The purpose of this study is:

• To investigate the optimal timing for revaccination after the initial RSVPreF3 OA vaccine dose,
• To evaluate the long-term immune persistence and safety up to 5 consecutive RSV seasons (approximately 60 months) of a single dose of RSVPreF3 OA vaccine,
• To give the opportunity to participants who received only placebo in the RSVOA=ADJ- 006 study, to receive a dose of the RSVPreF3 OA vaccine and collect additional safety information.

Inclusion Criteria:

• Male or female participants who were previously enrolled in the RSV OA=ADJ-006 study and received placebo (Placebo group) or a single dose of the RSVPreF3 OA vaccine (RSV_1dose group).
• Participants who, in the opinion of the investigator, can and will comply with the requirements of the protocol (e.g. completion of the diary cards, attend regular phone calls/study site visits, ability to access and utilize a phone or other electronic communications).
• Written or witnessed informed consent obtained from the participant prior to performance of any study specific procedure.
• Participants who are medically stable in the opinion of the investigator at study entry. Participants with chronic stable medical conditions with or without specific treatment, such as diabetes, hypertension or cardiac disease, are allowed to participate in this study.

Exclusion Criteria:

Medical Conditions:

• Any confirmed or suspected immunosuppressive or immunodeficient condition resulting from disease or immunosuppressive/cytotoxic therapy based on medical history and physical examination.
• History of any reaction or hypersensitivity likely to be exacerbated by any component of the study intervention.
• Hypersensitivity to latex.
• Serious or unstable chronic illness.
• Recurrent or un-controlled neurological disorders or seizures.
• Significant underlying illness that in the opinion of the investigator would be expected to prevent completion of the study.
• Any other medical condition that in the judgment of the investigator would make intramuscular injection unsafe.
• Any other clinical condition that, in the opinion of the investigator, might pose additional risk to the participant due to participation in the study.
• Any history of dementia or any medical condition that moderately or severely impairs cognition and understanding of the informed consent form and/or study procedures.
• Participants who experienced an SAE or pIMD from first study intervention administration in the RSV OA=ADJ-006 study until enrollment in this study that was considered to be possibly or probably related to the study vaccine or non-study concomitant vaccines, either by the investigator or the sponsor, including hypersensitivity reactions.
• Participants with a new onset of a pIMD or exacerbation of a pIMD from first study intervention administration in the RSV OA=ADJ-006 study until enrollment in this study, that, in the opinion of the investigator, exposes the participant to unacceptable risk from subsequent vaccination.

Prior/Concomitant Therapy:

• Use of any investigational or non-registered product other than the study vaccine during the period beginning 30 days before the first dose of study vaccine, or planned use during the study period. • Previous vaccination with an RSV vaccine (investigational or licensed vaccine) and/or planned administration of an RSV vaccine during the study period other than the RSVPreF3 OA vaccine administered during the RSV OA=ADJ-006 study.

Prior/Concurrent Clinical Study Experience:

• Concurrently participating in another clinical study, at any time during the study period, in which the participant has been or will be exposed to an investigational or a non-investigational vaccine/product.

Other Exclusion Criteria:

• History of chronic alcohol consumption and/or drug abuse as deemed by the investigator to render the potential participant unable/unlikely to provide accurate safety reports or comply with study procedures.
• Participation of any study personnel or their immediate dependents, family, or household members.
• Bedridden participants.

Specific exclusion criteria for Crossover group:

• Planned or administration of a vaccine not foreseen by the study protocol in the period starting 30 days before and ending 30 days after study intervention administration, with the exception of COVID vaccines which can be administered up to 14 days before or from 14 days after study vaccination. Inactivated seasonal influenza vaccines can be co-administered or administered at any time.

Specific exclusion criteria for RSV_PreS4, RSV_PreS5 and RSV_1Dose groups:

• Planned or administration of a vaccine not foreseen by the study protocol in the period starting 30 days before and ending 30 days after study intervention administration, with the exception of COVID vaccines and inactivated seasonal influenza vaccines which can be administered up to 14 days before or from 14 days after study intervention administration.
• Administration of long-acting immune-modifying drugs or planned administration at any time during the study period.
• Administration of immunoglobulins and/or any blood products or plasma derivatives during the period starting 90 days before the first study visit or planned administration during the study period.
• Chronic administration of immunosuppressants or other immunemodifying drugs during the period starting 90 days prior to the first study visit or planned administration during the study period. For corticosteroids, this will mean prednisone >= 20 mg/day, or equivalent. Inhaled and topical steroids are allowed.

GSK will assess requests from qualified researchers for anonymized individual patient-level data and related study documents. Data sharing is subject to certain criteria, conditions, and exceptions. For further information, refer to https://www.gsk-studyregister.com/About\_GSK\_Patient\_Level\_Data\_Sharing\_Final\_13July2023.pdf.

Anonymized IPD will be made available within 6 months of publication of primary, key secondary and safety results for studies in product with approved indication(s) or terminated asset(s) across all indications.

Anonymized IPD is shared with researchers whose proposals are approved by an Independent Review Panel and after a Data Sharing Agreement is in place. Access is provided for an initial period of 12 months but an extension may be granted, when justified, for up to 6 months.