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The health and economic benefits of influenza vaccination for healthy and at-risk persons aged 65 to 74 years |
Nichol K L, Goodman 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 Influenza vaccination was given to members of a managed care organisation during 6 consecutive influenza seasons (October to December).
Economic study type Cost-effectiveness analysis and cost-benefit analysis.
Study population The study population comprised members of a health maintenance programme who were aged between 65 and 74 years. Two thirds of the members were healthy, while the remaining third were at increased risk of complications from influenza.
Setting The setting was primary care. The economic study was carried out in the USA.
Dates to which data relate The effectiveness evidence was obtained from 1990-91 to 1995-96. The resource evidence was obtained from 1990 to 1996. The price year was 1996.
Source of effectiveness data The effectiveness data were derived from a single study.
Link between effectiveness and cost data The costing was carried out on the same patient sample that provided the effectiveness evidence. It was unclear whether the costing was carried out after the effectiveness results were known.
Study sample No power calculations to determine the sample size were reported. There was no sample selection, as all members of the health organisation were included in the study. Each person-period was considered a separate individual. There were 100,195 person-periods and 59.7% of the individuals were vaccinated against influenza.
Study design This was a multiple cohort study using vaccinated and unvaccinated participants. It was conducted in multiple centres in the same geographical area (Minneapolis-St Paul, USA).
Analysis of effectiveness All the patients in the study were accounted for in the analysis. The primary health outcomes used in the analysis were hospitalisation for all acute and chronic respiratory conditions (HACRC), hospitalisation for pneumonia and influenza (HPI) and death. The authors described those in the study as being healthy or at increased risk of complications from influenza. Patients were described as being at risk if they had a prior diagnosis of heart disease, lung disease, diabetes mellitus, chronic renal disease, cancer, stroke/dementia or rheumatological disease. A total of 54.3% of healthy individuals and 70.3% of those at increased risk received the vaccine. Among the healthy individuals, those who were vaccinated were more likely to have had a prior diagnosis of pneumonia (1.9% versus 0.9%, p<0.001) and higher rates of prior health resource utilisation. Although the vaccinated and nonvaccinated were not shown to be comparable, the regression model enabled other variables that might influence hospitalisation and the death rate to be considered. These variables included age, gender, vaccination status, past history of pneumonia, and numbers of physician visits and hospitalisations during the previous 12 months.
Effectiveness results The odds ratio (OR) was 0.76 (95% confidence interval, CI: 0.61 - 0.94) for HPI, (p=0.01), 0.86 (95% CI: 0.77 - 0.97) for HACRC, (p=0.01), 0.47 (95% CI: 0.39 - 0.55) for death, (p<0.0001).
When the authors analysed the results according to whether people were described as at risk or healthy, the results showed a greater effect for vaccination among the at-risk group.
For the at-risk group, the OR was 0.76 (95% CI: 0.58 - 0.98) for HPI, (p=0.04), 0.85 (95% CI: 0.74 - 0.97) for HACRC, (p=0.02), and 0.44 (95% CI: 0.36 - 0.54) for death, (p<0.0001).
For the healthy group, the OR was 0.74 (95% CI: 0.49 - 1.11) for HPI, (p=0.14), 0.88 (95% CI: 0.71 - 1.09) for HACRC, (p=0.23), and 0.60 (95% CI: 0.42 - 0.86) for death, (p=0.006).
The number-needed-to-treat (NNT) to prevent one HPI was 1,389 for all patients, 1,923 for the healthy group and 463 for the at-risk group.
The NNT to prevent one HACRC was 595 for all patients, 1,667 for the healthy group and 196 for the at-risk group.
The NNT to prevent one death was 270 for all patients, 1,250 for the healthy group and 85 for the at-risk group.
Clinical conclusions Influenza vaccination reduced the incidence of hospitalisation for influenza, pneumonia and all respiratory conditions. It also reduced the death rate. The effect on the death rate showed the greatest statistical significance, as did the effects on those at risk compared to healthy individuals.
Modelling Multiple "logistic" regression was used to assess the effects of vaccination on hospitalisation and on the death rate, thus taking account of the effect of other crucial variables.
Measure of benefits used in the economic analysis The measure of benefits used in the economic analysis was the lives saved. The authors also took a cost-benefit approach to calculate the net costs, using the human capital approach to calculate the values of a human life.
