Clinical and economic impact of universal varicella vaccination in Norway: A modeling study

BACKGROUND

Norway has not implemented universal varicella vaccination, despite the considerable clinical and economic burden of varicella disease.

METHODS

An existing dynamic transmission model of varicella infection was calibrated to age-specific seroprevalence rates in Norway. Six two-dose vaccination strategies were considered, consisting of combinations of two formulations each of a monovalent varicella vaccine (Varivax® or Varilrix®) and a quadrivalent vaccine against measles-mumps-rubella-varicella (ProQuad® or PriorixTetra®), with the first dose given with a monovalent vaccine at age 15 months, and the second dose with either a monovalent or quadrivalent vaccine at either 18 months, 7 or 11 years. Costs were considered from the perspectives of both the health care system and society. Quality-adjusted life-years saved and incremental cost-effectiveness ratios relative to no vaccination were calculated. A one-way sensitivity analysis was conducted to assess the impact of vaccine efficacy, price, the costs of a lost workday and of inpatient and outpatient care, vaccination coverage, and discount rate.

RESULTS

In the absence of varicella vaccination, the annual incidence of natural varicella is estimated to be 1,359 per 100,000 population, and the cumulative numbers of varicella outpatient cases, hospitalizations, and deaths over 50 years are projected to be 1.81 million, 10,161, and 61, respectively. Universal varicella vaccination is projected to reduce the natural varicella incidence rate to 48-59 per 100,000 population, depending on the vaccination strategy, and to reduce varicella outpatient cases, hospitalizations, and deaths by 75-85%, 67-79%, and 75-79%, respectively. All strategies were cost-saving, with the most cost-saving as two doses of Varivax® at 15 months and 7 years (payer perspective) and two doses of Varivax® at 15 months and 18 months (societal perspective).

CONCLUSIONS

All modeled two-dose varicella vaccination strategies are projected to lead to substantial reductions in varicella disease and to be cost saving compared to no vaccination in Norway.

Health Impact and Cost-effectiveness Assessment for the Introduction of Universal Varicella Vaccination in Switzerland

BACKGROUND

Varicella, caused by the varicella-zoster virus, is a highly contagious infectious disease with substantial health and economic burden to society. Universal varicella vaccination (UVV) is not yet recommended by the Swiss National Immunization Program, which instead recommends catch-up immunization for children, adolescents and adults 11-40 years of age who have no reliable history of varicella or are varicella-zoster virus-IgG seronegative. The objective of this study was to perform an assessment of health impact and cost-effectiveness comparing UVV with current practice and recommendations in Switzerland.

METHODS

A dynamic transmission model for varicella was adapted to Switzerland comparing 2 base-case schedules (no infant vaccination and 10% coverage with infant vaccination) to 3 different UVV schedules using quadrivalent (varicella vaccine combined with measles-mumps-rubella) and standalone varicella vaccines administered at different ages. Modeled UVV coverage rates were based on current measles-mumps-rubella coverage of approximately 95% (first dose) and 90% (second dose). Direct medical costs and societal perspectives were considered, with cost and outcomes discounted and calculated over a 50-year time horizon.

RESULTS

UVV would reduce the number of varicella cases by 88%-90%, hospitalizations by 62%-69% and deaths by 75%-77%. UVV would increase direct medical costs by Swiss Franc (CHF) 39-49 (US $43-54) per capita and costs from a societal perspective by CHF 32-40 (US $35-44). Incremental quality-adjusted life-years per capita increased by 0.0012-0.0014. Incremental cost-effectiveness ratios for the UVV schedules versus the base-case were CHF 31,194-35,403 (US $34,452-39,100) per quality-adjusted life-year from the direct medical cost perspective and CHF 25,245-29,552 (US $27,881-32,638) from the societal perspective.

CONCLUSIONS

UVV appears highly effective and cost-effective when compared with current clinical practice and recommendations in Switzerland from both a direct medical costs perspective and societal perspective.

Cost-effectiveness of varicella and herpes zoster vaccination in Sweden: An economic evaluation using a dynamic transmission model

OBJECTIVES

Comprehensive cost-effectiveness analyses of introducing varicella and/or herpes zoster vaccination in the Swedish national vaccination programme.

DESIGN

Cost-effectiveness analyses based on epidemiological results from a specifically developed transmission model.

SETTING

National vaccination programme in Sweden, over an 85- or 20-year time horizon depending on the vaccination strategy.

PARTICIPANTS

Hypothetical cohorts of people aged 12 months and 65-years at baseline.

INTERVENTIONS

Four alternative vaccination strategies; 1, not to vaccinate; 2, varicella vaccination with one dose of the live attenuated vaccine at age 12 months and a second dose at age 18 months; 3, herpes zoster vaccination with one dose of the live attenuated vaccine at 65 years of age; and 4, both vaccine against varicella and herpes zoster with the before-mentioned strategies.

MAIN OUTCOME MEASURES

Accumulated cost and quality-adjusted life years (QALY) for each strategy, and incremental cost-effectiveness ratios (ICER).

RESULTS

It would be cost-effective to vaccinate against varicella (dominant), but not to vaccinate against herpes zoster (ICER of EUR 200,000), assuming a cost-effectiveness threshold of EUR 50,000 per QALY. The incremental analysis between varicella vaccination only and the combined programme results in a cost per gained QALY of almost EUR 1.6 million.

CONCLUSIONS

The results from this study are central components for policy-relevant decision-making, and suggest that it was cost-effective to introduce varicella vaccination in Sweden, whereas herpes zoster vaccination with the live attenuated vaccine for the elderly was not cost-effective-the health effects of the latter vaccination cannot be considered reasonable in relation to its costs. Future observational and surveillance studies are needed to make reasonable predictions on how boosting affects the herpes zoster incidence in the population, and thus the cost-effectiveness of a vaccination programme against varicella. Also, the link between herpes zoster and sequelae need to be studied in more detail to include it suitably in health economic evaluations.

What We Know Now: An Economic Evaluation of Chickenpox Vaccination and Dose Timing Using an Agent-Based Model

OBJECTIVES

The value of chickenpox vaccination is still debated in the literature and by jurisdictions worldwide. This uncertainty is reflected in the inconsistent uptake of the vaccine, where some countries offer routine childhood immunization programs, others have targeted programs, and in many the vaccine is only privately available. Even across the countries that have universal funding for the vaccine, there is a diversity of schedules and dosing intervals. Using an agent-based model of chickenpox and shingles, we conducted an economic evaluation of chickenpox vaccination in Alberta, Canada.

METHODS

We compared the cost-effectiveness of 2 common chickenpox vaccination schedules, specifically a long dosing interval (first dose: 12 months; second dose: 4-6 years) and a short dosing interval (first dose: 12 months; second dose: 18 months).

