This study is testing a vaccine called mRNA-1189 for the Epstein-Barr Virus (EBV). EBV is a virus that can make people sick. This study is for healthy people aged 10 to 30 years. It has three parts: Part A is for healthy adults aged 18 to 30, Part B is for healthy adolescents aged 12 to less than 18 who have not had EBV before, and Part C is for healthy people aged 10 to 21. The study checks if the vaccine is safe and how people feel after getting it (this is called reactogenicity). People joining must be in good health. You cannot join if you've been very close to someone with COVID-19 recently and haven't been fully vaccinated, or if you have certain other health problems or have had certain vaccines recently.

• Study Duration: The length of the study will depend on the part you join.
• Visits Needed: Participants will need to visit the study site for screening and vaccinations.
• Risks: Participants may experience side effects from the vaccine.