A Study to Evaluate Safety, Reactogenicity and Immunogenicity of GSK Biologicals' RSV Investigational Vaccine Based on Viral Proteins Encoded by Chimpanzee-derived Adenovector (ChAd155-RSV) (GSK3389245A) in RSV-seropositive Infants

Assessed solicited local symptoms are pain, redness and swelling at injection site. Any = occurrence of the symptom regardless of intensity grade. Any redness and swelling symptom = symptom reported with a surface diameter greater than 0 millimeters.

Assessed solicited general symptoms are drowsiness, fever [defined as temperature equal to or above (≥) 37.5 degrees Celsius (°C)/99.5 degrees Fahrenheit (°F) for oral, axillary or tympanic route, or ≥ 38.0°C/100.4°F for rectal route, the preferred route for recording temperature in this study being axillary], irritability/fussiness and loss of appetite. Any = occurrence of the symptom regardless of intensity grade or relation to study vaccination.

An unsolicited AE covers any untoward medical occurrence in a clinical investigation subject temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. Unsolicited AEs are reported in addition to those solicited during the clinical study and any solicited symptom with onset outside the specified period of follow-up for solicited symptoms. Any is defined as the occurrence of any unsolicited AE regardless of intensity grade or relation to study vaccination.

Assessed SAEs include any untoward medical occurrences that resulted in death, were life-threatening, required hospitalization or prolongation of hospitalization or resulted in disability/incapacity. Any = occurrence of SAE regardless of intensity grade or relation to study vaccination.

Any episode of spontaneous or excessive bleeding if occurring after vaccination was to be fully investigated with a full range of hematological tests to identify the underlying cause and reported as an AE of specific interest.

Assessed hematological laboratory parameters include hemoglobin level [HgL] white blood cells [WBC] and platelet count [PLC]. Hematological abnormalities refer to range indicator at timing, categorized as Below, Within or Above normal ranges, and compared to baseline range indicator of the same parameter, at Screening (Day-29 to Day 1) i.e. Unknown, Below, Within or Above. [e.g. HgL, Below, Below = HgL below normal ranges at baseline versus below normal ranges at Day 2].

Assessed hematological laboratory parameters include hemoglobin level [HgL] white blood cells [WBC] and platelet count [PLC]. Hematological abnormalities refer to range indicator at timing, categorized as Below, Within or Above normal ranges, and compared to baseline range indicator of the same parameter, at Screening (Day-29 to Day 1) i.e. Below, Within or Above. [e.g. HgL, Below, Below = HgL below normal ranges at baseline versus below normal ranges at Day 8].

Assessed hematological laboratory parameters include hemoglobin level [HgL] white blood cells [WBC] and platelet count [PLC]. Hematological abnormalities refer to range indicator at timing, categorized as Below, Within or Above normal ranges, and compared to baseline range indicator of the same parameter, at Screening (Day-29 to Day 1) i.e. Unknown, Below, Within or Above. [e.g. HgL, Below, Below = HgL below normal ranges at baseline versus below normal ranges at Day 31].

Assessed hematological laboratory parameters include hemoglobin level [HgL] white blood cells [WBC] and platelet count [PLC]. Hematological abnormalities refer to range indicator at timing, categorized as Below, Within or Above normal ranges, and compared to baseline range indicator of the same parameter, at Screening (Day-29 to Day 1) i.e. Unknown, Below, Within or Above. [e.g. HgL, Below, Below = HgL below normal ranges at baseline versus below normal ranges at Day 32].

Assessed hematological laboratory parameters include hemoglobin level [HgL] white blood cells [WBC] and platelet count [PLC]. Hematological abnormalities refer to range indicator at timing, categorized as Below, Within or Above normal ranges, and compared to baseline range indicator of the same parameter, at Screening (Day-29 to Day 1) i.e. Below, Within or Above. [e.g. HgL, Below, Below = HgL below normal ranges at baseline versus below normal ranges at Day 38].

Assessed hematological laboratory parameters include hemoglobin level [HgL] white blood cells [WBC] and platelet count [PLC]. Hematological abnormalities refer to range indicator at timing, categorized as Below, Within or Above normal ranges, and compared to baseline range indicator of the same parameter, at Screening (Day-29 to Day 1) i.e. Unknown, Below, Within or Above. [e.g. HgL, Below, Below = HgL below normal ranges at baseline versus below normal ranges at Day 61].