RESULTS

The economic evaluation demonstrated a shorter dosing interval may be marginally preferred, although it consistently led to higher costs from both the societal and healthcare perspectives. We found that chickenpox vaccination would be cost-saving and highly cost-effective from the societal and healthcare perspective, assuming there was no impact on shingles.

CONCLUSION

Chickenpox vaccine was cost-effective when not considering shingles and remained so even if there was a minor increase in shingles following vaccination. However, if chickenpox vaccination did lead to a substantial increase in shingles, then chickenpox vaccination was not cost-effective from the healthcare perspective.

Impact of Model, Methodological, and Parameter Uncertainty in the Economic Analysis of Vaccination Programs

Guidelines for economic evaluations insist that the sensitivity of model results to alternative parameter values should be thoroughly explored. However, differences in model construction and analytical choices (such as the choice of a cost-effectiveness or cost-benefit framework) also introduce uncertainty in results, though these are rarely subjected to a thorough sensitivity analysis. In this article, the authors quantify the effect of model, methodological, and parameter uncertainty, taking varicella vaccination as an example. They used 3 different models (a static model, a dynamic model that only looks at the effect of vaccination on varicella, and a dynamic model that also assesses the implications of vaccination for zoster epidemiology) and 2 forms of analysis (cost-benefit and cost-utility). They also varied the discount rate and time frame of analysis. Probabilistic sensitivity analyses were performed to estimate the impact of parameter uncertainty. In their example, model and methodological choice had a profound effect on estimated cost-effectiveness, but parameter uncertainty played a relatively minor role. Under cost-utility analysis, the probabilistic sensitivity analysis suggested that there was a near certainty that vaccination dominates no vaccination, or the other way around, depending on model choice and perspective. Under cost-benefit analysis, vaccination always appeared to be attractive. Thus, the authors clearly show that model and methodological assumptions can have greater impact on results than parameter estimates, although sensitivity analyses are rarely performed on these sources of uncertainty.

Economic evaluation of pediatric influenza immunization program compared with other pediatric immunization programs: A systematic review

This study compared the economic value of pediatric immunisation programmes for influenza to those for rotavirus (RV), meningococcal disease (MD), pneumococcal disease (PD), human papillomavirus (HPV), hepatitis B (Hep B), and varicella reported in recent (2000 onwards) cost-effectiveness (CE) studies identified in a systematic review of PubMed, health technology, and vaccination databases. The systematic review yielded 51 economic evaluation studies of pediatric immunisation - 10 (20%) for influenza and 41 (80%) for the other selected diseases. The quality of the eligible articles was assessed using Drummond's checklist. Although inherent challenges and limitations exist when comparing economic evaluations of immunisation programmes, an overall comparison of the included studies demonstrated cost-effectiveness/cost saving for influenza from a European-Union-Five (EU5) and United States (US) perspective; point estimates for cost/quality-adjusted life-years (QALY) from dominance (cost-saving with more effect) to ≤45,444 were reported. The economic value of influenza programmes was comparable to the other vaccines of interest, with cost/QALY in general considerably lower than RV, Hep B, MD and PD. Independent of the perspective and type of analysis, the economic impact of a pediatric influenza immunisation program was influenced by vaccine efficacy, immunisation coverage, costs, and most significantly by herd immunity. This review suggests that pediatric influenza immunisation may offer a cost effective strategy when compared with HPV and varicella and possibly more value compared with other childhood vaccines (RV, Hep B, MD and PD).

Clinical and economic impact of various strategies for varicella immunity screening and vaccination of health care personnel

BACKGROUND

Exposure to patients with varicella or herpes zoster causes considerable disruption to a health care facility's operations and has a significant health and economic impact. However, practices related to screening for immunity and immunization of health care personnel (HCP) for varicella vary widely.

METHODS

A decision tree model was built to evaluate the cost-effectiveness of 8 different strategies of screening and vaccinating HCP for varicella. The outcomes are presented as probability of acquiring varicella, economic impact of varicella per employee per year, and cost to prevent additional cases of varicella. Monte Carlo simulations and 1-way sensitivity analyses were performed to address the uncertainties inherent to the model. Alternative epidemiologic and technologic scenarios were also analyzed.

RESULTS

Performing a clinical screening followed by serologic testing of HCP with negative history diminished the cost impact of varicella by >99% compared with not having a program. Vaccinating HCP with negative screen cost approximately $50,000 per case of varicella prevented at the current level of U.S. population immunity, but was projected to be cost-saving at 92% or lower immunity prevalence. Improving vaccine acceptance rates and using highly sensitive assays also optimize cost-effectiveness.

CONCLUSION

Strategies relying on screening and vaccinating HCP for varicella on employment were shown to be cost-effective for health care facilities and are consistent with current national guidelines for varicella prevention.

Systematic review of models assessing the economic value of routine varicella and herpes zoster vaccination in high-income countries

BACKGROUND

A systematic review was conducted to assess the cost-effectiveness of routine varicella and herpes zoster (HZ) vaccination in high-income countries estimated by modelling studies.

METHODS

A PubMed search was performed to identify relevant studies published before October 2013. Studies were included in the review if they (i) evaluated the cost-effectiveness of routine childhood or adolescent varicella vaccination and/or HZ vaccination targeting the elderly, and if they (ii) reported results for high-income countries.

RESULTS

A total of 38 model-based studies were identified that fulfilled the inclusion criteria. Routine childhood or adolescent varicella vaccination was cost-effective or cost-saving from a payer perspective and always cost-saving from a societal perspective when ignoring its potential impact on HZ incidence due to reduced or absent exogenous boosting. The inclusion of the potential impact of childhood varicella vaccination on HZ led to net quality-adjusted life-year (QALY) losses or incremental cost-effectiveness ratios exceeding commonly accepted thresholds. Additional HZ vaccination could partially mitigate this effect. Studies focusing only on the evaluation of HZ vaccination reported a wide range of results depending on the selected target age-group and the vaccine price, but most found HZ vaccination to be a cost-effective or marginally cost-effective intervention. Cost-effectiveness of HZ vaccination was strongly dependent on the age at vaccination, the price of the vaccine, the assumed duration of protection and the applied cost per QALY threshold.

CONCLUSIONS

While HZ vaccination is mostly considered cost-effective, cost-effectiveness of varicella vaccination primarily depends on the in- or exclusion of exogenous boosting in the model. As a consequence, clarification on the role of exogenous boosting is crucial for decision-making regarding varicella vaccination.

