Targeted hepatitis B vaccination--a cost effective immunisation strategy for the UK?

Using integrated modeling to support the global eradication of vaccine-preventable diseases

The long-term management of global disease eradication initiatives involves numerous inherently dynamic processes, health and economic trade-offs, significant uncertainty and variability, rare events with big consequences, complex and inter-related decisions, and a requirement for cooperation among a large number of stakeholders. Over the course of more than 16 years of collaborative modeling efforts to support the Global Polio Eradication Initiative, we developed increasingly complex integrated system dynamics models that combined numerous analytical approaches, including differential equation-based modeling, risk and decision analysis, discrete-event and individual-based simulation, probabilistic uncertainty and sensitivity analysis, health economics, and optimization. We discuss the central role of systems thinking and system dynamics in the overall effort and the value of integrating different modeling approaches to appropriately address the trade-offs involved in some of the policy questions. We discuss practical challenges of integrating different analytical tools and we provide our perspective on the future of integrated modeling.

Inclusion of the value of herd immunity in economic evaluations of vaccines. A systematic review of methods used

OBJECTIVE

The objectives of this review were to identify vaccine economic evaluations that include herd immunity and describe the methodological approaches used.

METHODS

We used Kim and Goldie's search strategy from a systematic review (1976-2007) of modelling approaches used in vaccine economic evaluations and additionally searched PubMed/MEDLINE and Embase for 2007-2015. Studies were classified according to modelling approach used. Methods for estimating herd immunity effects were described, in particular for the static models.

RESULTS

We identified 625 economic evaluations of vaccines against human-transmissible diseases from 1976 to 2015. Of these, 172 (28%) included herd immunity. While 4% of studies included herd immunity in 2001, 53% of those published in 2015 did this. Pneumococcal, human papilloma and rotavirus vaccines represented the majority of studies (63%) considering herd immunity. Ninety-five of the 172 studies utilised a static model, 59 applied a dynamic model, eight a hybrid model and ten did not clearly state which method was used. Relatively crude methods and assumptions were used in the majority of the static model studies.

CONCLUSION

The proportion of economic evaluations using a dynamic model has increased in recent years. However, 55% of the included studies used a static model for estimating herd immunity. Values from a static model can only be considered reliable if high quality surveillance data are incorporated into the analysis. Without this, the results are questionable and they should only be included in sensitivity analysis.

Economic evaluation of delivering hepatitis B vaccine to injection drug users

BACKGROUND

Injection drug users (IDUs) are at high risk of hepatitis B (HBV) infection, and hepatitis B vaccination coverage in IDUs is low. Recent studies demonstrate that syringe exchange programs are effective venues to reach and immunize IDUs. The purpose of this paper was to determine if targeting IDUs for HBV vaccination through syringe exchange programs is economically desirable for the healthcare system and to assess the relative effectiveness of several different vaccination strategies.

METHODS

Active IDUs in Chicago IL and Hartford and Bridgeport CT (N=1964) were recruited and screened through local syringe exchange programs, randomized to a standard (0, 1, 6 months) or accelerated (0, 1, 2 months) vaccination schedule, and followed from May 2003 to March 2006. Analyses were conducted in 2007. The vaccination program's costs were balanced against future HBV-associated medical costs. Benefits in terms of prevented acute HBV infections and quality-adjusted life years were estimated based on a Markov model.

RESULTS

HBV vaccination campaigns targeting IDUs through syringe exchange programs are cost-saving. The most cost-saving strategies include giving the first dose to everyone at screening, administering the vaccination under the accelerated schedule (0, 1, 2 months), and obtaining highly discounted vaccine from local health departments.

CONCLUSIONS

It is economically inappropriate to offer HBV screening in the absence of vaccination. Existing syringe exchange programs in the U.S. should include HBV vaccination.

Retrospective cost-effectiveness analyses for polio vaccination in the United States

The history of polio vaccination in the United States spans 50 years and includes different phases of the disease, multiple vaccines, and a sustained significant commitment of resources. We estimated cost-effectiveness ratios and assessed the net benefits of polio vaccination applicable at various points in time from the societal perspective and we discounted these back to appropriate points in time. We reconstructed vaccine price data from available sources and used these to retrospectively estimate the total costs of the U.S. historical polio vaccination strategies (all costs reported in year 2002 dollars). We estimate that the United States invested approximately US dollars 35 billion (1955 net present value, discount rate of 3%) in polio vaccines between 1955 and 2005 and will invest approximately US dollars 1.4 billion (1955 net present value, or US dollars 6.3 billion in 2006 net present value) between 2006 and 2015 assuming a policy of continued use of inactivated poliovirus vaccine (IPV) for routine vaccination. The historical and future investments translate into over 1.7 billion vaccinations that prevent approximately 1.1 million cases of paralytic polio and over 160,000 deaths (1955 net present values of approximately 480,000 cases and 73,000 deaths). Due to treatment cost savings, the investment implies net benefits of approximately US dollars 180 billion (1955 net present value), even without incorporating the intangible costs of suffering and death and of averted fear. Retrospectively, the U.S. investment in polio vaccination represents a highly valuable, cost-saving public health program. Observed changes in the cost-effectiveness ratio estimates over time suggest the need for living economic models for interventions that appropriately change with time. This article also demonstrates that estimates of cost-effectiveness ratios at any single time point may fail to adequately consider the context of the investment made to date and the importance of population and other dynamics, and shows the importance of dynamic modeling.

