Long-term immunogenicity of an inactivated virosome hepatitis A vaccine

Sex differences in hepatitis A incidence rates-a multi-year pooled-analysis based on national data from nine high-income countries

BACKGROUND

Possible sex differences in hepatitis A virus (HAV) incidence rates in different age groups are not well documented. We aimed to obtain stable pooled estimates of such differences based on data from a number of high-income countries.

METHODS

We obtained data on incident cases of HAV by sex and age group over a period of 6-25 years from nine countries: Australia, Canada, Czech Republic, Finland, Germany, Israel, Netherland, New Zealand and Spain. Male to female incidence rate ratios (IRR) were computed for each year, by country and age group. For each age group, we used meta-analytic methods to combine the IRRs. Meta-regression was conducted to estimate the effects of age, country, and time period on the IRR.

RESULTS

A male excess in incidence rates was consistently observed in all age groups, although in the youngest and oldest age groups, where the numbers tended to be lower, the lower bounds of the 95% confidence intervals for the IRRs were less than one. In the age groups <1, 1-4, 5-9, 10-14, 15-44, 45-64 and 65+, the pooled IRRs (with 95% CI) over countries and time periods were 1.18 (0.94,1.48), 1.22 (1.16,1.29), 1.07 (1.03,1.11), 1.09 (1.04,1.14), 1.46 (1.30,1.64), 1.32 (1.15,1.51) and 1.10 (0.99,1.23) respectively.

CONCLUSIONS

The excess HAV incidence rates in young males, pooled over a number of countries, suggest that the sex differences are likely to be due at least in part to physiological and biological differences and not just behavioral factors. At older ages, differential exposure plays an important role. These findings, seen in the context of the excess incidence rates in young males for many other infectious diseases, can provide further keys to the mechanisms of the infection.

Within-host modeling to measure dynamics of antibody responses after natural infection or vaccination: A systematic review

BACKGROUND

Within-host models describe the dynamics of immune cells when encountering a pathogen, and how these dynamics can lead to an individual-specific immune response. This systematic review aims to summarize which within-host methodology has been used to study and quantify antibody kinetics after infection or vaccination. In particular, we focus on data-driven and theory-driven mechanistic models.

MATERIALS

PubMed and Web of Science databases were used to identify eligible papers published until May 2022. Eligible publications included those studying mathematical models that measure antibody kinetics as the primary outcome (ranging from phenomenological to mechanistic models).

RESULTS

We identified 78 eligible publications, of which 8 relied on an Ordinary Differential Equations (ODEs)-based modelling approach to describe antibody kinetics after vaccination, and 12 studies used such models in the context of humoral immunity induced by natural infection. Mechanistic modeling studies were summarized in terms of type of study, sample size, measurements collected, antibody half-life, compartments and parameters included, inferential or analytical method, and model selection.

CONCLUSIONS

Despite the importance of investigating antibody kinetics and underlying mechanisms of (waning of) the humoral immunity, few publications explicitly account for this in a mathematical model. In particular, most research focuses on phenomenological rather than mechanistic models. The limited information on the age groups or other risk factors that might impact antibody kinetics, as well as a lack of experimental or observational data remain important concerns regarding the interpretation of mathematical modeling results. We reviewed the similarities between the kinetics following vaccination and infection, emphasising that it may be worth translating some features from one setting to another. However, we also stress that some biological mechanisms need to be distinguished. We found that data-driven mechanistic models tend to be more simplistic, and theory-driven approaches lack representative data to validate model results.

Hepatitis A vaccine immunogenicity 25 years after vaccination in Alaska

The hepatitis A vaccine is recommended for all children greater than or equal to 1 year of age, however, the duration of vaccine protection is unknown and protection through adulthood is crucial to prevent symptomatic hepatitis later in life. We report on 25 years of follow-up of a cohort of Alaska Native individuals who were vaccinated in early childhood. We assessed the duration of vaccine protection by calculating the geometric mean concentration and proportion of participants with protective levels of IgG antibody to hepatitis A virus (anti-HAV) (≥20 mIU/mL) every 2 to 3 years. We estimated the amount of time until the anti-HAV dropped below protective levels using survival analyses. At 25 years, 43 of the original 144 participants were available, mean anti-HAV levels were 91.5 mIU/mL, and 35 (81.4%) had protective levels of anti-HAV. Using data from all persons and all time points, a survival analysis estimated 78.7% of participants had protective levels of anti-HAV at 25 years. The high level of protective antibodies in this cohort indicate that supplemental doses of hepatitis A vaccine are not needed 25 years after completion of the vaccine series.

Hepatitis A vaccination and its immunological and epidemiological long-term effects - a review of the evidence

Hepatitis A virus (HAV) infections continue to represent a significant disease burden causing approximately 200 million infections, 30 million symptomatic illnesses and 30,000 deaths each year. Effective and safe hepatitis A vaccines have been available since the early 1990s. Initially developed for individual prophylaxis, HAV vaccines are now increasingly used to control hepatitis A in endemic areas. The human enteral HAV is eradicable in principle, however, HAV eradication is currently not being pursued. Inactivated HAV vaccines are safe and, after two doses, elicit seroprotection in healthy children, adolescents, and young adults for an estimated 30-40 years, if not lifelong, with no need for a later second booster. The long-term effects of the single-dose live-attenuated HAV vaccines are less well documented but available data suggest they are safe and provide long-lasting immunity and protection. A universal mass vaccination strategy (UMV) based on two doses of inactivated vaccine is commonly implemented in endemic countries and eliminates clinical hepatitis A disease in toddlers within a few years. Consequently, older age groups also benefit due to the herd protection effects. Single-dose UMV programs have shown promising outcomes but need to be monitored for many more years in order to document an effective immune memory persistence. In non-endemic countries, prevention efforts need to focus on 'new' risk groups, such as men having sex with men, prisoners, the homeless, and families visiting friends and relatives in endemic countries. This narrative review presents the current evidence regarding the immunological and epidemiological long-term effects of the hepatitis A vaccination and finally discusses emerging issues and areas for research.

