New methods to prevent the transmission of HIV from pregnant women to their unborn babies have gained much attention recently. Indeed, while the effort to reduce mother-to-child HIV transmission (vertical transmission) is important worldwide, it is particularly so in many developing nations where transmission rates remain alarming high due to complex social and economic complex factors.
In much of the developed world, reductions in vertical transmission rates have been seen with advances in anti-HIV treatment. However, these advances have not been shared in developing nations or in poorer communities in the developed world because they are too expensive and complex to allow widespread use. This imbalance may be shifting somewhat as the result of new research.
Previous study results showed that mother-to-child HIV transmission (vertical transmission) can be significantly reduced by a three-step AZT (zidovudine, Retrovir®) regimen. The regimen includes giving AZT after 14 weeks of pregnancy, intravenously (into the vein) during labor and to the newborn for the first six weeks of life. By using this regimen, vertical transmission rates dropped from 25% to 8%.
While this remains one of the few proven regimens for preventing vertical transmission, its use is decreasing in most of the developed world. AZT as a single therapy has long been shown to be less effective than combination therapy in treating HIV disease itself. Consequently, the standard protocol for reducing vertical transmission is seen as inadequate for the mother's health. Thus, pregnant women are commonly encouraged to consider combination anti-HIV strategies that best benefit their own health, while refraining from certain drugs like efavirenz (Sustiva®), which may harm the developing baby.
Ongoing research continues to evaluate the benefits of using AZT in different ways, primarily to make vertical transmission prevention more accessible and affordable in developing nations.
Two Short-Course AZT Studies
Results from a New York study indicate that, when given during labor or within 48 hours of birth, shortened courses of AZT reduce HIV transmission similar to the longer regimen described above (10% and 9.3% rates respectively). Also, a Thailand study evaluated AZT given twice daily in the 36th week of pregnancy until the onset of labor and then every three hours from the onset of labor until delivery. It yielded similar results, with transmission rates dropping more than 50% (9.2% transmission rate).
These studies show that shorter AZT courses appear to be roughly as effective in preventing vertical transmission as the longer course of treatment. But while the cost of shortened AZT courses is less than the three-part regimen, it still remains prohibitive for people in many countries. Moreover, this approach assumes a significant level of prenatal care and clinic support during birth. These may not be realistic expectations in much of the developing world.
A Simpler Approach Using Nevirapine
Preliminary results from a Uganda study, funded by the manufacturer of nevirapine (Viramune®), suggest that a simple, two-dose regimen of nevirapine can reduce vertical transmission rates more than a short course of AZT. In the group treated with nevirapine, women received a single dose of the drug at the onset of labor and their newborns were given a single dose sometime during the first three days of life. In the control group given a short course of AZT, women received that drug at the onset of labor until delivery and the infants were then given AZT twice daily for the first week of life.
At 14-16 weeks of age, 13.1% of children given nevirapine were HIV-positive compared to 25.1% of those given AZT. In other words, women receiving nevirapine were only half as likely to transmit HIV as those receiving AZT. While these results might still seem less effective than those achieved in longer term AZT treatment for the mother and newborn, other factors may contribute to the difference. In any case, the results still are quite an improvement compared to no treatment.
The babies in this study will be followed until they turn 18 months old. Since HIV passes through breast milk, it's possible that over time the benefits of either preventive course may diminish. Indeed, 95% of the mothers in the study breast-feed. Finally, it remains unknown if these regimens offer long-term risks or benefits to the mother's or child's health.
While these results are preliminary, they represent a hopeful advance in developing a low cost preventive regimen. The cost of the two-dose nevirapine treatment totals about US $4, a price many believe could be affordable for the developing world. Nevertheless, even these simpler and less expensive regimens should not be viewed as a panacea for the problem of mother-to-child HIV transmission in the developing world. Indeed, they require a certain level of medical infrastructure to implement. In some areas, this simply may not exist.
Finally, longer-term solutions to the challenge of vertical transmission must go beyond preventing the transmission of HIV from mother-to-child. Coupled with this effort must be the assurance of healthy mothers, families and communities who can care for and nurture children affected by HIV worldwide.
For more information on this topic, call Project Inform's National HIV/AIDS Treatment Hotline and ask for the "Mother-to-Child HIV Transmission Prevention Discussion Paper."
Back to the Project Inform Perspective September 1999 contents page.