(1) an oral, enteric coated capsule containing live Type 21A whole cell vaccine, 'Vivotif'; and

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1 A cost-effectiveness analysis of typhoid fever vaccines in US military personnel Warren T A, Finder S F, Brier K L, Ries A J, Weber M P, Miller M R, Potyk R P, Reeves S, Moran E L, Tornow J J 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 Three typhoid vaccines were investigated: (1) an oral, enteric coated capsule containing live Type 21A whole cell vaccine, 'Vivotif'; and (2) a subunit vaccine, 'Typhim-Vi'; and (3) a whole cell, heat-phenol killed vaccine, Typhoid Vaccine USP. Type of intervention Primary prevention. Economic study type Cost-effectiveness analysis. Study population US military personnel. Setting Primary care. The economic study was carried out in Texas, USA. Dates to which data relate The data for the effectiveness analysis were obtained from studies published in 1987, and a report from The dates for the resource use were not reported but are assumed to be The prices used were from Source of effectiveness data Effectiveness data were derived from a review of previously published studies. Modelling A probability model was used in order to estimate costs and benefits. Outcomes assessed in the review The review assessed the efficacy rates, compliance and incidence of adverse effects associated with the vaccines for subjects deployed to an endemic area and those not so deployed. Study designs and other criteria for inclusion in the review Page: 1 / 5

2 Sources searched to identify primary studies Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Number of primary studies included 16 studies were reported in the review. Methods of combining primary studies Narrative method. Investigation of differences between primary studies Results of the review The typhoid vaccine USP had an efficacy rate range of 51-77%, 'Vivotif', had a range of 60-71%, and 'Typhim-Vi' a range of 64-72%. The adverse effects rate ranges were 10-85% for the Typhoid vaccine USP (both 'severe local pain or swelling' and 'fever and flu-like syndrome' combined), 0-8% for 'Vivotif' (both 'fever and headache' and ' gastrointestinal adverse effects' combined), and 4-13% for 'Typhim-Vi' (both 'severe local pain or swelling' and 'fever and flu-like syndrome'). The efficacy rates used in baseline analysis were 70% for all strategies. The compliance with the oral vaccine (Vivotif) was assumed to be 65% due to its complex administration schedule. The other strategies were assumed to have a 100% compliance rate. The typhoid fever attack rate was 2%. Measure of benefits used in the economic analysis The measures of benefits used were cases of typhoid averted in the 'no-deployment scenario' and working hours saved in the 'deployment' scenario. A probability model was used to deal with the lack of information and the uncertainty involved in the outcomes of the strategies. Direct costs Direct costs were not discounted. Quantities were reported separately from the prices. The costs measured were operating costs and costs of complications. The boundary adopted was the hospital (military hospital or government). The estimation of resources used and costs was based on actual data, assumptions and information published in the literature. The unit costs used "reflect average costs borne by the US government". The sources of quantities and costs were the US Department of Veterans Affairs Federal Supply Schedule or US Defence Personnel Support Center and Medicare reimbursement data and US military data. The prices used were from The costs associated with morbidity and mortality resulting from failures of the vaccines (cases of personnel acquiring typhoid fever despite being immunized) were excluded from the analysis because they were assumed to be common to all the strategies. Statistical analysis of costs Page: 2 / 5

