Hepatitis-B virus endemicity: heterogeneity, catastrophic dynamics and control

Modelling the epidemiology of hepatitis B in New Zealand

Hepatitis B is a vaccine preventable disease caused by the hepatitis B virus (HBV) that can induce potentially fatal liver damage. It has the second highest mortality rate of all vaccine preventable diseases in New Zealand. Vaccination against HBV was introduced in New Zealand in 1988, and the country is now categorised with overall low endemicity but with areas of both high and medium endemic levels. We present an SECIR compartmental mathematical model, with the population divided into age classes, for the transmission of HBV using local data on incidence of infection and vaccination coverage. We estimate the basic reproduction number, R(0), to be 1.53, and show that the vaccination campaign has substantially reduced this below one. However, a large number of carriers remain in the population acting as a source of infection.

Dynamical behavior of a hepatitis B virus transmission model with vaccination

Hepatitis B virus (HBV) infection is a globally health problem. In 2005, the WHO Western Pacific Regional Office set a goal of reducing chronic HBV infection rate to less than 2% among children five years of age by 2012, as an interim milestone towards the final goal of less than 1%. Many countries made some plans (such as free HBV vaccination program for all neonates in China now) to control the transmission HBV. We develop a model to explore the impact of vaccination and other controlling measures of HBV infection. The model has simple dynamical behavior which has a globally asymptotically stable disease-free equilibrium when the basic reproduction number R(0)< or =1, and a globally asymptotically stable endemic equilibrium when R(0)>1. Numerical simulation results show that the vaccination is a very effective measure to control the infection and they also give some useful comments on controlling the transmission of HBV.

Population collapse to extinction: the catastrophic combination of parasitism and Allee effect

Infectious diseases are responsible for the extinction of a number of species. In conventional epidemic models, the transition from endemic population persistence to extirpation takes place gradually. However, if host demographics exhibits a strong Allee effect (AE) (population decline at low densities), extinction can occur abruptly in a catastrophic population crash. This might explain why species suddenly disappear even when they used to persist at high endemic population levels. Mathematically, the tipping point towards population collapse is associated with a saddle-node bifurcation. The underlying mechanism is the simultaneous population size depression and the increase of the extinction threshold due to parasite pathogenicity and Allee effect. Since highly pathogenic parasites cause their own extinction but not that of their host, there can be another saddle-node bifurcation with the re-emergence of two endemic equilibria. The implications for control interventions are discussed, suggesting that effective management may be possible for ℛ(0)≫1.

Modeling the transmission dynamics and control of hepatitis B virus in China

Hepatitis B is a potentially life-threatening liver infection caused by the hepatitis B virus (HBV) and is a major global health problem. HBV is the most common serious viral infection and a leading cause of death in mainland China. Around 130 million people in China are carriers of HBV, almost a third of the people infected with HBV worldwide and about 10% of the general population in the country; among them 30 million are chronically infected. Every year, 300,000 people die from HBV-related diseases in China, accounting for 40-50% of HBV-related deaths worldwide. Despite an effective vaccination program for newborn babies since the 1990s, which has reduced chronic HBV infection in children, the incidence of hepatitis B is still increasing in China. We propose a mathematical model to understand the transmission dynamics and prevalence of HBV infection in China. Based on the data reported by the Ministry of Health of China, the model provides an approximate estimate of the basic reproduction number R(0)=2.406. This indicates that hepatitis B is endemic in China and is approaching its equilibrium with the current immunization program and control measures. Although China made a great progress in increasing coverage among infants with hepatitis B vaccine, it has a long and hard battle to fight in order to significantly reduce the incidence and eventually eradicate the virus.

A new strategy for constructing in vitro replication-competent 1.3 copies of hepatitis B virus genome

In the absence of a robust infectable cell culture system, assays related to replication of clinical HBV isolates are based on the transfection of replication-competent HBV DNA into hepatoma cell lines that are able to replicate and secrete HBV virions. Current methods for constructing HBV 1.1 genomes work well for drug susceptibility assays, but are not very suitable for research on HBV replication capacity or regulation since a heterogeneous promoter is required to drive pgRNA transcription. A new strategy for constructing HBV 1.3 genomes that contain HBV intrinsic promoter necessary for pgRNA transcription is reported in this paper. Using this strategy, three HBV 1.3 genomes from isolates of three patients were constructed. When the three HBV 1.3 genomes were transfected into the HepG2 cell line, replicative intermediates were detectable by Southern blotting with digoxigenin-labeled DNA probe in two of the three constructs. Using overlap extension PCR and avoiding as much as possible the digestion-and-ligation process, this strategy could be applied to constructing longer-than-genome units for most genotypes of HBV strains.

