A Clinical Study of Islatravir and Ulonivirine for People With HIV-1 Who Have Not Been Treated Before (MK-8591B-062)

Inclusion Criteria: * Phase 2: Is human immunodeficiency virus type 1 (HIV-1) positive with Plasma HIV-1 ribonucleic acid (RNA) ≥500 and ≤100,000 copies/mL. * Phase 3: Is HIV-1 positive with Plasma HIV-1 RNA ≥500 copies/mL. * Phase 2: Has cluster of differentiation 4-positive (CD4+) T-cell count ≥200 cells/mm\^3. * Is naïve to antiretroviral therapy (ART), defined as having received no prior therapy with any antiretroviral agent following a diagnosis of HIV 1 infection. Exclusion Criteria: * Has human immunodeficiency virus type 2 (HIV-2) infection. * Has a diagnosis of an active acquired immune deficiency syndrome (AIDS)-defining opportunistic infection. * Has active hepatitis C virus (HCV) or active hepatitis B virus (HBV) infection. * Has a history of malignancy ≤5 years prior to providing documented informed consent except for adequately treated basal cell or squamous cell skin cancer, in situ cervical or in situ anal cancer, or cutaneous Kaposi's sarcoma. * Has prior exposure to islatravir (ISL) or ulonivirine (ULO) for any duration any time prior to Day 1.