A cost benefit analysis of routine varicella vaccination in Spain

Systematic review of economic evaluations of varicella vaccination programmes

OBJECTIVES

This study carried out a systematic literature review of economic evaluations of varicella vaccination programmes from the earliest publication to the present day, including programmes in the workplace and in special risk groups as well as universal childhood vaccination and catch up programmes.

METHODS

Articles published from 1985 until 2022 were sourced from PubMed/Medline, Embase, Web of Science, NHSEED and Econlit. Eligible economic evaluations, which included posters and conference abstracts, were identified by two reviewers who scrutinised each other's selections at both title and abstract and full report stages. The studies are described in terms of their methodological characteristics. Their results are aggregated by type of vaccination programme and the nature of the economic outcome.

RESULTS

A total of 2575 articles were identified of which 79 qualified as economic evaluations. A total of 55 studies focused on universal childhood vaccination, 10 on the workplace and 14 on high risk groups. Twenty-seven studies reported estimates of incremental cost per quality-adjusted life year (QALY) gained, 16 reported benefit-cost ratios, 20 reported cost-effectiveness outcomes in terms of incremental cost per event or life saved and 16 reported cost-cost offset results. Most studies of universal childhood vaccination reported an increase in overall costs to health services, but often a reduction in cost from a societal perspective.

CONCLUSIONS

The evidence surrounding the cost-effectiveness of varicella vaccination programmes remains sparse with contrasting conclusions in some areas. Future research should particularly aim to encompass the impact of universal childhood vaccination programmes on herpes zoster among adults.

Economic burden of varicella in Europe in the absence of universal varicella vaccination

Background

Though the disease burden of varicella in Europe has been reported previously, the economic burden is still unknown. This study estimated the economic burden of varicella in Europe in the absence of Universal Varicella Vaccination (UVV) in 2018 Euros from both payer (direct costs) and societal (direct and indirect costs) perspectives.

Methods

We estimated the country specific and overall annual costs of varicella in absence of UVV in 31 European countries (27 EU countries, plus Iceland, Norway, Switzerland and the United Kingdom). To obtain country specific unit costs and associated healthcare utilization, we conducted a systematic literature review, searching in PubMed, EMBASE, NEED, DARE, REPEC, Open Grey, and public heath websites (1/1/1999–10/15/2019). The number of annual varicella cases, deaths, outpatient visits and hospitalizations were calculated (without UVV) based on age-specific incidence rates (Riera-Montes et al. 2017) and 2018 population data by country. Unit cost per varicella case and disease burden data were combined using stochastic modeling to estimate 2018 costs stratified by country, age and healthcare resource.

Results

Overall annual total costs associated with varicella were estimated to be €662,592,061 (Range: €309,552,363 to €1,015,631,760) in Europe in absence of UVV. Direct and indirect costs were estimated at €229,076,206 (Range €144,809,557 to €313,342,856) and €433,515,855 (Range €164,742,806 to €702,288,904), respectively. Total cost per case was €121.45 (direct: €41.99; indirect: €79.46). Almost half of the costs were attributed to cases in children under 5 years, owing mainly to caregiver work loss. The distribution of costs by healthcare resource was similar across countries. France and Germany accounted for 49.28% of total annual costs, most likely due to a combination of high numbers of cases and unit costs in these countries.

Conclusions

The economic burden of varicella across Europe in the absence of UVV is substantial (over 600 M€), primarily driven by caregiver burden including work productivity losses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-12343-x.

How resource limitations and household economics may compromise efforts to safeguard children during outbreaks

Background

Epidemiological models have been employed with great success to explore the efficacy of alternative strategies at combating disease outbreaks. These models have often incorporated an understanding of age-based susceptibility and severity of outcome, considering how to limit the adverse outcomes or disease burden relative to an age structure. Such models frequently recommend the preferential treatment/vaccination of children or the elderly, demonstrating how prevention of serious disease within these etiological subgroups can provide both protection within the subgroup itself and indirect protection to the broader population. However, it is most frequently the case that these target populations are consumers, rather than providers, of household resources. In areas of the globe where continued health of household members relies on continued provision of resources, these models may fail to provide the most effective overall strategies for health outcomes in both target populations and overall. This is particularly important for tropical diseases impacting rural and low-income areas in which the disease may be endemic or newly emergent, particularly in the wake of natural disasters.

Methods

We propose a modified epidemiological model with targeted treatment in resource-limited populations. We evaluate the model over a broad parameter space.

Results

This model demonstrates how economic limitations may shift the optimal strategy. It may be advantageous to treat populations at lesser direct risk if they are responsible for providing secondary protection to higher-risk population(s) by producing household resources. Evaluation of this model over the parameter space reveals that, in some cases, targeting treatment towards consumers may result in greater numbers of consumer infections.

