The difficult quest for data on "vanishing" vaccine-preventable infections in Europe: the case of measles in Flanders (Belgium)

Clustering of susceptible individuals within households can drive measles outbreaks: an individual-based model exploration

When estimating important measures such as the herd immunity threshold, and the corresponding efforts required to eliminate measles, it is often assumed that susceptible individuals are uniformly distributed throughout populations. However, unvaccinated individuals may be clustered in a variety of ways, including by geographic location, by age, in schools, or in households. Here, we investigate to which extent different levels of within-household clustering of susceptible individuals may impact the risk and persistence of measles outbreaks. To this end, we apply an individual-based model, Stride, to a population of 600,000 individuals, using data from Flanders, Belgium. We construct a metric to estimate the level of within-household susceptibility clustering in the population. Furthermore, we compare realistic scenarios regarding the distribution of susceptible individuals within households in terms of their impact on epidemiological measures for outbreak risk and persistence. We find that higher levels of within-household clustering of susceptible individuals increase the risk, size and persistence of measles outbreaks. Ignoring within-household clustering thus leads to underestimations of required measles elimination and outbreak mitigation efforts.

Using Individual-Based Models to Look Beyond the Horizon: The Changing Effects of Household-Based Clustering of Susceptibility to Measles in the Next 20 Years

Recent measles outbreaks in regions with a high overall vaccination coverage have drawn attention to other factors - aside from the overall immunity level - determining the spread of measles in a population, such as heterogeneous social mixing behavior and vaccination behavior. As households are an important context for measles transmission, the clustering of susceptible individuals within households can have a decisive effect on the risk for measles outbreaks. However, as the population ages and household constitutions change over the next 20 years, that effect may change as well. To adequately plan for the control and eventual elimination of measles, we need to understand how the effect of within-household susceptibility clustering will evolve. Individual-based models enable us to represent the different levels of heterogeneity in a population that are necessary to understand the spread of a disease in a highly immunized population. In this paper, we use such an individual-based model to investigate how the effect of household-based susceptibility clustering is expected to change over the next two decades in Flanders, Belgium. We compare different scenarios regarding the level of within-household susceptibility clustering for three different calendar years between 2020 and 2040, using projections for the age distribution of the population, the constitution of households and age-specific immunity levels. We find that a higher level of susceptibility clustering within households increases the risk for measles outbreaks and their potential to spread through the population, in current as well as in future populations.

An economic evaluation of the current measles vaccination program: A case study in Zhejiang Province, east China

OBJECTIVE

To evaluate the economic impact of the current measles vaccination program in Zhejiang Province, east China.

METHODS

A decision tree-Markov model with parameters from published literatures, government documents and surveys was developed and used to simulate over 40 years of a birth cohort in Zhejiang Province during the year 2014. The expected cost and effectiveness of the current measles vaccination program was compared against no vaccination. Costs were assessed from the payer's perspective. Benefits were defined as savings on the direct cost of measles treatment, and the effectiveness was measured according to the number of measles cases and deaths averted. The net present value (NPV), benefit-cost ratio (BCR) and incremental cost-effectiveness ratio (ICER) were also calculated. A threshold for cost-effectiveness of less than 3 times the Gross Domestic Product (GDP) per capita was used. One-way sensitivity analysis was performed to assess parameter uncertainties.

RESULTS

The total vaccination cost was estimated to be $2.52 million. The BCR of the current measles program was found to be 6.06 with a NPV of $73.38 million. It was also calculated that a total of 195,165 measles cases and 191 measles-related deaths would be prevented by vaccination. The ICER was approximately $12.91 per case averted and $13,213.43 per death averted, respectively, which was cost-effective. The models were proven to be robust.

CONCLUSIONS

The current measles vaccination program appeared to be cost-effective and to offer substantial benefits. The results of this analysis sought to contribute to the justification of future investments to achieve the goal of measles elimination.