Review of the United States universal varicella vaccination program: Herpes zoster incidence rates, cost-effectiveness, and vaccine efficacy based primarily on the Antelope Valley Varicella Active Surveillance Project data

In a cooperative agreement starting January 1995, prior to the FDA's licensure of the varicella vaccine on March 17, the Centers for Disease Control and Prevention (CDC) funded the Los Angeles Department of Health Services' Antelope Valley Varicella Active Surveillance Project (AV-VASP). Since only varicella case reports were gathered, baseline incidence data for herpes zoster (HZ) or shingles was lacking. Varicella case reports decreased 72%, from 2834 in 1995 to 836 in 2000 at which time approximately 50% of children under 10 years of age had been vaccinated. Starting in 2000, HZ surveillance was added to the project. By 2002, notable increases in HZ incidence rates were reported among both children and adults with a prior history of natural varicella. However, CDC authorities still claimed that no increase in HZ had occurred in any US surveillance site. The basic assumptions inherent to the varicella cost-benefit analysis ignored the significance of exogenous boosting caused by those shedding wild-type VZV. Also ignored was the morbidity associated with even rare serious events following varicella vaccination as well as the morbidity from increasing cases of HZ among adults. Vaccine efficacy declined below 80% in 2001. By 2006, because 20% of vaccinees were experiencing breakthrough varicella and vaccine-induced protection was waning, the CDC recommended a booster dose for children and, in 2007, a shingles vaccination was approved for adults aged 60 years and older. In the prelicensure era, 95% of adults experienced natural chickenpox (usually as children)-these cases were usually benign and resulted in long-term immunity. Varicella vaccination is less effective than the natural immunity that existed in prevaccine communities. Universal varicella vaccination has not proven to be cost-effective as increased HZ morbidity has disproportionately offset cost savings associated with reductions in varicella disease. Universal varicella vaccination has failed to provide long-term protection from VZV disease.

[Economical effectiveness of vaccination of cohort of children aged 2 years against chickenpox in the Russian Federation]

AIM

Perform calculation of the economical effectiveness of realization of a program of vaccination of children aged 2 years against chickenpox (CP) in the Russian Federation.

MATERIALS AND METHODS

Data of Federal service on customers rights protection and human well-being surveillance on evaluation of morbidity and losses caused by CP in the Russian Federation in 2008 - 2010 were used. A cohort of children (1 760 000) aged 2 years subject to vaccination against CP in 2011, evaluation of cost of 1 case of the infection, the amount of losses per vaccination of 1 child were approximately determined; analysis of prevented losses by implementation ofvaccination program by using mathematical modeling methods was performed.

RESULTS

Without vaccination program in the Russian Federation the cost of losses per 1 case of CP related to hospitalization and outpatient visits as well as temporary disability of one of the parent in various age groups was: for children aged 1 - 2 years--8 333 RUB (Russian rubles), 3 - 6 years--21 171 RUB, 7 - 14 years--21 295 RUB. The cost of vaccination against CP of 1 child including 2 doses of vaccines with physician examination and vaccination procedure would be 1600 RUB. In the case of realization of vaccination program against CP in 2011 of children aged 2 years its cost would be 2 488.9 million RUB. Cost prevention already exceeds the cost of vaccination in 1 age cohort of children at year 2 and in 5 years the amount of prevented losses would exceed 15 billion RUB per 1 vaccinated cohort and would continue to increase steadily.

CONCLUSION

The performed calculations show that vaccination against CP in the Russian Federation is a highly efficient investment. Self-sufficiency of a program implemented in 2011 may be obtained already at the start of year 2 after the realization and by 2016 the net economical benefit would be around 8 milliards RUB.

Routine vaccination against chickenpox?

Varicella-zoster virus (VZV) causes both varicella and herpes zoster. In 1995 a varicella vaccine was licensed in the USA and was incorporated into the routine vaccination programme for children; a decline of varicella among children and adults, and a reduction in associated hospitalisation, complications and mortality, has resulted. In the UK, a policy of targeted vaccination of at-risk groups has been in place since the vaccine was introduced. Here we review the evidence for the different approaches to VZV vaccination policy.

Effectiveness of state-level vaccination mandates: evidence from the varicella vaccine

This paper utilizes longitudinal data on varicella (chickenpox) immunizations in order to estimate the causal effects of state-level school-entry and daycare-entry immunization mandates within the United States. We find significant causal effects of mandates upon vaccination rates among preschool children aged 19-35 months; these effects appear in the year of mandate adoption, peak two years after adoption, and show a minimal difference from the aggregate trend about six years after adoption. For a mandate enacted in 2000, the model and estimates imply that roughly 20% of the short-run increase in state-level immunization rates was caused by the mandate introduction. We find no evidence of differential effects for different socioeconomic groups. Combined with previous cost-benefit analyses of the varicella vaccine, the estimates suggest that state-level mandates have been effective from an economic standpoint.

[Incorporation of varicella-zoster virus vaccination in childhood immunization schedules]

Varicella is a highly infectious disease caused by the varicella-zoster virus (VZV). Usually chickenpox is a self-limiting and relatively mild disease of childhood, although it is frequently more severe with significant complications, and less often, is responsible for case fatalities. Varicella disease is more severe and its complications are more frequent and severe amongst high risk groups (neonates, pregnant women and immunocompromised patients). After the initial infection, the VZV remains dormant in dorsal root ganglia and may reactivate with declining cellular immunity to cause herpes zoster, particularly in the elderly and immunocompromised. Varicella vaccine is an effective preventive tool for decreasing the burden attributable to the disease and its complications. The incorporation of VZV vaccination in childhood immunization schedules was restricted until recently. Nowadays, many countries implement it. A few years ago, the Israeli Ministry of Health recommended adding the vaccine to the childhood immunization schedule. This was not enacted because of budgetary constraints. This is due in September this year, together with an additional dose of pertussis vaccine for pupils in 8th grade. During the next few years there are plans for other new vaccines, that are being incorporated in the routine vaccination programs in developed countries, also to be added to the Israeli childhood immunization schedule: the conjugated pneumococcal vaccine, the vaccine against the rotavirus and the HPV vaccine.

Factors affecting an economic model for zoster vaccination

Results from the recent Shingles Prevention Study indicate that zoster vaccination can reduce the incidence and severity of herpes zoster and post-herpetic neuralgia (PHN), raising the possibility of a widespread vaccination programme. Such a programme would incur substantial costs, mandating the need for rigorous cost-effectiveness analyses prior to implementation. Suitably robust analyses of the cost benefits of zoster vaccination, capturing the duration of benefits and impact on quality of life resulting from vaccination, are lacking. Any economic model would need to consider current estimates of the economic burden of zoster and PHN in unvaccinated populations, as well the predicted effects of zoster vaccination on health improvements (e.g. reductions in zoster and PHN morbidity, improved quality of life, incidence of adverse effects), and costs for the health system and society at large (e.g. reductions in healthcare costs, variations in the costs of administering the vaccine) in different regions. Economic estimates of the burden of zoster and PHN in unvaccinated populations are scarce, and further studies are needed to measure the impact of these prevention strategies in different regions of the world.