Lipid-based nanoparticle formulations for small molecules and RNA drugs

Introduction: Liposomes and lipid-based nanoparticles (LNPs) effectively deliver cargo molecules to specific tissues, cells, and cellular compartments. Patients benefit from these nanoparticle formulations by altered pharmacokinetic properties, higher efficacy, or reduced side effects. While liposomes are an established delivery option for small molecules, Onpattro® (Sanofi Genzyme, Cambridge, MA) is the first commercially available LNP formulation of a small interfering ribonucleic acid (siRNA). Areas covered: This review article summarizes key features of liposomal formulations for small molecule drugs and LNP formulations for RNA therapeutics. We describe liposomal formulations that are commercially available or in late-stage clinical development and the most promising LNP formulations for ASOs, siRNAs, saRNA, and mRNA therapeutics. Expert opinion: Similar to liposomes, LNPs for RNA therapeutics have matured but still possess a niche application status. RNA therapeutics, however, bear an immense hope for difficult to treat diseases and fuel the imagination for further applications of RNA drugs. LNPs face similar challenges as liposomes including limitations in biodistribution, the risk to provoke immune responses, and other toxicities. However, since properties of RNA molecules within the same group are very similar, the entire class of therapeutic molecules would benefit from improvements in a few key parameters of the delivery technology.

Factors That Influence the Immune Response to Vaccination

There is substantial variation between individuals in the immune response to vaccination. In this review, we provide an overview of the plethora of studies that have investigated factors that influence humoral and cellular vaccine responses in humans. These include intrinsic host factors (such as age, sex, genetics, and comorbidities), perinatal factors (such as gestational age, birth weight, feeding method, and maternal factors), and extrinsic factors (such as preexisting immunity, microbiota, infections, and antibiotics). Further, environmental factors (such as geographic location, season, family size, and toxins), behavioral factors (such as smoking, alcohol consumption, exercise, and sleep), and nutritional factors (such as body mass index, micronutrients, and enteropathy) also influence how individuals respond to vaccines. Moreover, vaccine factors (such as vaccine type, product, adjuvant, and dose) and administration factors (schedule, site, route, time of vaccination, and coadministered vaccines and other drugs) are also important. An understanding of all these factors and their impacts in the design of vaccine studies and decisions on vaccination schedules offers ways to improve vaccine immunogenicity and efficacy.

Liposomal Formulations in Clinical Use: An Updated Review

Liposomes are the first nano drug delivery systems that have been successfully translated into real-time clinical applications. These closed bilayer phospholipid vesicles have witnessed many technical advances in recent years since their first development in 1965. Delivery of therapeutics by liposomes alters their biodistribution profile, which further enhances the therapeutic index of various drugs. Extensive research is being carried out using these nano drug delivery systems in diverse areas including the delivery of anti-cancer, anti-fungal, anti-inflammatory drugs and therapeutic genes. The significant contribution of liposomes as drug delivery systems in the healthcare sector is known by many clinical products, e.g., Doxil®, Ambisome®, DepoDur™, etc. This review provides a detailed update on liposomal technologies e.g., DepoFoam™ Technology, Stealth technology, etc., the formulation aspects of clinically used products and ongoing clinical trials on liposomes.

Immunogenicity and estimation of antibody persistence following vaccination with an inactivated virosomal hepatitis A vaccine in adults: A 20-year follow-up study

PURPOSE

This was a 20-year follow-up study to assess long-term persistence of protective antibody levels against the hepatitis A virus (HAV) in healthy participants vaccinated with 2 doses of inactivated hepatitis A vaccine (Epaxal®) between 1992 and 1995.

METHODS

Blood samples for anti-HAV antibody concentrations were obtained during a follow-up visit 20years after vaccination and were analyzed in parallel with samples still available from previous visits using AxSYM® HAVAB 2.0 assay.

RESULTS

Mean (SD) age of the participants was 44.71 (3.905) years at year 20 follow-up (N=95). Participants completing 0/12-month Epaxal® immunization regimen (N=94) had seroprotection rate of 100% (95% CI: 96.2, 100.0) with ⩾10mIU/mL seropositivity cut-off and 98.9% (95% CI: 94.2, 100.0) with ⩾20mIU/mL cut-off. With ⩾10mIU/mL cut-off, the estimated median duration of protection was 77.3years (95% CI: 71.8, 83.5) with 95% of the vaccinated participants predicted to be protected for at least 41.5years. At ⩾20mIU/mL cut-off, the estimated median duration of protection was 64.8years (95% CI: 60.1, 68.4) with 95% of the vaccinated participants predicted to be protected for at least 33years. Anti-HAV antibody geometric mean concentrations were higher in women (277.9; 95% CI: 217.7, 354.7) than in men (167.7; 95% CI: 125.2, 224.6).

CONCLUSION

The data from this 20-year follow-up study confirm previous observations that two doses of Epaxal® provide protection against hepatitis A infection for at least 30years in over 95% of healthy participants.

Predictors of durable immune responses six months after the last vaccination in preventive HIV vaccine trials

BACKGROUND

The evaluation of durable immune responses is important in HIV vaccine research and development. The efficiency of such evaluation could be increased by incorporating predictors of the responses in the statistical analysis. In this paper, we investigated whether and how baseline demographic variables and immune responses measured two weeks after vaccination predicted durable immune responses measured six months later.

METHODS

We included data from seven preventive HIV vaccine regimens evaluated in three clinical trials: a Phase 1 study of four DNA, NYVAC and/or AIDSVAX vaccine regimens (HVTN096), a Phase 2 study of two DNA and/or MVA vaccine regimens (HVTN205), and a Phase 3 study of a single ALVAC/AIDSVAX regimen (RV144). Regularized random forests and linear regression models were used to identify and evaluate predictors of the positivity and magnitude of durable immune responses.

RESULTS

We analyzed 201 vaccine recipients with data from 10 to 127 immune response biomarkers, and 3-5 demographic variables. The best prediction of participants' durable response positivity based on two-week responses rendered up to close-to-perfect accuracy; the best prediction of participants' durable response magnitude rendered correlation coefficients between the observed and predicted responses ranging up to 0.91. Though prediction performances differed among biomarkers, durable immune responses were best predicted by the two-week response level of the same biomarker. Adding demographic information and two-week response levels of different biomarkers provided little or no improvement in the predictions.

