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Cost-effectiveness of models for prevention of vertical HIV transmission: voluntary counseling and testing and choices of drug regimen |
Teerawattananon Y, Vos T, Tangcharoensathien V, Mugford M |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology The present study compared four antiretroviral therapy (ART) regimens given in addition to voluntary counselling and testing (VCT) for preventing mother-to-child transmission of the human immunodeficiency virus (HIV). The four ART regimens were:
a short course zidovudine (AZT) regimen, the practice before 2004 (regimen A);
a regimen consisting of a single dose of nevirapine (NVP) (regimen B);
a combination regimen of short-course AZT for antenatal clinic arrivals at 34 weeks- gestation, and NVP for late arrivals beyond 34 weeks and for those who refuse the AZT regimen (regimen C); and
AZT plus NVP (the current practice by 2004; regimen D).
The regimens were described in full in the paper. Further, the analysis assessed the value of a second round of VCT by comparing the cost-effectiveness of one and two maternal VCT sessions for each of the four regimens, thus comparing eight alternative regimens.
Type of intervention Primary and secondary prevention, and treatment.
Economic study type Cost-effectiveness analysis.
Study population The target population was a hypothetical cohort of 100,000 pregnancies.
Setting The setting was the Thai health services. The economic evaluation was carried out in Nonthaburi, Thailand.
Dates to which data relate The studies providing effectiveness evidence dated from 1999 to 2004, while those providing utilisation and cost data dated from 1997 to 2004. The price year was 2003.
Source of effectiveness data The evidence was derived from a review or synthesis of completed studies and estimates based on authors' opinions.
Modelling A decision analytic model was built. This was based on a decision tree presenting a flow of the programme options (described under the ,Health Technologies- section). Base-case values were determined for each parameter in the model. To handle uncertainty, they were ascribed a distribution and entered in a probabilistic uncertainty analysis. The results from 1,000 calculations were presented in a cost-effectiveness acceptability curve.
Outcomes assessed in the review The outcomes assessed as input parameters included epidemiological parameters, the efficacy of ART, and compliance with the programme. Parameters for efficacy of ART included:
the odds of transmitting the virus when the mother received AZT for at least 4 weeks versus placebo;
the odds of transmitting the virus when the mother received AZT for less than 4 weeks versus at least 4 weeks;
the risk of transmitting the virus with the NVP regimen versus placebo;
the risk of transmitting the virus with the AZT plus NVP regimen versus receiving AZT for at least 4 weeks.
Study designs and other criteria for inclusion in the review No inclusion or exclusion criteria for a review of any of the parameters were reported. However, the authors included a Cochrane systematic review and primary studies of varying design, including randomised controlled trials and cohort studies.
Sources searched to identify primary studies Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Number of primary studies included Twelve primary studies provided effectiveness evidence.
Methods of combining primary studies A narrative method was used to combine the studies.
Investigation of differences between primary studies Results of the review For the outcomes assessed, the authors reported the point estimates, 95% confidence intervals, the parameter distribution, and the corresponding data source reference. The base-case values were as follows.
Efficacy of ART parameters included:
an odds of 0.46 of transmitting the virus when the mother received AZT for at least 4 weeks versus placebo;
an odds of 1.40 of transmitting the virus when the mother received AZT for less than 4 weeks versus at least 4 weeks;
a 0.51 risk of transmitting the virus with the NVP regimen versus placebo; and
a 0.23 risk of transmitting the virus with the AZT plus NVP regimen versus receiving AZT for at least 4 weeks.
Methods used to derive estimates of effectiveness The study was based on published data and authors' assumptions.
Estimates of effectiveness and key assumptions In the absence of evidence of the efficacy of regimen D started after 28 weeks but before 36 weeks of gestation, the authors assumed the same efficacy if treatment was started before 34 weeks, and the lower efficacy of regimen A for those starting after 34 weeks. In addition, since women who make their first antenatal visit late in pregnancy tend to report low education and socioeconomic status, the authors assumed that a lower proportion of 65% of infected pregnant women who knew their HIV status after 36 weeks would accept AZT in programmes A and C, and that 75% of those would accept AZT plus NVP in programme D. For those who refused AZT treatment for whatever reason, they assumed 50% would accept the simpler regimen of NVP in programme C.
Measure of benefits used in the economic analysis The main measure of benefit was the number of cases of paediatric HIV averted. The authors said that all effectiveness was converted to the present value with discounting at 5%, but it was unclear what this would mean for this benefit measure.
Direct costs The cost analysis was conducted from the perspective of the MOPH as the Thai government pays all costs for VCT, ART and substitute feeding. The authors measured the programme outcomes as the net cost to the public sector payer. The cost categories included:
VCT for HIV negative and positive pregnancies;
HIV testing for a baby born to an infected mother;
the cost of antepartum and intrapartum AZT (per week);
the cost of infant AZT (per week);
the cost of NPV for the mother and infant;
breast milk substitutes (per year);
the incremental cost of switching from a non-nucleoside reverse transcriptase inhibitor-based treatment regimen to a protease inhibitors-based regimen; and
the lifetime treatment cost of paediatric HIV or acquired immune deficiency syndrome (AIDS) supported mostly by the public sector.
The costs of providing VCT and maternal and infant ART were derived from 160 public hospitals. Data on the units of each category of resources used and valued were gathered by a questionnaire sent to each hospital participating in the study. The unit costs for the intervention included recurrent labour and non-labour expenditures but excluded capital depreciation. The quantities and the costs were analysed separately but were not reported. All the costs were discounted at a rate of 5%. The price year was 2003 and all cost figures from previous years were converted to 2003 values using the general Consumer Price Index.
