A Phase 3, Double-Blinded, Multicenter, Randomized Study to Evaluate Safety and Efficacy of Twice Yearly Long-Acting Subcutaneous Lenacapavir, and Daily Oral Emtricitabine/Tenofovir Alafenamide for Pre-Exposure Prophylaxis in Adolescent Girls and Young Women at Risk of HIV Infection

Incidence Phase: Recent Infection Testing Algorithm (RITA) Estimate of the Background Human Immunodeficiency-1 Virus Infection Incidence Rate (bHIV) Per 100 Person Years (PY)

Time Frame: Incidence Phase Screening Visit (Day 1)

bHIV per 100 PY in the Incidence Phase was calculated using RITA. The RITA incorporated HIV-1 testing results and recency assay testing results to estimate the bHIV. Recency assay testing was performed for participants in the All Screened Set found to have HIV-1 infection at the Incidence Phase Screening Visit as defined below. Participants were considered to have recent HIV-1 infection if the normalized optical density (ODn) was below 1.5 threshold using the Sedia limiting antigen avidity enzyme immunoassay (LAg-EIA) and the HIV-1 RNA (viral load) was \> 75 copies/mL of blood. HIV-1 infection was defined as participants having at least one of the following central lab results at the Incidence Phase screening visit: * Positive HIV-1/2 differentiation Ab, OR * Positive HIV-1 ribonucleic acid (RNA) qualitative test, OR * HIV-1 RNA quantitative test ≥200 copies/mL.

Randomized Blinded Phase: HIV-1 Incidence Reported Per 100 PY for LEN and F/TAF Compared to Participants in All Screened Set

Time Frame: When at least 50% of the participants completed 52 weeks of follow-up after randomization or permanently discontinued from the study (maximum 143 weeks)

HIV-1 incidence per 100 PY for LEN and F/TAF was calculated as the number of participants who acquired HIV-1 divided by the total of a) for participants not diagnosed with HIV-1, sum of all duration of follow-up time in years, while at risk of HIV-1 infection (where a year is 365.25 days) and b) for participants diagnosed with HIV-1, sum of all duration of follow-up time up to confirmed HIV-1 diagnoses. HIV-1 diagnosis was determined by an HIV adjudication committee who reviewed potential HIV-1 infection events in the randomized participants. The committee, in a blinded, consistent, and unbiased manner, determined whether HIV test results confirmed HIV-1 infection and determined the date of diagnosis for each case, defined as the date of the earliest study visit with evidence of HIV infection considering both prospective HIV testing and back-testing of archived samples. bHIV incidence per 100 PY in All Screened Set was estimated as described in outcome measure#1.