Conclusions

Our results demonstrate how household resource limitation can drastically affect the impact of targeted treatment strategies for limiting epidemics. Depending on the economic circumstances, it is possible that focusing treatment on consumers such as children can produce a counter-intuitive outcome in which more children contract the disease.

Outbreak control of hospital acquired varicella infection amongst health care workers in a tertiary care hospital

Background

Adult and immunocompromised patients suffering from varicella (chicken pox) are potential source of infection to healthcare workers. An outbreak of varicella among healthcare workers in a tertiary care centre was investigated, and preventive measures were implemented.

Methods

Cases of chicken pox between 05 Feb 2017 and 11 Feb 2017 in a tertiary healthcare establishment were investigated. An epidemiological investigation by developing case definitions, spot map and contact tracing was conducted. Eight cases were identified among healthcare workers. Suitable preventive measures including identification of susceptible contacts and vaccination of susceptible ones with two doses of varicella vaccine was undertaken.

Results

Index case was a 21-year-old nurse who was exposed to a 34-year-old male patient transferred from a secondary care hospital on 24 Jan 2017 as a case of acute liver failure and coagulopathy. Primary case was later diagnosed as case of varicella based on serological and clinical evidence. Among a total of 8 cases identified in the outbreak, the cases occurred among healthcare workers of secondary care centre, healthcare workers managing the primary case in the intensive care unit and who conducted the autopsy. A total of 181 contacts were identified in the epidemiological investigation, and 54 were susceptible to chicken pox. Two-dose immunization with varicella vaccination of susceptible ones was found to be effective in preventing further cases.

Conclusion

Two-dose vaccination of healthcare workers with varicella vaccine is an effective strategy to prevent nosocomial varicella among healthcare workers.

Implementing Universal Varicella Vaccination in Europe: The Path Forward

Varicella is a common vaccine-preventable disease that usually presents as a mild disorder but can lead to severe complications. Before the implementation of universal varicella vaccination (UVV) in some European countries, the burden of varicella disease was broadly similar across the region. Despite this, countries adopted heterogeneous varicella vaccination strategies. UVV is currently recommended in 12 European countries. Known barriers to UVV implementation in Europe include (1) a perceived low disease burden and low public health priority; (2) cost-effectiveness and funding availability; (3) concerns related to a shift in varicella disease and incidence of herpes zoster and (4) safety concerns related to measles, mumps, rubella and varicella-associated febrile seizures after the first dose. Countries that implemented UVV experienced decreases in varicella incidence, hospitalizations and complications, showing overall beneficial impact. Alternative strategies targeting susceptible individuals at higher risk of complications have been less effective. This article discusses ways to overcome the barriers to move varicella forward as a truly vaccine preventable disease.

Chickenpox and measles clusters among college students in Pune, Maharashtra

Chickenpox and measles, both vaccine preventable febrile rash illnesses, present in a comparatively severe form among young adults/adults than among children. Immunity levels against chickenpox are not known in India and those against measles have been found variable across the country. Places where students or adults/young adults from various parts of the country come together pose a peculiar challenge in preventive policy making regarding these diseases. In this article, we present findings from parallel outbreaks of the two diseases in a graduate/postgraduate institute in the city of Pune. A team from National Institute of Virology [Pune] investigated outbreak of febrile rash illness in a premier graduate institute and found that it was a case of two parallel outbreaks of chickenpox and measles. In this outbreak chickenpox cases did not present with greater severity but measles cases were severe. The concerned institute hosts more than 800 students and 300 staff including faculty. These outbreaks were contained because of the alert physician in the institute; but it also highlights a need for uniform policies across such educational institutions in the country.

Estimation of the burden of varicella in Europe before the introduction of universal childhood immunization

BACKGROUND

Varicella is generally considered a mild disease. Disease burden is not well known and country-level estimation is challenging. As varicella disease is not notifiable, notification criteria and rates vary between countries. In general, existing surveillance systems do not capture cases that do not seek medical care, and most are affected by underreporting and underascertainment. We aimed to estimate the overall varicella disease burden in Europe to provide critical information to support decision-making regarding varicella vaccination.

METHODS

We conducted a systematic literature review to identify all available epidemiological data on varicella IgG antibody seroprevalence, primary care and hospitalisation incidence, and mortality. We then developed methods to estimate age-specific varicella incidence and annual number of cases by different levels of severity (cases in the community, health care seekers in primary care and hospitals, and deaths) for all countries belonging to the European Medicines Agency (EMA) region and Switzerland.

RESULTS

In the absence of universal varicella immunization, the burden of varicella would be substantial with a total of 5.5 million (95% CI: 4.7-6.4) varicella cases occurring annually across Europe. Variation exists between countries but overall the majority of cases (3 million; 95% CI: 2.7-3.3) would occur in children <5 years. Annually, 3-3.9 million patients would consult a primary care physician, 18,200-23,500 patients would be hospitalised, and 80 varicella-related deaths would occur (95% CI: 19-822).