3 Not undertaken. Indirect Costs The costs of lost work time of military personnel acquiring typhoid fever within the 'deployment scenario' were measured. The boundary adopted was hospital (military hospital or government). The estimate of costs was based on actual data from the US Department of Veterans Affairs Federal Supply Schedule and Military data. The date when the resources used were measured was not reported. The prices used were from Currency US dollars ($). Sensitivity analysis Sensitivity analysis was performed to deal with variability in the data. The ranges used in the model for typhoid fever attack rate, compliance with 'Vivotif', efficacy and adverse effects for each vaccine were analysed. One way and multiway sensitivity analyses were performed. Estimated benefits used in the economic analysis The number of working hours saved per 1,000 vaccinees was for the 'Typhim-Vi' vaccine, for 'Vivotif' vaccine, and for Typhoid Vaccine USP vaccine relative to no vaccination, under the deployment scenario. The nodeployment scenario resulted in 994, 989, 994, and 980 cases of typhoid fever averted per 1000 vaccinees with Typhim- Vi, Vivotif, Typhoid vaccine USP, and no immunisation, respectively. Cost results The incremental cost per person protected was $11.21 with 'Typhim-Vi'; $19.59 for 'Vivotif', and $79.87 for Typhoid Vaccine USP, relative to the no-vaccination option under the no-deployment scenario. The corresponding figures for the deployment scenario were: -$71.21, -$49.11, and $12.37, respectively. Synthesis of costs and benefits The measure of synthesis of costs and benefits used in the deployment scenario was cost per working hours saved, whereas in the no-deployment scenario it was the cost per case of typhoid fever averted (not incremental). The cost per case of fever averted, for the no-deployment scenario in 1996 prices, was $37.30 for the 'Typhim-Vi' strategy, $45.99 for the 'Vivotif' strategy, $106.4 for the Typhoid vaccine USP, and $26.42 for the no-vaccination option. The cost per working hours saved for the deployment scenario were as follows: $49.36, $113.7, $ for Typhim-Vi, Vivotif, and Typhoid vaccine USP, respectively. Sensitivity analysis yielded a value of 3% for the attack rate at which the 'donothing' option becomes more expensive than 'Typhim-Vi' in the no-deployment scenario. It was also found that 'Vivotif' was the optimal strategy when the efficacy of 'Typhim-Vi' decreased to 64% and the efficacy of 'Vivotif' increased to 71%, provided the attack rate was greater than 5%. Also when the patient compliance rate for 'Vivotif' was at 80%, that strategy had the lowest cost per immunisation (however, in that scenario the costs of supervision of vaccination were not included). Authors' conclusions The authors concluded that 'Typhim-Vi' is the optimal typhoid vaccine strategy for personnel deployed to endemic areas of typhoid fever. The US continental infection rates of 0.002% makes the 'no-vaccination' option the optimal strategy for the no-deployment scenario. The authors concluded that"instead of immunising all personnel who are deploymenteligible, immunisation of personnel for typhoid fever could be done on a deployment-by-deployment basis, where personnel are only immunised if the typhoid fever attack rate is known to be high". Typhim-Vi was the most costeffective choice for the US military. Page: 3 / 5

4 CRD COMMENTARY - Selection of comparators The reason for the choice of comparator is clear. However, preventive educational strategies should be included in the analysis. Validity of estimate of measure of benefit The validity of the estimate of measure of benefits cannot be assessed due to the lack of detailed information about the nature of the literature search, the criteria for assessing the validity of the primary studies and the importance of the differences between those studies, and the foundations of the assumptions used. Validity of estimate of costs The authors provided inadequate details of when the data for resource use were collected. Important cost items were omitted, such as the costs of supervision of oral drug administration in the no deployment scenario and assumed common costs due to morbidity and mortality with failure of vaccine. Other issues The authors' conclusions are supported by the sensitivity analysis. The authors argued that the results are likely to apply only to military personnel from industrialised nations eligible to be sent to geographic areas with endemic typhoid fever. Implications of the study The authors stated that "US military personnel who are not considered to be in an imminent deployment status should not be immunised against typhoid fever. Personnel requiring immunisation, who are in a basic training environment where supervision of all vaccine doses is performed, should be immunised with 'Vivotif'". Those not in that environment and needing immunisation should be vaccinated with 'Typhim-Vi'. Source of funding None stated. Bibliographic details Warren T A, Finder S F, Brier K L, Ries A J, Weber M P, Miller M R, Potyk R P, Reeves S, Moran E L, Tornow J J. A cost-effectiveness analysis of typhoid fever vaccines in US military personnel. PharmacoEconomics 1996; 10(5): PubMedID Indexing Status Subject indexing assigned by NLM MeSH Cost-Benefit Analysis /economics; Humans; Military Personnel; Typhoid Fever /prevention & control; United States; Vaccines /economics AccessionNumber Date bibliographic record published 31/05/1999 Date abstract record published Page: 4 / 5

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