Results from two very large clinical trials involving African women have demonstrated that one or two doses of nevirapine during and after labour can reduce the rate of HIV transmission significantly. As women in resource-limited settings do not always have access to antenatal care, many are not tested for HIV until they come to the clinic in labour. Treatment during labour and after childbirth can still reduce mother-to-child transmission of HIV particularly if that treatment is potent.

In the HIVNET 012 study, 626 women took a single dose of 200mg nevirapine at the onset of labour and a dose of 2mg/kg was given to the baby three days after birth. Compared with an AZT regimen involving treatment of the mother during labour and the infant during the first week of life, the nevirapine-treated group had a 47% reduction in the risk of transmission (Guay 1999). Further follow-up from HIVNET 012 suggested that the reduction in the risk of transmission associated with nevirapine prophylaxis persists for at least the first year of life, despite the ongoing risk posed by breastfeeding. Furthermore, nevirapine was most effective in reducing transmission than AZT in women with CD4 counts below 200 cells/mm³ (Jackson 2003).

HIVNET 012s findings were corroborated by the South African SAINT study, which showed that giving a dose of nevirapine at labour, and after childbirth for both mother and infant was as effective in reducing the rate of perinatal mother to child transmission of HIV as a seven-day course of therapy with AZT and 3TC (Moodley 2000). However, a high rate of nevirapine resistance was detected among mothers and infants when the mother took two doses of nevirapine. Because of these concerns, future studies only used single-dose nevirapine: one dose at the onset of labour and one dose for the child within 72 hours of birth.

This cheap and effective way of reducing vertical transmission made possible the widespread implementation of programmes to prevent mother-to-child transmission of HIV in the most resource poor countries. It is so simple that the drug can be given to pregnant women with HIV, with instructions to take one dose for themselves when they go into labour and then to give one dose of nevirapine syrup to their child. This approach was shown to be effective in a study from Uganda, reducing transmission by approximately 60% compared with historic levels (Kagaayi 2005).

More recent studies have examined the effect of combining short courses of AZT with single-dose nevirapine. A large randomised, double-blind, placebo-controlled Thai study called Perinatal HIV Prevention Trial-2 (PHPT-2) demonstrated that providing mothers and newborns with a single dose of nevirapine, in addition to short-course AZT treatment leads to a greater reduction the rates of mother-to-child transmission. Transmission rates were 2% in these mother / child pairs, compared with 3% when the infants were given placebo in place of nevirapine and 7% with AZT alone (Lallemant 2004). This is most effective when AZT treatment is started at week 28 or as soon as possible thereafter: delay to the last two weeks of pregnancy or later results in higher rates of transmission (Jourdain 2005).

Single-dose nevirapine given only to the infant has been shown to lead to fewer transmissions than six weeks of AZT. This may therefore be a useful strategy in situations where the mother does not access antenatal care or HIV testing. Risk factors for transmission were lower CD4 cell count and higher viral load in the mother and breastfeeding (Gray 2005a).