Universal mass vaccination against varicella in Germany using an MMRV combination vaccine with a two-dose schedule: an economic analysis

Former economic analyses have shown that universal mass vaccination of infants against varicella using a one-dose schedule is cost-saving in Germany. In July 2006, an MMRV combination vaccine has been approved in Germany which shall be given in a two-dose schedule. We re-analysed our former analysis with the EVITA model in order to prove whether our former conclusion that universal mass vaccination against varicella is cost-saving is still valid when using a two-dose schedule vaccine. Indeed we found that universal mass vaccination of infants against varicella with a two-dose vaccine is cost-saving from societal as well as from health care perspective.

Prevention of varicella: recommendations of the Advisory Committee on Immunization Practices (ACIP)

Two live, attenuated varicella zoster virus-containing vaccines are available in the United States for prevention of varicella: 1) a single-antigen varicella vaccine (VARIVAX, Merck & Co., Inc., Whitehouse Station, New Jersey), which was licensed in the United States in 1995 for use among healthy children aged > or = 12 months, adolescents, and adults; and 2) a combination measles, mumps, rubella, and varicella vaccine (ProQuad, Merck & Co., Inc., Whitehouse Station, New Jersey), which was licensed in the United States in 2005 for use among healthy children aged 12 months-12 years. Initial Advisory Committee on Immunization Practices (ACIP) recommendations for prevention of varicella issued in 1995 (CDC. Prevention of varicella: recommendations of the Advisory Committee on Immunization Practices [ACIP]. MMWR 1996;45 [No. RR-11]) included routine vaccination of children aged 12-18 months, catch-up vaccination of susceptible children aged 19 months-12 years, and vaccination of susceptible persons who have close contact with persons at high risk for serious complications (e.g., health-care personnel and family contacts of immunocompromised persons). One dose of vaccine was recommended for children aged 12 months-12 years and 2 doses, 4-8 weeks apart, for persons aged > or = 13 years. In 1999, ACIP updated the recommendations (CDC. Prevention of varicella: updated recommendations of the Advisory Committee on Immunization Practices [ACIP]. MMWR 1999;48 [No. RR-6]) to include establishing child care and school entry requirements, use of the vaccine following exposure and for outbreak control, use of the vaccine for certain children infected with human immunodeficiency virus, and vaccination of adolescents and adults at high risk for exposure or transmission. In June 2005 and June 2006, ACIP adopted new recommendations regarding the use of live, attenuated varicella vaccines for prevention of varicella. This report revises, updates, and replaces the 1996 and 1999 ACIP statements for prevention of varicella. The new recommendations include 1) implementation of a routine 2-dose varicella vaccination program for children, with the first dose administered at age 12-15 months and the second dose at age 4-6 years; 2) a second dose catch-up varicella vaccination for children, adolescents, and adults who previously had received 1 dose; 3) routine vaccination of all healthy persons aged > or = 13 years without evidence of immunity; 4) prenatal assessment and postpartum vaccination; 5) expanding the use of the varicella vaccine for HIV-infected children with age-specific CD4+ T lymphocyte percentages of 15%-24% and adolescents and adults with CD4+ T lymphocyte counts > or = 200 cells/microL; and 6) establishing middle school, high school, and college entry vaccination requirements. ACIP also approved criteria for evidence of immunity to varicella.

An outbreak of chickenpox at a child care centre in Western Australia. Costs to the community and implications for vaccination policy

OBJECTIVE

Between May and June 2002 an outbreak of chickenpox (CP) occurred at a child care centre in Perth, Western Australia. An epidemiological study was undertaken in order to determine the characteristics of the outbreak, assess vaccine effectiveness, and to define the direct and indirect costs associated with CP infections in young children.

METHODS

A cohort study of the outbreak utilising attendance records and a telephone survey of parents was conducted.

RESULTS

Of the 211 children attending the child care centre at the time of the outbreak, 44 contracted CP (attack rate 25.7%). In addition, two staff members, five secondary household contacts (secondary attack rate 38.5%) and four secondary non-household associated contacts were infected. There were no severe complications or any hospitalisations recorded in infected persons. Two cases had been vaccinated previously. Vaccine effectiveness for CP of any severity was 78.0% (95% CI 15.4-94.3%) while vaccine effectiveness against severe CP was 100%. Direct costs during this outbreak were estimated to be $54 per case and the total costs, including cost of parental time off work or study, were estimated to be $525.73 per case.

CONCLUSIONS AND IMPLICATIONS

Although morbidity associated with CP in young children is not great, infection in childhood is almost universal. This study found that the average costs associated with each CP case were considerable. Since varicella vaccine affords good protection against CP, the recent inclusion of this vaccine in the Australian childhood vaccination schedule should save the community a considerable amount in direct and indirect costs if high coverage rates can be achieved.

Survey of the status of self-paid varicella vaccination among children one to six years of age in Taiwan

BACKGROUND AND PURPOSE

Prior to 2004, the mass immunization program in Taiwan did not include varicella vaccine; however, parents could have their children vaccinated by the self-payment option.

METHODS

In April 2002, we distributed 1271 questionnaires to the caregivers of children aged 1 to 6 years in Taoyuan county, Taiwan, to survey the status of vaccination rate against varicella, parental attitudes toward self-paid varicella vaccine, and the demographic characteristics of the family.

RESULTS

Based on the answers provided in the questionnaires (99% response rate), we learned that until April 2002, the vaccination rate against varicella was 26%. Most children received this vaccine by the age of 1 to 2 years (64%) mainly at local clinics (66%). Majority of the caregivers (94%) would have immunized their children against varicella if the vaccines were freely provided or partially paid for. Caregivers living in the city, those children whose parents had a relatively high education level, those from families with fewer children, those whose children were inoculated with other self-paid vaccines, and those parents with a higher family income were significantly (p<0.0001) willing to have their children inoculated.

CONCLUSIONS

In Taiwan, most caregivers were willing to have their children immunized against varicella if the vaccines were freely provided, or even if they were partially paid for. In case of other effective vaccines of high cost and not included in mass immunization, partially paying for the vaccine may be an option, since the parents' willingness was substantially greater when the cost is lowered.

Parent-dependent barriers to varicella immunization in Israel: the importance of adequate information

AIM

To examine the parent-dependent barriers to varicella immunization in Israel.

METHODS

Data were collected by questionnaire from parents of children aged 1 to 18 years who attended an outpatient paediatric centre in five cities in Israel from March to May 2003.