CONCLUSIONS

Varicella disease burden is substantial. Most cases occur in children <5 years old but adults require hospitalisation more often and are at higher risk of death. This information should be considered when planning and evaluating varicella control strategies. A better understanding of the driving factors of country-specific differences in varicella transmission and health care utilization is needed. Improving and standardizing varicella surveillance in Europe, as initiated by the European Centre for Disease Prevention and Control (ECDC), is important to improve data quality to facilitate inter-country comparison.

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.

Estimating the cost of cholera-vaccine delivery from the societal point of view: A case of introduction of cholera vaccine in Bangladesh

Cholera is a major global public health problem that causes both epidemic and endemic disease. The World Health Organization recommends oral cholera vaccines as a public health tool in addition to traditional prevention practices and treatments in both epidemic and endemic settings. In many developing countries like Bangladesh, the major issue concerns the affordability of this vaccine. In February 2011, a feasibility study entitled, "Introduction of Cholera Vaccine in Bangladesh (ICVB)", was conducted for a vaccination campaign using inactivated whole-cell cholera vaccine (Shanchol) in a high risk area of Mirpur, Dhaka. Empirical data obtained from this trial was used to determine the vaccination cost for a fully immunized person from the societal perspective. A total of 123,661 people were fully vaccinated receiving two doses of the vaccine, while 18,178 people received one dose of the same vaccine. The total cost for vaccine delivery was US$ 492,238 giving a total vaccination cost per fully-vaccinated individual of US$ 3.98. The purchase cost of the vaccine accounted for 58% of the overall cost of vaccination. Attempts to reduce the per-dose cost of the vaccine are likely to have a large impact on the cost of similar vaccination campaigns in the future.

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.

Use of immunization as strategy for outbreak control of varicella zoster in an institutional setting

BACKGROUND

Outbreaks of varicella gets reported often in India. However, outbreak in health care providers living in closed institutional setting and role of vaccination as post exposure prophylaxis for control of outbreak has not been studied extensively. This paper presents epidemiological investigation and control strategy undertaken in such scenario.

METHODS

This is an epidemiological investigation of chickenpox in nursing students which highlights role of early identification and appropriate control strategy to prevent explosive outbreak in high risk vulnerable population. Vaccination of all susceptible in addition to isolation of cases, quarantine of suspects and proper screening for new cases was the major control strategy adopted.

RESULTS

The index case was imported and all eight cases occurred within the incubation period of the case. Two cases occurred in students previously vaccinated for chickenpox. No second or third wave of infection occurred showing vaccination as effective tool in outbreak control strategy.

CONCLUSION

Early identification of cases and vaccination of all susceptible contributed to effective control of the outbreak.

Successes and challenges in varicella vaccine

Varicella is a highly contagious disease caused by primary infection with varicella zoster virus (VZV). VZV infection, as well as varicella vaccination, induces VZV-specific antibody and T-cell-mediated immunity, essential for recovery. The immune responses developed contribute to protection following re-exposure to VZV. When cell-mediated immunity declines, as occurs with aging or immunosuppression, reactivation of VZV leads to herpes zoster (HZ). It has been almost 20 years since universal varicella vaccination has been implemented in many areas around the globe and this has resulted in a significant reduction of varicella-associated disease burden. Successes are reviewed here, whilst emphasis is put on the challenges ahead. Most countries that have not implemented routine childhood varicella vaccination have chosen to vaccinate high-risk groups alone. The main reasons for not introducing universal vaccination are discussed, including fear of age shift of peak incidence age and of HZ incidence increase. Possible reasons for not observing the predicted increase in HZ incidence are explored. The advantages and disadvantages of universal vs targeted vaccination as well as different vaccination schedules are discussed.

Economic evaluation of Varicella vaccination: results of a systematic review

INTRODUCTION

The aim of the present study is to review the economic burden of varicella disease and the benefit of universal varicella vaccination in different settings pending its implementation in all Italian regions.

MATERIALS AND METHODS

Research was conducted using PubMed, Scopus and ISI databases. Score quality and data extraction were performed for all included studies.

RESULTS

Twenty-three articles met the criteria: 15 cost-effectiveness, 8 cost-benefit and one cost-utility analysis. Varicella vaccination could save the society from €637,762 (infant strategy) to 53 million annually (combined infant and adolescent strategy). The median and the mean quality scores resulted in 91.8% and 85.4% respectively; 11 studies were considered of high quality and 12 of low quality.

DISCUSSION

The studies are favorable to the introduction of universal varicella vaccination in Italy, being cost saving and having a positive impact on morbidity. The quality score of the studies varied greatly: recent analyses were of comparable quality to older studies.