Inferring rubella outbreak risk from seroprevalence data in Belgium

Rubella is usually a mild disease for which infections often pass by unnoticed. In approximately 50% of the cases, there are no or only few clinical symptoms. However, rubella contracted during early pregnancy could lead to spontaneous abortion, to central nervous system defects, or to one of a range of other serious and debilitating conditions in a newborn such as the congenital rubella syndrome. Before the introduction of mass vaccination, rubella was a common childhood infection occurring all over the world. However, since the introduction of rubella antigen-containing vaccines, the incidence of rubella has declined dramatically in high-income countries. Recent large-scale mumps outbreaks, one of the components in the combined measles-mumps-rubella vaccine, occurring in countries throughout Europe with high vaccination coverage, provide evidence of pathogen-specific waning of vaccine-induced immunity and primary vaccine failure. In addition, recent measles outbreaks affecting populations with suboptimal vaccination coverages stress the importance of maintaining high vaccination coverages. In this paper, we focus on the assessment of rubella outbreak risk using a previously developed method to identify geographic regions of high outbreak potential. The methodology relies on 2006 rubella seroprevalence data and vaccination coverage data from Belgium and information on primary and secondary vaccine failure obtained from extensive literature reviews. We estimated the rubella outbreak risk in Belgium to be low, however maintaining high levels of immunisation and surveillance are of utmost importance to avoid future outbreaks.

The Costs and Valuation of Health Impacts of Measles and Rubella Risk Management Policies

National and global health policymakers require good information about the costs and benefits of their investments in measles and rubella immunization programs. Building on our review of the existing measles and rubella health economics literature, we develop inputs for use in regional and global models of the expected future benefits and costs of vaccination, treatment, surveillance, and other global coordination activities. Given diversity in the world and limited data, we characterize the costs for countries according to the 2013 World Bank income levels using 2013 U.S. dollars (2013$US). We estimate that routine immunization and supplemental immunization activities will cost governments and donors over 2013$US 2.3 billion per year for the foreseeable future, with high-income countries accounting for 55% of the costs, to vaccinate global birth cohorts of approximately 134 million surviving infants and to protect the global population of over 7 billion people. We find significantly higher costs and health consequences of measles or rubella disease than with vaccine use, with the expected disability-adjusted life year (DALY) loss for case of disease generally at least 100 times the loss per vaccine dose. To support estimates of the economic benefits of investments in measles and/or rubella elimination or control, we characterize the probabilities of various sequelae of measles and rubella infections and vaccine adverse events, the DALY inputs for health outcomes, and the associated treatment costs. Managing measles and rubella to achieve the existing and future regional measles and rubella goals and the objectives of the Global Vaccine Action Plan will require an ongoing commitment of financial resources that will prevent adverse health outcomes and save the associated treatment costs.

Assessing mumps outbreak risk in highly vaccinated populations using spatial seroprevalence data

Mumps is a potentially severe viral infection. The incidence of mumps has declined dramatically in high-income countries since the introduction of mumps antigen-containing vaccines. However, recent large outbreaks of mumps in highly vaccinated populations suggest waning of vaccine-induced immunity and primary vaccine failure. In this paper we present a simple method for identifying geographic regions with high outbreak potential, demonstrated using 2006 mumps seroprevalence data from Belgium and Belgian vaccination coverage data. Predictions of the outbreak potential in terms of the effective reproduction number in future years signal an increased risk of new mumps outbreaks. Literature reviews on serological information for both primary vaccine failure and waning immunity provide essential information for our predictions. Tailor-made additional vaccination campaigns would be valuable for decreasing local pockets of susceptibility, thereby reducing the risk of future large-scale mumps outbreaks.

Methodological issues and new developments in the economic evaluation of vaccines

The application of economic evaluation in healthcare, including vaccination programs, has increased exponentially since the 1980s. There are a number of aspects of economic evaluation of vaccine programs that present particular challenges to the analyst. These include the development of the appropriate epidemiological models from which to estimate the costs and benefits; the accurate prediction of uptake rates; the incorporation of quality adjusted survival gains; and the inclusion of intangible but nonetheless important benefits and costs associated with infectious disease and vaccination. The estimation of marginal intervention costs presents specific difficulties, especially for multivalent vaccines and valuing costs and benefits over time is heavily influenced by the choice of discount rate, which is still a controversial topic. Developments in the next 5 years are likely to address all of these issues and result in more sophisticated and accurate models of vaccination programs.

