Background:  A single-dose of nevirapine (sdNVP), administered at the onset of labor to HIV-infected mothers and newborn infants is an efficacious method of reducing mother-to-child transmission (MTCT) of HIV. More than half a million women have received sdNVP already and it is likely that more women will be returning a second time. It has been shown that sdNVP results in genotypic non-nucleoside reverse transcriptase inhibitor (NNRTI) resistance in the majority of women who receive it and repeated doses result in higher risk. The effect of previous exposure to sdNVP on the effectiveness of subsequent sdNVP-containing regimens has not yet been reported. We compare MTCT rates in successive children of women exposed to sdNVP alone or in combination with other ART at 2 sites:  Soweto, where clade C is predominant, and Abidjan, where CRF02 is common. 

Methods:  In Soweto, 76 HIV-infected women were identified at MTCT voluntary counseling and testing, who had received sdNVP in a previous pregnancy, delivered live infants on both occasions, did not breastfeed their first infant, and both infants were HIV tested. In Abidjan, a similar group of 35 women attending either the MTCT-Plus program or the DITRAME Plus randomized trial who had been exposed to sdNVP in combination with a short course of other ART in 2 consecutive pregnancies were identified and included in the analysis.

Results:  In Soweto, the median age of women at their initial exposure to sdNVP was 26 (IQR 22 to 30) and in Abidjan 27 (IQR 23 to 31) years. The median time between pregnancies in the two groups was 22 (IQR 15 to 29) and 23 (IQR 16 to 30) months respectively. Mothers who transmitted to their infants at both sites for the first and second pregnancies when they were exposed to sdNVP are shown in the table.  

Conclusions:  Transmission rates in a second pregnancy in the presence of sdNVP are similar to those in the first pregnancy. It appears that the effectiveness of sdNVP alone or in combination is not reduced by previous exposure. This may be due to reversion to wild type virus in the absence of a sustained selection pressure. Despite progression of disease between pregnancies, women who transmitted HIV to their infant in the first pregnancy do not necessarily transmit to their subsequent infant. No alteration in guidelines should be considered for the use of sdNVP alone or in combination in women attending the prevention of MTCT program a second time.