The epidemiology and economic impact of varicella-related hospitalizations in Turkey from 2008 to 2010: a nationwide survey during the pre-vaccine era (VARICOMP study)

Varicella can cause complications that are potentially serious and require hospitalization. Our current understanding of the causes and incidence of varicella-related hospitalization in Turkey is limited and sufficiently accurate epidemiological and economical information is lacking. The aim of this study was to estimate the annual incidence of varicella-related hospitalizations, describe the complications, and estimate the annual mortality and cost of varicella in children. VARICOMP is a multi-center study that was performed to provide epidemiological and economic data on hospitalization for varicella in children between 0 and 15 years of age from October 2008 to September 2010 in Turkey. According to medical records from 27 health care centers in 14 cities (representing 49.3% of the childhood population in Turkey), 824 children (73% previously healthy) were hospitalized for varicella over the 2-year period. Most cases occurred in the spring and early summer months. Most cases were in children under 5 years of age, and 29.5% were in children under 1 year of age. The estimated incidence of varicella-related hospitalization was 5.29-6.89 per 100,000 in all children between 0-15 years of age in Turkey, 21.7 to 28 per 100,000 children under 1 year of age, 9.8-13.8 per 100,000 children under 5 years of age, 3.96-6.52 per 100,000 children between 5 and 10 years of age and 0.42 to 0.71 per 100,000 children between 10 and 15 years of age. Among the 824 children, 212 (25.7%) were hospitalized because of primary varicella infection. The most common complications in children were secondary bacterial infection (23%), neurological (19.1%), and respiratory (17.5%) complications. Secondary bacterial infections (p < 0.001) and neurological complications (p < 0.001) were significantly more common in previously healthy children, whereas hematological complications (p < 0.001) were more commonly observed in children with underlying conditions. The median length of the hospital stay was 6 days, and it was longer in children with underlying conditions (<0.001). The median cost of hospitalization per patient was $338 and was significantly higher in children with underlying conditions (p < 0.001). The estimated direct annual cost (not including the loss of parental work time and school absence) of varicella-related hospitalization in children under the age of 15 years in Turkey was $856,190 to $1,407,006. According to our estimates, 882 to 1,450 children are hospitalized for varicella each year, reflecting a population-wide occurrence of 466-768 varicella cases per 100,000 children. In conclusion, this study confirms that varicella-related hospitalizations are not uncommon in children, and two thirds of these children are otherwise healthy. The annual cost of hospitalization for varicella reflects only a small part of the overall cost of this disease, as only a very few cases require hospital admission. The incidence of this disease was higher in children <1 year of age, and there are no prevention strategies for these children other than population-wide vaccination. Universal vaccination is therefore the only realistic option for the prevention of severe complications and deaths. The surveillance of varicella-associated complications is essential for monitoring of the impact of varicella immunization.

Burden of chickenpox on families: A study in Quebec

OBJECTIVE

To estimate the nonhospital costs of treating chickenpox and to ascertain the opinion of parents regarding the usefulness of vaccination.

DESIGN

Retrospective postal survey.

SETTING

Province of Quebec.

PARTICIPANTS

Random sample of 3333 families with children aged six months to 12 years.

OUTCOME MEASURES

For cases of chickenpox that occurred between September 1, 1997 and August 31, 1998, the use of health services, time away from school or work, patient care required, direct and indirect costs for the families and the health care system, and the opinion of parents regarding chickenpox and the vaccine were evaluated.

RESULTS

The response rate was 64.7%, and 18.8% of households reported a history of chickenpox, a total of 693 cases. A physician was consulted in 45.8% of these cases, and medication was used in 91.7%. The frequency of hospitalizations was 0.6%. Time away from work or school caused by the disease was 4.1 days on average, with 46.5% of absences being attributed to the risk of contagion. The total average cost of a case of chickenpox was $225. Direct expenses for households accounted for 11% of the total cost, public sector direct costs 7%, indirect costs related to absence from work 38% and caregiving time 45%. A majority of parents (70%) were in favour of a systematic childhood immunization program.

CONCLUSIONS

Chickenpox without complications is disruptive for families, but the direct costs for families and the public sector are relatively small.

The use of modeling in the economic evaluation of vaccines

As a consequence of the increased role of pharmacoeconomics in policy-making, economic evaluations are performed at more and more early stages in the development of a therapeutic. This implies the development of models to assess the future impact of an intervention and to account for the level of uncertainty in the associated parameters. This also applies for economic evaluations of vaccines, where not only progression of disease and associated costs are important, but the transmission of the causing agent in the target population also has to be modelled. In this review, we provide an overview of the models that have been used in recent publications on the pharmacoeconomics of vaccines and go deeper into some of the methodological issues associated with the use of models in the economic evaluation of vaccines.

[Varricela vaccination policy subsidy evaluation]

OBJECTIVES

Mitoyo and Kanonji cities in Kagawa prefecture began a varicella vaccination subsidy in April 1, 2007. To evaluate this policy, we studied morbidity and vaccination coverage before and after subsidy went into effect, vaccination efficacy for severity and family nursing burden, and cooperation with the Mitoyo Kanonj medical association and Mitoyo and Kanonji municipalities.