Are we hitting immunity targets? The 2006 age-specific seroprevalence of measles, mumps, rubella, diphtheria and tetanus in Belgium

Susceptibility to vaccine-preventable diseases in Belgium in 2006 was estimated from a serum survey. Immunoglobulins against measles, mumps, rubella (MMR) and diphtheria at all available ages (1-65 years), and against tetanus in >40-year-olds, were measured by ELISA. Age-standardized overall seronegativity for MMR was low (3·9%, 8·0%, 10·4%, respectively). However, the World Health Organization's targets for measles elimination were not met in 5- to 24-year-olds and about 1 in 7 women at childbearing age (15-39 years) were seronegative for rubella. In adults >40 years, tetanus immunity (87·2%, >0·16 IU/ml) largely exceeded diphtheria immunity (20-45%, >0·1 IU/ml). Despite free universal vaccination against MMR for more than 20 years and against diphtheria and tetanus for almost 60 years, our study revealed specific age groups remaining at risk for infection with these pathogens.

Cost-Effectiveness of Rotavirus Vaccination: Exploring Caregiver(s) and ``No Medical Care'' Disease Impact in Belgium

Aim . To estimate the cost-effectiveness of universal childhood rotavirus vaccination in Belgium, taking into account the impact of caregiver burden and the burden of sick children for whom no medical care is sought (``no medical care''). Methods . A cohort of newborns is modeled in relation to costs and health outcomes for rotavirus disease, distinguishing episodes leading to consultations, hospitalizations, and deaths from no medical care episodes. Fully funded universal vaccination is compared with no vaccination as well as with the current situation in Belgium, whereby the 2-dose Rotarix or the 3-dose RotaTeq vaccine can be bought at market prices, which are partially reimbursed. Results . Compared with no vaccination, fully funded universal rotavirus vaccination would cost 51,030 per quality-adjusted life year (QALY) gained with Rotarix and 65,767 with RotaTeq (for society, 7572 and 30,227 per QALY, respectively). However, there is considerable uncertainty due to some analytical choices: the proportion of simulations with an acceptable incremental cost-effectiveness ratio (given a willingness to pay 50,000 for an additional QALY), increases from 2%/0.6% (Rotarix/RotaTeq) to 86%/59% when considering no medical care, and including 2 caregivers to estimate QALY loss instead of zero. Uncertainty is greater still under the societal than under the health care payer perspective. Conclusion . For the Belgian health care payer, at current vaccine prices, universal childhood rotavirus vaccination is unlikely to be judged cost-effective versus no vaccination but would be a more efficient and equitable choice than continuing with current practice.

The health and economic burden of rotavirus disease in Belgium

For health economic evaluations of rotavirus vaccination, estimates of the health and cost burden of rotavirus are required. Due to differences in health care systems and surveillance organisations, this is difficult to achieve by imputing estimates from one country to others. This study aimed to estimate the burden of rotavirus disease in Belgium. In children younger than 7 years of age, rotavirus is predicted to account annually for about 5,600 hospitalisations (676:100,000 children); 26,800 outpatient, general practitioner and paediatrician visits; and about 44,600 episodes for which no medical care is sought. This burden is estimated to represent direct costs of 7.7 million Euro and indirect costs of 12.8 million Euro. Rotavirus disease causes a substantial health and economic burden in Belgium.

Long-term persistence of antibodies after one or two doses of MMR-vaccine

Outbreaks of measles, mumps and rubella have occurred recently despite long-standing mass immunization with MMR. Antibody titres for measles, mumps and rubella of 160 students (17-23 years) with proof of at least one MMR-vaccine were studied according to the number of MMR-vaccines received. The proportion of subjects with positive antibody titres was significantly higher in those who received two vaccines against measles (77.1% versus 58.7%, p=0.05), mumps (67.5% versus 55.6%, p=0.009) and rubella (99.2% versus 71.4%, p=0.008). Comparable significant trends were seen for GMTs for measles and mumps. A similar non-significant trend was noted for rubella.

Health burden and economic impact of measles-related hospitalizations in Italy in 2002-2003

Background

A large measles outbreak occurred in Italy in 2002–2003. This study evaluates the health burden and economic impact of measles-related hospitalizations in Italy during the specified period.

Methods

Hospital discharge abstract data for measles hospitalizations in Italy during 2002–2003 were analysed to obtain information regarding number and rates of measles hospitalizations by geographical area and age group, length of hospital stay, and complications. Hospitalization costs were estimated on the basis of Diagnosis-Related Groups.

