The main purpose of this clinical study is to evaluate a 6-valent OspA-based Lyme disease vaccine (VLA15) for prevention of Lyme disease within North America and Europe. Approximately 9,400 healthy participants (this number excludes participants from 8 sites which were terminated for quality issues) 5 years and older will be recruited from areas with high levels of endemic Lyme disease to receive VLA15 or placebo (an inactive substance consisting of saltwater). Each participant will have about a 50% chance of receiving VLA15 and about a 50% chance of receiving placebo. A subset of participants will receive VLA15 from 3 different lots or placebo (1:1:1:3 ratio) to assess lot equivalence.

Participants will receive a 3-dose primary vaccination series at about 0, 2, and 5 to 9 months and then receive a booster dose about 12 months after end of primary vaccination series. Vaccination of participants will occur at a time of year such that the primary series is completed before the peak Lyme disease season followed by a booster dose just prior to the beginning of the second Lyme disease season. A subset of participants will be followed for a third Lyme disease season.

Comparison will be made between the Lyme disease cases of people receiving the study vaccine to those of the people who are not. This will help us determine if the study vaccine is safe and effective.

If enrolled, participants will need to visit the research site at least 7 times during the study, and for a subset of participants up to 9 times. There will also be at least 5 telephone contacts. It is expected that each participant will take part in this study for up to about 2 and a half years. The subset of participants followed for a third Lyme disease season will take part in this study for up to about to 3 and a half years.

Key Inclusion Criteria:

• Participants who reside in areas with endemic Lyme disease and who lead lifestyles that put them at increased risk for Lyme disease. For example, this could include, but not be limited to:
• Individuals who work in B burgdorferi-infected/tick-infested areas, especially those with occupations that may be associated with higher risk of exposure, such as landscaping, forestry, and wildlife and parks management.
• Individuals who pursue recreational activities such as hiking, camping, fishing, hunting, jogging, or gardening in such areas.
• Individuals who live on land plots with tree lines and come into contact with these trees regularly.
• Individuals who have dogs that regularly are outdoors and frequently return with attached ticks.
• Individuals who participate in activities in areas with tall grass, smaller wooded areas beside forests, open fields, lakesides, and riversides.

Key Exclusion Criteria:

• Any female participants that are pregnant (or have a positive urine pregnancy test) or are breastfeeding.
• Any diagnosis of Lyme disease within the past 3 months.
• Any history of Lyme carditis, neuroborreliosis, or arthritis, or other disseminated Lyme disease regardless of when diagnosed.
• Known tick bite within the past 4 weeks.
• Newly developed or unstable underlying conditions that may interfere with the assessment of Lyme disease, including but not limited to chronic arthralgia/arthritis, second/third-degree AV heart block, chronic pain syndromes, and chronic skin conditions that reduce the ability to detect cutaneous manifestations of Lyme disease.
• Any unstable autoimmune condition with a manifestation (eg, arthritic and neurologic) that may interfere with the assessment of Lyme disease.
• Chronic systemic doxycycline or minocycline or other tetracycline class drug use for acne or any other chronic suppressive antibiotics used to treat other conditions.

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.