METHODS

Mitoyo and Kanonji implemented a varicella vaccination subsidy for residents under 5-years-old born after April 1, 2002, and having previous varicella infection. We surveyed health checkups for children, for doctor or family members with varicella, and subsidy bills from May 1, 2007, to March 31, 2008.

RESULT

The response rate of family member report was about 60% of doctor, varicella broke out in Decemeber 2007. Health surveys showed that varicella vaccination efficacy was 74% at up to three-years-old, but declined to 63% among those older. Morbidity averaged 5 days duration regardless of vaccination. Subsidy vaccination coverage at 1-year-old rose from 8.0% to 17.2% in Mitoyo and from 13.0% to 28.9% in Kanonji, averaging 17.2% in Mitoyo and 28.9% in Kanonji for these under 5-years-old.

DISCUSSION

Vaccination coverage rose, but remained below the national average. We estimate that 6,867,000 yen in total cost and 455,000 yen in direct medical cost on average are saved by the subsidy.

Impact of methodology on the results of economic evaluations of varicella vaccination programs: is it important for decision-making?

This study aims to review the literature on economic evaluation of childhood varicella vaccination programs and to discuss how heterogeneity in methodological aspects and estimation of parameters can affect the studies' results. After applying the inclusion criteria, 27 studies published from 1980 to 2008 were analyzed in relation to methodological differences. There was great heterogeneity in the perspective adopted, evaluation of indirect costs, type of model used, modeling of the effect on herpes zoster, and estimation of vaccine price and efficacy parameters. The factor with the greatest impact on results was the inclusion of indirect costs, followed by the perspective adopted and vaccine price. The choice of a particular methodological aspect or parameter affected the studies' results and conclusions. It is essential that authors present these choices transparently so that users of economic evaluations understand the implications of such choices and the direction in which the results of the analysis were conducted.

Cost-effectiveness of varicella vaccination programs: an update of the literature

Varicella is one of the most common infectious diseases in childhood, caused by the varicella zoster virus. Although vaccines are available, there are only a few countries with an early-childhood vaccination program. Most countries mainly focus on vaccination of high-risk groups, such as susceptible healthcare workers. One of the main concerns with a routine early-childhood vaccination program is a potential (temporal) increase of the incidence of herpes zoster among elderly adults. In this review, we focus on the cost-effectiveness of varicella vaccination and on the methodology used in the health-economic studies. In particular, we focus on the perspective adopted, type of model used, the modeled effect on herpes zoster, the vaccine efficacy and price, and on the value of time lost by infection. The vast majority of studies show vaccination of high-risk groups - including susceptible adolescents - to be cost saving. Routine early-childhood vaccination programs are always cost saving if indirect costs of production losses are included, or cost effective, as long as the potential negative effects on zoster are not taken into account. We note that most studies included in the review used old vaccine prices and a single dose of the varicella vaccine, whereas multiple doses are now becoming the standard. Despite that, those aspects limit the timeliness of our review and we believe that the current work does provide useful insights in the cost-effectiveness of varicella vaccination.

Varicella vaccination in Europe: are we ready for a universal childhood programme?

Safe and effective vaccines against varicella zoster virus (VZV), the aetiological agent of varicella and shingles, have been available in Europe for the last 5-10 years. The USA has had a universal childhood vaccination policy since 1995 and this has resulted in a dramatic decrease in the incidence, morbidity and mortality related to varicella. The economic and medical burden of VZV has led to discussions regarding both the desirability and feasibility of a similar routine immunisation policy for all European children. This article examines the epidemiology of varicella in Europe and how the data emerging from the USA can be used to achieve adequate prevention of the disease. It looks into the current evidence of the health economic evaluation of universal varicella vaccination and explores the concerns surrounding such a policy, including the postulated impact on the incidence of zoster. In conclusion, the Society of Independent European Vaccination Experts (SIEVE) recommends that the immunisation of susceptible adolescents needs to be urgently implemented, in addition to the current recommendations targeting high-risk patients, their close contacts with a negative history of varicella and seronegative health-care workers. A universal policy, optimally incorporating a two-dose schedule, will be needed to finally reduce the burden of disease of varicella from a societal point of view. The SIEVE recommends the implementation of such a policy as soon as financially and practically possible.

Review of the Varilrix varicella vaccine

Varicella zoster virus causes an acute infection that affects most children globally, but the age of infection can be greater in residents of tropical areas. It has generally been considered a mild disease, although there are accumulating data to show that it can cause significant morbidity and mortality in immunocompetent as well as immunocompromised children and adults. Oka-strain live attenuated varicella vaccines were developed in the 1970s. Varilrix developed by GlaxoSmithKline Biologicals (Rixensart, Belgium), is one of the vaccines produced and marketed in over 80 countries. Similar to the other Oka-strain vaccines, Varilrix is safe, immunogenic and efficacious in both immunocompromised and immunocompetent children and adults.

