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Costs and benefits of routine varicella vaccination in German children |
Beutels P, Clara R, Tormans G, Van Doorslaer E, Van Damme P |
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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 Routine varicella vaccination strategies.
Economic study type Cost-effectiveness analysis.
Study population A hypothetical cohort of healthy children between the ages of 12 and 18 months and 12-year-olds with a negative history of varicella infection. The model excluded immunodeficient patients and those with cancer, due to the accepted efficiency of the intervention in those populations.
Setting Primary care. The study was carried out in Germany.
Dates to which data relate The effectiveness data mainly related to 1991 and 1994 US data and reports. Costs were derived from 1986 and 1991-94 studies, and were adjusted to 1995. 1995 prices were used.
Source of effectiveness data Effectiveness data derived from a single study and opinion.
Study sample The study sample comprised eighty-two children who had been previously administered one of five production lots of varicella vaccine (VARIVAX), reported to have been exposed to varicella in their household within one year of vaccination. These formed the vaccinated group, against which a control group of unvaccinated children who were also exposed to varicella in the household were compared. No additional details were provided on the latter group. No power calculations were reported.
Study design The study was a non-randomised study with historical controls. The duration of follow-up was one year after vaccination.
Analysis of effectiveness It was not clear whether the analysis was based on intention to treat or on treatment completers only. The efficacy rate was defined by the reduction in the development of varicella (attack rate).
Effectiveness results The attack rate of varicella in the intervention group was 12%, whilst the corresponding figure for the control group was reported as 86%. The efficacy of vaccine during the first year after vaccination was 86% (87% when based on laboratory-confirmed cases only). The information in this section was based on the study by White et al, 1991.
Modelling A Markov simulation model was used to assemble epidemiological and efficacy data from different sources in order to represent a German setting. The model calculated costs and benefits accruing over a 70-year time period.
Methods used to derive estimates of effectiveness Assumptions about the coverage rate of, and adverse events due to, vaccination were based on a report on the coverage of measles vaccination in Germany, and two reports referred to in the study, respectively. In addition, the estimate of life-long protection was derived from a study reporting a corresponding figure (and plausible ranges) based on the opinion of a panel of six experts. In turn, this opinion was founded on the literature and on the experts' own beliefs.
Estimates of effectiveness and key assumptions The assumptions used in the model were as follows: one dose for healthy children, the coverage rate was set at 70% and it was assumed that no adverse events occurred due to vaccination. The median estimate obtained from the panel of experts for the "proportion of people who are initially completely protected by vaccine" and "become only partially protected by the time they die, if their immunity is not boosted by natural infection" was 15% (mean, 20%; range: 5 -60%). The figures for the latter estimate were derived from the study by Halloran et al, 1994.
Measure of benefits used in the economic analysis Infections prevented, deaths prevented, and life-years saved were used in the cost-effectiveness analysis of results from a model.
Direct costs A medical care payer point of view and a societal perspective were adopted in the cost analysis. Costs were discounted to their present values. Quantities and costs were reported separately. Direct costs were visits to the physician, medication, Hospitalization and follow-up for uncomplicated varicella and for varicella giving rise to complications. The sources of quantity and cost data were physician surveys and medical economics literature. Total costs were estimated using a model. 1995 German prices were used.
Indirect Costs The costs were discounted and quantities and costs were reported separately. Indirect costs were production losses incurred by parents in taking care of their children with varicella infections. The estimation of the quantities and costs were based on published information and other studies. 1995 price data were used.
Sensitivity analysis One-way sensitivity analysis was carried out. The parameters varied were as follows: vaccine efficacy, treatment costs, costs of work loss, discount rate, costs of vaccine, determination of susceptibility (DM, sensitivity, specificity), coverage, waning of immunity, and an additional booster dose after 10 years.
Estimated benefits used in the economic analysis The vaccination strategies resulted in a reduction of infections relative to 'no vaccination'. The proportion of infections under 'no vaccination' which can be prevented using the 'children' and 'adolescent' strategies were 57% (384,620 infections for annual birth cohorts of 800,000 German neonates) and 37% (29,327 infections prevented in 800,000 German neonates) respectively. The corresponding figure for the 'children including catch-up' strategy was 55% (413,947 infections). Similarly, the proportion of deaths under 'no vaccination' which would be prevented by the programmes were 20% (3.9 deaths avoided), 35% (4.2 deaths avoided), and 25% (8.1 deaths avoided), respectively. The life-years gained with the intervention strategies were as follows: 401 (children), 175 (adolescents), and 576 (children including catch-up).
