performing any protocol-related procedures, including screening evaluations.

• Subject's parent(s)/legal representative(s) able to understand and comply with the requirements of the protocol including follow-up visits as judged by the investigator.

• Subject is available to complete the follow-up period, which will be approximately 1 year after receipt of nirsevimab

Exclusion Criteria:

• Subject who meets any of the palivizumab indications approved in Japan other than immunocompromised condition.

  1. Subject born at ≤ 28 weeks gestation and is ≤ 12 months of age
  2. Subject born at 29 to 35 weeks gestation and is ≤ 6 months of age
  3. Age ≤ 24 months with a history of bronchopulmonary dysplasia requiring medical management within the past 6 months
  4. Age ≤ 24 months with current hemodynamically significant congenital heart disease (CHD)
  5. Age ≤ 24 months with Down syndrome

• Requirement for oxygen supplementation, mechanical ventilation, extracorporeal membrane oxygenation, continuous positive airway pressure, or other mechanical respiratory or cardiac support at screening

• A current, active infection, including RSV infection, at the time of screening or at the time of investigational product administration.

• Any fever (≥ 100.4°F [≥ 38.0°C], regardless of route) or acute illness within 7 days prior to investigational product administration.

• Any serious concurrent medical condition (renal failure, hepatic dysfunction, suspected active or chronic hepatitis infection, seizure disorder, unstable neurologic disorder, etc), except those resulting in an immune deficiency condition.

• Clinically significant congenital anomaly of the respiratory tract.

• Receipt of palivizumab.

• Any known allergy or history of allergic reaction to any component of nirsevimab.

• Any known allergy or history of allergic reaction to immunoglobulin products, blood products, or other foreign proteins.

• Concurrent enrollment in another interventional study, or prior receipt of any investigational agent.

• Anticipated survival of less than 1 year at the time of informed consent.

• Any condition that, in the opinion of the investigator, would interfere with evaluation of the investigational product or interpretation of study results.

• Children of employees of the sponsor, clinical study site, or any other individuals involved with the conduct of the study, or immediate family members of such individuals.

Qualified researchers can request access to anonymized individual patient-level data from AstraZeneca group of companies sponsored clinical trials via the request portal.

All request will be evaluated as per the AstraZeneca (AZ) disclosure commitment:

https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure. Yes, indicates that AstraZeneca (AZ) are accepting requests for Individual Participant Data (IPD), but this does not mean all requests will be shared.

AstraZeneca will meet or exceed data availability as per the commitments made to the European Federation of Pharmaceutical Industries and Associations (EFPIA) Pharma Data Sharing Principles. For details of our timelines, please rerefer to our disclosure commitment at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

When a request has been approved AstraZeneca will provide access to the deidentified individual patient-level data in an approved sponsored tool . Signed Data Sharing Agreement (non-negotiable contract for data accessors) must be in place before accessing requested information. Additionally, all users will need to accept the terms and conditions of the SAS MSE to gain access. For additional details, please review the Disclosure Statements at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

Open: no masking is used. All involved know the identity of the intervention assignment.