CONCLUSIONS

For some biomarkers and for the vaccines we studied, two-week post-vaccination responses can well predict durable responses six months later. Therefore, if immune response durability is only assessed in a sub-sample of vaccine recipients, statistical analyses of durable responses will have increased efficiency by incorporating two-week response data. Further research is needed to generalize the findings to other vaccine regimens and biomarkers. Clinicaltrials.gov identifiers: NCT01799954, NCT00820846, NCT00223080.

Comparison of immunogenicity and persistence between inactivated hepatitis A vaccine Healive® and Havrix® among children: A 5-year follow-up study

BACKGROUND

Inactivated vaccines for hepatitis A virus (HAV) infection are widely used in China. Mass vaccination programs drive the need for data on long-term persistence of vaccine-induced protection.

METHODS

A prospective, randomized, open-label clinical trial was conducted to compare geometric mean concentrations (GMCs) and seroconversion rates (SRs) of anti-HAV antibody elicited by the inactivated vaccines Healive and Havrix for 5 y post immunization, in which 400 healthy children were randomly assigned in a 3:1 ratio to receive 2 doses of Healive or Havrix at 0 and 6 month. Anti-HAV antibody concentration was detected by microparticle enzyme immunoassay (MEIA) during the study. Furthermore, an attempt was made to predict persistence of protective immunogenicity by using a suitable statistical model.

RESULTS

The GMCs were significantly higher after vaccination with Healive than after Havrix as comparator vaccine at 1, 6, 7, 18, 30, 42, 54 and 66 month (P < 0.01) with the peak point at 7 month (3427.2 mIU/ml for Healive and 1441.9 mIU/ml for Comparator). Similarly significant differences of SRs were found between the 2 groups at 1 and 6 month (P < 0.01). Afterwards, the SRs of both groups reached 100% at 7 month and did not decline until 66 month(99.1% for Healive and 97.5% for Comparator). A linear mixed model with a change point at 18 month(Model 3) was found to be suitable to predict persistence of protective immunogenicity induced by vaccines. It was estimated that the duration of protection for Healive was at least 20 y with a lower limit of GMC 95% confidence interval (CI) no less than 20 mIU/mL.

CONCLUSIONS

Compared with Havrix, the new preservative-free inactivated hepatitis A vaccine (Healive) in 2 doses showed better persistence of antibody concentrations for 5 y after full-course immunization among children and the persistence of protective immunogenicity was estimated for at least 20 y.

Long-term Serologic Follow-up of Children Vaccinated with a Pediatric Formulation of Virosomal Hepatitis A Vaccine Administered With Routine Childhood Vaccines at 12-15 Months of Age

BACKGROUND

The aim of this open-label, active-controlled, parallel group, phase 2 follow-up study was to assess the long-term immunogenicity of Epaxal Junior, the pediatric dose of an aluminum-free virosomal inactivated hepatitis A virus (HAV) vaccine, in children receiving routine childhood vaccines (RCV).

METHODS

Healthy children (12-15 months old, ≥8 kg weight) were randomized (1:1:1) to group A: Epaxal Junior + RCV (day 1); group B: Epaxal Junior (day 1) + RCV (day 29) and group C: Havrix 720 + RCV (day 1). All 3 groups received 2 doses of HAV vaccines 6 months apart. Children who completed the primary study were followed up from 18 months to 7.5 years post booster.

RESULTS

Of 291/327 randomized children who had completed the primary study, 157 were followed for the 7.5-year analysis (group A: 50; group B: 54; and group C: 53). Of these, 152 children had protective levels of anti-HAV antibodies [≥10 mIU/mL; 98% (group A); 96.3% (group B); 96.2% (group C)]. Anti-HAV geometric mean concentrations were similar in groups A and B at all the time points (1.5-, 2.5-, 3.5-, 5.25- and 7.5-year time point) but slightly lower in group C. Predictions of the median duration of persistence of seroprotective antibody levels, using the linear mixed model were similar in all groups: (group A: 19.1 years, group B: 18.7 years, group C: 17.3 years).

CONCLUSIONS

Immunization with Epaxal Junior administered with RCVs at 12 months elicited protective response beyond 7.5 years in almost all children. Assessing the kinetic of anti-HAV antibody titers decline over time, the moment to reach antibody concentrations below the accepted protective level may occur earlier than previously estimated.

Immunogenicity and safety of a pediatric dose of a virosomal hepatitis A vaccine in healthy children in India

As India is transitioning from high to intermediate hepatitis A endemicity, the need for hepatitis A vaccination programs increases. This study investigated the immunogenicity and safety of a virosomal hepatitis A vaccine (HAVpur Junior) compared with an aluminum-adsorbed hepatitis A vaccine (Havrix 720 Junior) in Indian children. Healthy children aged 18-47 months, stratified by age, were randomized to either HAVpur Junior or Havrix 720 Junior. The first dose of vaccine was administered on Day 1 and the second (booster) dose 6 months later. Antibodies against hepatitis A virus (HAV) were measured using a microparticle enzyme immunoassay. The primary objective assessed non-inferiority of HAVpur Junior to Havrix 720 Junior in terms of seroprotection rates (≥ 10 mIU/mL anti-HAV antibodies) at 1 month after the first vaccination. Non-inferiority was demonstrated if the lower limit of the 90% confidence interval of the group difference was greater than -10%. Local and systemic adverse events were recorded. The seroprotection rate at 1 month was 95.9% in the HAVpur Junior group and 96.6% in the Havrix 720 Junior group. As the lower limit of the 90% confidence interval of the group difference was greater than -10% (-4.7), non-inferiority of HAVpur Junior to Havrix 720 Junior was established. The overall incidence of adverse events (solicited and unsolicited) after each vaccination was similar in both groups. In conclusion, the aluminum-free virosomal vaccine HAVpur Junior induced a similar immune response to Havrix 720 Junior in healthy Indian children aged 18 to 47 months. Both vaccines were well tolerated. The study shows that the low-dose virosomal HAV vaccine is consistently efficacious and well tolerated in children of all age groups and is suitable for inclusion into Indian childhood vaccination schedules.

