A Phase I Study of an HIV Vaccine in Healthy, HIV Uninfected Adults

This is a Phase I, placebo-controlled (the use of an inactive substance identical in appearance to the active vaccine), double-blind (neither the participant or study personnel will know the identity of the treatment administered) study where participants will be randomized (treatment type assigned by chance) to receive a Modified Vaccinia Ankara (MVA) Mosaic vaccine (at 1x10E8 pfu) or placebo. This design is intended to reduce the likelihood of observer and selection bias, provide control for confounding variables, and aid an unbiased analysis of the study results. The study will include 4 groups of participants, 2 groups having previously been vaccinated with Ad26.ENVA.01 (A recombinant adenovirus \[rAd\] vaccine for HIV-1) and 2 groups not previously vaccinated with Ad26.ENVA.01. Participants will be randomized in a 4:1 ratio to receive either a MVA Mosaic vaccine or placebo. The trial comprises a 4-week screening period, a 12-week vaccination period during which participants will be vaccinated at baseline (Day 1) and Week 12 (Day 84), and a 40-week follow-up period to the final visit at Week 52.