Safety, tolerability, and immunogenicity of a two-dose regimen of high-titer varicella vaccine in subjects ≥13 years of age

A new manufacturing process, known as process upgrade varicella vaccine (PUVV) was developed for a refrigerated formulation of varicella vaccine and for an investigational zoster vaccine. Safety and tolerability of a two-dose regimen of high-titered (approximately 50,000 PFU) PUVV were compared to a lower-titer formulation (approximately 5400 PFU) of VARIVAX; in 1366 healthy subjects > or =13 years old. Only one vaccine-related clinical serious adverse experience (pruritus; no hospitalization) was reported, in the VARIVAX group. Injection-site adverse experiences following any dose were higher in the PUVV group, 70.0%, than in the VARIVAX group, 56.2%, but generally were mild. Immunogenicity were similar in both groups in seronegative subjects. PUVV was generally well tolerated, and elicited an immune response similar to that induced by the marketed formulation of VARIVAX.

Incidencia y costes de la hospitalización por bronquiolitis y de las infecciones por virus respiratorio sincitial en la Comunidad Valenciana. Años 2001 y 2002

OBJECTIVE

To assess the incidence and costs of hospitalizations for bronchiolitis and respiratory syncytial virus (RSV) infections the Autonomous Community of Valencia, Spain.

METHODS

The minimum data set (MDS) of the Autonomous Community of Valencia was analyzed. Hospital discharges with the codes for bronchiolitis (with or without etiologic determination) and RSV infections occurring in 2001 and 2002 in children less than 2 years old were included. Second cases of bronchiolitis and RSV infections of possible nosocomial origin occurring during prolonged hospitalization were excluded. The average cost of hospitalization in a pediatric ward was estimated at euro 310.30 per day. To calculate the incidence, we assumed that 95 % of the hospitals reported to the MDS; the population used was that of the National Census, 2001.

RESULTS

A total of 3,705 hospitalizations were obtained, of which 3,507 were coded as bronchiolitis and 42.2 % of these were RSV-positive. Virological assessment varied greatly among hospitals. Hospitalizations were most frequent between October and April, with no differences between the two years. The incidence of bronchiolitis hospitalization was 40.2 cases/1000 children < 1 year/year, with an average annual cost of 3,618 thousand Euros.

CONCLUSIONS

The cost of bronchiolitis hospitalizations is high. Microbiological investigation is low in some hospitals, leading the economic impact of RSV on society to be underestimated.

[Burden of hospitalizations attributable to rotavirus infection in children in the Autonomous Region of Madrid, Spain, period 1999-2000]

OBJECTIVE

To assess rotavirus infection requiring hospitalization in children aged < or = 5 years between 1999 and 2000 in the Autonomous Region of Madrid (Spain).

MATERIAL AND METHOD

A retrospective study was conducted, based on the hospital data surveillance system (Conjunto Mínimo Básico de Datos [CMBD]) and on the Spanish national microbiological information system (Sistema de Información Microbiológica [SIM]). CMBD data for all hospital admissions in children aged < or = 5 years with a first-listed diagnosis of intestinal infectious disease (ICD-9-CM codes: 001-009) or non-infective gastroenteritis (ICD-9-CM code: 558) and the reports to the SIM of the major pathogen groups responsible for acute gastroenteritis were analyzed.

RESULTS

The annual incidence of hospitalizations for acute gastroenteritis was 69 cases per 10,000 children aged < or = 5 years. Fourteen percent of the 32,541 infections produced by pathogens responsible for acute gastroenteritis reported to the SIM were rotavirus. The estimated annual incidence of hospitalizations due to rotavirus infections was 12 cases per 10,000 children aged (3/4) 5 years. The mean length of stay was 4.0 days, the annual mean number of days of hospitalization was 1,382 days, and the annual cost was 565,907 J. During the rotavirus epidemic months (December and January), the percentage of excess hospitalizations was 67 %.

CONCLUSIONS

Rotavirus causes a significant proportion of hospital admissions due to acute gastroenteritis in children aged < or = 5 years in the Autonomous Region of Madrid.

Economic evaluation of varicella vaccination in Spain: results from a dynamic model

Varicella is a universal childhood disease in Spain, causing approximately 400,000 cases, 1,500 hospitalizations and 15 deaths every year. The aim of this study is to determine the economic impact of childhood varicella vaccination on the burden of disease and associated costs by using a dynamic model. The analysis is based on the varicella transmission model developed by Halloran and adapted to the Spanish context. Cost data (Euro, 2004) were derived from previous studies and official tariffs. Two vaccination scenarios were analysed: (1) routine vaccination program for children aged 1-2 years, and (2) routine vaccination program for children aged 1-2 years completed by a catch-up program during the first year of vaccine marketing for children aged 2-11 years. The analysis considers that a similar coverage rate to the MMR one would be achieved (97.15%). A societal perspective, including direct and indirect costs, and a health care payor perspective were adopted. A probabilistic sensitivity analysis was performed. A routine vaccination program has a positive impact on varicella-related morbidity: the number of varicella cases is estimated to be reduced by 89%, and 1230 hospitalizations are prevented. From the societal perspective, scenario (1) is cost-saving whether or not indirect costs are considered (-51 and -4%, respectively). From the Health Care System the strategy is cost-effective, with a cost-effectiveness ratio estimated at 3,982 Euro per life-year gained, although it leads to a small increase in the costs. Considering the impact of vaccination on morbidity and costs, a routine childhood vaccination program against varicella is worth while in Spain without taking into account the potential impact on HZ.

