Safety of the Acne mRNA Vaccine in Adolescents 12 to 17 Years of Age With Moderate to Severe Acne

The purpose of this study is to assess the safety profile of intramuscular injections of the Acne mRNA vaccine at 3 dose levels compared with placebo in 12 to 17 years old participants with moderate to severe acne. An early safety data review (ESDR) will be conducted after each subcohort has completed an injection round; enrollment of the next higher dose level subcohort or progression of a subcohort to the subsequent injection round will only proceed if no safety concerns are identified. This sequential process will allow a cautious approach to vaccine injection in the adolescent population. Study details are as follows: * Before being enrolled in the study, participants complete a 4-week (ie, 1-month) screening period during which they will be called over the telephone approximately in the middle of the screening period to check they are not using prohibited medications and to remind them about the facial hygiene requirements. * Once the screening period has been completed, the study duration will be up to 13 months for each participant * Participants will be invited to a long-term extension study through a separate protocol.