Determining the viral load threshold for initiating neonatal combination antiretroviral therapy prophylaxis in HIV exposed newborns


BACKGROUND: Neonatal combination antiretroviral (cART) prophylaxis is recommended in situations at high-risk of vertical transmission, however, the maternal viral load threshold at time of delivery (dVL) for which neonatal cART is warranted is not clear. The objective of this study was to describe cART use and risk of vertical transmission at low levels of dVL.
METHODS: Data were analyzed from mother-infant pairs (MIPs) in the Canadian Perinatal HIV Surveillance Program between 1997-2020, collected annually from 22 perinatal HIV centers in Canada. Infants were categorized as high-risk (dVL '¥1000c/ml, or maternal cART <4 weeks prior to delivery), medium-risk (dVL detectable and <1000c/ml, and maternal cART '¥4 weeks prior to delivery), and low-risk (dVL undetectable, and maternal cART '¥4 weeks prior to delivery). Neonatal ART regimens and HIV transmission risk was compared between groups.
RESULTS: A total of 4743 MIPs were included; overall, 1.8% of newborns received no prophylaxis, 70.4% received monotherapy, 14.5% a dual-combination regimen, and 13.3% cART. The most commonly prescribed cART regimens were zidovudine (ZDV)/lamivudine (3TC)/nelfinavir (NFV) (6.5%), followed by AZT/3TC/nevirapine (NVP) (5.6%), and AZT/3TC/NVP/NFV (0.5%). Raltegravir based cART was used in only 0.3% of infants. A total of 2891 MIPS were categorized into risk categories (incomplete data for n=1854); 65.1 % were categorized low risk, 6.8% medium-risk, and 28.1% high-risk. An equal proportion of high and medium-risk infants received cART (25.7% vs. 26.6%). There were 55 HIV transmissions events; this included 49 (6.2%) of those in the high-risk, 1 (0.5%) in the medium-risk, and 5 (0.3%) in the low-risk category (p<0.001). Among those prescribed cART, transmission occurred among 12.6% of infants in the high-risk group, 2.1% of those in the medium risk group, and 4.8% of those in the low-risk group. There were no transmissions among infants receiving single, dual or no ART in both low and medium-risk groups.
CONCLUSIONS: While cART was equally prescribed in both high and medium-risk situations, the benefits in the medium-risk group with low level detectable viremia are not clear. These data suggest that efforts may be better directed towards ensuring access to cART in high-risk situations, and limiting cART exposure in others.

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