Background: In the PROMISE 1077BF trial, breastfeeding women with CD4 >350 cells/mm3 (or >country-specific ART threshold if higher) and their uninfected neonates were randomized to maternal ART (mART) or infant nevirapine prophylaxis (iNVP) until breastfeeding cessation or 18 months post-delivery, (whichever occurred first) and had low infant HIV-1 infection rates (0.7% overall). We assessed whether maternal viral load (MVL) or CD4 were associated with perinatal HIV transmission risk.
Methods: MVL was measured retrospectively on batched specimens collected at entry (7-14 days postpartum) and weeks 6, 14, 26, and 50 postpartum. CD4 was measured real-time at entry and weeks 14, 26, 38, and 50 postpartum. Infant HIV-1 NAT was obtained at weeks 1, 6, every 4 weeks until week 26, then every 12 weeks. Infant infection was defined as a positive HIV-1 NAT at any two post-entry timepoints. The associations of baseline and time-varying MVL and CD4 with transmission risk were assessed using proportional hazards regression models by randomized treatment arm, with MVL categorized as < 1000 or ≥1,000 copies/ml and CD4 categorized as < 500 or ≥ 500 cells/mm3, and adjustment for mART receipt during pregnancy.
Results: 2431 mother-infant pairs were randomized. Baseline MVL and CD4 are shown in Table 1. Baseline MVL (p= 0.11) and CD4 (p=0.51) were not significantly associated with infant HIV-1 infection. Time-varying MVL was significantly associated with infant HIV-1 infection in the mART arm (hazard ratio (95% CI): 12.04 (2.54, 57.06) but not in the iNVP arm (hazard ratio (95% CI): 1.04 (0.20 - 5.52)). Time-varying CD4 was not significantly associated with infant HIV-1 infection in either arm (hazard ratio (95% CI): 0.29 (0.05-1.59) in mART arm and 0.33 (0.07-1.57) in iNVP arm). Of 7 postnatal infections in mART arm, 2 had proximal MVL< 40 copies/ml.
Conclusions: With iNVP, MVL was not significantly associated with HIV-1 transmission during breastfeeding. However, among women receiving mART, increased MVL during breastfeeding was associated with increased risk of infant HIV-1 infection. These data emphasize the important role of adherence to mART in controlling MVL and preventing infant infection and suggest that iNVP should be considered in situations with documented poor maternal ART adherence.

 mART n=1,220iNVP n=1,211
Baseline CD4 count  
< 500 cells/mm3162 (13%)170 (14%)
≥ 500 cells/mm31,058 (87%)1,041 (86%)
Baseline Maternal Viral Load  
<400 copies/mL672 (55%)604 (50%)
400 - 1,000 copies/mL239 (20%)210 (17%)
≥ 1,000 copies/mL309 (25%)397 (33%)
[Table 1]

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