Preventing vertical HIV transmission
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The new prevention strategy is shorter effective and without additional risk of toxicity for either mother or child.
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Vertical transmission is about 35 per cent if no treatment is given. Compared to this the transmission rate dropped to 2 per cent in the group where both mothers and children were treated with nevirapine in addition to zidovudine (AZT).
VIRAL TRANSMISSION of AIDS, which takes place during pregnancy at the moment of childbirth or even during breastfeeding is one of the principal causes of infant mortality in many developing countries.
The virus is transmitted to about 35 per cent of children of infected mothers if no treatment is given. Since the 1990s, the use of a preventive treatment with zidovudine (AZT) has cut this risk to a third. However, because of their duration, complexity and cost, access to these treatments remains scarcely possible for seropositive women living in developing countries.
Cutting down risk
It is now possible to reduce the risk of mother-child HIV transmission to below the 2% threshold as a clinical trial conducted in Thailand by a team of Thai, American and French researchers as part of the international programme Perinatal HIV Prevention Trial (PHPT-2), showed. Using a combination of a short AZT treatment and a single dose of another antiretroviral, nevirapine (NVP), this is possible.
The short treatment usually prescribed in Thailand, for prevention of mother-child HIV transmission is based on the administration of AZT in the course of the last three months of pregnancy and during labour and childbirth, and for one week in the newborn child.
In order to avoid the child's contamination by its mother's milk, bottle-feeding is also recommended.
The administration of a single dose of NVP to both mother and child was suggested by researchers to add to this treatment.
With a distribution over 37 hospitals over the whole country the trial had the participation of 1844 pregnant HIV-infected women. They were split at random into three groups.
In the first group mothers and children received only the standard treatment using AZT. In the second group mothers received, in addition to the AZT treatment, a single dose of NVP at the moment of childbirth.
For the third group, a single dose of NVP was added to the treatment of mothers and children.
In groups taking the AZT-nevirapine combination a significantly lower transmission rate was observed, compared with the group receiving AZT (respectively 1.1 and 6.3 per cent). This prompted the administration of nevirapine to all the women in the study. To determine if it was also necessary to give NVP to children, as an additive to milk, the trial was continued.
The final analysis showed a transmission rate of 2.0 per cent in the group where both mothers and children had been treated with NVP and 2.8 per cent in the group where only the mothers had taken it.
Magic of nevirapine
This new prevention strategy, shorter and more straightforward than triple therapy during pregnancy, showed itself to be just as effective, and without additional risk of toxicity for either mother or child.
The low cost of additional doses of NVP makes the treatment applicable in developing countries. In those countries that currently use short AZT regimens for the prevention of mother-child HIV transmission, in the way Thailand does, many more children could be saved by adding just a single dose of NVP to the treatment of the mother and her child. It creates hope for the eradication of HIV transmission to children. However, in this trial women who were exposed to NVP and who, six months after giving birth, started a triple therapy containing this medicine, showed initially higher risk of treatment of treatment failure than those who had not been exposed to it.
This increased risk could be linked to the selection of a viral population resistant to this product, in the weeks following the single dose of NVP. Studies in partnership with the Ministry of Health of Thailand have been launched to find a solution to this problem.
The researchers are currently working on the administration of triple therapies during pregnancy for women who can or whose clinical status requires this, and also on the use of an antiretroviral treatment covering the period that follows the single dose of NVP in order to prevent the appearance of resistance mutations.
— Our Bureau
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