Global stability of an SIR epidemic model with information dependent vaccination

We study the global behavior of a non-linear susceptible-infectious-removed (SIR)-like epidemic model with a non-bilinear feedback mechanism, which describes the influence of information, and of information-related delays, on a vaccination campaign. We upgrade the stability analysis performed in d'Onofrio et al. [A. d'Onofrio, P. Manfredi, E. Salinelli, Vaccinating behavior, information, and the dynamics of SIR vaccine preventable diseases, Theor. Popul. Biol. 71 (2007) 301) and, at same time, give a special example of application of the geometric method for global stability, due to Li and Muldowney. Numerical investigations are provided to show how the stability properties depend on the interplay between some relevant parameters of the model.

Different evolutionary rates and epidemic growth of hepatitis B virus genotypes A and D

The epidemiological history of HBV genotypes A and D and subgenotypes A2 and D3 was studied on 132 isolates drawn between 1980 and 2005 from patients living in a homogenous geographical area. Evolutionary rates and divergence dates were estimated and HBV demographic history was reconstructed by using a statistical approach based on coalescent theory. The evolutionary rate of A2 was significantly lower than that of D3. The growth rate of D3 epidemic was significantly faster than that of A2; both subgenotypes showed a decreasing growth rate from the mid-1980s. Our data suggest that the important discrepancies observed in the evolutionary rates of HBV genotypes A and D may reflect different population dynamics of their epidemics. These results show the usefulness of phylodynamic studies in reconstructing the history of epidemics due to highly variable DNA viruses, and in evaluating the long-term efficacy of prophylactic measures.

Epidemiology of hepatitis B virus infection among the tribes of Andaman and Nicobar Islands, India

The Andaman and Nicobar Islands, Union Territory of India, are home to six primitive tribes, namely the Great Andamanese, Onges, Jarawas and Sentinelese (Negrito race), and the Shompens and Nicobarese (Mongoloid race). These tribes account for about 8% of the island's population and the Nicobarese constitute >95% of the tribal population. Hepatitis B virus (HBV) infection is highly endemic among them with the prevalence of hepatitis B surface antigen (HBsAg) ranging from 23% among the Nicobarese to 66% among the Jarawas. The high HBsAg prevalence among pregnant mothers (20.5%), a linear increase in the age-specific rates of HBV exposure and the presence of HBsAg-positive individuals in every family suggested a combination of perinatal and horizontal transmission among the Nicobarese. Molecular studies of HBV isolates from the Onges, Nicobarese and Great Andamanese indicated a predominance of genotype D and there was a close similarity between these isolates and isolates from mainland India, suggesting that HBV may have been introduced from mainland India. In contrast, genotype C predominated among the Jarawas, with isolates similar to strains from Southeast Asian countries. Due to its high prevalence, hepatitis B vaccine is included in the childhood vaccination programme in these islands. It might be worth considering a pilot screening programme for chronic HBV patients to detect hepatocellular carcinoma.

Prospects for malaria eradication in sub-Saharan Africa

Background

A characteristic of Plasmodium falciparum infections is the gradual acquisition of clinical immunity resulting from repeated exposures to the parasite. While the molecular basis of protection against clinical malaria remains unresolved, its effects on epidemiological patterns are well recognized. Accumulating epidemiological data constitute a valuable resource that must be intensively explored and interpreted as to effectively inform control planning.

Methodology/Principal Finding

Here we apply a mathematical model to clinical data from eight endemic regions in sub-Saharan Africa. The model provides a quantitative framework within which differences in age distribution of clinical disease are assessed in terms of the parameters underlying transmission. The shorter infectious periods estimated for clinical infections induce a regime of bistability of endemic and malaria-free states in regions of mesoendemic transmission. The two epidemiological states are separated by a threshold that provides a convenient measure for intervention design. Scenarios of eradication and resurgence are simulated.

Conclusions/Significance

In regions that support mesoendemic transmission, intervention success depends critically on reducing prevalence below a threshold which separates endemic and malaria-free regimes.