RESULTS

A total of 1474 parents completed the questionnaire. A history of chicken pox was reported in 850 children (57.8%), mostly (83%) between ages 1-6 years. Of the 624 children without a history of chicken pox, 213 (34.1%) were immunized against varicella. Immunization rates were significantly lower in families with lower parental education and in patients from cities with a lower socioeconomic ranking (p < 0.05). The main reasons for not being vaccinated (49%) were related to insufficient information about the vaccine itself and the vaccination process. These reasons were more common in families with lower parental education and from cities with lower socioeconomic ranking (p < 0.01). Other reasons included fear of adverse effects (12%) and waning immunity (6%), preference of natural illness over immunization (12%), and financial limitations (5%).

CONCLUSIONS

Promoting parental knowledge about the varicella vaccine appears to be a key factor in improving the immunization rate, especially in families of lower education, and from cities with low socioeconomic ranking.

The case against universal varicella vaccination

In 1995, the United States became the first country to implement a Universal Varicella Vaccination Program. Several questions remain: Is the varicella (chickenpox) vaccine needed? Is it cost effective as a routine immunization for all susceptible children? Or is it more beneficial for the disease to remain endemic so that adults may receive periodic exogenous exposures (boosts) that help suppress the reactivation of herpes zoster (shingles). In addition, as vaccination coverage becomes widespread, does loss of immunologic boosting cause a decline in vaccine efficacy and result in a reduced period of immunity? Scientific literature regarding safety of the varicella vaccine and its associated cost-benefit analysis have often reported optimistic evaluations based on ideal assumptions. Deleterious outcomes and their associated costs must be included when making a circumspect assessment of the Universal Varicella Vaccination Program.

Measles, rubella, mumps, and varicella seroprevalence among health care workers in Turkey: is prevaccination screening cost-effective?

BACKGROUND

To investigate the immune status of health care workers (HCWs) against measles, rubella, mumps, and varicella zoster (MMRV) in Turkey and to define an appropriate vaccination program among HCWs.

METHODS

Voluntary HCWs from a children's hospital and a general hospital were included in the study between March and May 2005. The specific IgG antibodies against MMRV viruses were screened by ELISA.

RESULTS

Three hundred sixty-three HCWs participated in the study; 186 (51%) were physicians, 118 (33%) were nurses, 36 (10%) were housekeeping staff, and 23 (6%) were medical technicians. The proportion of HCWs who had antibodies against measles was 98.6%; rubella, 98.3%; mumps, 92.2%; and varicella, 98%. No association was found between the susceptibility to at least 1 of MMRV virus infections and gender, age, duration of work, profession, and department of work in analysis either among the whole study group, or each hospital. The positive predictive value for the history of varicella was 100%, whereas it was 92% for MMR. The cost of vaccination for varicella was significantly expensive without screening before vaccination. However, there was not much difference for MMR infections.

CONCLUSION

A policy based on obtaining the history of varicella infection from the staff and then screening the ones with negative history and vaccination of only seronegative HCWs was found to be appropriate.

[Impact of universal varicella vaccination in Germany: an epidemiological and economic analysis]

Varicella is a highly contagious viral disease which mainly affects young children and usually is perceived as infection with a mild disease course. However, there is increasing evidence indicating that the morbidity and mortality as well as the economic impact associated with varicella are significant. While universal childhood vaccination against varicella is currently not recommended in Germany, the availability of safe and efficacious vaccines offers the opportunity for preventive intervention. Detailed and reliable data on the consequences of varicella and the possible impact of a universal vaccination program are missing to date for Germany. In order to generate this information, we conducted a comprehensive evaluation. The objective was to quantify the medical consequences and the economic impact of varicella on third-party payers and the society by means of a model analysis, and particularly to assess the effects of various universal vaccination strategies. The study confirms that varicella represents a significant health and economic burden in Germany. Following mathematical modelling, universal varicella vaccination for children at the age of 12-18 months could prevent more than 82 % of cases and complications on average per year. Economically, universal vaccination would lead to net cost savings not only for the society but also for the third-party payers. From these findings it can be concluded that universal varicella vaccination is a strategy which should be encouraged, from a medical, epidemiological, but also economic viewpoint.

Varicella epidemiology and cost-effectiveness analysis of universal varicella vaccination program in Taiwan

Varicella zoster virus is highly contagious and affects people worldwide. In this study, we collected local epidemiological data and evaluated the cost-effectiveness of varicella vaccination program in Taiwan. To examine the economical consequences of universal vaccination, a model of the incidence and the associated costs in a hypothetical cohort was created each year for 30 years. The incidence increased sharply after the infancy and peaked in children aged 5 years. The hospitalization rate among cases was the highest in infants, followed by adults 30 to 44 years old. The benefit-cost analysis showed that one dollar invested in the program would cost extra 46 cents in direct medical expense, but would save extra 45 cents considering the societal expenses. Substantial economical benefits can occur due to the averted unproductive days for parents. Sensitive surveillance of both varicella and zoster is essential in countries that have implemented or are about to implement varicella vaccination.

Uptake of varicella vaccine—a cross sectional survey of parental attitudes to nationally recommended but unfunded varicella immunisation

The aim of this study was to assess the uptake of varicella vaccine in South Australian children under circumstances where varicella immunisation is recommended, but is not funded by Government. The study examined the main reasons that determined a parent's decision whether or not to have their child immunised with varicella vaccine. A cross-sectional survey was conducted by Computer Aided Telephone Interviews (CATI) in June 2004. Data were obtained from 613 households containing 1148 children aged from birth to 17 years of age. Statistical analyses were performed using data weighted to the South Australian population. Six hundred and eighty children (55.7%) had a history of varicella infection and 446 children (42.0%) had received varicella vaccine (weighted data). The most common reasons cited for not having children immunised included lack of knowledge about the vaccine and cost. One year after inclusion of varicella vaccine in the Australian Standard Vaccination Schedule there is evidence of incomplete coverage in children in South Australia due to absence of government funding for vaccine provision.

Varicella vaccination in Australia

Varicella zoster virus (VZV) causes both chickenpox and herpes zoster and is responsible for a significant disease burden, including hospitalizations and deaths, in Australian children and adults. Varicella vaccine has been available in Australia for 5 years; however, from November 2005, it will be funded for use in all susceptible children at 18 months and 10-13 years of age under the National Immunisation Program. Experience with universal varicella vaccination of children in the USA over the last 10 years has shown that the vaccine is safe and highly effective in reducing varicella-related disease. This review summarizes the epidemiology of VZV-related disease in Australia, the use of varicella vaccine and the international experience with vaccine efficacy and safety. The potential impact of varicella vaccination on the incidence of herpes zoster is also discussed.

