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Influenza vaccination in an occupational setting: effectiveness and cost-benefit study |
Cohen P, Darling C, Hampson A, Downs K, Tasset-Tisseau 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 Healthy adults were given parenteral influenza vaccine (VAXIGRIP supplied by Aventis Pasteur) whose formulation was determined by the Australian Influenza Vaccine Committee for 2000. The vaccine was administered by deep subcutaneous injection into the leg or upper arm.
Economic study type Cost-effectiveness analysis.
Study population The study population comprised full-time employees of a steel works, aged 18 to 64 years. Individuals were excluded if they were in a high-risk group recommended for influenza vaccination, had already been vaccinated against influenza in 2000, or had current influenza or upper respiratory tract infections. They were also excluded if they had any of the contraindications to influenza vaccine that were listed in the approved product information.
Setting The setting was the workplace. The economic study was carried out in New South Wales, Australia.
Dates to which data relate The effectiveness and resource evidence were from 2000. The price year seems to have been 2000.
Source of effectiveness data The effectiveness data were derived from a single study.
Link between effectiveness and cost data The same patients provided both the effectiveness and cost evidence data. The costing was carried out prospectively.
Study sample Power calculations were reported. It was expected that the rate of influenza incidence would be 15% among the unvaccinated and 4.65% among the vaccinated, and that the vaccine would have an efficacy rate of 69%. It was intended that there should be 1,000 participants in the study, but instead there were 603 randomised to the two groups. Six participants allocated to the non-vaccination group refused to participate, leaving 301 in the non-vaccinated group and 296 in the vaccinated group.
Study design This was a single-centre randomised controlled trial (RCT), in which participants were allocated to the study groups according to a computer-generated blocked randomisation schedule. Follow-up lasted for 6 months after randomisation. Forty-seven participants were lost to follow-up.
Analysis of effectiveness The basis of the analysis was intention to treat. The primary health outcomes used were the incidence of influenza-like illness (ILI) episodes during the whole 6-month period and febrile illness (FI) episodes during the 3 months from July to September. The information on the health outcomes was obtained from self-assessment questionnaires. ILI was defined as at least one of fever, chills or aches, and at least one of runny nose, sore throat, cough or hoarse voice. The symptoms had to last for at least 2 days. FI was defined as an episode of at least 2 days of fever and at least two of the specified symptoms (chills, aches, runny nose, sore throat, cough or hoarse voice). The two groups appear to have been comparable at baseline.
Effectiveness results The incidence of ILI was 38.6% (95% confidence interval, CI: 32.75 - 44.6% in the non-vaccinated group and 38.1% (95% CI: 32.3 - 43.9) in the vaccinated group.
The incidence of FI during July to September 2000 was 17.4% (95% CI: 12.8 - 22.0) in the non-vaccinated group and 10.9% (95% CI: 7.1 - 14.6) in the vaccinated group. The difference was statistically significant using a log-rank test, (p=0.041).
The effectiveness of the vaccination programme was defined as the difference in incidence rates as a percentage of the rate in the non-vaccinated group. This was 0.8% for ILI and 37.5% for FI.
There were no adverse events recorded in the first week after randomisation or vaccination.
In the first week after randomisation, ILI symptoms were recorded. The results showed 30.9% of the non-vaccinated group and 55.7% of the vaccinated group had at least one symptom.
Clinical conclusions Although the vaccination programme resulted in a small reduction in episodes of ILI, it showed a marked reduction in episodes of FI.
Measure of benefits used in the economic analysis No summary measure of health benefits was produced. The authors described the reduction in indirect costs as a health benefit.
Direct costs Discounting was not carried out as the costs were incurred during less than 2 years. The direct costs measured were for the vaccine and materials, and the administration of the vaccine. The unit costs were given. The cost data came from the company and the organisers of the vaccination programme. The price year was 2000.
Statistical analysis of costs No statistical analysis of the costs was carried out.
Indirect Costs Discounting was not carried out as the costs were incurred during less than 2 years. The cost was derived from actual data. The work time lost as a result of vaccination was valued at the salary level of the employee. The firm's costs resulting from FI and ILI were the indirect costs (productivity losses) of FI and ILI. Therefore, the reduction in these costs as a result of the vaccination programme represented the benefit to the firm of this programme. The data was obtained from the company. The price year was 2000.
Currency Australian dollars (Aus$).