Modeling the long-term antibody response of a hepatitis E vaccine

BACKGROUND

The first commercialized hepatitis E vaccine, HEV 239, has been shown to be safe and highly immunogenic, the protection as well as the vaccine-induced anti-HEV maintained for at least 4.5 years. However, the longer term persistence of the vaccine-induced anti-HEV responses is unknown.

METHODS

Two statistical models, the power-law model and the modified power-law model, were applied to predict the long-term antibody response of the HEV 239 vaccine. The models were fit using the anti-HEV IgG data from a modeling subpopulation of 1278 baseline seronegative vaccinees who seroconverted within one month after finishing the whole vaccination course in the phase 3 trial of HEV 239. In addition, antibody data from a validation subpopulation were used to validate the robustness of the derived models.

RESULTS

In the vaccinees without pre-vaccination immunity, the power-law model and the modified power-law model estimated that the median duration of the detectable antibody (≥0.077 WU/ml) was 8 years and 13 years, respectively. The power-law model and the modified power-law model estimated that 50% of these vaccinees will maintain detectable levels of anti-HEV IgG for 8 years and >30 years, respectively.

CONCLUSIONS

The recombinant hepatitis E vaccine HEV 239 is predicted to provide from 8 years to nearly life-long persistence of anti-HEV IgG above detectable levels. Model predictions are based on conservative mathematical assumptions. (NCT01014845).

Long-term antibody persistence in children after vaccination with the pediatric formulation of an aluminum-free virosomal hepatitis A vaccine

BACKGROUND

The pediatric dose of the virosomal hepatitis A vaccine Epaxal, Epaxal Junior, is safe and immunogenic in children from 1 to 17 years of age. The present study investigated the long-term immunogenicity of Epaxal Junior. The standard doses of Epaxal and aluminum-adsorbed hepatitis A vaccine (Havrix Junior) were used as comparators.

METHODS

A total of 271 children who had completed a 0/6-month immunization schedule (priming and booster dose) participated in this follow-up study. Anti-hepatitis A virus (HAV) antibody levels were measured using a microparticle enzyme immunoassay (HAVAB 2.0 Quantitative; Abbott Diagnostics, Wiesbaden, Germany) starting at 18 months following the second dose, and then yearly until 66 months (ie, 5.5 years) after the second dose.

RESULTS

All subjects tested at Month 66 still had protective anti-HAV antibodies (≥10 mIU/mL). Antibody titers were generally lower in subjects 1-7 years old than in subjects 8-17 years old and higher in females 11-17 years old than in males 11-17 years old. In addition, an age-dependent decay was observed, that is, antibody decreased more rapidly in younger than in older children.

CONCLUSIONS

Vaccination of children with two doses of Epaxal Junior confers a real-time protection of at least 5.5 years. This protection is estimated to last approximately 25 years. Younger children showed lower antibody titers and a faster antibody decline than older children. Additional follow-up studies are needed beyond 5.5 years to further assess the long-term immunogenicity of Epaxal Junior.

Model based estimates of long-term persistence of inactivated hepatitis A vaccine-induced antibodies in adults

BACKGROUND

In this paper, we review the results of existing statistical models of the long-term persistence of hepatitis A vaccine-induced antibodies in light of recently available immunogenicity data from 2 clinical trials (up to 17 years of follow-up).

METHODS

Healthy adult volunteers monitored annually for 17 years after the administration of the first vaccine dose in 2 double-blind, randomized clinical trials were included in this analysis. Vaccination in these studies was administered according to a 2-dose vaccination schedule: 0, 12 months in study A and 0, 6 months in study B (NCT00289757/NCT00291876). Antibodies were measured using an in-house ELISA during the first 11 years of follow-up; a commercially available ELISA was then used up to Year 17 of follow-up. Long-term antibody persistence from studies A and B was estimated using statistical models for longitudinal data. Data from studies A and B were modeled separately.

RESULTS

A total of 173 participants in study A and 108 participants in study B were included in the analysis. A linear mixed model with 2 changepoints allowed all available results to be accounted for. Predictions based on this model indicated that 98% (95%CI: 94-100%) of participants in study A and 97% (95%CI: 94-100%) of participants in study B will remain seropositive 25 years after receiving the first vaccine dose. Other models using part of the data provided consistent results: ≥95% of the participants was projected to remain seropositive for ≥25 years.

CONCLUSION

This analysis, using previously used and newly selected model structures, was consistent with former estimates of seropositivity rates ≥95% for at least 25 years.

Review of 10 years of marketing experience with Chinese domestic inactivated hepatitis A vaccine Healive®

In 2002, the first Chinese domestic preservative-free inactivated hepatitis A vaccine, Healive®, was introduced in China. It is highly immunogenic, and provides lasting protection in healthy individuals and generates protective levels of antibodies in other at-risk individuals. Over 10 years since its first licensure, postmarketing surveillance data have confirmed the outstanding safety profile of the vaccine. Comparative clinical trials indicated that Healive® induce equal or similar immunogenicity with other currently available inactivated hepatitis A vaccines and are interchangeable for the course of HAV immunization in Chinese children. The vaccine is effective in curbing outbreaks of hepatitis A due to rapid seroconversion and the long incubation period of the disease. Additional issues surrounding the use of the vaccine are also reviewed.