[ENVOL study on the medical management of varicella and its complications in French ambulatory care]

OBJECTIVE

The authors had for aim to describe the management of varicella and its complications in French ambulatory care.

METHODS

A descriptive prospective national survey was carried out in France on patients visiting a random sample of French GPs and pediatricians (investigators) having diagnosed varicella. During an inclusion period of 4 months, the investigators enrolled all patients (adults-children) who presented with varicella or varicella related complications, and who had not previously visited the investigator for this episode. Three questionnaires were used to record the data.

RESULTS

One thousand two hundred patients were enrolled by 393 physicians 75% of whom were GPs. Ninety-four percent of patients were children under 13 years of age (group I). The sex ratio (M/F) was 1.1. The mean age was 3.5 years in group I and 23.8 years in patients over 13 years of age (group II). The mean length of the varicella episode was about 10.7 days. Most patients were given a pharmaceutical prescription on inclusion, 1% were also prescribed medical procedures, 0.3% were given local treatment, and 0.09% underwent physical therapy sessions. A proportion of 12.6% of patients visited their physician twice or more for the same episode. Six group I children were hospitalized. Eighty-seven patients presented with at least one complication i.e. 7.8% (95%CI=6.3-9.3) of all episodes, mainly bacterial superinfections.

CONCLUSIONS

The rate of complications associated with varicella infection was higher than usually reported in France but in the same order of magnitude as in other developed countries. Bacterial superinfections were found to be the most frequent complications of varicella.

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.

Preventing varicella-zoster disease

Varicella-zoster virus (VZV), the cause of chickenpox and shingles, is a pathogen in retreat following the introduction of mass vaccination in the United States in 1995. The live attenuated Oka vaccine, which is safe and immunogenic, gives good protection against both varicella and zoster in the short to medium term. It has undoubtedly been highly effective to date in reducing all forms of varicella, especially severe disease. However, the huge pool of latent wild-type virus in the population represents a continuing threat. Both the biology and the epidemiology of VZV disease suggest that new vaccination strategies will be required over time.

Variability of cost-effectiveness estimates for pharmaceuticals in Western Europe: lessons for inferring generalizability

OBJECTIVES

It has long been suggested that, whereas the results of clinical studies of pharmaceuticals are generalizable from one jurisdiction to another, the results of economic evaluations are location dependent. There has been, however, little study of the causes of variation, whether differences in study results among countries are systematic, or whether they are important for decision making.

METHODS

A literature search was conducted to identify economic evaluations of pharmaceuticals conducted in two or more European countries. The studies identified were then classified by methodological type and analyzed to assess their level of variability and to identify the main causes of variation. Assessments were also made of the extent to which differences in study results among countries were systematic and whether they would lead to a different decision, assuming a range of values of the threshold willingness-to-pay for a life-year or quality-adjusted life-year (QALY).

RESULTS

In total 46 intercountry drug comparisons were identified, 29 in multicountry studies and 17 in comparable single country studies that were considered to be sufficiently similar in terms of methodology. The type of study (i.e., trial-based or modeling study) had some impact on variability, but the most important factor was the extent of variation across countries in effectiveness, resource use or unit costs, allowed by the researcher's chosen methodology. There were few systematic differences in study results among countries, so a decision maker in country B, on seeing a recent economic evaluation of a new drug in country A, would have little basis on which to predict whether the drug, if evaluated, would be more or less cost-effective in his or her country. Given the extent of variation in cost-effectiveness estimates among countries, the importance of this for decision making depends on decision makers' thresholds in willingness-to-pay for a QALY or life-year. If a cost-effectiveness threshold (i.e., willingness-to-pay) for a life-year or QALY of dollar 50,000 were assumed, the same conclusion regarding cost-effectiveness would be reached in most cases.

CONCLUSION

This review shows that cost-effectiveness results for pharmaceuticals vary from country to country in Western Europe and that these variations are not systematic. In addition, constraints imposed by analysts may reduce apparent variability in the estimates. The lessons for inferring generalizability are not straightforward, although the implications of variation for decision making depend critically on the cost-effectiveness thresholds applying in Western Europe.