Cost-effectiveness of varicella vaccination of healthcare workers

OBJECTIVE

Although transmission of VZV is recognized as an important cause for morbidity in health care workers (HCWs), there is no general agreement on the recommended immunization policy. This study aimed to evaluate several of such prevention policies in economic terms.

SETTINGS

Analysis of the cost per avoided future varicella cases among HCWs in Israel.

METHODS

A cost-effectiveness analysis was performed by comparing the cost per avoided case of varicella among a theoretical cohort of 63,353 physician and nurses aged less than 45 years in Israel. Four policies were examined: (a) do nothing (status quo); (b) vaccination of susceptible workers using VZV serotesting; with (c) or without anamnestic history of chickenpox; and (d) presumptive mass vaccination of all eligible workers. A Markov-based model was developed using data from our recent seroepidemiological study in target population and from the literature.

RESULTS

Screening and vaccination of susceptible workers using anamnestic selection is expected to reduce future cases, within 20 years since vaccination, from 58.3 to 33.0 with an incremental cost of 23,713 US dollars per avoided cases. Using only serological tests to detect susceptible workers would prevent additional 5.7 cases with an incremental cost of 206,692 US dollars per avoided case. Vaccinating all HCWs without serotesting, raises the costs markedly, with almost identical effectiveness, resulting in an incremental cost of 10.4 million US dollars per avoided case. Sensitivity analyses do not alter the ranking of the options.

CONCLUSION

From the employer's perspective, routine varicella vaccination program for HCWs with or without selection of susceptible workers is extremely expensive compared to other high-cost practiced approaches. Substantial reduction in cost of vaccination may alter this conclusion.

Disparities in varicella vaccine coverage in the absence of public funding

Varicella vaccine has been licensed in Canada since December 1998 but not provided free in all provinces. Through a cross-sectional telephone survey to a random sample of parents, we assessed factors associated with varicella vaccine uptake in the absence of public funding. Parents of children aged 2-3 years (Group I) and 6-7 years (Group II) were contacted between March and May 2003 in British Columbia, Canada. Response rate was 82% (Group I=571; Group II=704). Among susceptible children, varicella vaccine coverage was 21% (95% CI 18-25%) and 28% (95% CI 22-33%), respectively. There were significant disparities in vaccine coverage based on income and residence. Physician or nurse recommendation was a strong determinant of vaccine uptake as were belief in the safety and efficacy of vaccine. Among parents of susceptible children, 59% (343/582) would vaccinate their child if it were provided free; 25% (148/582) were undecided.

The economic value of childhood varicella vaccination in France and Germany

OBJECTIVE

To determine the economic impact of childhood varicella vaccination in France and Germany.

METHODS

A common methodology based on the use of a varicella transmission model was used for the two countries. Cost data (2002 per thousand) were derived from two previous studies. The analysis focused on a routine vaccination program for which three different coverage rates (CRs) were considered (90%, 70%, and 45%). Catch-up strategies were also analyzed. A societal perspective including both direct and indirect costs and a third-party payer perspective were considered (Social Security in France and Sickness Funds in Germany).

RESULTS

A routine vaccination program has a clear positive impact on varicella-related morbidity in both countries. With a 90% CR, the number of varicella-related deaths was reduced by 87% in Germany and by 84% in France. In addition, with a CR of 90%, routine varicella vaccination induces savings in both countries from both societal (Germany 61%, France 60%) and third-party payer perspectives (Germany 51%, France 6.7%). For lower CRs, routine vaccination remains cost saving from a third-party payer perspective in Germany but not in France, where it is nevertheless cost-effective (cost per life-year gained of 6521 per thousand in the base case with a 45% CR).

CONCLUSION

Considering the impact of vaccination on varicella morbidity and costs, a routine varicella vaccination program appears to be cost saving in Germany and France from both a societal and a third-party payer perspective. For France, routine varicella vaccination remains cost-effective in worst cases when a third-party payer perspective is adopted. Catch-up programs provide additional savings.

[Cost-effectiveness of varicella vaccination in Spanish adolescents]

INTRODUCTION

Varicella is a highly contagious disease. In Spain, in 1996, 91% of the population aged 13 years old had been infected. The complications of varicella are more frequent in adults. Herpes zoster infection can be reactivated after the initial infection in 15%. A vaccine against varicella has recently been authorized in Spain for use in individuals aged more than 13 years old with negative serology.

OBJECTIVE

To determine the cost-effectiveness of vaccination of the cohort aged 13 years old in 2001 and to perform a sensitivity analysis of the parameters that are affected.

MATERIAL AND METHOD

Tree decision: Decision Analysis by Tree-Age program. Probabilities and costs were calculated using Microsoft Excel. Population size was obtained from the 2001 Census of the National Institute of Statistics to which we applied the percentage of susceptibility from the seroepidemiological study in Spain. Probabilities were calculated by the Bayes Theorem, using the incidence rates by age of a country in the northern hemisphere. Hospital-related data were obtained from the minimum data set. We used the effectiveness of the vaccine licensed in the USA, with a total effectiveness of 71% and a partial effectiveness of 24%, represented by milder varicella in vaccinated individuals (breakthrough varicella). Only direct costs were considered. Costs were obtained by direct consultation of different sources. A discount rate of 3% was used.

RESULTS

Varicella vaccination could prevent 27,278 cases of the disease. Prevention of one case would cost the public health system 131 Euros.

DISCUSSION

This study constitutes an approach to the cost of introducing varicella vaccination in the Spanish vaccination schedule, from the payer's perspective. However, to take a decision, some unknown factors, such as the effect of vaccination on the incidence of herpes zoster, should be assessed. With currently available data, the introduction of vaccination in adolescence would seem to be the best strategy, but further studies are needed.

Comparison of varicella history with presence of varicella antibody in refugees

OBJECTIVE

To compare history of varicella with presence of varicella antibody in refugees and to determine the number of unnecessary doses of varicella vaccine administered to refugee children > or =7 years of age.

METHODS

Cross-sectional study of refugees > or =7 years of age evaluated between July 2000 and October 2002 by the Refugee Health Assessment Program at Boston Medical Center. We recorded age, sex, region of origin, varicella history, and results of serologic testing for presence of varicella antibodies.

RESULTS

Eighty-eight percent of individuals with a positive history of clinical varicella had varicella antibody; 65% of those with negative history had varicella antibody. The positive predictive value of a history of clinical varicella was 88%. The negative predictive value of a negative history was 39%.

CONCLUSION

History of varicella was not a reliable predictor of presence or absence of varicella antibody in refugees. Strategies to protect individuals with negative histories of clinical varicella include immediate immunization or serotesting followed by immunization of susceptible individuals. Relying on positive histories of clinical varicella may leave some individuals susceptible to varicella and impede efforts to eliminate varicella in the US.