Sensitivity analysis A one-way sensitivity analysis was carried out. The parameters investigated were the vaccine and vaccine administration costs, the incidence of ILI and the resulting number of sick leave days taken.
Estimated benefits used in the economic analysis In effect, the study has been considered a cost-consequences analysis. See the 'Effectiveness Results' section.
Cost results The vaccination programme costs for ILI were Aus$9,467.55 and the benefits for ILI were Aus$15,119.87. Thus, the global cost-savings were Aus$5,652.32, which equated to a cost-saving per vaccinated employee of Aus$20.93.
The vaccination programme costs for FI were Aus$9,255.63 and the benefits for FI were Aus$24,662.37. Thus, the global cost-savings were Aus$15,406.74, which equated to a cost-saving per vaccinated employee of Aus$58.36.
The costs were calculated for 6 months.
In the sensitivity analysis, varying the vaccination cost components did not substantially affect the costs. However, halving the incidence of ILI in the vaccinated group reduced the costs by Aus$37,695.65 (Aus$139.61 per vaccinated employee).
No adverse events were reported.
Synthesis of costs and benefits Authors' conclusions The vaccination programme had a beneficial effect on employee health (measured in terms of time off work) and the company benefited economically from funding a vaccination programme. The gain from fewer days off work was greater than the cost of the programme. This was seen more clearly when febrile illness (FI), rather than influenza-like illness (ILI), was used to define influenza.
CRD COMMENTARY - Selection of comparators The choice of the comparator (no vaccination for healthy adults) was justified as it represented current practice in the authors' setting. You should decide if this is current practice in your own setting.
Validity of estimate of measure of effectiveness The source of the effectiveness data was a single study. The study design, an RCT, was appropriate for the hypothesis. However, as the authors acknowledged, it would have been better if the non-vaccinated participants in the trial had received a placebo injection, as this would have avoided the problem of people randomised to non-vaccination dropping out of the study. The study sample appears to have been representative of the study population, although the potential for volunteer bias has not been eliminated. The patient groups appear to have been comparable at analysis. The analysis of effectiveness was handled credibly.
Validity of estimate of measure of benefit A summary measure of benefit was not derived. The measure of benefit considered was financial and was derived from the company's estimate of its monetary gain resulting from the intervention.
Validity of estimate of costs From the cost perspective adopted (i.e. that of the company), it would appear that all the relevant costs were included. The costs were reported separately from the quantities. The resource use quantities were taken from a single study. No statistical analysis of the quantities was performed. A sensitivity analysis of the time necessary for the worker to take off to receive the vaccination was carried out, using a range that seemed appropriate. However, the sensitivity analysis examining the effect of halving the incidence of ILI among the vaccinated seemed to cover an unjustifiable wide range. No other sources were used for resource quantities, and no other analysis of the quantities was conducted. The prices were taken from the authors' setting. No statistical analysis of the prices was conducted. A sensitivity analysis of the costs in the vaccination programme was carried out. The price year was not formally stated, but all the prices appear to have been recorded in 2000.
Other issues The authors made appropriate comparisons of their results with those from other studies. The issue of generalisability to other settings was not addressed. The authors did not present their results selectively and their conclusions would appear to reflect the scope of their analysis. The authors reported that their method of recording patient health, using self-reporting questionnaires, had not been validated before the study. In addition, the non-blinding of the treatment might have influenced the outcomes. These limitations should be considered when using these results to aid decision-making.
Implications of the study The authors recommended that future studies of the effectiveness of influenza vaccination include fever as a necessary condition, something that was not true of the definition of ILI. They also recommended that future studies get closer to the target of 1,000 participants, and implied that a study undertaken in a year of high influenza incidence might produce different results from the present study, which was undertaken in a year of low influenza incidence.
Source of funding Supported by Aventis Pasteur Pty Ltd.
Bibliographic details Cohen P, Darling C, Hampson A, Downs K, Tasset-Tisseau A. Influenza vaccination in an occupational setting: effectiveness and cost-benefit study. Journal of Occupational Health and Safety - Australia and New Zealand 2003; 19(2): 167-182 Indexing Status Subject indexing assigned by CRD MeSH Adult; Australia; Cost-Benefit Analysis; Female; Humans; Incidence; Influenza Vaccines /administration & Male; Middle Aged; Occupational Health; Orthomyxoviridae Infections /prevention & Voluntary Programs; Workplace; control; dosage /economics AccessionNumber 22003009406 Date bibliographic record published 30/11/2005 Date abstract record published 30/11/2005 |
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