Doravirine (DOR) in Human Immunodeficiency Virus (HIV)-Infected Children Aged 4 Weeks to <12 Years and <45 kg (MK-1439-066)

This is a single-group, open-label, multi-site study in pediatric participants with human immunodeficiency virus type 1 (HIV-1) infection, aged 4 weeks to \<12 years and weighing \<45 kg, who are treatment-naive (TN) or have been virologically suppressed (VS) on stable combination antiretroviral therapy (cART) for ≥3 months with no history of treatment failure. The primary objectives are: * To evaluate the steady state pharmacokinetics (PK) of doravirine (DOR) \[MK-1439\] when given in combination with 2 nucleoside/nucleotide analog reverse transcriptase inhibitors (NRTIs) or as part of the fixed-dose combination (FDC) of DOR/lamivudine (3TC)/tenofovir disproxil fumarate (TDF) in participants ≥6 to \<12 years and weighing ≥14 to \<45 kg. * To evaluate the safety and tolerability of DOR when given with 2 NRTIs or as part of the FDC of DOR/3TC/TDF, in participants ≥6 to 12 years and weighing ≥14 to \<45 kg, through Week 24.

Participants who complete the Week 96 visit will be eligible to enroll in an Extension Study and receive DOR until it is commercially available, or for up to an additional 224 weeks (whichever comes first).