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Monday, 24 October 2005
19

METHODOLOGICAL ISSUES IN COST EFFECTIVENESS EVALUATION OF HEPATITIS A VACCINE: A SYSTEMATIC REVIEW

Andrea Anonychuk, MSc1, Andrea C. Tricco, MSc2, Chris Bauch, PhD3, Vladimir Gilca, MD4, Bernard Duval, MD, MPH4, Ba Pham, MSc2, and Murray Krahn, MD, MSc1. (1) University Health Network, Toronto, ON, Canada, (2) GlaxoSmithKline, Canada, Oakville, ON, Canada, (3) University of Guelph, Guelph, ON, Canada, (4) Universite Laval, Beauport, QC, Canada

Purpose: Current policy regarding hepatitis A (HA) vaccination in high-endemicity regions and among high-risk groups is influenced by published cost-effectiveness analyses (CEA); however results of these CEA vary widely across studies. A systematic review was conducted to explore the effects of methodological quality on such variation. Key aspects of vaccination, such as adequate representation of vaccine-induced herd-immunity and accurate estimation of the degree of under-reporting (approximately 1:10) were assessed.

Methods: Cost-effectiveness studies of HA vaccine were identified (MEDLINE, EMBASE, HSTAR, and SSCI; MeSH “cost-effectiveness” AND “hepatitis A”), and included if they were cost-effectiveness/utility studies of HA vaccine. Citations and full-text articles were reviewed independently by two reviewers. Back referencing, author searches, and expert consultation ensured literature saturation.

Quality of reporting was assessed using a 21-item quality tool (Neumann 2000). Methodological issues specific to vaccine evaluations were appraised by Beutels' 2002 guidelines. Key modeling issues were examined using Sculpher's 2000 framework.

Results: Thirty-four cost-effectiveness studies were included from full-text-article review (n=95) and citation-screening (n=700). Nine conducted an additional cost-utility analysis and six a cost-benefit analysis. All were model-based studies, thirteen utilizing Markov models. One used a dynamic model, capturing effects of herd immunity. Strategies included mass childhood/adult (n=11/n=2) and selective childhood/adult vaccination (n=24/n=8). Populations assessed were healthy participants (n=31), and patients with chronic liver disease (n=3).

The median quality using Neumann's tool was 62% (13/21 range [14-90%]), similar to the median score of 58% reported for CEA studies in other clinical areas. Cost-utility studies attained higher quality (n=9, median 76% [57-90%]) than cost-effectiveness (n=25, median 52%[14-71%]).

Cost-utility studies assessed using Beutels' guidelines clearly stated model assumptions (7/9), utilized proper time span (7/9), and captured relevant costs (7/9). Many did not discuss alternative modeling approaches (7/9).

Using Sculpher's framework, cost-utility studies specified model assumptions (9/9), and most justified model parameters (7/9). Some did not discuss implications of relaxing model assumptions (3/9). None adjusted for herd immunity, though four acknowledged this as a study limitation. One study adjusted for under-reporting, though five studies discussed it.

Conclusions: Methods used to evaluate the cost-effectiveness of HA vaccination were inconsistent, resulting in variable cost-effectiveness ratios across studies. Failing to adjust for herd-immunity and underreporting weakens scientific evidence and may result in biased estimates of the economic attractiveness of HA vaccination policies.


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See more of The 27th Annual Meeting of the Society for Medical Decision Making (October 21-24, 2005)