Study To Evaluate Emtricitabine/Tenofovir Alafenamide (F/TAF) in Human Immunodeficiency Virus 1 (HIV-1) Infected Children and Adolescents Virologically Suppressed on a 2-Nucleoside/Nucleotide Reverse Transcriptase Inhibitor (2-NRTI)-Containing Regimen

Key Inclusion Criteria: * Human immunodeficiency virus 1 (HIV-1) infected male and female adolescents and children aged 1 month to \< 18 years at baseline/Day 1 (according to requirements of the enrolling cohort) * Must be able to give written assent prior to any screening evaluations * Parent or guardian able to give written informed consent prior to any screening evaluations and willing to comply with study requirements * Body weight at screening as follows: * Cohort 1: ≥ 35 kg * Cohort 2, Group 1: ≥ 25 kg * Cohort 2, Group 2: 17 kg to \< 25 kg * Cohort 3: to be updated per a protocol amendment * Cohort 4: to be updated per a protocol amendment * Currently on a stable 2-nucleoside/nucleotide reverse transcriptase inhibitor (NRTI) containing regimen that includes a 3rd antiretroviral (ARV) agent for ≥ 6 consecutive months prior to screening * Plasma HIV-1 ribonucleic acid (RNA) levels \< 50 copies/mL for ≥ 6 consecutive months preceding the screening visit * No opportunistic infection within 30 days of study entry (at baseline/Day 1) * A negative serum β-human chorionic gonadotropin (HCG) pregnancy test is required for females of childbearing potential only Key Exclusion Criteria: * An acquired immunodeficiency syndrome (AIDS) - indicator condition with onset within 30 days prior to screening * Life expectancy of \< 2 years * Active, serious infections (other than HIV-1 infection) requiring parenteral antibiotic or antifungal therapy within 30 days prior to bas…