A study to evaluate different dose levels of GlaxoSmithKline (GSK) Biologicals’ investigational Respiratory Syncytial Virus (RSV) vaccine (GSK3888550A), based on the vaccine safety and the antibodies (body defences) produced following vaccine administration, when given to healthy non-pregnant women

Subjects who the investigator believes will comply with the requirements of the protocol (e.g. completion of the diary cards/questionnaires, return for follow-up visits, have regular contact to allow evaluation during the study);

• Written informed consent obtained from the subject;
• Healthy female subjects; as established by medical history and clinical examination, aged 18 to 45 years at the time of the vaccination;
• Female subjects of childbearing potential may be enrolled in the study, if the subject:

Use of any investigational or non-registered product other than the study vaccine within 30 days preceding vaccination or any planned use during the study period;

• Concurrently participating in the active phase of 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
• Chronic administration (defined as more than 14 days in total) of immunosuppressant or other immune-modifying drugs, as well as administration of long acting immune modifying drugs, within 6 months prior to the vaccine dose (for corticosteroids, this will mean prednisone higher than or equal to (≥) 5 milligrams per day (mg/day), or equivalent). Inhaled and topical steroids are allowed;
• Administration of immunoglobulins and/or any blood products during the period starting 3 months before the study vaccination, or planned administration until 90 days post-vaccination;
• Planned administration/administration of a vaccine not foreseen by the study protocol within the period starting 30 days before and ending 30 days after study vaccination, with the exception of any licensed influenza vaccine which may be administered ≥ 15 days before or after study vaccination;
• Previous experimental vaccination against RSV;
• Presence of neurological or psychiatric diagnoses which, although stable, are deemed by the investigator to render the potential subject unable/unlikely to provide accurate safety reports;
• Family history of congenital or hereditary immunodeficiency;
• Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination;
• History of allergic disease or reactions likely to be exacerbated by any component of the vaccine;
• Any acute or chronic, clinically significant disease, as determined by physical examination, laboratory screening tests, subject personal report and/or health care provider information. The following conditions will be exclusionary:

Any other significant uncontrolled medical illness, defined as any illness requiring new medical and/or surgical treatment or significant modification of treatment dose due to uncontrolled symptoms or drug toxicity, within 3 months prior to study vaccination.

• History of or current autoimmune disease;
• Body mass index (BMI) > 40 Kilograms (kg)/square meters(m^2);
• Pregnant or lactating female;
• Female planning to become pregnant or planning to discontinue contraceptive precautions;
• Hypersensitivity to latex;
• Lymphoproliferative disorder or malignancy within previous 5 years;
• Acute disease and/or fever at the time of enrolment;

Subjects with a minor illness (such as mild diarrhoea, mild upper respiratory infection) without fever may be enrolled at the discretion of the investigator.

• Any clinically significant or any ≥ Grade 2* haematological (haemoglobin level, white blood cell, lymphocyte, neutrophil, eosinophil, and platelets) and biochemical (alanine aminotransferase [ALT] aspartate aminotransferase [AST], creatinine, blood urea nitrogen [BUN]) laboratory abnormality detected at the last screening blood sampling; *Grading of laboratory parameters will be based on the FDA Guidance for Industry “Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventive Vaccine Clinical Trials”. For Grade 1 laboratory abnormalities, the investigator should use clinical judgement to decide which ones are clinically relevant. Subjects with haematological/biochemical values out of normal range at screening which are expected to be temporary, may be re-screened 1 time at a later date.
• Any other condition that the investigator judges may interfere with study procedures or findings;
• Any medical condition that in the judgment of the investigator would make intramuscular injection unsafe;
• Alcoholism, drug abuse and/or use disorder within the past two years (as defined in Diagnostic and Statistical Manual of Mental Disorders [DSM-5] Diagnostic Criteria);
• Planned move to a location that will prohibit participating in the trial until study end.