The purpose of this study is to evaluate the safety and immunogenicity in parallel of heptavalent mRNA-1975 and monovalent mRNA-1982 against Lyme disease in healthy adult participants.

Inclusion Criteria:

• Body mass index of 18 to 39 kilograms/square meter (inclusive) at the Screening Visit.
• Participants of nonchildbearing potential may be enrolled in the study.
• For female participants of childbearing potential: negative pregnancy test, adequate contraception or has abstained from all activities that could result in pregnancy during the study intervention period, and agreement to continue adequate contraception or abstinence through 3 months following last study injection.

Exclusion Criteria:

• Have chronic illness related to Lyme disease or an active symptomatic Lyme disease infection as suspected or diagnosed by a physician.
• Received treatment for Lyme disease within the prior 3 months.
• Had previous vaccination against Lyme disease or participated in the past in any vaccine study for Lyme disease.
• Had a tick bite within 4 weeks prior to the study injection visit.
• Dermatologic conditions that could affect local solicited AR assessments (for example, tattoos; psoriasis patches affecting skin over the deltoid areas).
• Received systemic immunosuppressants for >14 days in total within 180 days prior to the Screening Visit (for corticosteroids, ≥10 milligrams/day of prednisone or equivalent) or is anticipating the need for systemic immunosuppressive treatment at any time during participation in the study.
• History of myocarditis, pericarditis, or myopericarditis regardless of the timing of past medical history.
• History of anaphylaxis, urticaria, or other significant adverse reaction requiring medical intervention after receipt of a vaccine or intervention that includes one or more of the same components contained in the study injection.
• Has received systemic immunoglobulins, long-acting biological therapies that affect immune responses (for example, infliximab) or blood products within 90 days prior to the Screening Visit or plans to receive them during the study.

Note: Other inclusion and exclusion criteria may apply.