Statistical analysis of costs The model input parameters of interest were ascribed a distribution that reflected the uncertainty associated with their true value, and were entered in a probabilistic uncertainty analysis. The gamma distribution was modelled for unit cost parameters.
Indirect Costs No indirect costs were included.
Currency US dollars ($). Exchange rates between the Thai Bhat and $ were reported for different years.
Sensitivity analysis The results from 1,000 calculations were presented in a cost-effectiveness acceptability curve.
Estimated benefits used in the economic analysis The mixed regimen of AZT and NVP with two VCT sessions was the most effective strategy, averting 353 infections. The regimens that were least effective were AZT with one maternal VCT session (233 infections averted) and AZT with two maternal VCT sessions (245 infections averted).
Cost results The programmes with the lowest net cost were AZT or NVP with one maternal VCT session ($160,000) and AZT with one maternal VCT session ($170,000). The highest was NVP alone with two VCT sessions ($480,000).
Synthesis of costs and benefits The average cost-effectiveness ratios were reported. These were calculated by dividing the cost of the programme by the infections averted in comparison with no intervention. Compared with no routine prophylactic ART, programme D with 1 VCT session was the most cost-effective regimen, costing $556 to avert one paediatric HIV infection. Regimen B with two VCT sessions was the least cost-effective regimen, at more than three times the cost per additional case prevented.
With relative little benefit gained from the second VCT, all regimens with the single VCT strategy were more cost-effective than those with two VCT sessions.
The cost-effectiveness acceptability curve for the base-case showed that regimen D became the most cost-effective option for a threshold willingness to pay of about $15,000. If the threshold was higher, the most cost-effective option was regimen D with two VCT sessions (data shown graphically.
Authors' conclusions Using international standards that suggest that the cost per life-year gained or quality-adjusted life-year threshold is three times per capita gross domestic product, the programme based on regimen D with two sessions of voluntary counselling and testing (VCT) clearly represents value for money. Thus, the evidence of this study supported the new policy of the Thai National Perinatal HIV Prevention programme having introduced regimen D with two VCT sessions as a national regimen for preventing mother-to-child transmission of the human immunodeficiency virus (HIV).
CRD COMMENTARY - Selection of comparators The authors gave a justification for the comparators. Specifically, several studies have raised a concern about the high rate of NVP resistance developing in mothers treated with a single regimen, and that this would affect the choice of ART if the mother needed to be treated later on. You should judge whether these prophylaxis interventions are relevant in your own setting, or whether other comparators from other commonly used drugs and regimens could also be relevant.
Validity of estimate of measure of effectiveness The authors used data from published sources, expert opinions and their own assumptions. They did not state that a systematic review of the literature had been undertaken. One cannot be sure that all relevant literature was identified. However, it is a positive feature that a Cochrane systematic review and randomised controlled trials were used to derive the effectiveness measures and that few authors' assumptions were made. The estimates of effectiveness were derived credibly from randomised clinical trials, which are an adequate source to estimate effectiveness. The authors justified their assumptions with reference to the medical literature. The estimates were investigated in sensitivity analyses using ranges from the literature, and the authors justified the ranges selected and reported.
Validity of estimate of measure of benefit The measure of health benefit chosen (number of cases of paediatric HIV averted) is context specific and can only be compared with other HIV studies (and not to other economic evaluation). Uncertainty analyses over adjusted effectiveness estimates were conducted and the ranges used were reported.
Validity of estimate of costs The authors reported that the costs were estimated from the perspective of a health care provider, thus productivity costs were appropriately not included. Although some costs might have been omitted from the analysis, these were unlikely to have affected the authors- conclusions since they were common to all regimens. The results were not well reported. The text did not appear to be consistent with table 3 and there appeared to be significant rounding errors in table 3. The resource use quantities and prices were taken from government sources and sensitivity analyses of the costs were conducted. Discounting was appropriately carried out and the prices were adjusted using the Consumer Price Index. The price year was reported.
Other issues The authors compared their findings with those of other studies. The issue of generalisability to other settings was explicitly addressed. The authors' conclusions reflected the scope of the analysis. The authors reported two limitations. First, the rate of accepting VCT in Thailand may be much higher than in other countries. Second, the percentage of HIV infection detected by the second VCT session used in this study was rather high.
Implications of the study According to the authors, this study offers a useful and comprehensive framework for evaluating programmes preventing mother-to-child transmission of HIV, especially in developing countries where resources do not permit adequate development of basic health need but shoulder a major burden of HIV or AIDS. However, because the authors chose to explore the costs and outcomes of preventing mother-to-child transmission in the particular context of a Thai setting and used only a government perspective, applying these findings elsewhere or using other viewpoints should be done with caution.
Source of funding Supported by the Thailand Research Fund and Health Systems Research Unit, and by the World Health Organization.
Bibliographic details Teerawattananon Y, Vos T, Tangcharoensathien V, Mugford M. Cost-effectiveness of models for prevention of vertical HIV transmission: voluntary counseling and testing and choices of drug regimen. Cost Effectiveness and Resource Allocation 2005; 3(7) Indexing Status Subject indexing assigned by CRD MeSH Cost-Benefit Analysis; Counseling; HIV infections /prevention & Infectious Disease Transmission, Vertical; Nevirapine /therapeutic use; Preventive Health Services; Thailand; Zidovudine /therapeutic use; control /transmission AccessionNumber 22005001818 Date bibliographic record published 30/06/2006 Date abstract record published 30/06/2006 |
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