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Cost effectiveness of hepatitis A virus immunisation in Spain |
Arnal J M, Frisas O, Garuz R, Antronanzas F |
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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 Hepatitis A Virus (HAV) immunisation.
Economic study type Cost-effectiveness analysis.
Study population Children aged 15 months, adolescents aged 13-14 years (either at high risk or not), young adults (around 20 years of age) and adults at high risk of acquiring the disease. The high risk group was defined as those travelling to endemic areas for periods longer than 6 months (either continuously or at repeated visits), or individuals, such as 'backpackers', travelling even for short periods under precarious conditions.
Setting Primary care. The study was carried out in Spain.
Dates to which data relate The data for the effectiveness analysis were obtained from studies published between 1991 and 1994. The cost data for the different components of a decision model were obtained from a study published in 1993. The prices used were from 1994.
Source of effectiveness data The evidence of effectiveness was based on a review of previously completed studies.
Modelling Two decision trees (one for the mass active immunisation strategy, and another for selective active or passive immunisation), incorporated in a Markov model using Monte Carlo simulation, were used to combine estimates of the probabilities, consequences and costs of treating infections. The model permitted analysis of the outcomes and costs from the initiation of the immunisations programme up to 10 years.
Outcomes assessed in the review The outcomes assessed in the review were the protection (coverage) provided by the vaccine, the duration of its benefits, rates of prevalence of anti-hepatitis A virus antibodies, and annual rate of infection.
Study designs and other criteria for inclusion in the review 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 Eight studies were cited.
Methods of combining primary studies Primary studies were not combined. Based on the information from the primary studies, the authors assigned probability values to the different possible outcomes in the model.
Investigation of differences between primary studies Results of the review The coverage (protection) of the vaccine was allotted a value of 90% for children and 70% (with a 10-year duration time) for adolescents under mass active immunisation. Incidence rates of 0.1% and 0.2% were used for both cases. The coverage for the high-risk individuals under selective active and passive immunisation was assumed to be 50%, for a 10-year time span. The corresponding incidence rates were 2, 3 and 4 % (both cases). The cumulative prevalence of anti-hepatitis A virus antibodies was estimated to be 2% for a 15-month-old child, increasing to 21% at 11 to 15 years of age, and to 87.5% at 31-35 years of age.
Measure of benefits used in the economic analysis The measure of benefits in the economic analysis was the number of cases of hepatitis A prevented.
Direct costs Costs were discounted. The resource quantities were reported separately from costs. The costs measured were operating costs (both for detection before immunisation, immunisation and treatment of illness). The cost boundary adopted was hospital, patient and relative (travel expenses for accompanying relatives to the children). The estimation of costs was based on data from a medium-sized state general hospital. The unit costs were originally recorded for 1992 and, for analysis, were adjusted to 1994 prices.
Currency European Currency Units (ECU). The results were also reported in 1994 US dollars, at a conversion rate of ECU1 = US$1.3.
Sensitivity analysis A one way simple sensitivity analysis was performed for the variables obtained from the probabilities included in the model and the unit costs used.
Estimated benefits used in the economic analysis Cost results The costs were discounted at 6%. No other information regarding overall expected cost estimates was reported.
Synthesis of costs and benefits An incremental discounted cost per additional case of hepatitis A prevented (against the 'do nothing' option) was used to present the synthesis of costs and benefits. The results were presented for different incidence rates in each case, at 1994 prices and using a 6% discount rate for both costs and benefits. The mass active immunisation option without screening had a cost per case prevented of ECU6394 in children with a 0.1% incidence rate, the figure for adolescents being the same. Those figures changed when the assumed incidence rate was varied to 0.2, becoming ECU3,498 and ECU2,679, respectively. The selective active immunisation programme for high-risk individuals at a 0.7 incidence rate resulted in costs of ECU6,701, ECU2,264, and ECU2,986, for adolescents, young adults, and adults, respectively. At a 2% incidence rate, these ratios would become ECU1,477, ECU352, and ECU627, respectively. At an incidence rate of 4% or more the selective active immunisation for high-risk individuals became the dominant strategy (cost saving) against the 'do-nothing' option for all three subpopulation groups. The passive immunisation programme of high-risk individuals (with screening) yielded cost-effectiveness ratios of ECU18,863, ECU9,169, and ECU3,696, for adolescents, young adults, and adults, respectively, at an incidence rate of 0.7. An incidence rate of 2% resulted in ratios of ECU7,718, ECU2,718, and ECU2,750, respectively. In sensitivity analysis it was found that, in the case of the mass immunisation for children and adolescents, a decrease of vaccine cost by 25% would result in the same proportional decrease in the discounted cost per case of hepatitis A prevented. The cost-effectiveness ratio would decrease by about 7% as a result of a25% reduction in coverage. A 25% reduction in the incidence rate would increase the cost-effectiveness ratio by about 7%. For selective immunisation of high-risk groups, the vaccine cost was the most sensitive variable, followed by the incidence (25% reduction in the incidence rate resulting in an increase of 12% in the cost-effectiveness ratio) and the prevalence rates.
Authors' conclusions Mass vaccination of children or adolescents in Spain is not cost-effective nor is it expected to be so in the future (due to the decreasing trend in incidence rates of Hepatitis A for that subpopulation group). However, immunisation of high-risk individualsis an advisable option. The active immunisation programme for occasional travellers to endemic areas is not a cost-effective option as long as the risk of acquiring the infection is lower that 4% annually. For this group, passive immunisation is preferable.
CRD COMMENTARY - Selection of comparators No justification was given for the comparator used. The comparator chosen was the 'do-nothing' option for all subpopulation groups and, for the high-risk group, two options were analysed: (1) selective active immunisation 3 vaccine doses after anti-HAV determination at a threshold of 18% prevalence rate, and (2) selective passive immunisation (Immune globulin 5 ml) with screening (anti-HAV determination at a threshold of 65% prevalence rate). The comparator chosen should normally represent a standard treatment strategy for the problem in question however, in the absence of any immunisation strategies for hepatitis A, the "do nothing" alternative may be justifiable. You, as a user of this database, should consider whether this is a widely used strategy in your own setting.
Validity of estimate of measure of benefit The parameter estimates used in the model were derived from a non-systematic review of published literature, and hence, may be subject to bias. However, a sensitivity analysis was carried out to address this problem.
Validity of estimate of costs The resource quantities were reported separately from the costs. Adequate details of cost estimation were given. The authors recognised that indirect costs were an important component omitted from the analysis, given the societal point of view adopted in the evaluation.
Other issues The authors' conclusions are justified, given the uncertainties in the data. The results of the sensitivity analysis highlight the importance to the results of the estimate of incidence rate, but lend support to the conclusions, since the model used was chosen to deal with those uncertainties. The effect of varying the prevalence of anti-hepatitis A virus antibodies was not analysed, and hence it is not clear how the results derived for Spain (intermediate prevalence) can be generalised to other countries.
Source of funding Financial support from the Health Research Fund of Spain (no 93/144).
Bibliographic details Arnal J M, Frisas O, Garuz R, Antronanzas F. Cost effectiveness of hepatitis A virus immunisation in Spain. PharmacoEconomics 1997; 12(3): 361-373 Indexing Status Subject indexing assigned by NLM MeSH Adult; Child; Child, Preschool; Cost-Benefit Analysis; Hepatitis A /economics /immunology /prevention & Hepatitis A Virus, Human /immunology; Humans; Immunization /economics; Spain; control AccessionNumber 21997008293 Date bibliographic record published 31/12/1998 Date abstract record published 31/12/1998 |
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