This randomized, double-blinded, placebo-controlled Phase 3 study is designed to evaluate the safety, tolerability, and immunogenicity of 3 lots of RSVpreF in healthy adults.

This randomized, double-blinded, placebo-controlled Phase 3 study will examine the immune response and the safety and tolerability profiles across 3 manufactured lots of RSVpreF when administered as a single 120 µg dose to healthy adults to demonstrate lot equivalence in manufacturing of RSVpreF.

Inclusion Criteria:

1. Healthy males or nonpregnant, nonbreastfeeding females between the ages of 18 and ≤49 years, inclusive, at Visit 1 (Day 1).
2. Participants who are willing and able to comply with scheduled visits, laboratory tests, lifestyle considerations, and other study procedures, including daily completion of the e diary for 7 days after study vaccination.
3. Healthy participants as determined by medical history, physical examination (if required), and the clinical judgment of the investigator to be eligible for inclusion in the study. Participants with preexisting chronic medical conditions determined to be stable in the clinical judgment of the investigator may be included.
4. Capable of giving signed informed consent as described in the protocol, which includes compliance with the requirements and restrictions listed in the ICD and in the protocol.

Exclusion Criteria:

1. Bleeding diathesis or condition associated with prolonged bleeding time that may contraindicate IM injection.
2. History of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention or any related vaccine.
3. Unstable chronic medical condition or disease requiring significant change in therapy or hospitalization for worsening disease within 3 months before receipt of study intervention.
4. Immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination.
5. Known infection with HIV, HCV, or HBV.
6. Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.
7. Previous vaccination with any licensed or investigational RSV vaccine at any time prior to enrollment or planned receipt throughout the study.
8. Receipt of any blood/plasma products or immunoglobulin, from 60 days before study intervention administration or planned receipt throughout the study.
9. Receipt of monoclonal antibodies from 60 days before study intervention administration or planned receipt throughout the study.
10. Receipt of systemic treatment with known immunosuppressant medications within 60 days before study intervention administration or the use of systemic corticosteroids (≥20 mg/day of prednisone or equivalent) for ≥14 days within 28 days prior to study enrollment. Prednisone use of <20 mg/day for <14 days is permitted. Inhaled/nebulized, intra-articular, intrabursal, or topical (skin, eyes, ears) corticosteroids are permitted.
11. Current alcohol abuse or illicit drug use. Note: Marijuana use is not considered an exclusion criterion for the study when elicited in participant screening, though it may be considered illicit in some locales.
12. Current use of any prohibited concomitant medication(s) or those unwilling/unable to use a permitted concomitant medication(s).
13. Participation in other studies involving investigational drug(s) or investigational vaccines within 28 days prior to consent and/or during study participation.
14. Pregnant females; breastfeeding females; and women of child bearing potential who are unwilling or unable to use a highly effective method of contraception as outlined in the protocol for the duration of the study.
15. Men who are unwilling to comply with contraception methods as outlined in the protocol for the duration of the study.
16. Investigator site staff or Pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.

This is a double-blinded, placebo controlled study