Economic burden of varicella in Singapore--a cost benefit estimate of implementation of a routine varicella vaccination

Varicella is a common childhood illness that can result in significant morbidity and mortality. As early as 1995, recommendations for routine varicella vaccination have been published, but have not been universally implemented, with cost of vaccination as a major reason. Though available from 1996, the vaccine has yet to be routinely implemented in Singapore. We set out to assess the economic burden of varicella and the cost-benefit of adding a varicella vaccine to the existing immunization schedule in Singapore. In this study, using data from 1994--1995 the direct cost estimates were based on all levels of medical care; inpatient care, emergency room visits, primary health care and medication. Indirect costs were estimated from the cost of time lost by patients and their families attending to medical needs, as well as loss of productivity due to absenteeism. The cost of a vaccination program targeted at 15-month old infants receiving concomitant measles-mumps-rubella immunization was also assessed. The cost-benefit ratio was then estimated. The total cost of varicella in Singapore was estimated to be US$11.8 million per annum. The loss of productivity accounted for a large proportion of the total cost as a lot of parents took leave when their children were ill. The estimates of total cost represent approximately US$188 per varicella case per year. In comparison, the cost of a vaccination program was found to be US$3.3 million per annum. The cost per case averted was US$104. From a societal point of view, for every dollar invested in a vaccination program, we would save about US$2 dollars.

Empirical data on the varicella situation in Germany for vaccination decisions

As epidemiological data concerning varicella in Germany were not available, a retrospective study was conducted to investigate the impact of the disease, focusing also on economic aspects. A representative German-wide sample of 1334 unvaccinated varicella cases was obtained in 1999 from randomly selected paediatric (P) and general, as well as internal, mainly adult (A), practices. Following representative weighting, the median age was 5 years, with 90% of cases aged < 12 years. The highest incidence was in children aged 5-6 years. Varicella-related complications occurred in 5.7% of patients, and accounted for 0.1 hospital days/case on average. Certificates of sick leave were issued for 1.3 sick days/case, with 0.6 days paid by health insurance funds to parents caring for their sick child, and 0.7 days paid by the employer. With an annual incidence of 760,000 diagnosed cases in Germany for the year 1999, this amounts to an annual cost of c.150 million Euro, with c. 50 million Euro paid by the statutory health insurance system. It was concluded that universal varicella vaccination in Germany would provide essential clinical improvements for patients and prevent hospital admissions. In addition, significant economic benefits can be expected, mainly because of the high level of indirect health costs in Germany.

Consensus: varicella vaccination of healthy children--a challenge for Europe

The seriousness of varicella-zoster virus (VZV) infection as a public health issue is becoming clearer as country-specific epidemiologic and pharmacoeconomic data become available. In Germany, for example, studies have shown that >5.5% of immunologically healthy individuals develop varicella-related complications such as bacterial superinfections, acute neurologic disorders, pneumonia, bronchitis and otitis media; whereas in Italy, 3.5 to 5% of childhood cases of varicella cause complications such as upper respiratory tract and cutaneous infections. Varicella vaccines are now available. These live attenuated Oka strain vaccines have been shown in extensive studies to be highly immunogenic and well-tolerated in immunocompetent and immunocompromised children, with seroconversion rates ranging from 94 to 100% and 53 to 100%, respectively. These vaccines are also highly effective against clinical disease. These considerations led to a reevaluation of varicella vaccination policies. A routine varicella vaccination program targeting healthy children has already been implemented in the US, and data produced are encouraging and valuable. Similar strategies have not yet been adopted across Europe. The European Working Group on Varicella (EuroVar) was formed in 1998 to address the issues surrounding varicella epidemiology in Europe. After a series of meetings, the EuroVar members prepared a consensus statement recommending routine varicella vaccination for all healthy children between 12 and 18 months and to all susceptible children before their 13th birthday, in addition to catch-up vaccination in older children and adults who have no reliable history of varicella and who are at high risk of transmission and exposure. However, such a policy is recommended only if a very high coverage rate can be achieved. This could be reached with a measles-mumps-rubella-varicella combined vaccine.

Cost containment analysis of childhood vaccination against varicella in Israel

OBJECTIVES

The low cost of safe and effective vaccines prompted a cost-containment evaluation of a nationwide vaccination campaign against varicella.

METHODS

A model incorporating demographic, epidemiologic and economic data from Israeli sources (supplemented by data from International literature) was constructed to estimate the decrease in morbidity and the consequent reductions in treatment costs and time-off work of a nationwide programme vaccinating children at 12 months.

RESULTS

A policy of aiming to immunize a cohort of all 1-year-olds in Israel in the year 2002, for an annual cost of $1.10 million to the health services and $1.27 million to society (including lost work and transport costs), would reduce the number of cases of varicella during the lifetime of a cohort from 123,984 to 10,170 cases. This morbidity reduction would reduce national expenditures by $1.80 million in health service resources alone and by $24.5 million to society, mainly due to inaverted work absences. In addition an estimated 0.93 lives, representing 38.6 life years will be saved in the cohort.

CONCLUSIONS

Under an assumption of neutrality relating to the potential effects of vaccination on herpes zoster virus, our model based calculations show that a national varicella vaccination programme is likely to be cost saving, not only from a societal perspective but also from the narrower health service perspective.

Varicella vaccination in Italy : an economic evaluation of different scenarios

AIM

To determine the economic impact (cost-benefit analysis) of childhood varicella vaccination, with the Oka/Merck varicella zoster virus vaccine live (Varivax) in Italy.

METHODS

This analysis is based on an epidemiological model of varicella zoster virus (VZV) dynamics adapted to the Italian situation. Cost data (Euro, 2002 values) were collected through a literature review. Several vaccination scenarios were analysed: (i) routine vaccination programme for children aged 1-2 years with different levels of vaccination coverage (90%, 70% and 45%) without any catch-up programme; (ii) routine vaccination programme for children aged 1-2 years with different levels of vaccination coverage (90%, 70% and 45%) completed by a catch-up programme for 6-year-old children over the first 5 years of vaccine marketing; and (iii) routine vaccination programme for children aged 1-2 years with different levels of vaccination coverage (90%, 70% and 45%) completed by a catch-up programme during the first year of vaccine marketing for children aged 2-11 years.

PERSPECTIVES

A societal perspective, including both direct and indirect costs, and a health-system perspective, limited to costs supported by Italian Health Authorities, were considered.

