S1 Dataset -

Introduction
We describe transition of HIV-positive children from efavirenz- or nevirapine-based antiretroviral therapy (ART) to optimal dolutegravir (DTG) or lopinavir/ritonavir (LPV/r) (solid formulation)-based ART in Lesotho.
Methods
We followed a cohort of children less than 15 years of age who were initiated on ART on or after January 1, 2018 from 21 selected health facilities in Lesotho. From March 2020 to May 2022, we collected data retrospectively through chart abstraction and prospectively through caregiver interviews to cover a period of 24 months following treatment initiation. We used a structured questionnaire to collect data on demographics, ART regimen, drug formulations and switches, viral suppression, retention, and drug administration challenges. Data were summarized as frequencies and percentages, using SAS ver.9.4.
Results
Of 310 children enrolled in the study, 169 (54.5%) were female, and median age at ART initiation was 5.9 years (IQR 1.1–11.1). During follow-up, 19 (6.1%) children died, 41 (13.2%) were lost to follow-up and 74 (23.9%) transferred to non-study sites. At baseline, 144 (46.4%) children were receiving efavirenz-based ART regimen, 133 (42.9%) LPV/r, 27 (8.7%) DTG, 5 (1.6%) nevirapine; 1 child had incomplete records. By study end, 143 (46.1%) children were receiving LPV/r-based ART regimen, 109 (35.2%) DTG, and 58 (18.7%) were on efavirenz or nevirapine-based regimen. Of 116 children with viral load results after six months or more on a consistent regimen, viral suppression was seen in 35/53 (66.0%) children on LPV/r, 36/38 (94.7%) children on DTG and 19/24 (79.2%) children on efavirenz.
Conclusion
Following optimal ART introduction in Lesotho, most children in the cohort were transitioned and many attained or maintained viral suppression after transition; however, we recommend more robust viral load monitoring and patient tracking to reduce losses and improve outcomes after ART transition.