Inefficient epidemic spreading in scale-free networks

Highly heterogeneous degree distributions yield efficient spreading of simple epidemics through networks, but can be inefficient with more complex epidemiological processes. We study diseases with nonlinear force of infection whose prevalences can abruptly collapse to zero while decreasing the transmission parameters. We find that scale-free networks can be unable to support diseases that, on the contrary, are able to persist at high endemic levels in homogeneous networks with the same average degree.

The pluses and minuses of R0

The concept of the basic reproduction number (R0) occupies a central place in epidemic theory. The value of R0 determines the proportion of the population that becomes infected over the course of a (modelled) epidemic. In many models, (i) an endemic infection can persist only if R0>1, (ii) the value of R0 provides a direct measure of the control effort required to eliminate the infection, and (iii) pathogens evolve to maximize their value of R0. These three statements are not universally true. In this paper, some exceptions to them are discussed, based on the extensions of the SIR model.

Implications of partial immunity on the prospects for tuberculosis control by post-exposure interventions

One-third of the world population (approximately 2 billion individuals) is currently infected with Mycobacterium tuberculosis, the vast majority harboring a latent infection. As the risk of reactivation is around 10% in a lifetime, it follows that 200 million of these will eventually develop active pulmonary disease. Only therapeutic or post-exposure interventions can tame this vast reservoir of infection. Treatment of latent infections can reduce the risk of reactivation, and there is accumulating evidence that combination with post-exposure vaccines can reduce the risk of reinfection. Here we develop mathematical models to explore the potential of these post-exposure interventions to control tuberculosis on a global scale. Intensive programs targeting recent infections appear generally effective, but the benefit is potentially greater in intermediate prevalence scenarios. Extending these strategies to longer-term persistent infections appears more beneficial where prevalence is low. Finally, we consider that susceptibility to reinfection is altered by therapy, and explore its epidemiological consequences. When we assume that therapy reduces susceptibility to subsequent reinfection, catastrophic dynamics are observed. Thus, a bipolar outcome is obtained, where either small or large reductions in prevalence levels result, depending on the rate of detection and treatment of latent infections. By contrast, increased susceptibility after therapy may induce an increase in disease prevalence and does not lead to catastrophic dynamics. These potential outcomes are silent unless a widespread intervention is implemented.

Molecular and serological characterization of hepatitis B virus in deferred Ghanaian blood donors with and without elevated alanine aminotransferase

Candidate blood donors in Ghana are frequent carriers of hepatitis B virus (HBV). A comparative study of 117 donor samples including 46 with alanine aminotransferase (ALT) > or = 60 IU/L and 71 with < or =40 IU/L level was undertaken. S and the basic core promoter-precore regions (BCP/PC) sequencing was used to identify genotypes and variants relevant to HBV natural history, respectively. Age, viral load, HBe status were correlated with molecular data. HBV genotype E (87%) was dominant with little genotypes A (10%) and D (3%). Comparing individuals with or without liver disease, an association between liver disease and older age (P = 0.004) and higher viral load (P = 0.002) whether as a whole population or only genotype E was found. Compared with a commercial assay, BCP/PC sequencing had lower sensitivity to detect mixtures of wild-type and variant viruses but detected BCP deletions. BCP 1762/1764 variants were positively correlated with older age (P < 0.0001) and elevated ALT levels (P = 0.01). PC 1896 stop codon was marginally correlated with viral load (P = 0.09). HBV genotype E infection natural history appears different from genotypes B and C prevalent in Asia. Donors with liver disease being older, with higher viral load and higher BCP variant proportion may be at higher risk of cirrhosis and hepatocellular carcinoma.

Modelling the impact of prison vaccination on hepatitis B transmission within the injecting drug user population of England and Wales

A vaccination programme offering hepatitis B (HBV) vaccine at reception into prison has been introduced into selected prisons in England and Wales. The work here considers the impact of prison vaccination on the incidence and prevalence of hepatitis B virus (HBV) in the injecting drug user (IDU) population of England and Wales. A dynamic model of the transmission of HBV in IDUs is developed with key model assumptions and parameters being subject to sensitivity analyses. The base case model (that assumes that the vaccination coverage on prison reception is 5% in 2002, 10% in 2003 and then increases linearly up to 50% of prison receptions being vaccinated by 2006) predicts that the incidence of HBV in IDUs might be reduced by almost 80% in 12 years, and the HBV prevalence (IDUs ever infected by HBV) may be reduced from approximately 18% in 2002 to 7% in 2015. The model presented here demonstrates that HBV vaccination on prison reception can have a significant impact on the prevalence and incidence of HBV in the IDU population over time.

