A Study to Assess the Safety, Reactogenicity and Immune Response of GlaxoSmithKline (GSK) Biologicals' Investigational Respiratory Syncytial Virus (RSV) Vaccine (GSK3844766A) in Older Adults

Inclusion Criteria

For all subjects:

• Subjects who, in the opinion of the investigator, can and will comply with the requirements of the protocol.
• Written informed consent obtained from the subject prior to performing any study specific procedure.

For Part A:

• A male or female between, and including, 18 and 40 years of age at the time of the first vaccination.

For Part B:

• A male or female between, and including, 60 and 80 years of age at the time of the first vaccination.
• Subjects with residence status allowing free mixing with general community or in an assisted-living facility that provides minimal assistance, such that the subject is primarily responsible for self-care and activities of daily living.

Exclusion Criteria

For all subjects:

• Use of any investigational or non-registered product other than the study vaccine during the period starting 30 days before the first dose of study vaccine, or planned use during the study period.
• Any medical condition that in the judgment of the investigator would make IM injection unsafe.
• Chronic administration of immunosuppressants or other immune-modifying drugs during the period starting 6 months prior to the first vaccine dose. For corticosteroids, this will mean prednisone (≥ 20 mg/day, or equivalent). Inhaled and topical steroids are allowed.
• Administration of long-acting immune-modifying drugs or planned administration at any time during the study period.
• Planned administration/administration of a vaccine not foreseen by the study protocol in the period starting 30 days before the first dose and ending 30 days after the last dose of study vaccine administration, with the exception of inactivated and subunit influenza vaccines which can be administered up to 14 days before or from 30 days after each study vaccination.
• Concurrently participating in another clinical study, at any time during the study period, in which the subject has been or will be exposed to an investigational or a non-investigational vaccine/product.
• Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination.
• History of any reaction or hypersensitivity likely to be exacerbated by any component of the vaccine.
• Hypersensitivity to latex.
• Serious or unstable chronic illness. Patients with chronic stable conditions with or without specific treatment, such as diabetes, hypertension or cardiac disease, are allowed to participate in this study.
• Any other condition (e.g. chronic obstructive pulmonary disease or severe respiratory condition) that, in the opinion of the investigator, might interfere with the evaluations required by the study.
• History of any neurological disorders or seizures.
• Acute disease and/or fever at the time of enrolment.
• Acute or chronic, clinically significant pulmonary, cardiovascular, hepatic or renal functional abnormality, as determined by the investigator based on medical history, physical examination or laboratory screening tests.
• Hepatomegaly, right upper quadrant abdominal pain or tenderness.
• Administration of immunoglobulins and/or any blood products during the period starting 3 months before the first dose of study vaccine or planned administration during the study period.
• History of chronic alcohol consumption and/or drug abuse as deemed by the investigator to render the potential subject unable/unlikely to provide accurate safety reports.
• Significant underlying illness that in the opinion of the investigator would be expected to prevent completion of the study.
• Previous vaccination with an RSV vaccine.
• Lymphoproliferative disorder and malignancy within 5 years.
• Body mass index > 40 kg/m².
• Planned move to a location that will prohibit participating in the trial until study end.
• At screening: Hematology parameters (complete blood cell count [red blood cells, white blood cells], white blood cells differential count [lymphocytes, neutrophils and eosinophils], plate