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Cost-effectiveness of vaccination versus treatment of influenza in healthy adolescents and adults |
Muennig P A, Khan K |
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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 Trivalent influenza vaccine was compared with oral oseltamivir (75 mg, twice daily for 5 days) and with supportive care. Supportive care consisted of rest, hydration symptom relief and medical care, as required in the treatment of influenza-like illnesses (ILI).
Type of intervention Primary prevention and treatment.
Economic study type Cost-effectiveness analysis.
Study population The study population comprised healthy adults aged between 15 and 65 years.
Setting The setting was primary care. The economic study was carried out in the USA.
Dates to which data relate The effectiveness and resource use data were gathered from studies published between 1986 and 2000. The cost data were taken from published and electronic sources relating to 1993 to 2000, and were adjusted to 1997 prices.
Source of effectiveness data The estimates for the final outcomes were derived from a synthesis of published studies. In addition, one of the model's assumptions was based on expert opinion.
Modelling A decision analysis model was used to estimate the costs and benefits of each strategy. Other details of the model were not provided.
Outcomes assessed in the review The authors did not describe how they identified the studies that provided the values of the model parameters. The parameters used in the model were the probabilities of the following:
the development of ILI;
compliance with oseltamivir;
Guillain-Barre syndrome;
hospitalisation for influenza;
proportionate improvement with oseltamivir;
physician prescribing oseltamivir within 48 hours;
medical visit for ILI in supportive care patients;
medical visit for ILI for patients receiving treatment;
medical visit for ILI in vaccination group;
medical visit for side effects; and
health-related quality of life.
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 The data were drawn from 11 studies.
Methods of combining primary studies The method used to combine the primary studies was not reported. Three values were presented for each model parameter. More specifically, the one used in the base-case, and a high and a low value for use in the sensitivity analysis.
Investigation of differences between primary studies Results of the review The following values, expressed as probabilities, were used in the model:
development of ILI, 0.49 (range: 0.21 - 0.50);
compliance with oseltamivir, 0.95 (range: 0.5 - 1);
Guillain-Barre syndrome, 1 x10^-6 (range: 0.5 x10^-6 - 9 x10^-6);
hospitalisation for influenza, 0.00024 (range: 0.00018 - 0.024);
proportionate improvement with oseltamivir, 0.213 (range: 0.18 - 0.248);
physician prescribing oseltamivir within 48 hours, 0.95 (range: 0.1 - 1);
medical visit for ILI in supportive care patients, 0.75 (range: 0.58 - 0.91);
medical visit for ILI in patients receiving treatment, 0.695 (range: 0.54 - 0.91);
medical visit for ILI in vaccination group, 0.38 (range: 0.23 - 0.53);
medical visit for side effects, 0.01 (range: 0 - 0.05); and
health-related quality of life, 0.61 (high value of 0.79).
Methods used to derive estimates of effectiveness Five assumptions were included in the model, one of which was justified by expert opinion.
Estimates of effectiveness and key assumptions Based on expert opinion, it was assumed that 10% of all patients with ILI will visit a clinician within 48 hours. The other assumptions were reported in full in the paper.
Measure of benefits used in the economic analysis The measure of health benefit used was the quality-adjusted life- years (QALYs), expressed as quality-adjusted hours (QAHs). The results from a published study that used the Quality of Well-Being scale were used to value health-related quality of life.
Direct costs The direct costs to the health service were included. These were for hospitalisation, Guillain-Barre syndrome, visit to a clinician for ILI, influenza vaccine and administration (including patient time as a component), prescriptions and over-the-counter medication, and transport. The cost of the patient's time to be vaccinated was incorporated in the total cost of vaccination. The caregivers' time was valued from 1998 national census data, labour statistics published in 2000, and medical literature published in 1998. The costs entered in the model were reported as a base-case figure with a range. The costs and the quantities were not reported separately.
Cost data taken from published and electronic sources relating to 1993 to 2000, and adjusted to 1997, were used to populate a decision analysis model. The method used to adjust the costs was not described.
Discounting was neither relevant, nor applied, as the costs were assumed to have been incurred in less than one year. The authors applied charge-to-cost ratios derived from the Medical Provider Analysis as a means of reflecting the true cost to society.
Statistical analysis of costs No statistical analysis of the costs was reported.
Indirect Costs The authors reported that the perspective of the study was societal. However, patient productivity losses were not included. In addition, no rationale for the exclusion of patient productivity losses due to ILI was given.
Sensitivity analysis The authors reported that all variables were included in a multivariate sensitivity analysis. Those variables showing effects on cost or effectiveness were further explored in one-way and bivariate sensitivity analyses. The ad hoc review provided the range over which the variables were tested to establish the generalisability of the results. In addition, a Monte Carlo simulation was used to explore parameter uncertainty. All the parameters were assigned a triangular distribution.
Estimated benefits used in the economic analysis Vaccinating all healthy adults generated a gain of 0.00853 QALYs per person. Treating people who developed ILI generated a gain of 0.00821 QALYs. Providing supportive care alone resulted in a gain of 0.00779 QALYs.
