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.

The study examined a strategy for vaccination against influenza in adults aged 65 years or older.

Primary prevention.

Cost-effectiveness analysis.

The target population was a hypothetical cohort of adults aged 65 years or older.

The setting was the community. The economic study was carried out in Cuernavaca, Mexico.

Studies providing effectiveness evidence dated from 2001 to 2004, while those providing cost data were from 2002 to 2003. The price year was 2004.

The estimates of effectiveness were derived from a review or synthesis of published studies and authors- assumptions.

A model was used to derive the likely benefits and costs of universal vaccination, compared with no vaccination, in a 12-year time horizon. No details of the model were given.

The parameters used in the model included:

the total number of deaths due to influenza and pneumonia,

the number of hospitalisations,

the total population of adults aged 65 years or older, and life expectancy for this population,

disability due to pneumonia,

the average length of a pneumonia or influenza episode, and

vaccine efficacy to avoid deaths and cases.

No inclusion criteria for the studies reviewed were reported. Published data from government and international organisations were considered in the review.

Not reported.

Not reported.

Not reported.

At least eight published studies were reviewed.

The authors did not state the method used to combine the primary studies, although a narrative method appears to have been used.

Not reported.

The following represent selected model parameters that were included:

there were 6,753 deaths and 12,951 hospitalisations due to influenza and pneumonia in adults aged 65 or older;

the total population of adults aged 65 years or older was 5.42 million;

life expectancy varied from 12.8 years for women aged 65 years or older to 0.5 years for men aged 100 years or older;

disability due to pneumonia was 0.28;

the average length of a pneumonia or influenza episode was 12.7 days; and

vaccine efficacy to avoid cases was between 20 and 30%.

The authors made assumptions to estimate some effectiveness parameters.

The authors assumed a high level of coverage, meaning a high acceptance rate (the specific value was not reported).

The authors used both life-years (LYs) and disability-adjusted life-years (DALYs) as measures of benefit. A disability for pneumonia was taken from World Health Organization (WHO) reports. Discounting was performed at a rate of 3%. Two alternative scenarios were considered. Scenario 1 considered vaccine efficacy for a 30% reduction in deaths, while scenario 2 considered a 20% reduction in deaths. Sub-group analyses were performed for scenario 1. These considered the age at which vaccination was implemented (70 or older, 75 or older, and 80 or older). A sub-group analysis was not reported for scenario 2.

The direct costs included in the economic analysis appear to have been those of the health care provider. Estimates of medical direct costs included costs of vaccination (including vaccine doses), medical care for pneumonia, transportation and storage. All of these were estimated from published sources. Future costs were discounted at an annual rate of 3%. The quantities and the costs were not analysed separately. Estimates of the quantities and the costs were both based on actual data and were derived using modelling. The price year was 2004. The same scenarios and sub-group analyses used in the estimation of health benefits (see 'Measure of Benefit used in the Economic Analysis') were considered for the estimation of the costs.

Not reported.

No indirect costs were reported.

Mexican pesos (MXN).

A probabilistic sensitivity analysis was performed to assess uncertainty in the study results. Ranges and probabilistic distributions were reported for vaccination coverage, vaccine efficacy to avoid cases, vaccine efficacy to avoid deaths (two scenarios: 20 - 40% and 10 - 30% of deaths avoided), hospitalisation costs and discount rate. Also 100,000 iterations of the model were carried out to explore uncertainty in the results. The ranges appear to have been based on authors- assumptions and derived from published literature.

An average of 37,272 LYs lost were due to deaths caused by influenza; 126 healthy LYs lost were due to the morbidity caused by influenza infections;

vaccination saved 11,169 LYs under scenario 1 and 7,454 LYs under scenario 2.