Should universal hepatitis B immunisation be introduced in the UK?

Yes. But how?

Optimal reactive vaccination strategies for a foot-and-mouth outbreak in the UK

Foot-and-mouth disease (FMD) in the UK provides an ideal opportunity to explore optimal control measures for an infectious disease. The presence of fine-scale spatio-temporal data for the 2001 epidemic has allowed the development of epidemiological models that are more accurate than those generally created for other epidemics and provide the opportunity to explore a variety of alternative control measures. Vaccination was not used during the 2001 epidemic; however, the recent DEFRA (Department for Environment Food and Rural Affairs) contingency plan details how reactive vaccination would be considered in future. Here, using the data from the 2001 epidemic, we consider the optimal deployment of limited vaccination capacity in a complex heterogeneous environment. We use a model of FMD spread to investigate the optimal deployment of reactive ring vaccination of cattle constrained by logistical resources. The predicted optimal ring size is highly dependent upon logistical constraints but is more robust to epidemiological parameters. Other ways of targeting reactive vaccination can significantly reduce the epidemic size; in particular, ignoring the order in which infections are reported and vaccinating those farms closest to any previously reported case can substantially reduce the epidemic. This strategy has the advantage that it rapidly targets new foci of infection and that determining an optimal ring size is unnecessary.

Hepatitis B vaccination in a school age population: a feasibility study

There remains no consensus on whether to adopt a universal hepatitis B vaccination strategy in the United Kingdom, where the endemicity of hepatitis B virus (HBV) is considered to be very low in the general population. To assess the feasibility and acceptance of a school-based adolescent vaccination approach, 11-13 years old pupils in local secondary schools in the London Borough of Camden and Islington were contacted and offered a three-dose hepatitis B vaccination course using a 0, 1, and 12 months schedule. The adult dose of hepatitis B vaccine (Engerix B GlaxoSmithKline) containing 20 mug recombinant hepatitis B surface antigen (HBsAg) in 1 ml suspension was administered. This dosage is normally intended for adults and children older than 15 years of age, but can be administered in 10-15 years old children when compliance may be low, since a higher proportion of those vaccinated develop protective antibody levels following administration of only two doses of vaccine. Overall, a total of 528 pupils were contacted, with 122 (23%) consenting to be vaccinated. Of these, 117 (96%) received the complete three-dose regimen according to the schedule (four did not receive vaccine: three were non-attendees and one was previously vaccinated; one withdrew following a flu-like adverse event). The results of this study show that it is feasible and practical to administer hepatitis B vaccination to adolescents in a school setting, and that it is possible to achieve high rates of uptake for the complete three-dose course among adolescents. However, in order to attain and sustain high coverage rates among pupils, this would require additional general health promotion, including health education and provision of information, targeting of teachers, pupils, and parents in order to increase participation in a school-based hepatitis B vaccination programme. A further requirement includes the availability of good local health support within schools so as to allow for an efficient vaccine delivery system to maximize vaccination in this setting.

Costs of running a universal adolescent hepatitis B vaccination programme

In the first UK study to examine feasibility and acceptability of universal adolescent hepatitis B vaccination, the costs associated with the administration and uptake (80.2 and 89.3% for three doses and at least two doses, respectively), of a three-dose regimen in pupils in Glasgow schools (2001/2002) were measured. These data were used to estimate the economic outlay for the delivery of a routine, ongoing three-dose and two-dose hepatitis B vaccine programme in schools. Vaccine, accounting for almost 70% of the overall costs, was the largest cost item for both the pilot and routine programmes, using either regimen. However, the ongoing, two-dose regimen was the cheapest option in this analysis, irrespective of vaccine price. Cost data from this study may be useful for other countries wishing to implement a similar programme.

Modelling vaccination strategies against foot-and-mouth disease

Vaccination has proved a powerful defence against a range of infectious diseases of humans and animals. However, its potential to control major epidemics of foot-and-mouth disease (FMD) in livestock is contentious. Using an individual farm-based model, we consider either national prophylactic vaccination campaigns in advance of an outbreak, or combinations of reactive vaccination and culling strategies during an epidemic. Consistent with standard epidemiological theory, mass prophylactic vaccination could reduce greatly the potential for a major epidemic, while the targeting of high-risk farms increases efficiency. Given sufficient resources and preparation, a combination of reactive vaccination and culling might control ongoing epidemics. We also explore a reactive strategy, 'predictive' vaccination, which targets key spatial transmission loci and can reduce markedly the long tail that characterizes many FMD epidemics. These analyses have broader implications for the control of human and livestock infectious diseases in heterogeneous spatial landscapes.