RESULTS

A routine vaccination programme has a clearly positive impact on chickenpox morbidity. Respectively, 68% and 57% of chickenpox-related hospitalisations and deaths could be prevented with a 90% coverage rate. With vaccination costs being more than offset by a reduction in chickenpox treatment costs in the base case, such a programme could also induce savings from both a societal and a health-system perspective (40% and 12% savings, respectively for a 90% coverage rate). A lower coverage rate reduces cost savings, but there is still a 9% decrease in overall societal costs for a 45% coverage rate. Although the reduction in total societal costs was robust to the sensitivity analyses performed, a slight uncertainty remains regarding cost reduction from a health-system perspective. However, in this latter perspective, even in the worst-case scenario of the sensitivity analysis, routine vaccination programmes may be cost effective, the worst-case scenario for cost parameters leading to cost per life-year gained of Euro2853. Catch-up programmes combined with routine vaccination should lead to further cost reductions from a societal perspective: 15% for a massive catch-up during the first year of vaccine marketing compared with toddlers' vaccination alone, and 11% for a catch-up focused on 6-year-old children for a period of 5 years. However, the impact of catch-up programmes on the costs from an Italian health-system perspective remains close to zero (+/-1%).

CONCLUSION

This model suggests, with its underlying assumptions and data, that routine ZVZ vaccination may be cost saving from both a societal and a health system perspective in the base case. In the worst-case scenario of the sensitivity analysis, vaccination remains cost effective.

Varicella vaccination in England and Wales: cost-utility analysis

AIMS

To assess the cost-effectiveness of varicella vaccination, taking into account its impact on zoster.

METHODS

An age structured transmission dynamic model was used to predict the future incidence of varicella and zoster. Data from national and sentinel surveillance systems were used to estimate age specific physician consultation, hospitalisation, and mortality rates. Unit costs, taken from standard sources, were applied to the predicted health outcomes.

RESULTS

In England and Wales, the annual burden of VZV related disease is substantial, with an estimated 651 000 cases of varicella and 189 000 cases of zoster, resulting in approximately 18 000 QALYs lost. The model predicts that although the overall burden of varicella will significantly be reduced following mass infant vaccination, these benefits will be offset by a significant rise in zoster morbidity. Under base case assumptions, infant vaccination is estimated to produce an overall loss of 54 000 discounted QALYs over 80 years and to result in a net cost from the health provider (NHS) and the societal perspectives. These results rest heavily on the impact of vaccination on zoster. Adolescent vaccination is estimated to cost approximately 18 000 pounds sterling per QALY gained from the NHS perspective.

CONCLUSION

Routine infant varicella vaccination is unlikely to be cost-effective and may produce an increase in overall morbidity. Adolescent vaccination is the safest and most cost-effective strategy, but has the least overall impact on varicella.

Varicella in French adolescents and adults: individual risk assessment and cost-effectiveness of routine vaccination

Age-specific force of varicella infection, hospitalisation and death rates in non-immune persons were calculated using an age-based mathematical model and national data for France. A cost-effectiveness model was then applied to hypothetical cohorts of persons aged 15-45 years with a negative or uncertain history of varicella. Vaccination strategies with and without prior serotesting, and healthcare payer perspective and societal perspective were considered. A sensitivity analysis was performed. Vaccination prevented more than one third of all varicella-related deaths. With serotesting, compared with no intervention, the cost per case avoided and per year of life saved for subjects aged 15 years were 335 and 55,100 Euro, respectively. When work-loss costs were also included, savings were associated with screening and vaccination of subjects less than 30 years old. Without serotesting, the costs raised markedly, with an almost identical effectiveness, resulting in an unfavourable incremental cost-effectiveness. Based on medical costs, routine serotesting and varicella vaccination for French adolescents and young adults with a negative or uncertain history of varicella affords health benefits at a cost comparable to those of other very expensive therapies considered worthwhile. From the societal perspective, such screening and vaccination might save costs.

Cost-benefit analysis of routine childhood vaccination against chickenpox in Taiwan: decision from different perspectives

Cost-benefit analysis was conducted to determine whether it is worthwhile to initiate a routine varicella vaccination program in Taiwan from different perspectives. Using the human capital approach, the discounted net cost for vaccination program was New Taiwan Dollars (NTD) 281 million from health care payer's perspective. Taking indirect costs into account, the net saving due to vaccination program was NTD 425 million from the societal perspective. In terms of benefit-cost ratio, a mass varicella vaccination program could only save NTD 0.34 in discounted costs for each dollar incurred in a vaccination program from health care payer's perspective whereas save NTD 2.06 from the societal viewpoint. Results based on the willingness-to-pay (WTP) method showed the Net Present Value (NPV) of the vaccination program was estimated as -NTD 272 million. We conclude that a routine varicella vaccination program is worthwhile from the societal perspective but neither from health care payer's nor from consumer decision based on the perspective of WTP.

Validation of health economic models: the example of EVITA

OBJECTIVES

The credibility of models rests on their validity. An age-structured decision analytic model, Economic Varicella Vaccination Tool for Analysis (EVITA), has been developed to examine the epidemiologic and economic effects of universal varicella (chicken pox) vaccination in Germany. EVITA combines a varicella transmission module describing the spread of infection in a population over time with a second module describing the course of disease in case of an infection. Any vaccination strategy can be assessed dependent on coverage levels and targeted age group. Model input data include epidemiologic, clinical, and economic information, which were mainly derived from actual varicella cases (retrospective survey). The objective of this study was to illustrate the efforts undertaken to validate the EVITA model.

METHODS

We assess the descriptive validity, i.e., whether the model provides an adequate picture of the reality and covers all relevant aspects of the spread of varicella and the course of disease. Analyzing the consistency of the model results with observable data does technical verification. Face validity, i.e., the consistency with the underlying theoretical basis of the spread of varicella, is analyzed with respect to results on possible age shifts and elimination of varicella. Tests of corroboration, or convergent validity, are performed by comparisons with other models.

RESULTS

Without vaccination, the EVITA model predicts undiscounted, indirect costs of 154 million euros, nearly 40,000 complications and 5,700 hospitalizations per year owing to varicella. These results, especially the distribution of complications and hospitalizations, fit well with population-based survey data. The development of the EVITA model is based on an established epidemiologic model and on real-life data from the survey, ensuring descriptive validity. Results on age shifts and elimination show face validity. Although other models differ considerably with respect to methods applied, the economic results of EVITA, i.e., a benefit-cost ratio of 4.12 when vaccinating young children, lies in the range found in other studies. This underscores its convergent validity. Comparable with other studies, discount rates and price of vaccine proved to be most sensitive variables.

CONCLUSIONS

EVITA provides a powerful tool to simulate the highly complex processes associated with varicella infections and the impact of vaccination. The results of EVITA provide a reliable tool for informed decision making and should enhance the acceptance of such models.