An economic evaluation of varicella vaccination in Italian adolescents

An economic evaluation was performed to assess five varicella vaccination scenarios targeted to 11-year-old Italian adolescents. The scenarios were: "compulsory vaccination" of all adolescents, recommended vaccination of susceptible adolescents on the basis of an "anamnestic screening", a "blood test" or a combination of both ("both tests") and vaccination of adolescents in the private sector, at the parents' charge ("private vaccination"). Probabilities and unit costs were taken from published sources and experts opinion. The accuracy of the anamnestic screening (81.6% sensitivity and 87.3% specificity) was derived from a separate descriptive study among 344 Italian adolescents. The costs and benefits of each scenario were simulated using a Markov model and cost-effectiveness, budget-impact and cost-benefit analyses were conducted. Of all considered scenarios, "both tests" and "anamnestic screening" were the most appealing options with an estimated net direct cost of 5058 and 8929 per life-year gained (compared to no vaccination) versus 14,693-42,842 for the other scenarios. These two scenarios further resulted in substantial net savings for society (over 600,000 per cohort, BCR: 2.17). The need for a serological confirmation was highly dependent on the sensitivity of the anamnestic screening, which is believed to increase once such a program is launched. For practical considerations, "anamnestic screening" seems to be the most convenient option.

Burden of hospitalizations attributable to rotavirus infection in children in Spain, period 1999–2000

The aim of this study is to provide estimates on the incidence of rotavirus infection requiring hospitalization in children <or=5 years of age during the 1999-2000 period in Spain and the associated direct cost of these hospitalizations. Hospital admissions attributable to rotavirus were estimated by using data on confirmed laboratory reports of rotavirus and hospital admissions due to acute gastroenteritis. During the study period a total of 32541 cases of pathogens responsible for acute gastroenteritis were reported to the microbiological information national system (SIM) and 14.0% were rotavirus. The proportion of laboratory-confirmed rotavirus cases was extrapolated to the total number of hospitalizations for acute gastroenteritis in children <or=5 years of age. An annual incidence of 1.0 hospital admissions attributable to rotavirus per 1000 persons <or=5 years of age was found, although during the winter season it reached 2.5 hospitalizations per 1000. Overall, the estimated annual number of days of hospitalization attributable to rotavirus was 8742 days that results in a cost of 3.6 million per year.

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.

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 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.

[Hospital admissions for varicella complications in children aged less than 15 years old]

BACKGROUND

The complications of varicella are one of the arguments in favor of universal vaccination programs in children.

OBJECTIVE

To describe the complications of varicella requiring hospital admission in a well-defined population (Gipuzkoa, Spain) and to compare the incidence of hospitalization with that reported in other series.

MATERIAL AND METHODS

Observational, retrospective, multicenter study of admissions for varicella. The medical histories codified as varicella (minimum data set, CIE-0, codes 952.0-052.9) from 1 January 1993 to 31 December 2002 were reviewed. Calculation of hospitalization rates was based on emergency department visits and population data. The pediatric population of Gipuzkoa seeking medical attention at one of the four Basque Country Health Service hospitals in the area: Hondarribia, Mendaro, San Sebastian and Zumarraga. The mean coverage in Gipuzkoa is 54,999 children aged less than 15 years/year. All the children aged 0-15 years old admitted for more than 24 h with a discharge diagnosis of varicella complications. The variables studied are: age, gender, personal history, varicella immunization, immune status, fever, chest X-ray, complementary investigations, length of hospital stay, treatment, discharge diagnosis, clinical course, complications and sequelae at discharge.

RESULTS

Seventy-one children were hospitalized. None had been vaccinated against the varicella-zoster virus. Eighty percent were aged less than 5 years and three were immunocompromised. Fifty-six percent had bacterial superinfection and invasive forms were found in seven patients. The mean length of admission was 6.5 days +/- 5.1. No deaths or sequelae were reported.

CONCLUSIONS

The annual incidence rate of admissions longer than 24 hours due to varicella complications was 12.9 cases per 100,000 children aged less than 15 years, representing 0.31% of all annual admissions in this age group.

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.

Epidemiology and economic impact of varicella in immunocompetent children in Spain. A nation-wide study

The epidemiology and burden of varicella was assessed through the prospective study of 683 children under 15 years, by 58 primary care paediatricians working on seven autonomous communities of Spain. The mean age was 4.5+/-2.7 years, and 566 (83%) were secondary cases. There were 111 complications in 101 children (14.8%), skin superinfection being the most frequent (8.9%), followed by respiratory tract (4.5%) and eye (2.2%) infections. The mean number of visits to the paediatric clinic was 1.42 (95% C.I. 1.37-1.47), and 5.6% of the children were attended in the emergency department of a hospital previously. All children had at least one prescription, being antihistamines and antipyretics the most prescribed. Thirteen percent received systemic antibiotics and 11% acyclovir. Children were mainly cared by grandparents, and parents were off work for a mean of 0.97 days (1.61 if children under 5 years attended day-care facilities; 0.51 if they did not). Costs derived from medical attention totalled 32.5, and social indirect costs were 63.77.