Prevention of mother-to-child/vertical transmission

1. Introduction

The risk of vertical transmission from an infected mother to her baby ranges from 21% to 43% in developing countries, depending on breastfeeding patterns ⁽¹²²⁾. The virus may be transmitted during pregnancy (in utero), childbirth (intra-partum), or through breastfeeding (post-partum). The primary strategy for preventing vertical transmission is avoiding HIV infection in girls and women. However, there are a number of interventions which are known to be effective during pregnancy, childbirth and post-natally to lower the probability of transmission from an HIV positive mother to her baby. The key interventions for prevention of mother-to-child transmission (MTCT) which are currently relevant for low and middle income countries include:

1). Antiretroviral (ARV) Therapies.

Transmission to the baby can be reduced by two-thirds with the administration of long-course (ACTG 076) antiretroviral therapy with zidovudine (ZDV) ⁽¹²³⁾. However, the administration of this regimen is complex and expensive for use. Several clinical trials have examined shorter and cheaper ARV regimens. The success of the Thai short-course trial in reducing MTCT by 50% among a non-breastfeeding population led to a greater emphasis on non-breastfeeding strategies in developing countries ^(124,125). Studies among breastfeeding populations find a 38% - 44% reduction in MTCT using a short-course ZDV regimen ^(126,138). In 1999, a Ugandan clinical trial found that a single-dose of nevirapine (NVP) taken during labour and by the infant after birth was almost 50% more effective than the short-course ZDV regimen ⁽¹²⁷⁾.

2) Provision and Advice on Infant Feeding.

Given the success of ARV therapy in these clinical trials, there is increasing focus on infant feeding and MTCT in developing countries. It is estimated that breastfeeding doubles the transmission of HIV ⁽¹²⁸⁾. Factors which increase the risk of transmission include longer duration of breastfeeding and the stage of infectivity. Evidence from one trial suggests that exclusively breastfed infants were less likely to become infected than non-breastfed or mixed-fed infants ⁽¹²⁹⁾. It is unclear how the duration of breastfeeding and early weaning affects these results ⁽¹³⁰⁾. MTCT through breastfeeding has become a very significant source of debate, given the intensive efforts on the part of both national and international communities to promote breastfeeding over the past 20 years. There are significant concerns about the use of formula feeding leading to increased morbidity/mortality of infants and other feeding options such as early weaning, surrogate breast-feeding and pasteurisation of breast milk are being discussed. There is concern about the difficult logistics of pasteurisation, and there have been cases where surrogate mothers have acquired the HIV infection from infected infants ⁽¹³¹⁾.

VCT has received also received increased prominence due to the high profile of MTCT prevention.

Given the efficacy of the ARV interventions, there have been several studies looking at the cost-effectiveness of MTCT prevention interventions ^(133-136). However, there is limited information on the cost of implementing such activities, particularly outside a trial context. In general, the cost of the intervention has been inferred by mixing data from a number of sources and countries ^{(133,134,136)}. While this approach can guide priority-setting in a global context, it is harder to infer costs and resource requirements. The focus of analysis has been mainly on the cost of ARV drugs, and there have been only a few attempts to model the infrastructure requirements required for such an intervention ⁽¹³⁷⁾. It is important to consider what additional infrastructure and staff are needed and also where they might come from. There is very limited cost information on the provision and distribution of formula feeding for HIV positive, nor the costs of using replacement methods for HIV positive women and their families.

2. Description of potential projects

The implementation of MTCT prevention interventions is still in early phases in many countries. Testing and offering of antiretrovirals generally occur within the existing health and antenatal care infrastructure. The actual timing of the HIV testing and counselling will depend on the type of regimen which is being undertaken and the stage of pregnancy at which a woman first attends antenatal services. There are significant problems associated with women consenting to and then returning for HIV test results, before undertaking antiretroviral therapy (as discussed in the VCT strategy). Different models of VCT and feeding advice are currently being piloted.

3. Variables which affect costs

Key issues affecting costs that have been highlighted are:

· Antiretroviral regimen The choice and price of drugs for a particular regimen will significantly the costs of the intervention.

· HIV prevalence. As prevalence rises, the costs of testing and delivery of the regimen will increase. However, economies of scale may also be observed.

· Extent of additional capacity which is required to administer the regimen. Existing facilities and services may need to be strengthened (e.g. laboratory capacity, additional staff to attend deliveries).

· Feeding strategies. Provision of replacement feeding methods such as formula-milk will significantly increase costs.

· The geographical and social accessibility of the population: this will influence the workload of the service.

· The number attending relative to the capacity of the service

· The type of test and number of tests: various alternatives exist for the test itself, and the cost of HIV antibody testing can be reduced in a number of ways