In an average influenza season, the incremental effectiveness of vaccination compared with treatment (oseltamivir) was an estimated net gain of 3.2 QAHs per person among the healthy adult population. Likewise, compared with supportive care, vaccination resulted in an estimated net gain of 6.5 QAHs per person.
The probabilities of developing Guillain-Barre syndrome as a side effect of vaccination, and of requiring a medical visit because of the side effects of vaccination or treatment, were included.
Cost results The undiscounted cost per person was $52.92 for vaccination, $77.99 for treatment and $66.39 for supportive care.
The incremental cost of vaccination compared with treatment was a saving of $25.07.
The incremental cost of treatment compared with supportive care was $11.60.
The duration of follow-up was limited to one influenza season for the intervention and components.
Synthesis of costs and benefits The authors reported that vaccination was the dominant strategy, being both the most effective and the most cost-effective. Although both the total cost and total effectiveness were reported, these were not combined to give a cost per QALY ratio. Instead, vaccination compared with treatment was reported to give a net gain of 3.2 hours with a cost-saving of $25 per person per season. Vaccination compared with supportive care was reported to give a net gain of 6.5 hours with a cost-saving of $13 per person per season.
An incremental cost-effectiveness ratio of $27,619 per QALY was reported for treatment relative to supportive care.
The model was most sensitive to the incidence of ILI, followed by transportation costs, caregiver costs, the cost of a medical visit in the vaccination arm, and the cost of the influenza vaccine.
Authors' conclusions The vaccination of healthy adults, aged between 15 and 65 years, against influenza was cost-saving compared with treatment with oseltamivir or with the provision of supportive care alone.
CRD COMMENTARY - Selection of comparators Although no explicit justification was given for the comparator used, it appears to have represented current practice in the authors' setting. You should decide if the comparator represents current practice in your own setting.
Validity of estimate of measure of effectiveness A systematic review of the literature was not undertaken. Although this is common practice with models, it does not always ensure that the best available data are used in the model. There was no description of how the data from the studies were used, although a range for the sensitivity analysis was presented. The authors did not consider the impact of differences between the primary studies when estimating the effectiveness. One of the assumptions of the model was based on expert opinion. However, no further details were provided and this assumption was not explored in the sensitivity analysis. Given the lack of detail of the methods used to derive the model inputs, it is difficult to comment on their quality.
Validity of estimate of measure of benefit The measure of benefit used was health utility, measured in terms of QALYs and QAHs, and measured over one influenza season. The results from a published study using the Quality of Well-Being scale were used to estimate the health-related quality of life score for people with ILI. Technically, this instrument does not produce utilities, although they have been reported as such. The authors discussed this limitation. The estimation of benefits was modelled. The instrument used to derive the measure of health benefit, a decision analysis model, was appropriate.
Validity of estimate of costs The authors reported that the costs were estimated from a societal perspective, but the indirect costs were not included. The patients' productivity losses were not calculated. The cost-utility of the intervention might have been underestimated since the analysis did not include productivity losses. All the relevant direct costs were included and the authors applied charge-to-cost ratios to reflect the wider perspective. Discounting was not relevant since the costs were incurred during less than one year. A sensitivity analysis of the prices was undertaken.
Other issues The authors did not compare their findings with those from other studies, so it is not possible to assess the extent to which their results agree with other published results. In addition, the issue of the generalisability of the results to other settings was not directly addressed. The authors do not appear to have reported their results selectively and their conclusions reflected the scope of the analysis.
The authors chose not to model herd immunity and reported four limitations of their study. First, there was difficulty in adjusting data to the World Health Organization definition of ILI, which affected the comparability of the different parameters used. Second, it was not possible to obtain a precise incidence rate for ILI in unvaccinated persons. Third, no data on the reduction of medical resource consumption, or mortality due to oseltamivir use, were available. Finally, the Quality of Well-Being scale is not designed or, presumably, validated to produce utilities impacting on the health-related quality of life values obtained.
Several typographical errors were found in the reporting of the incremental effectiveness.
Implications of the study Vaccination is the most cost-effective method of decreasing health care costs, morbidity and mortality and should be considered for all persons, with the exception of those for whom it is contraindicated.
Source of funding Financial support from the Program in Cost-effectiveness and Outcomes.
Bibliographic details Muennig P A, Khan K. Cost-effectiveness of vaccination versus treatment of influenza in healthy adolescents and adults. Clinical Infectious Diseases 2001; 33(11): 1879-1885 Indexing Status Subject indexing assigned by NLM MeSH Acetamides /therapeutic use; Adolescent; Adult; Aged; Antiviral Agents /therapeutic use; Cost-Benefit Analysis; Enzyme Inhibitors /therapeutic use; Humans; Influenza Vaccines /economics; Influenza, Human /economics /prevention & Middle Aged; Neuraminidase /antagonists & Oseltamivir; Vaccines, Inactivated /economics; control /therapy; inhibitors AccessionNumber 22001002088 Date bibliographic record published 31/01/2005 Date abstract record published 31/01/2005 |
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