Results

A total of 5,154 hospitalizations were identified, 3,478 (67%) of which occurred in children <15 years of age. Most hospitalizations occurred in southern Italy (71 %) and children below 1 year of age presented the greatest hospitalization rates (46.2/100,000 and 19.0/100,000, respectively in 2002 and 2003). Pneumonia was diagnosed in 594 cases (11.5%) and encephalitis in 138 cases (2.7%). Total hospital charges were approximately € 8.8 million.

Conclusion

The nationwide health burden associated with measles during the 2002–2003 outbreak was substantial and a high cost was incurred by the Italian National Health Service for the thousands of measles-related hospitalizations which occurred. By assuming that hospital costs represent 40–50% of the direct costs of measles cases, direct costs of measles for the two years combined were estimated to be between €17.6 – 22.0 million, which equates to the vaccination of 1.5–1.9 million children (3–4 birth cohorts) with one dose of MMR. The high cost of measles and the severity of its complications fully justify the commitment required to reach measles elimination.

Cost-of-illness studies : a review of current methods

The number of cost-of-illness (COI) studies has expanded considerably over time. One outcome of this growth is that the reported COI estimates are inconsistent across studies, thereby raising concerns over the validity of the estimates and methods. Several factors have been identified in the literature as reasons for the observed variation in COI estimates. To date, the variation in the methods used to calculate costs has not been examined in great detail even though the variations in methods are a major driver of variation in COI estimates. The objective of this review was to document the variation in the methodologies employed in COI studies and to highlight the benefits and limitations of these methods. The review of COI studies was implemented following a four-step procedure: (i) a structured literature search of MEDLINE, JSTOR and EconLit; (ii) a review of abstracts using pre-defined inclusion and exclusion criteria; (iii) a full-text review using pre-defined inclusion and exclusion criteria; and (iv) classification of articles according to the methods used to calculate costs. This review identified four COI estimation methods (Sum_All Medical, Sum_Diagnosis Specific, Matched Control and Regression) that were used in categorising articles. Also, six components of direct medical costs and five components of indirect/non-medical costs were identified and used in categorising articles.365 full-length articles were reflected in the current review following the structured literature search. The top five cost components were emergency room/inpatient hospital costs, outpatient physician costs, drug costs, productivity losses and laboratory costs. The dominant method, Sum_Diagnosis Specific, was a total costing approach that restricted the summation of medical expenditures to those related to a diagnosis of the disease of interest. There was considerable variation in the methods used within disease subcategories. In several disease subcategories (e.g. asthma, dementia, diabetes mellitus), all four estimation methods were represented, and in other cases (e.g. HIV/AIDS, obesity, stroke, urinary incontinence, schizophrenia), three of the four estimation methods were represented. There was also evidence to suggest that the strengths and weaknesses of each method were considered when applying a method to a specific illness. Comparisons and assessments of COI estimates should consider the method used to estimate costs both as an important source of variation in the reported COI estimates and as a marker of the reliability of the COI estimate.

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.

The average cost of measles cases and adverse events following vaccination in industrialised countries

BACKGROUND

Even though the annual incidence rate of measles has dramatically decreased in industrialised countries since the implementation of universal immunisation programmes, cases continue to occur in countries where endemic measles transmission has been interrupted and in countries where adequate levels of immunisation coverage have not been maintained. The objective of this study is to develop a model to estimate the average cost per measles case and per adverse event following measles immunisation using the Netherlands (NL), the United Kingdom (UK) and Canada as examples.

METHODS

Parameter estimates were based on a review of the published literature. A decision tree was built to represent the complications associated with measles cases and adverse events following immunisation. Monte-Carlo Simulation techniques were used to account for uncertainty.

RESULTS

From the perspective of society, we estimated the average cost per measles case to be US$276, US$307 and US$254 for the NL, the UK and Canada, respectively, and the average cost of adverse events following immunisation per vaccinee to be US$1.43, US$1.93 and US$1.51 for the NL, UK and Canada, respectively.

CONCLUSIONS

These average cost estimates could be combined with incidence estimates and costs of immunisation programmes to provide estimates of the cost of measles to industrialised countries. Such estimates could be used as a basis to estimate the potential economic gains of global measles eradication.