Antibody persistence and immune memory in healthy adults following vaccination with a two-dose inactivated hepatitis A vaccine: long-term follow-up at 15 years

Long-term persistence of vaccine-induced immune response in adults was assessed annually for 15 years following primary immunization with a two-dose inactivated hepatitis A vaccine. In 1992, 119 and 194 subjects aged 17-40 years and naïve for hepatitis A virus (HAV) were enrolled in two studies to receive 1,440 ELISA units (El.U) of inactivated hepatitis A vaccine (Havrix™, GlaxoSmithKline Biologicals, Belgium) according to a standard 0, 6 or an extended 0, 12 months schedule, respectively. Serum samples were taken 1 month after the second vaccine dose and every consecutive year up to 15 years after primary vaccination for measurement of anti-HAV antibody concentrations (NCT00291876 and NCT00289757). At year 15, 100% (48/48) and 97.3% (108/111) of subjects vaccinated at 0, 6 or 0, 12 months remained seropositive for anti-HAV antibodies, with geometric mean concentrations (GMCs) of 289.2 and 367.4 mIU/ml, respectively. An additional dose of HAV vaccine (1,440 El.U) was administered to the six subjects who had become seronegative for anti-HAV antibodies since year 11. All subjects mounted a humoral immune response to the additional HAV challenge dose, although post-challenge anti-HAV antibody levels remained low in one subject. These studies represent the longest annual follow-up of hepatitis A vaccine in healthy adults. The immune response induced by two doses of this inactivated HAV vaccine was shown to persist for at least 15 years. No difference in long-term antibody persistence was observed between the two primary vaccination schedules, reinforcing the potential for flexibility in the timing of the second primary vaccine dose.

Travel health: routine, recommended and required vaccines

Vaccines are an important public health measure and may be the prompt for travellers to attend for pre-travel health advice. Nurses involved in the provision of travel health advice require a sound knowledge of available vaccines together with the diseases they prevent and other risk management strategies. Travel vaccines should always be administered following a travel health consultation and risk assessment, taking into account the informed choice of the traveller. This paper discusses vaccine preventable disease in the context of travel health, and the appropriate use of routine, recommended and required pre-travel vaccines, which can be considered following individual risk assessment.

Immunogenicity and safety of combined adsorbed low-dose diphtheria, tetanus and inactivated poliovirus vaccine (REVAXIS (®)) versus combined diphtheria, tetanus and inactivated poliovirus vaccine (DT Polio (®)) given as a booster dose at 6 years of age

This randomized, comparative, phase-IIIb study conducted in France aimed to demonstrate whether seroprotection against diphtheria, tetanus and poliomyelitis 1 month after a single dose of REVAXIS (low-dose diphtheria) is non-inferior to seroprotection 1 month after a single dose of DT Polio (standard-dose diphtheria), both vaccines being given as a second booster to healthy children at 6 years of age. Children were randomly assigned to receive a single intramuscular dose of REVAXIS or DT Polio. Primary endpoints were the 1-month post-booster seroprotection rates for diphtheria, tetanus and poliovirus type-1, -2 and -3 antigens. Secondary endpoints were immunogenicity and safety observations. Of 788 children screened, 760 were randomized: REVAXIS group, 384 children; DT Polio group, 376 children. No relevant difference in demographic characteristics at baseline was observed between REVAXIS and DT Polio groups. Non-inferiority of REVAXIS compared with DT Polio for seroprotection was demonstrated against diphtheria (respectively 98.6% and 99.3%), tetanus (respectively 99.6% and 100%), and poliovirus antigens (100% for each types in both groups). No allergic reactions to REVAXIS were reported. A benefit/risk ratio in favor of REVAXIS was suggested by the trend towards a better tolerability of REVAXIS compared with DT Polio regarding the rate of severe solicited injection-site reactions. The results support the use of REVAXIS as a booster at 6 years of age in infants who previously received a three-dose primary series within the first 6 months of life and a first booster including diphtheria, tetanus and poliovirus vaccine(s) given before 2 years of age.

Epaxal: a virosomal vaccine to prevent hepatitis A infection

Over the last few decades, different types of inactivated hepatitis A virus (HAV) vaccines have been developed: several aluminum-adjuvanted vaccines and an aluminum-free, virosome-formulated vaccine. Both types of vaccines are whole-virus preparations that are produced by growth of HAV strains in human diploid cell cultures and are subsequently inactivated with formaldehyde. This review summarizes all published papers on a virosome-formulated vaccine, Epaxal, based on formalin inactivated HAV (strain RG-SB) adsorbed to the surface of special liposomes (virosomes), that replace aluminum hydroxide as the adjuvant principle. A single injection of virosomal HAV vaccine is well tolerated and highly immunogenic, with 88-97% of seroprotection 2 weeks after a first dose. HAV virosomal vaccine can be administered concomitantly with other vaccines, without inducing antigenic competition. Direct comparison with aluminum-adsorbed vaccine has shown that the immunogenicity was similar, but fewer local reactions were reported with Epaxal. Recent studies in children have demonstrated that Epaxal Junior is also an excellent HAV vaccine for mass vaccination programs.

Has the time come to control hepatitis A globally? Matching prevention to the changing epidemiology

For the first time a global meeting on hepatitis A virus (HAV) infection as vaccine preventable disease was organized at the end of 2007. More than 200 experts from 46 countries gathered to investigate the changing global HAV epidemiology reflecting the increasing numbers of persons at risk for severe clinical disease and mortality from HAV infection. The benefits of childhood and adult hepatitis A (HepA) vaccination strategies and the data needed by individual countries and international health organizations to assess current HepA prevention strategies were discussed. New approaches in preventing HAV infection including universal HepA vaccination were considered. This introductory paper summarizes the major findings of the meeting and describes the changing epidemiology of HAV infections and the impact of HepA vaccination strategies in various countries. Implementation of HepA vaccination strategies should take into account the level of endemicity, the level of the socio-economic development and sanitation, and the risk of outbreaks. A stepwise strategy for introduction of HepA universal immunisation of children was recommended. This strategy should be based on accurate surveillance of cases and qualitative documentation of outbreaks and their control, secure political support on the basis of high-quality results, and comprehensive cost-effectiveness studies. The recognition of the need for increased global attention towards HepA prevention is an important outcome of this meeting.