Pathogen adaptation under imperfect vaccination: implications for pertussis

Mass vaccination campaigns have drastically reduced the burden of infectious diseases. Unfortunately, in recent years several infectious diseases have re-emerged. Pertussis poses a well-known example. Inspired by pertussis, we study, by means of an epidemic model, the population and evolutionary dynamics of a pathogen population under the pressure of vaccination. A distinction is made between infection in immunologically naive individuals (primary infection) and infection in individuals whose immune system has been primed by vaccination or infection (secondary infection). The results show that (i) vaccination with an imperfect vaccine may not succeed in reducing the infection pressure if the transmissibility of secondary infections is higher than that of primary infections; (ii) pathogen strains that are able to evade the immunity induced by vaccination can only spread if escape mutants incur no or only a modest fitness cost and (iii) the direction of evolution depends crucially on the distribution of the different types of susceptibles in the population. We discuss the implications of these results for the design and use of vaccines that provide temporary immunity.

Future trends of HCV-related cirrhosis and hepatocellular carcinoma under the currently available treatments

The epidemic of hepatitis C virus (HCV) infection is a major public health issue. We conducted a comprehensive analysis to estimate future HCV-related morbidity and mortality, using a model which is the first to take into account currently available treatments. We reconstructed the incident infections per year in the past that progressed to chronic hepatitis C (CHC) in Greece. Then, the natural history of the disease was simulated in subcohorts of newly infected subjects in the presence or absence of treatment using yearly estimates of the number of treated patients obtained from national databases. Annual estimates of the incidence and prevalence of CHC by fibrosis stage, hepatocellular carcinoma (HCC) and mortality were obtained up to 2030. The current proportion of naïve CHC patients receiving treatment in Greece is 1.2% per year. Treatment of 1.2-10% of naïve CHC patients per year would reduce the cumulative number of incident cirrhosis and HCC cases from 2002 to 2030 by 10.8-39.4% and 12.8-39.8%, respectively and decrease the number of prevalent cirrhosis and HCC cases in 2030 by approximately 17-48% compared with the number estimated under the assumption of no treatment. Approximately 17 cirrhosis cases or six HCC cases or 10 premature deaths would be prevented for every 100 treated patients. However, the prevalent cirrhotic/HCC cases because of HCV and HCV-related deaths would not plateau until 2030. Despite the introduction of effective treatment, HCV-related morbidity and mortality will likely increase during the next 20-30 years in Greece. Intensive primary prevention efforts coupled with increased access to the currently available treatments are necessary to control the chronic consequences of HCV epidemic.

Mathematical model of influenza A virus production in large-scale microcarrier culture

A mathematical model that describes the replication of influenza A virus in animal cells in large-scale microcarrier culture is presented. The virus is produced in a two-step process, which begins with the growth of adherent Madin-Darby canine kidney (MDCK) cells. After several washing steps serum-free virus maintenance medium is added, and the cells are infected with equine influenza virus (A/Equi 2 (H3N8), Newmarket 1/93). A time-delayed model is considered that has three state variables: the number of uninfected cells, infected cells, and free virus particles. It is assumed that uninfected cells adsorb the virus added at the time of infection. The infection rate is proportional to the number of uninfected cells and free virions. Depending on multiplicity of infection (MOI), not necessarily all cells are infected by this first step leading to the production of free virions. Newly produced viruses can infect the remaining uninfected cells in a chain reaction. To follow the time course of virus replication, infected cells were stained with fluorescent antibodies. Quantitation of influenza viruses by a hemagglutination assay (HA) enabled the estimation of the total number of new virions produced, which is relevant for the production of inactivated influenza vaccines. It takes about 4-6 h before visibly infected cells can be identified on the microcarriers followed by a strong increase in HA titers after 15-16 h in the medium. Maximum virus yield Vmax was about 1x10(10) virions/mL (2.4 log HA units/100 microL), which corresponds to a burst size ratio of about 18,755 virus particles produced per cell. The model tracks the time course of uninfected and infected cells as well as virus production. It suggests that small variations (<10%) in initial values and specific rates do not have a significant influence on Vmax. The main parameters relevant for the optimization of virus antigen yields are specific virus replication rate and specific cell death rate due to infection. Simulation studies indicate that a mathematical model that neglects the delay between virus infection and the release of new virions gives similar results with respect to overall virus dynamics compared with a time delayed model.