Economic evaluations of hepatitis B immunization: a global review of recent studies (1994-2000)

A search was carried out for economic evaluations of hepatitis B (HBV) vaccination, published between 1994 and 2000. The results of these studies are discussed according to the level of HBV endemicity. The great majority of these evaluations were carried out for industrialized countries, for the most part situated in areas of low to very low HBV endemicity. In countries of very low endemicity economic evaluations have yielded contradictory results, depending on the type of epidemiological model they used. The cost-effectiveness of adding universal to selective vaccination strategies in these countries depends on the selective strategies' ability to sufficiently identify, reach and fully vaccinate persons in various risk groups. In areas of low, intermediate and high endemicity, universal vaccination seems justifiable on the basis of economic evaluation. In general, the accuracy of the models has improved over the years, but still the transparency, completeness and comparability of analyses could improve considerably. By noting this, the suitability of different methodologies for different areas of endemicity and vaccination strategies is discussed. It is recommended that specific guidelines for economic evaluation of the prevention of infectious diseases be developed to guarantee the relevance of and to improve the comparability between studies.

Do we need 3 doses of hepatitis B vaccine?

The hepatitis B virus (HBV) vaccine may provide protection through the clonal expansion of specific memory cells without necessarily having to produce high serum antibody levels. We develop a mathematical model which distinguishes between the accumulation of sensitive memory B and T-helper cells prior to a booster and the high circulating antibody levels present in an individual after a booster. We suggest this immune memory accumulates primarily in an antigen-independent fashion. These phenomena suggest individuals may be immune to infection six months after the priming vaccine dose(s) regardless of whether they receive a booster or not. This hypothesis is supported by immunogenicity data and by two independent vaccine efficacy trials comparing 0, 1 month schedules with 0, 1 and 6 month schedules.

Hepatitis B virus infection in patients attending a genitourinary medicine clinic: risk factors and vaccine coverage

BACKGROUND

The hepatitis B virus (HBV) immunisation policy in the United Kingdom includes offering vaccines selectively to those at risk by sexual contact. Among genitourinary medicine (GUM) clinic attenders, homosexual men are offered vaccine, but estimates of the vaccine uptake are required to monitor policy and estimate the possible impact on transmission; heterosexuals are not routinely offered vaccine, but this policy might change if the prevalence was found to be high.

OBJECTIVE

To determine the prevalence of HBV infection and vaccine uptake among patients attending a GUM clinic.

METHODS

HBV seroprevalence determined by unlinked anonymous testing of consecutive blood samples sent for syphilis serology. Demographic and risk factor data and history of HBV immunization extracted from clinic notes before unlinking. Prevalence data were compared with a population of first time blood donors from the same area.

SETTING

Open access GUM clinic in central London.

RESULTS

Samples were obtained and tested from 441 homosexual and 527 heterosexual men and from 821 women over a 4 month period in 1990. After exclusion of injecting drug users and their sexual partners (n = 30) and HBV carriers attending for follow up (n = 12), the prevalence of antibody to HBV core (anti-HBc) was 38.7% in homosexual men, 5.9% in heterosexual men, and 3.5% in women (50.0%, 6.0%, 3.7% respectively if previous vaccinees were also excluded). The prevalence of HBV surface antigen positivity was 4.2%, 0.60%, and 0.39% respectively after exclusion of vaccinees (chi(2) p < 0.001 for homosexual men versus others). The prevalence of the anti-HBc in first time blood donors was 1.1% (8/749). Among male GUM clinic attenders, the prevalence of anti-HBc was higher in those of non-UK origin or place of birth and/or non-white ethnicity (odds ratios 2.87, 95% CI 1.57-5.24 and 8.06, CI 3.39-19.1, in homosexuals and heterosexuals respectively). In homosexual men anti-HBc prevalence increased with age (OR 1.05, CI 1.02-1.07 for each year) and lifetime number of STDs (OR 6.36, CI 3.77-10.8 for > or = 2 versus < 2) and in clinic reattenders compared with new patients (OR 5.42, 95% CI 3.32-9.16). Among heterosexuals, age was associated with anti-HBc prevalence in women (OR 1.09, CI 1.04-1.12) but not men (OR 0.99, 95% CI 0.95-1.02). There were no other associations in heterosexuals. A history of HBV immunisation in homosexual men was recorded in 13/131 (9.9%) of new patients and 103/305 (33.8%; OR 4.63, CI 2.49-8.60) clinic reattenders.

CONCLUSIONS

Although higher than a sample of blood donors, the prevalence of serological markers of HBV infection among heterosexuals was low, providing little support for extending HBV immunisation to all heterosexuals attending GUM clinics as a targeted strategy for control of HBV infection. Homosexual men remain at high risk of infection, but many are now being immunised. Efforts to improve compliance with existing vaccine policies in GUM clinics should be encouraged.