Direct costs The costs were derived using actual data from the health maintenance organisation and 1996 as the price year. Discounting was not relevant since the costs for each person-period were calculated for less than 2 years. The costs were for hospitalisations, purchase of the vaccine, vaccine administration (it was unclear who did this) and the vaccination programme. The cost of the vaccination programme was given per vaccinated person, but otherwise there was no breakdown of the costs into prices and quantities. The hospital costs were derived using the overall median 1996 charges per hospitalisation adjusted by the Medicare cost-to-charge ratio.
Statistical analysis of costs No statistical analysis of the costs was carried out
Indirect Costs Discounting was not carried out since the costs were calculated for less than 2 years. The indirect vaccination costs were calculated by assuming each vaccination took one hour, which was valued in 1996 dollars. The 1990 US Census bureau data for the average annual value of labour and housekeeping activities weighted for age and the proportion estimated to be in the labour/housekeeping force, were used. The value of a life saved was calculated using age-adjusted values for the present value of future earnings and a 5% discount rate. The quantities and the costs were not analysed separately. The indirect costs were calculated only for healthy people, as they were the ones considered capable of working.
Sensitivity analysis No sensitivity analysis was carried out.
Estimated benefits used in the economic analysis The vaccination programme prevented 8 deaths per 10,000 persons vaccinated in the healthy group and 117.6 per 10,000 persons in the at-risk group. There was no follow-up after the 'influenza season' of the year studied. The question of side effects was discussed and the results of other studies were used to justify their exclusion.
Cost results The net total costs of vaccinating 10,000 people were -$393,462 in the healthy group and -$345,507 in the at-risk group. Therefore, vaccination reduced costs for both categories of vaccinated individuals.
The greater cost-saving for the healthy group can be explained by the gain in output caused by healthy people working.
Synthesis of costs and benefits The authors calculated a negative cost per life saved as the vaccination programme was cost-saving and was the dominant strategy.
Authors' conclusions An influenza vaccination programme for people aged 65 to 74 years saves lives and reduces costs. This unambiguous benefit was especially marked for those considered at risk.
CRD COMMENTARY - Selection of comparators The authors explicitly justified their choice of the comparator (no influenza vaccination).
Validity of estimate of measure of effectiveness The study design, a multiple cohort study, may have some limitations in terms of bias and confounding in comparison with a randomised controlled trial. However, a randomised controlled trial could not be defended on ethical grounds. All the people eligible for vaccination were included in the study, there was no sample selection. Patients in the two groups were not shown to be comparable at analysis. Therefore, the degree to which the non comparability of the groups would affect the results depends on whether multiple regression has taken all the variables that influence HPI, HACRC and death into consideration.
Validity of estimate of measure of benefit The measure of benefit, lives saved, was obtained directly from the effectiveness analysis. The authors implicitly justified this measure in that they described death as the most severe complication of influenza. The authors also calculated a net benefit (cost) using the human capital approach, which was appropriate. However, it could only be applied to the 'healthy' member of each cohort.
Validity of estimate of costs Most of the relevant categories of costs were included in the analysis. However, the non-hospital medical costs were excluded and may be relevant. The costs and the quantities were not reported separately. The prices were taken from the authors' setting and published sources.
Other issues The authors compared their results with the findings of other studies. The issue of generalisability was not addressed, although the authors were clearly aware of the desirability of generalisable results. The lack of a breakdown into prices and quantities limits the generalisability of the cost results.
Implications of the study Research that breaks down the costs into prices and quantities would help policy makers, in other countries with different wage rates and hospital costs, to decide whether influenza vaccination is cost-saving as well as clinically effective for those aged 65 to 74 years.
Bibliographic details Nichol K L, Goodman M. The health and economic benefits of influenza vaccination for healthy and at-risk persons aged 65 to 74 years. PharmacoEconomics 1999; 16(Supplement 1): 63-71 Indexing Status Subject indexing assigned by NLM MeSH Aged; Cohort Studies; Comorbidity; Direct Service Costs; Europe /epidemiology; Female; Hospitalization /statistics & Humans; Influenza Vaccines; Influenza, Human /economics /epidemiology /prevention & Male; Minnesota /epidemiology; Pneumonia, Viral /economics /epidemiology /prevention & Risk Factors; Vaccination /economics; control; control; numerical data AccessionNumber 22000008071 Date bibliographic record published 29/02/2004 Date abstract record published 29/02/2004 |
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