Development and psychometric validation of a self-administered questionnaire assessing the acceptance of influenza vaccination: the Vaccinees' Perception of Injection (VAPI) questionnaire.

BACKGROUND: Influenza is among the most common infectious diseases. The main protection against influenza is vaccination. A self-administered questionnaire was developed and validated for use in clinical trials to assess subjects' perception and acceptance of influenza vaccination and its subsequent injection site reactions (ISR). METHODS: The VAPI questionnaire was developed based on interviews with vaccinees. The initial version was administered to subjects in international clinical trials comparing intradermal with intramuscular influenza vaccination. Item reduction and scale construction were carried out using principal component and multitrait analyses (n = 549). Psychometric validation of the final version was conducted per country (n = 5,543) and included construct and clinical validity and internal consistency reliability. All subjects gave their written informed consent before being interviewed or included in the clinical studies. RESULTS: The final questionnaire comprised 4 dimensions ("bother from ISR"; "arm movement"; "sleep"; "acceptability") grouping 16 items, and 5 individual items (anxiety before vaccination; bother from pain during vaccination; satisfaction with injection system; willingness to be vaccinated next year; anxiety about vaccination next year). Construct validity was confirmed for all scales in most of the countries. Internal consistency reliability was good for all versions (Cronbach's alpha ranging from 0.68 to 0.94), as was clinical validity: scores were positively correlated with the severity of ISR and pain. CONCLUSION: The VAPI questionnaire is a valid and reliable tool, assessing the acceptance of vaccine injection and reactions following vaccination.

Economic evidence of influenza vaccination in children.

OBJECTIVE: We review published economic evaluations of influenza vaccination for children, including direct individual benefits and indirect societal benefits, to determine whether more studies are needed to fully understand the expected benefits of such strategies. METHODS: We searched MEDLINE and EMBASE databases to May 2006 and in-press articles to October 2006 for studies including economic analyses of influenza vaccination in children. Abstracts of all potentially relevant articles were screened. RESULTS: Fifteen relevant articles from 1983 were retained. Most were based on modelling, using previously published data and considered the societal perspective. Three were a part of prospective clinical trials. Various paediatric vaccination scenarios and parameters were considered. Vaccinating children against influenza was cost saving or cost effective in 10/15 studies, cost saving or effective only under certain conditions in three studies, and not cost saving or effective in two studies whatever the outcome or perspective considered. CONCLUSIONS: Most published evidence points to an economic interest for society of vaccinating children against influenza. However, differences in study design hinder the comparison of the various vaccination strategies considered. Comparable and complete data on the burden and cost of disease, and the cost of vaccination are needed, especially outside of North America.

Do we fully understand the economic value of vaccines?

Although many vaccination strategies are cost-effective, some of the newer vaccines are more expensive and may raise concerns about value for money. However, standard methods of economic evaluation may not adequately assess the true cost-effectiveness of vaccines, with the consequent under-application of vaccine strategies. Therefore, this paper reviews the evidence on cost-effectiveness of vaccines and vaccination strategies for pneumococcal disease, meningococcal disease, Hepatitis A and influenza. In each case the evidence is considered alongside existing vaccination policies in the major developed countries. The paper also highlights areas where traditional economic evaluations may not adequately reflect the value of vaccines.

Invasive meningococcal disease epidemiology and control measures: a framework for evaluation.

BACKGROUND: Meningococcal disease can have devastating consequences. As new vaccines emerge, it is necessary to assess their impact on public health. In the absence of long-term real world data, modeling the effects of different vaccination strategies is required. Discrete event simulation provides a flexible platform with which to conduct such evaluations. METHODS: A discrete event simulation of the epidemiology of invasive meningococcal disease was developed to quantify the potential impact of implementing routine vaccination of adolescents in the United States with a quadrivalent conjugate vaccine protecting against serogroups A, C, Y, and W-135. The impact of vaccination is assessed including both the direct effects on individuals vaccinated and the indirect effects resulting from herd immunity. The simulation integrates a variety of epidemiologic and demographic data, with core information on the incidence of invasive meningococcal disease and outbreak frequency derived from data available through the Centers for Disease Control and Prevention. Simulation of the potential indirect benefits of vaccination resulting from herd immunity draw on data from the United Kingdom, where routine vaccination with a conjugate vaccine has been in place for a number of years. Cases of disease are modeled along with their health consequences, as are the occurrence of disease outbreaks. RESULTS: When run without a strategy of routine immunization, the simulation accurately predicts the age-specific incidence of invasive meningococcal disease and the site-specific frequency of outbreaks in the Unite States. 2,807 cases are predicted annually, resulting in over 14,000 potential life years lost due to invasive disease. In base case analyses of routine vaccination, life years lost due to infection are reduced by over 45% (to 7,600) when routinely vaccinating adolescents 12 years of age at 70% coverage. Sensitivity analyses indicate that herd immunity plays an important role when this population is targeted for vaccination. While 1,100 cases are avoided annually when herd immunity effects are included, in the absence of any herd immunity, the number of cases avoided with routine vaccination falls to 380 annually. The duration of vaccine protection also strongly influences results. CONCLUSION: In the absence of appropriate real world data on outcomes associated with large-scale vaccination programs, decisions on optimal immunization strategies can be aided by discrete events simulations such as the one described here. Given the importance of herd immunity on outcomes associated with routine vaccination, published estimates of the economic efficiency of routine vaccination with a quadrivalent conjugate vaccine in the United States may have considerably underestimated the benefits associated with a policy of routine immunization of adolescents.

Vaccinating adolescents against meningococcal disease in Canada: a cost-effectiveness analysis.

BACKGROUND: One dose of serogroup C meningococcal conjugate vaccine (MCV-C) at 12 months of age is the most common immunization schedule in Canada, but immunity may wane over time. OBJECTIVES: To assess the cost-effectiveness of a booster dose at 12 years of age with either MCV-C or a quadrivalent ACYW135 meningococcal conjugate vaccine (MCV-4). METHODS: A simulation model for assessing both the direct and indirect effects of vaccination was developed. Age- and serogroup-specific incidence and fatality rates were derived from Canadian surveillance data. Vaccine efficacy was estimated from data from the U.K. and Spain, assuming an age-dependent decline of vaccine efficacy over time. Expected vaccine coverage rates were 90% at 12 months, and 70% at 12 years. Herd immunity was modeled using UK data. Vaccine purchase price per dose was $23 for MCV-C and $70 for MCV-4. Costs and health outcomes were discounted at 3% per year. Results, expressed in 2004 Canadian $ and from a societal perspective, were presented for a steady state situation and a population of 1 million. RESULTS: Under the "no vaccination" base scenario, 5.7 cases of vaccine-preventable meningococcal disease would occur each year. Vaccination at 12 months using MCV-C would reduce the burden of disease by 32%. Adding MCV-C at 12 years of age would reduce the number of cases by 55% at no marginal cost, while using MCV-4 would result in a disease reduction of 78% for a marginal cost of $31000 per QALY gained. Comparing MCV-4 with MCV-C as a booster dose, the incremental cost-effectiveness ratio would be $113000 per QALY. The efficacy of C-MCV vaccination at 12 months and the differential price between the two vaccines were the parameters having the strongest impact on the cost/QALY ratios. Any increase in the incidence of serogroup Y will improve the marginal cost-effectiveness ratio associated with MCV-4. CONCLUSION: Adolescent revaccination would be beneficial. Using C-MCV would be the most cost-effective option, while using MCV-4 would be more effective but would also require more investment.