This study checks if a new vaccine, VIR-1388, is safe and effective for people without HIV. HIV is a virus that attacks the body's defense system. The study is for adults aged 18 to 55 who are in good health and have a history of CMV (a common virus). There are two parts: Part A is for people who can't have children, and Part B is for those who can have children but must use two types of birth control. Participants will get either the VIR-1388 or a placebo (a harmless pill or shot that looks like the real treatment). The study has a lot of safety checks and can last up to three years if you join the optional follow-up. You need to be in good health, not have HIV, and be willing to use protection during the study. You cannot join if you have a weak immune system, an autoimmune disease, or if you're breastfeeding.

• Study duration can be up to 3 years.
• Participants must use protection during study.
• Frequent safety check-ups are required.