• Presumed or confirmed maternal HIV infection:

‣ Mothers will be eligible to enroll with EITHER:

• Presumed HIV infection defined as at least one positive rapid HIV antibody-based test result from a sample collected in the peripartum period. Presumed infection must be confirmed within 10 business days of enrollment OR

∙ Confirmed HIV infection defined as positive results from two samples collected at different timepoints

• Willing and able to provide written informed consent for participation of herself and her infant. The mother must be of legal age or circumstance to provide independent informed consent as determined by site standard operating procedures (SOPs) and consistent with IRB/EC policies and procedures. Otherwise, informed consent must be obtained from a legal guardian and the mother must provide written assent.

• Was not previously enrolled in this study with another infant.

• Did not receive ARVs during the current pregnancy.

• Infant is eligible per inclusion criteria.

• Less than or equal to 48 hours of age.

• Greater than or equal to 36 weeks gestational age at birth (assessment of gestational age will be based on the best clinical estimate determined by date of last menstrual period, antenatal ultrasound, fundal height, or Ballard Score).

• Greater than or equal to 2 kilograms (kg) at birth.

• Able to take ARVs by mouth, nasogastric tube, or gastrostomy tube.

• Has no clinically significant diseases (other than HIV infection) or clinically significant findings during review of medical history or physical examination prior to entry that, in the site investigator's opinion, would interfere with study participation or interpretation.

• Mother is eligible per inclusion criteria.

• Enrolled in Step 1.

• Confirmed in utero HIV infection.

• Able to take ARVs by mouth, nasogastric tube, or gastrostomy tube.

• Has no clinically significant diseases (other than HIV infection) or clinically significant findings during review of medical history or physical examination prior to entry that, in the site investigator's opinion, would interfere with study participation or interpretation.

• Mother (or legal guardian if applicable) is willing and able to provide written informed consent for child's participation in Step 2.

• Enrolled in Step 2.

• Has reached Step 2 Week 96.

• Has the following results based on testing:

‣ No confirmed plasma HIV RNA ≥200 copies/mL at Step 2 Week 24 and up to but excluding Step 2 Week 48.

⁃ No plasma HIV RNA detected at Step 2 Week 48 and thereafter, with two possible exceptions

• (i) First possible exception: If HIV RNA is detected at or after Step 2 Week 48 with a result \<200 copies/mL, testing will be repeated within three weeks (specimen collection for the confirmatory test must occur within three weeks of specimen collection for the initial test).

∙ If no HIV RNA is detected on the confirmatory test, or if HIV RNA is detected with a result \<200 copies/mL, the infant will be potentially eligible for Step 3 after an additional 48 weeks of follow-up in Step 2, provided no HIV RNA is detected on any subsequent tests in Step 2.

∙ If HIV RNA is detected on the confirmatory test with a result ≥200 copies/mL, the infant will not be eligible for Step 3.

∙ (ii) Second possible exception: If HIV RNA is detected after Step 2 Week 48 with a result \<LOD, the infant will be potentially eligible for Step 3 after an additional 48 weeks of follow-up in Step 2 with no RNA detected. There is no limit on the number of times HIV RNA may be detected with a result \<LOD after Week 48. However, infants with detectable RNA with a result \<LOD after Week 48 will not be considered for entry into Step 3 until after an additional 48 weeks of no RNA detected.

∙ Participants may experience either or both exceptions at different timepoints during follow-up in Step 2.

• If breastfed, must have permanently ceased breastfeeding, with no exposure to breast milk for at least six weeks prior to specimen collection for the testing specified in the criterion (#5) below.

• Has met ALL of the following additional criteria while in Step 2, based on testing between Step 2 Week 84 and Step 2 Week 192 (inclusive):

‣ Two consecutive negative HIV antibody tests by fourth generation ELISA at least eight weeks apart.

⁃ Two consecutive HIV DNA tests with no DNA detected in at least 850,000 PBMCs assayed at least eight weeks apart.

⁃ CD4 cell percentage greater than or equal to 25% and CD4 cell absolute count greater than or equal to the lower limit of normal for age (≥1000 cells/mL if 2 to less than 3 years of age; ≥750 cells/mL if 3 to less than 5 years of age; ≥500 cells/mL if 5 years of age or older).

⁃ Infant assessed by the site investigator or designee as expected to adhere to the Step 3 Schedule of Evaluations.

⁃ Mother (or legal guardian if applicable) willing and able to provide written informed consent for child's participation in Step 3 and Step 4.

• No plasma HIV RNA detected by testing after criteria have been confirmed, with specimen collection for the assay within 14 days prior to Step 3 Entry.

• Enrolled in Step 3.

• Has met at least one of the following:

‣ Plasma HIV RNA ≥LOD based on two assays.

⁃ Plasma HIV RNA ≥1000 copies/mL in the presence of fever or other sign or symptom of acute retroviral syndrome.

⁃ Confirmed or suspected diagnosis of acute retroviral syndrome.

⁃ Confirmed or suspected diagnosis of a new WHO Clinical Stage 3 or 4 condition.

⁃ Confirmed CD4 cell percentage less than 25% and CD4 cell absolute count less than the lower limit of normal for age (\<1000 cells/mL if 2 to less than 3 years of age; \<750 cells/mL if 3 to less than 5 years of age; \<500 cells/mL if 5 years of age or older).

⁃ Otherwise assessed by the site investigator or designee, in consultation with the Clinical Management Committee (CMC), as having an indication to re-initiate treatment.