Sexual dimorphism of humoral immunity with human vaccines

It has been contended that limited data exist on sex-difference in immune response with vaccines in humans. However, a comprehensive search of the literature retrieved 97 studies with 14 vaccines influenza (7 studies), hepatitis A (15 studies), hepatitis B (50 studies), pnuemococcal polysaccaride (4 studies), diphtheria (4 studies), rubella (3 studies), measles (2 studies), yellow fever (3 studies), meningococcal A (1 study), meningococcal C (1 study), tetanus (1 study), brucella (1 study), Venezuelan equine encephalitis (1 study) and rabies (4 studies), with sex-difference in humoral (antibody) response. These differences are associated with sex-difference in the clinical efficacy of influenza, hepatitis A, hepatitis B, pneumococcal polysaccharide and diphtheria vaccines and significant adverse reactions with rubella, measles and yellow fever vaccines. The genesis of these differences is uncertain but not entirely related to gonadal hormones (differences are seen in pre-pubertal and post-menopausal subjects not on hormone replacement therapy) or female sex (males had greater serological response for pneumococcal, diphtheria, yellow fever, Venezuelan equine encephalitis and in some studies with rabies vaccine. As sex-difference in humoral immune response was seen with most vaccines which cover the spectrum of mechanisms by which infectious agents cause disease (mucosal replication, viral viraemia, bacterial bacteraemia, toxin production and neuronal invasion), it is mandatory that vaccine trialists recruit a representative sample of females and males to be able to assess sex-differences which may have clinical implications.

Modeling the long-term antibody response of a human papillomavirus (HPV) virus-like particle (VLP) type 16 prophylactic vaccine

The duration over which antibody responses persist following HPV vaccination is unknown. To estimate the longevity of responses induced by HPV-16 vaccination, two models were fitted to serum anti-HPV-16 levels measured during a 48-month study period. The first was a conventional model of antibody decay and the second was a modified model that accounts for long-lived immune memory. Using the antibody decay model, it was estimated that following administration of a three-dose regimen of HPV-16 vaccine in women aged 16-23 years, anti-HPV-16 levels will remain above those induced naturally by HPV-16 infection for 12 years, and above detectable levels for 32 years in 50% of vaccinees. With the modified model, which fitted the data better (p<0.001), it was estimated that near life-long persistence of anti-HPV-16 following vaccination is expected at titer levels above those associated with reduction of natural HPV-16 infection in 76% of these subjects, and above detectable levels in 99% of these subjects.

A review of the long-term protection after hepatitis A and B vaccination

Vaccine-preventable viral hepatitis continues to be a cause of considerable morbidity and mortality: on worldwide basis, approximately 1.4 million cases of hepatitis A are reported every year. The true incidence, however, has been estimated to be 3-10 times higher. Regarding hepatitis B, more than a third of the world's population has been infected. The World Health Organization has estimated (2000) that there are 367 million chronic carriers of hepatitis B worldwide, and approximately 1 million deaths per year as a consequence of chronic complications and acute fulminant disease. Hepatitis B vaccines have been licensed since 1982, and hepatitis A vaccines since 1992. In 1996, a combined hepatitis A and B vaccine became available. An update on the long-term protection conferred by hepatitis A and hepatitis B vaccines as well as the combined hepatitis A and B vaccine is offered in this paper. Long-term efficacy and booster policy for hepatitis B vaccines have often been a topic of discussion. Based on current data and field experience there is, in general, no necessity for booster doses for fully vaccinated immunocompetent individuals. Long-term protection has been demonstrated by the rapid (5-7 days) development of anamnestic antibody responses among vaccinees who no longer have detectable anti-HBs. Anamnestic responses correlate with lymphoproliferative T-cell responses following challenge with hepatitis B vaccine. Furthermore, employing Spot-ELISA techniques, circulating B-cells were shown to be able to produce anti-HBs in vaccinees who lost their detectable antibodies. The accumulated data from a large number of studies indicate that despite antibody decline or loss, immune memory exhibits long-term persistence. There is somewhat less information available for hepatitis A vaccines, yet an increasing number of studies indicate that the findings for hepatitis B vaccines are also applicable to hepatitis A vaccines. The necessity to provide a booster dose was based on early projections of observed antibody levels. However, recent follow-up studies with up to 12 year observation, as well as studies employing mathematical models predict that following primary vaccination, antibodies will persist for at least 25 years. In addition, experimental studies confirm that vaccination against hepatitis A induces immunological memory. Therefore hepatitis A booster vaccination is presently considered as unnecessary in fully vaccinated individuals. The above findings are of importance in the context of administering combined hepatitis A and B vaccine for which similar long-term data have been observed. All available data on monovalent and combined hepatitis A and hepatitis B vaccines indicates that there is no support for a hepatitis A or hepatitis B booster when a complete primary vaccination course is offered to immunocompetent individuals.

Persistence of seroprotection 10 years after primary hepatitis A vaccination in an unselected study population

Hepatitis A vaccines have been demonstrated to be highly immunogenic. Mathematical models have predicted antibodies to persist for at least 20-25 years. Most of these studies have been conducted in young and healthy study populations. We aimed to evaluate long-term immunity 10 years following complete primary immunization according to a 3-dose schedule (Havrix 720 El.U at months 0, 1, 6-12) in an adult and unselected study population. In total, 999 (98.3%) of 1016 vaccinees (mean age 54.7+/-S.D. 13.0), tested 10 years after primary vaccination, still had protective antibody levels (> or = 10 mIU/ml) as measured by ELISA. An anti-HAV titer cut off level of 11,400 mIU/ml was calculated to differentiate between vaccine-induced and infection-induced titer levels. The vaccine-induced geometric mean titer (GMT) was 406.1 mIU/ml (95% CI: 369.2-446.7 mIU/ml), showing an age-related trend, the 10-years seroprotection rate (SPR) was 97.9%. Females exhibited significantly higher GMTs than male vaccinees (p<0.001). The only parameter predicting a titer below 10 mIU/ml 10 years after vaccination was the body mass index (p=0.001). This study confirms that protection following primary hepatitis A vaccination persists for more than 10 years.

Ten-year antibody persistence induced by hepatitis A and B vaccine (Twinrix) in adults

BACKGROUND

Hepatitis A and B infections are prevalent worldwide and cause significant morbidity and mortality. A combined vaccine providing dual protection against hepatitis A and B is available (Twinrix, GlaxoSmithKline Biologicals).