Assessed biochemical laboratory parameters include alanine aminotransferase [ALT], aspartate aminotransferase [AST] and creatinine [CREA]. Biochemical abnormalities refer to range indicator at timing, categorized as Below, Within or Above normal ranges, and compared to baseline range indicator of the same parameter, at Screening (Day-29 to Day 1) i.e. Unknown, Below, Within or Above. [e.g. ALT, Below, Below = ALT below normal ranges at baseline versus below normal ranges at Day 31].

Assessed biochemical laboratory parameters include alanine aminotransferase [ALT], aspartate aminotransferase [AST] and creatinine [CREA]. Biochemical abnormalities refer to range indicator at timing, categorized as Below, Within or Above normal ranges, and compared to baseline range indicator of the same parameter, at Screening (Day-29 to Day 1) i.e. Below, Within or Above. [e.g. ALT, Below, Below = ALT below normal ranges at baseline versus below normal ranges at Day 61].

Assessed SAEs include any untoward medical occurrences that resulted in death, were life-threatening, required hospitalization or prolongation of hospitalization or resulted in disability/incapacity. Any = occurrence of SAE regardless of intensity grade or relation to study vaccination.

Subjects experiencing an LRTI associated with RSV infection were reported as AE of specific interest. To identify RSV-LRTI for the purpose of AE of specific interest, the diagnosis was based on the investigators' clinical judgment taking into account the clinical history, the examination, relevant medical investigations and locally-available diagnostic test for RSV.

RSV-RTI refers to subject having runny nose OR blocked nose OR cough AND confirmed RSV infection [RSV infection confirmed on nasal swab positive for RSV A or B by quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR) performed at sponsor level]. RSV-LRTI refers to subject with history of cough OR difficulty breathing [based on history reported by parents/legally acceptable representatives (LARs) and includes difficulty breathing (e.g. showing signs of wheezing or stridor, tachypnoea, flaring of nostrils, chest in-drawing, apnoea) associated with nasal obstruction] AND Blood Oxygen Saturation (SpO2) lower than (<) 95 percent (%), OR respiratory rate (RR) increase [defined as ≥ 40/minute (12 months of age or above)] AND confirmed RSV infection. RSV-severe LRTI are cases meeting the case definition of RSV-LRTI AND SpO2 < 93%, OR lower chest wall in-drawing.

Assessed SAEs include any untoward medical occurrences that resulted in death, were life-threatening, required hospitalization or prolongation of hospitalization or resulted in disability/incapacity. Any = occurrence of SAE regardless of intensity grade or relation to study vaccination.

Subjects experiencing an LRTI associated with RSV infection were reported as AE of specific interest. To identify RSV-LRTI for the purpose of AE of specific interest, the diagnosis was based on the investigators' clinical judgment taking into account the clinical history, the examination, relevant medical investigations and locally-available diagnostic test for RSV.

RSV-RTI refers to subject having runny nose OR blocked nose OR cough AND confirmed RSV infection (RSV infection confirmed on nasal swab positive for RSV A or B by qRT-PCR performed at sponsor level). RSV-LRTI refers to subject with history of cough OR difficulty breathing [based on history reported by parents/LARs and includes difficulty breathing (e.g. showing signs of wheezing or stridor, tachypnoea, flaring of nostrils, chest in-drawing, apnoea) associated with nasal obstruction] AND Sp02 < 95% OR respiratory rate (RR) increase [defined as ≥ 40/minute (12 months of age or above)] AND confirmed RSV infection. RSV-severe LRTI are cases meeting the case definition of RSV-LRTI AND SpO2 < 93%, OR lower chest wall in-drawing.

Magnitude of cell mediated immunity (CMI) response to the investigational RSV vaccine was measured in terms of frequency of RSV-specific CD4+ T-cells expressing at least two markers upon stimulation with F, N and M2-1 peptide pools and expressed in RSV-specific CD4+ T-cells/million cells.

Assessed markers were CD40-L, IL-2, TNF-α and IFN-ɣ.

Humoral response to the investigational RSV vaccine was measured in terms of anti-RSV-A neutralizing antibody titers and expressed as geometric mean titers (GMTs) in Estimated Dilution 60 (ED60) titers.

Humoral response to the investigational RSV vaccine was measured as anti-RSV F antibody concentrations and expressed as geometric mean concentrations (GMCs) in enzyme-linked immunosorbent assay (ELISA) units per milliliter (EU/mL).

Humoral response to the investigational RSV vaccine was measured as Palivizumab-competing antibody concentrations and expressed as geometric mean concentrations (GMCs) in microgram/milliliter (µg/mL).