The purpose of the study is to learn about the immune response after a RSVpreF vaccination. This study is being conducted in Japan. RSV is a common virus that can cause infections of the lungs and airways.

The study is seeking participants who are:

• 18 to 59 years of age
• adults with health condition(s) that can put them at an increased risk of severe RSV disease

It will also learn about the safety of RSVpreF vaccination. The study lasts about 2 months. Adults need to visit the research site at least 2 times. The participant will receive a phone call 2 months after vaccination for health checks.

This is a Phase 3, multicenter, single-arm, open-label study that will assess the safety, tolerability, and immunogenicity of Pfizer's RSVpreF in adults 18 to 59 years of age considered to be at high risk of RSV disease due to certain chronic medical conditions in Japan.

Approximately 130 participants 18 to 59 years of age considered at high risk of RSV disease due to certain chronic medical conditions will be enrolled to receive RSVpreF.

The total duration of trial participation for each participant will be 2 months.

After screening and confirmation of eligibility, a prevaccination blood sample will be collected for immunogenicity assessments and a single dose of study intervention (RSVpreF) will be administered.

Participants will report daily reactogenicity data using an electronic device for 7-days or until resolution.

Participants will return approximately 1 month later for a follow-up blood draw for immunogenicity assessments and collection of safety information.

A telephone follow-up visit will be conducted approximately 2 months after vaccination to collect safety information.

Key Inclusion Criteria:

• Underlying health condition(s) that can put the participant at an increased risk of severe RSV/complications including chronic lung , heart, kidney, liver, nervous system, blood, or metabolic diseases

Key Exclusion Criteria:

• Received any kind of RSV vaccine before participating in this study
• Determined as not eligible by the investigator based on the participant's past and present health condition(s), medication(s) and treatment(s)

Please refer to the study contact for further eligibility details.

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 an open label study. Participant, investigators and other site staff, and sponsor staff will be unblinded to the participant's assigned study intervention.