The purpose of this study is to learn about the safety effects of the Lyme disease vaccine (called VLA15), and its ability to protect people from Lyme disease after a 5th dose of the vaccine.

This study is seeking participants who:

• are generally healthy and 7 years of age and older,
• have already been vaccinated with 4 doses of VLA15 (from the VALOR study), and have blood sample taken post dose 4.
• are not currently taking, or haven't recently taken, medicines like chemotherapy, blood products, or blood thinners.
• are not pregnant or breastfeeding and do not plan to become pregnant while receiving the study vaccine.

All participants in this study will receive a total of 1 dose through a shot in the upper arm, either VLA15 or saline shot (saltwater).

The study will compare the experiences of people receiving the study vaccine or saltwater shot.

Participants will take part in this study for about 12 months. During this time, they will have 4 planned clinic visits. The clinic visits may include having a health check, giving a small amount of blood and getting the study vaccine or saltwater as a shot at the first visit.

A Phase 3, Randomized, Placebo-Controlled, Double-Blinded Study to Evaluate the Safety, Tolerability, and Immunogenicity of a Fifth Dose of 6-Valent OspA-Based Lyme Disease Vaccine, VLA15, in Healthy Participants ≥7 Years of Age

Participants will be randomized in a 5:1 ratio to receive either one dose of VLA15 or placebo (saline) at the first visit. This study will use an external data monitoring committee (EDMC). The EDMC is independent of the Pfizer study team and includes only external members. The EDMC charter describes the role of the EDMC in more detail.

Approximately 1712 participants will be enrolled in the study.

Healthy individuals 7 years of age and older who have received 4 prior doses of active VLA15 from the C4601003 study, have a blood sample taken post dose 4, are willing to comply with all study procedures, and provide signed informed consent will be enrolled. Pregnant or breastfeeding individuals and fertile individuals who are unwilling or unable to use effective contraceptive methods as outlined in this protocol will not be enrolled. Individuals who have contraindication to vaccination, conditions or treatments that can inhibit the ability to mount an immune response to a vaccine, or other conditions that may increase the risk of study participation will be excluded from this study.

Inclusion Criteria:

• Participants who are healthy as determined by medical history and clinical judgment.
• Participants willing and able to comply with all scheduled visits, IP receipt, and other procedures throughout the study.
• Able to provide Informed Consent.
• Participants must have received 4 doses of VLA15 in the C4601003 study, and have a V7 blood sample available.

Exclusion Criteria:

• Pregnant or breastfeeding participants.
• Allergies or contraindications to vaccines or their components.
• Health issues including: blood clotting deficiencies, immunodeficiencies, bone marrow disorder, or uncontrolled psychiatric conditions.
• Receipt of therapies to treat malignancies, blood/plasma products and immunoglobulins, systemic corticosteroids and immunosuppressants, or anticoagulant therapy in recent medical history.
• Recent or concurrent participation in a separate interventional study.
• Staff or direct family of the study site staff and Sponsor.

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.

Third-party blind unblinded