Dynamical behaviour of epidemiological models with sub-optimal immunity and nonlinear incidence

In this paper we analyze the dynamics of two families of epidemiological models which correspond to transitions from the SIR (susceptible-infectious-resistant) to the SIS (susceptible-infectious-susceptible) frameworks. In these models we assume that the force of infection is a nonlinear function of density of infectious individuals, I. Conditions for the existence of backwards bifurcations, oscillations and Bogdanov-Takens points are given.

Structured model of influenza virus replication in MDCK cells

Intracellular events that take place during influenza virus replication in animal cells are well understood qualitatively. However, to better understand the complex interaction of the virus with its host cell and to quantitatively analyze the use of cellular resources for virion formation or the overall dynamic for the entire infection cycle, a mathematical model for influenza virus replication has to be formulated. Here, we present a structured model for the single-cell reproductive cycle of influenza A virus in animal cells that accounts for the individual steps of the process such as attachment, internalization, genome replication and translation, and progeny virion assembly. The model describes an average cell surrounded by a small quantity of medium and infected by a low number of virus particles. The model allows estimation of the cellular resources consumed by virus replication. Simulation results show that the number of cellular surface receptors and endosomes, as well as other resources, such as the number of free nucleotides or amino acids, is not significantly influenced by influenza virus propagation. A factor that limits the growth rate of progeny viruses and their release is the total amount of matrix proteins (M1) in the nucleus while other newly synthesized viral proteins (e.g., nucleoprotein NP) and viral RNAs accumulate. During budding, synthesis of vRNPs (viral ribonucleoprotein complexes) represents another limiting factor. Based on this model it is also possible to analyze effects of parameter changes on the dynamics of virus replication, to identify possible targets for molecular engineering, or to develop strategies for improving yields in vaccine production processes. Furthermore, a better insight into the interactions of viruses and host cells might help to improve our understanding of virus-related diseases and to develop therapies.

The reinfection threshold promotes variability in tuberculosis epidemiology and vaccine efficacy

Population patterns of infection are determined largely by susceptibility to infection. Infection and vaccination induce an immune response that, typically, reduces susceptibility to subsequent infections. With a general epidemic model, we detect a 'reinfection threshold', above which reinfection is the principal type of transmission and, consequently, infection levels are much higher and vaccination fails. The model is further developed to address human tuberculosis (TB) and the impact of vaccination. The bacille Calmette-Guérin (BCG) is the only vaccine in current use against TB, and there is no consensus about its usefulness. Estimates of protection range from 0 to 80%, and this variability is aggravated by an association between low vaccine efficacy and high prevalence of the disease. We propose an explanation based on three postulates: (i) the potential for transmission varies between populations, owing to differences in socio-economic and environmental factors; (ii) exposure to mycobacteria induces an immune response that is partially protective against reinfection; and (iii) this protection is not significantly improved by BCG vaccination. These postulates combine to reproduce the observed trends, and this is attributed to a reinfection threshold intrinsic to the transmission dynamics. Finally, we demonstrate how reinfection thresholds can be manipulated by vaccination programmes, suggesting that they have a potentially powerful role in global control.

Incidence and routes of transmission of hepatitis B virus in England and Wales, 1995–2000: implications for immunisation policy

BACKGROUND

The incidence of hepatitis B virus (HBV) infection in the UK is low. Since the infection can have serious sequelae, there is a continuing need to examine its epidemiology so as to inform control measures.

OBJECTIVES

We aimed to describe the current HBV incidence and patterns of transmission in the UK, to estimate the rate of new carrier infections, and to discuss implications for the control of HBV through immunisation.

STUDY DESIGN

We analysed routine England and Wales laboratory surveillance data of acute HBV infection (1995-2000) and data on migration and global HBsAg prevalence.

RESULTS

The estimated annual incidence of HBV infection in England and Wales was 7.4 per 100,000. Injecting drug use was the most frequently reported route of transmission. The number of cases attributed to heterosexual contact was fairly stable, whereas the number of cases in men having sex with men decreased. These observations continue trends reported for the early 1990s. Transmission during childhood was rarely reported, but was more frequent among South Asians. The incidence in South Asians is relatively high, and their main risk factors are medical treatment overseas and heterosexual contact. For about a third of cases of acute HBV infection no route of transmission is reported, but analysis of secular trends and age distribution suggest that many of these may be related to injecting drug use. Endemic transmission gives rise to only a small proportion of all new chronic infections, with the vast majority arising from immigration of established HBV carriers.