Cost results The total net savings for the cohort of 800,000 German neonates under the 'children', 'adolescent' and "children including catch-up" strategies against varicella were DM 161.3 million, DM 21.0 million and DM 182.3 respectively. The incremental direct cost ranged from DM 3.9 million ('adolescent and children catch-up' strategy) to DM 7.9 million (children strategy). Only the adolescent strategy resulted in direct cost saving. The discounting rate was set at 5%.
Synthesis of costs and benefits The 'adolescent' strategy turned out to dominate the comparator (no-intervention) both with and without incorporating indirect costs into the analysis. Similarly, all other intervention strategies dominated the comparator when indirect costs were included in the analysis. Cost-effectiveness ratios were reported for analyses excluding indirect costs (savings) for the 'children' and 'children and catch up' strategies. The discounted costs per discounted life years gained (using a 5% discount rate for both costs and benefits and 1995 prices) were, respectively, DM 23,139 (children) and DM 9,538 (children and catch up). The corresponding results without discounting benefits (life years saved), were DM 19,735 and DM 6,915 per life year saved. The sensitive parameters on total net saving reported were the costs of work loss, vaccine efficacy, coverage, vaccine price and treatment costs. No incremental analyses were reported.
Authors' conclusions The authors concluded that, from a societal perspective, the optimal feasible varicella prevention strategy is to start vaccinating 15-month-old children, to use catch-up vaccination of 12 years old for 11 years and, from the 12th year onward, to continue routinely immunising 15-month-old children.
CRD Commentary Validity of estimate of measure of benefit:The source of the main effectiveness data (i.e. estimates of efficacy and duration of protection) may lead to biased estimates of benefits due to the underlying study designs. In fact the primary study used to derive the estimate of duration of vaccine protection noted the "scant data" upon which the opinions of the panel of experts were supported. Similarly, the primary study, on which the estimate of efficacy was based, used a non-random, historical-control design, which is unlikely to account for possible biases due to changes between the different periods of observation associated with the clinical study groups. Sensitivity analyses showed the results to be sensitive to variations in the estimate of efficacy, although the conclusions seemed robust over a plausible range.
Validity of estimate of costs:The costing methodology was adequately described. The data have not been used selectively. The resource quantities were reported separately from the costs and no important cost items appear to have been omitted. The study conclusions were adequately justified.
Other issues:The generalisability of the results to other countries was addressed, and results may be applicable to other European countries. As to the German setting, the authors noted that the validity of the conclusions depends on the integration of the programme into the current MMR vaccination programme in Germany and on its full public provision. Appropriate comparisons with other studies were made and the results were not presented selectively.
Implications of the study Further studies and data on the benefits (effectiveness) of varicella vaccination may be needed to reduce the uncertainty in the absolute impact of the intervention studied by the authors. However, their conclusions seem to be valid to a German setting and to some other European cases.
Bibliographic details Beutels P, Clara R, Tormans G, Van Doorslaer E, Van Damme P. Costs and benefits of routine varicella vaccination in German children. Journal of Infectious Diseases 1996; 174(Supplement 3): S335-S341 Other publications of related interest 1. White C J, Kuter B J, Hildebrand C S et al. Varicella vaccine (Varivax) in healthy children and adolescents: results from clinical trails, 1987 to 1989. Pediatrics 1991;87:604-610.
2. Halloran M E, Cochi S L, Lieu T A, Wharton M, Fehrs L. Theoretical epidemiologic and morbidity effects of routine varicella immunization of preschool children in the United States. American Journal of Epidemiology 1994;140:81-104.
Indexing Status Subject indexing assigned by NLM MeSH Adolescent; Adult; Chickenpox /prevention & Chickenpox Vaccine /immunology; Child; Child, Preschool; Cost-Benefit Analysis; Germany; Humans; Infant; Vaccination /economics; control AccessionNumber 21996001003 Date bibliographic record published 31/08/1999 Date abstract record published 31/08/1999 |
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