METHOD

Two cohorts of adults aged 17-43 years were vaccinated with Twinrix according to a 0, 1, 6 months schedule and followed up for 10 years.

RESULTS

One month after the primary vaccination course (Month 7), all subjects were seropositive for anti-HAV and all had anti-HBs> or = 10 mIU/ml. At month 120, 100% of subjects (N=34; N=29) in both cohorts were seropositive for anti-HAV; 94.1% and 86.2% of subjects had anti-HBs > or = 10 mIU/ml. The geometric mean concentrations (GMC; mIU/ml) were 373.9 and 674.6 in the two cohorts for anti-HAV, and 103.8 and 320.0, respectively, for anti-HBs. None of the serious adverse events reported throughout the follow-up period were considered by the investigator to be causally related to vaccination.

CONCLUSIONS

Combined hepatitis A and B vaccine, Twinrix, is safe, well-tolerated and has demonstrated a highly immunogenic profile. Persistence of anti-HAV and anti-HBs antibodies in adults remains high for at least 10 years after primary vaccination.

Prevention of hepatitis A by Havrix: a review

Hepatitis A is one of the most common vaccine-preventable infectious diseases in the world. With at least 1.5 million cases of hepatitis A worldwide each year, disease management constitutes a substantial economic burden. The first effective vaccine against hepatitis A, Havrix was introduced in 1992. This review summarizes data accumulated following more than a decade of clinical experience with this vaccine and compares clinical data with other currently available hepatitis A vaccines. Based on this data and on the current immunological knowledge, a recent consensus concluded that hepatitis A vaccines induce lifelong protection, and thus booster vaccinations against hepatitis A are unnecessary in fully immunized, healthy people. In view of this, current regulatory recommendations for the use of hepatitis A vaccines are reviewed and possible future strategies identified.

Hepatitis A vaccines: the growing case for universal immunisation of children

Hepatitis A virus (HAV) infection results in a debilitating, multi-week illness in older children and adults that can be avoided with pre-exposure immunisation. Inactivated HAV vaccines are safe, highly effective and induce long-lasting protection. Immunisation has typically been recommended only for groups at highest risk of infection or complications, with variable success. This paper reviews the outcomes of several new programmes of universal HAV immunisation of children and/or adolescents. These programmes were associated with substantial disease rate reductions, extending beyond the immunised individuals and age groups (herd immunity), and promise additional benefits as immunised cohorts enter adulthood risk groups. Universal programmes are cost-effective, especially when a combined hepatitis A and B vaccine can be used to minimise incremental costs, and deserve wider consideration in developed countries.

Combined typhoid fever and hepatitis A vaccine: comparison of immunogenicity and safety to concomitant monovalent vaccine over 3 years

BACKGROUND

The safety and immunogenicity of Viatim, a combined hepatitis A (HA) and typhoid fever (Vi) vaccine, were compared with the monovalent component vaccines up to and 1 month after a booster dose at 3 years.

METHODS

Healthy, adult volunteers were randomized to receive Viatim (group A, n = 179) or separate HA and Vi vaccines (group B, n = 181); subgroups were boosted after 3 years with Viatim (groups C and D, n = 56 and 46, respectively). Local and systemic reactions were recorded for 28 days postvaccination. Seroconversion and seroprotection rates and geometric mean antibody concentrations were measured at 14 and 28 days, 1, 2, and 3 years postvaccination, and 28 days after the booster dose.

RESULTS

Local and systemic safety profiles were equivalent between the two groups. Immediate local reactions were infrequent (1 in group A and 2 in group B). Local reactions, consisting mostly of mild or moderate pain, were least frequent with monovalent HA. Antibody concentrations to both antigens were similar in groups A and B, in which HA seroprotection rates (> or = 20 mIU/mL) were respectively, 98.7% and 100% at day 28, and 99.1% and 99.0% after 3 years, achieving 100% after the booster. Vi seroprotection rates (> or = 1 microg/mL) of 85.2% and 84.9% after 28 days fell to 32.1% and 35.6% after 3 years, increasing to 67.3% and 69.8% after the booster dose.

CONCLUSIONS

The combined HA/Vi vaccine, Viatim, had equivalent tolerability and safety and was as rapidly immunogenic as its component monovalent vaccines when given concurrently. A booster dose after 3 years significantly increased antibody levels with some evidence of relative hyporesponsiveness of the typhoid response.

Cost-effectiveness of universal childhood hepatitis A vaccination in Chile

Hepatitis A is an important public health problem in Chile. Childhood vaccination has reduced hepatitis A rates in several countries, prompting this evaluation of its cost-effectiveness in Chile. Using a Markov model, we project mass vaccination would reduce hepatitis A cases among birth cohort members and their personal contacts >80%. Vaccination costs of US dollars 5.3-6.4 million would be offset by US dollars 9.2-9.4 million reductions in disease costs. Further, approximately 70 fatal infections would be averted and >4600 quality-adjusted life years would be saved. This analysis supports the cost-effectiveness of universal childhood hepatitis A vaccination in Chile.

Interchangeability and tolerability of a virosomal and an aluminum-adsorbed hepatitis A vaccine

The interchangeability of virosomal (Epaxal) and aluminum-adsorbed (Havrix 1440) hepatitis A virus (HAV) vaccines was studied in 111 healthy adults who were vaccinated in a randomized, single-blind, crossover clinical trial. Anti-HAV antibody titers were measured at days 0 (first dose), 14, and 28, and months 3, 6, 12 (second dose), 13, 24, 36, 48, 60 and 72. Most subjects (>95%) had sero-converted 14 days after the first dose of either vaccine. The second dose with either vaccine induced a high antibody response in all vaccines, irrespective of the type of vaccine administered as the first dose. Although both vaccines were well tolerated, the incidence of local adverse events (in particular pain) was significantly lower in subjects receiving the virosomal vaccine. Six-year follow-up data did not reveal any significant differences between the vaccination groups.