CONCLUSIONS

The incidence of acute HBV infection in England and Wales has remained low, with a similar pattern of reported routes of transmission compared to the early 1990s. The UK prevalence of HBV infection is dependant on global rather than national immunisation policy. Endemic transmission may be reduced by improving immunisation coverage among injecting drug users, which is expected to also reduce the number of cases without a risk factor reported. In addition, immunisation options that better suit the needs of ethnic minorities need to be explored.

Increase in susceptibility of young adults to hepatitis B infection in the Republic of Yemen

Susceptibility to hepatitis B virus (HBV) infection among 987 young adult male blood donors in 2 major Yemeni cities was investigated. Hepatitis B surface antigen (HBsAg) was detected in 10.8% (107/987) of donors and 284 (28.8%) had evidence of ongoing or past HBV infection. Hepatitis B surface antibody (anti-HBs) only was detected in 34 (3.4%) donors. Thus, 67.8% (669/987) of donors had no detectable HBV-markers indicating susceptibility to infection. The proportion of HBV-susceptible donors decreased from 70.9% (249/351) in donors aged < 25 years to 69.4% (334/481) in those aged 25-34 years and 55.5% (86/155) in donors aged > 34 years (P = 0.002). The high proportion of susceptible young adults in a community with a high HBsAg carrier rate could be the result of changing epidemiology of hepatitis B in Yemen. Consideration should therefore be given to immunizing young adults as an adjunct to the current expanded infant immunization programme.

Assessment of cost-effectiveness of universal hepatitis B immunization in a low-income country with intermediate endemicity using a Markov model

BACKGROUND/AIMS

Most countries with high hepatitis B (HB) virus endemicity and most high-income countries have introduced immunization programmes against this infection. However, several low-income countries with intermediate HB endemicity have not done so. We performed a cost-effectiveness analysis of universal childhood HB immunization in such countries using India as an example, since available data on this aspect are limited.

METHODS

Marginal cost of every life-year and quality-adjusted life-year (QALY) gained with universal HB vaccination was calculated using a Markov model. Two types of analyses (including and excluding expenditure on treatment of long-term complications of HB infection) were done. Several sensitivity analyses and Monte-Carlo simulation were performed.

RESULTS

Universal immunization reduced the HB carrier rate by 71%, and increased the number of years and QALY lived by a birth-cohort by 0.173 years (61.072 vs. 60.899 years) and 0.213 years (61.056 vs. 60.843 years), respectively. Marginal costs were US$16.27 per life-year gained and US$13.22 per QALY gained, much lower than annual per capita income. One-way sensitivity analysis and Monte-Carlo simulation confirmed the robustness of the conclusions.

CONCLUSIONS

Universal HB immunization is highly cost-effective in low-income countries with intermediate endemicity rates.

Results of an enhanced-outreach programme of hepatitis B vaccination in the Netherlands (1998-2000) among men who have sex with men, hard drug users, sex workers and heterosexual persons with multiple partners

BACKGROUND/AIMS

The Dutch Ministry of Health funded a pilot vaccination project targeting groups at high risk for sex- and drug-related hepatitis B transmission.

METHODS

In seven Municipal Health Service (MHS) areas, three-part hepatitis B vaccination was offered free to men who have sex with men (MSM), drug users (DUs), and heterosexuals with multiple partners, including sex workers (SWs). Four intervention areas recruited participants through care-givers and opinion leaders and offered vaccination at non-MHS sites. Three control areas only used flyers to offer vaccination at MHS during regular hours.

RESULTS

Over 18 months, 13808 persons enrolled for the first vaccination, representing 63% of the targeted population in the intervention areas and 23% in control areas. In intervention areas, only 19% of DUs enrolled, versus 4% in control areas. In both areas, enrollment of the targeted heterosexual population (64%) was satisfactory. MSM were most compliant in having the full series. Of vaccination sources, general practitioners (GPs) attained highest compliance (71%, odds ratio 1.82).

CONCLUSIONS

Dutch MHS facilities can reach high-risk individuals, but DUs require additional outreach. Vaccine coverage was disappointing, but our experience will be deployed nationwide and successful strategies might be employed elsewhere in countries of low endemicity.