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Is immunising all patients with chronic lung disease in the community against influenza cost effective? Evidence from a general practice based clinical prospective cohort study in Utrecht, the Netherlands |
Hak E, van Essen G A, Buskens E, Stalman W, de Melker R A |
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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 An influenza vaccination programme to prevent complications in a general practice based cohort of adult patients with a chronic lung disease.
Economic study type Cost-effectiveness analysis.
Study population Adult patients with a chronic lung disease.
Setting Primary care. The economic study was carried out in the Netherlands.
Dates to which data relate Effectiveness and resource use data were collected between October 1995 and March 1996. The price year was 1995.
Source of effectiveness data The effectiveness data were derived from a single study.
Link between effectiveness and cost data Costing was prospectively undertaken on the same patient sample as that used in the effectiveness analysis.
Study sample Power calculations were not reported as having been used to determine the sample size. The study sample consisted of 1,696 adult patients with chronic lung disease. 453 patients remained unvaccinated with 80% being in the 18-64 age category. 1,243 patients were vaccinated of whom 57% were aged 18-64. The overall vaccination rate was 73% (66% for the 18-64 age category and 85% for the 65 years and over age category).
Study design This was a prospective cohort study, carried out in a single network centre, which consisted of six computerised primary care group practices employing 23 general practitioners and covering about 50,000 patients. The patients were followed from the moment of vaccination until the end of the influenza A epidemic of 1995/96 (starting in week 46 of 1995 and ending in week 10 of 1996). The loss to follow-up was not reported. A computerised search using a software selection module was used to identify all potential patients with chronic lung disease. The patient status, indicative of the need for vaccination, was determined by the participating GPs using the guidelines of the Dutch College of General Practitioners. The authors split the cohort into age bands (18-64, and 65 years and over) and underlying lung disease into COPD (chronic bronchitis/bronchiectasis and emphysema) or asthma. All medical data were checked in the medical records by a physician in April 1996.
Analysis of effectiveness The principle (intention to treat or treatment completers only) used in the analysis of effectiveness was not explicitly specified. The clinical outcomes were all cause death, exacerbation of pre-existing lung disease, pneumonia, congestive heart failure, acute myocardial infarction, and angina pectoris in week 46 (1995) to week 12 (1996). The effects of potentially confounding variables were adjusted using multivariable logistic regression modelling (with EGRET). The robustness of the models was investigated using regression diagnostics, including distributional and residual plots, and assessment of outliers. Mantel-Haenszel weighted relative risks were used to verify the estimates employing odds ratios with frequent outcomes.
Effectiveness results The overall complication rate was 15% and lower respiratory tract illness (LRTI) was the main cause (14%). Exacerbation of lung disease was reported to be 12.7%. The effectiveness of the immunisation programme cannot be established for those aged under 65, after adjustment for confounding variables (adjusted odds ratio 0.95, 95% CI: 0.62 - 1.48). The effectiveness of the programme could only be established for patients aged over 65. After adjustment for confounding variables it was found to reduce the occurrence of any complications by 50% (95% CI: 17 - 70%), acute LRTI by 46%, and cardiac disease by 57% (not statistically significant). The effectiveness of the programme in preventing cardiac disease for patients with cardiac comorbidity (n=197) was 80% (95% CI: 32 - 98%).
Clinical conclusions Vaccination effectiveness could only be demonstrated in patients aged 65 years and over. The study finding that vaccination was not effective in younger adults was in agreement with an earlier report.
Measure of benefits used in the economic analysis No summary benefit measure was identified in the economic analysis, and only separate clinical outcomes were reported. As vaccine effectiveness could only be demonstrated in patients aged 65 years and over, the economic analysis was limited to those subjects.
Direct costs Costs were not discounted due to the short follow-up period adopted in the study (less than one year). Some quantities were reported separately from the costs. Cost components were reported separately. The direct costs included in the analysis were the costs of immunisation, hospital stay and intensive care facilities. The cost of immunisation included the costs of vaccines and supplies, promotion, delivery, vaccination, and overhead. Net savings produced by the intervention were defined as immunisation costs - cost of medical care averted. The cost of medical care averted included the hospital stay and intensive care avoided for respiratory disease and cardiac disease. The perspective adopted in the analysis was that of society. The unit costs related to the hospital stay and intensive care were obtained from national data. 1995 price data were used. As vaccine effectiveness could only be demonstrated in patients aged 65 years and over, the cost analysis was limited to these subjects. The cost analysis did not cover the costs resulting from consultations for side effects, as few such consultations occurred in this study.
Indirect Costs Indirect costs were not included since the economic analysis was limited to elderly patients for whom costs incurred due to productivity loss were deemed less important.
Sensitivity analysis A multi-way simple sensitivity analysis was performed varying the estimates of effectiveness, the proportion of patients needing medical care and the median length of hospital care within a plausible range of plus or minus 20%.
Estimated benefits used in the economic analysis Cost results The estimated direct cost of influenza vaccination per 100 vaccinated patients with chronic lung disease (over 65 years) was 1,250. The total cost of medical care avoided for respiratory disease was 2,176 (1,848 for hospital stay and 328 for intensive care). The total cost of care avoided for cardiac disease was 4,080 (3,259 for hospital stay and 821 for intensive care). The net total saving per 100 vaccinated patients was 5,007. The estimated net saving was 50 (range: 16 - 101) per elderly person vaccinated.
Synthesis of costs and benefits Costs and benefits were not combined since, in the elderly patients, the intervention was the dominant strategy.
Authors' conclusions This study suggests that, in the Netherlands, immunisation of elderly patients with chronic lung disease against influenza is effective and cost-saving, and therefore those patients should be given high priority.
CRD COMMENTARY - Selection of comparators The reason for the choice of the comparator is clear.
Validity of estimate of measure of benefit As acknowledged by the authors, the internal validity of the effectiveness measure cannot be guaranteed mainly due to lack of complete comparability of those vaccinated and those unvaccinated with regard to the prognosis of developing influenza-related complications (the adjustment was only for known confounders). The study may be regarded as a cost-consequences analysis.
Validity of estimate of costs Some quantities were reported separately from the costs and adequate details of the methods of cost estimation were given.
Other issues The authors' conclusion appears to be justified given the uncertainties in the data. The issue of generalisability to other settings or countries was not addressed although appropriate comparisons were made with other studies.
Implications of the study Experimental studies are needed to establish whether adult patients with lung disease under 65 years should be given priority as well.
Source of funding Financially supported by the Dutch Council of the Sick Fund.
Bibliographic details Hak E, van Essen G A, Buskens E, Stalman W, de Melker R A. Is immunising all patients with chronic lung disease in the community against influenza cost effective? Evidence from a general practice based clinical prospective cohort study in Utrecht, the Netherlands. Journal of Epidemiology and Community Health 1998; 52: 120-125 Indexing Status Subject indexing assigned by NLM MeSH Adult; Aged; Cost of Illness; Cost-Benefit Analysis; Female; Humans; Influenza Vaccines /administration & Influenza, Human /prevention & Lung Diseases, Obstructive /complications /economics; Male; Middle Aged; Netherlands; Prospective Studies; control; dosage /economics AccessionNumber 21999008054 Date bibliographic record published 31/10/2000 Date abstract record published 31/10/2000 |
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