A review of licensed viral vaccines, some of their safety concerns, and the advances in the development of investigational viral vaccines

Viral vaccines could be considered among the most important medical achievements of the 20th century. They have prevented much suffering and saved many lives. Although some curative antiviral drugs exist, we desperately depend on efforts by academic, governmental and industrial scientists in the advancement of viral vaccines in the prevention and control of infectious diseases. In the next decade, we hope to see advancement in the development of current and investigational viral vaccines against childhood and adult infections. In this article, we will review the licensed viral vaccines, some of their safety concerns, and the advances in the development of investigational viral vaccines.

Antibody titres after primary and booster vaccination of infants and young children with a virosomal hepatitis A vaccine (Epaxal)

To evaluate the immunogenicity and tolerability of Epaxal in infants and children, 30 infants (aged 6-7 months) and 30 children (aged 5-7 years) received a single intramuscular dose of the aluminium-free virosomal hepatitis A virus (HAV) vaccine Epaxal and a booster dose after 12 months. Anti-HAV antibody titres were measured at baseline (before injection), at 1 and 12 months after primary vaccination, and 1 month after the booster vaccination. Sixteen evaluable infants had maternal anti-HAV antibodies at baseline. Complete seroprotection (titre >/= 20 mIU/ml) was achieved by all infants and children at Month 1 and at Month 12. Additionally, all subjects showed a strong antibody response to booster vaccination. In infants without maternal anti-HAV antibodies, the response was four-fold higher than in those with maternal anti-HAV antibodies. Both doses of Epaxal were well tolerated. These preliminary data suggest that Epaxal is an effective hepatitis A vaccine for children and infants from 6 months of age.

Cost effectiveness of hepatitis A/B versus hepatitis B vaccination for US prison inmates

Hepatitis B immunization is provided in many US prison systems. We examined the cost effectiveness of substituting bivalent hepatitis A/B vaccine in this setting, considering regional variation in hepatitis A risks and the potential for disease transmission by former prisoners. Where hepatitis A rates are >200, 100-200, and <100% the national average, declines in hepatitis A treatment costs would offset 137, 88, and 40% of the bivalent vaccine's added cost. In the three regions considered, cost effectiveness would be US$ <0, 2131, and 22,819 per life-year saved, respectively. Prison-based hepatitis A/B immunization would meet accepted standards of cost effectiveness throughout the US.

Cost-Effectiveness of Hepatitis A/B Vaccine versus Hepatitis B Vaccine in Public Sexually Transmitted Disease Clinics

BACKGROUND

Many patients seen at U.S. sexually transmitted disease (STD) clinics are offered hepatitis B vaccination. Substituting hepatitis A/B vaccine would provide additional protection but increase costs.

GOAL

The goal was to estimate the cost effectiveness of hepatitis A/B versus B vaccination for 1,000,000 public STD clinic attenders.

STUDY DESIGN

A Markov model of hepatitis A outcomes was developed using published literature, U.S. government databases, and expert panel opinion. Added vaccination costs were compared with savings from reduced hepatitis A treatment. Net costs were compared with life-years saved and quality-adjusted life-years (QALYs) gained.

RESULTS

Substituting hepatitis A/B vaccine would prevent 2263 overt hepatitis A infections, 292 hospitalizations, 8 premature deaths, and the loss of 281 QALYs. Net health system costs would be $20,892 per life-year saved, or $13,397 per QALY gained.

CONCLUSION

Substituting hepatitis A/B for hepatitis B vaccine would reduce morbidity and mortality in a cost-effective manner.

Regional variation in the cost effectiveness of childhood hepatitis A immunization

BACKGROUND

Routine childhood hepatitis A immunization is recommended in regions with incidence rates twice the national average, but it may be cost-effective in a wider geographic area.

OBJECTIVE

To evaluate the costs and benefits of potential hepatitis A immunization of healthy US children in regions with varying hepatitis A incidences.

METHODS

We considered vaccination of the 2000 US birth cohort in states defined by historic hepatitis A incidence rates. Infections among potential vaccinees and their personal contacts were predicted from age 2 through 85 years. Net vaccination costs were estimated from health system and societal perspectives and were compared with life-years saved and quality-adjusted life years (QALYs) gained using a 3% discount rate. RESULTS Nationally vaccination would prevent >75 000 cases of overt hepatitis A disease. Approximately two-thirds of health benefits would accrue to personal contacts rather than to vaccinees themselves. In states with incidence rates of > or =200%, 100 to 199%, 50 to 99% and <50% the national average, societal costs per QALY gained would be <0, <0, 13,800 and 63,000 US dollars, respectively. Nationally vaccination would cost 9100 US dollars per QALY gained from the perspective of the health system and 1400 US dollars per QALY gained from society's perspective. Results are most sensitive to vaccination costs and rates of disease transmission through personal contact.

CONCLUSION

Childhood hepatitis A vaccination is most cost-effective in areas with the highest incidence rates but would also meet accepted standards of economic efficiency in most of the US. A national immunization policy would prevent substantial morbidity and mortality, with cost effectiveness similar to that of other childhood immunizations.

Prevention of hepatitis A by vaccination

Inactivated hepatitis A vaccines have been available for more than a decade. Characteristics of the vaccines, comparative data among different formulations and the possibility of combination and association with other vaccines are reviewed in this article. Hepatitis A vaccines show high immunogenicity with different schedules and associations, induce long-term protection irrespective of timing of booster dose, and present an excellent safety profile. Pre-exposure efficacy has been demonstrated in large trials and postexposure protection has been described in family contacts of acute cases. The recommendations for the use of hepatitis A vaccines for immunisation campaigns and for targeted groups, such as travellers and people at risk for occupational and iatrogenic exposure or lifestyle behaviours, are discussed. Aspects related to economic analysis of vaccination strategies are also considered.

Virosomal adjuvanted antigen delivery systems

The development of novel and increasingly safer vaccines frequently utilizes well-characterized antigens, in particular highly purified proteins or synthetic peptides. In spite of some achievements, this approach is frequently impeded by the fact that such antigens are often poor immunogens when administered alone. This fact has necessitated the development of suitable adjuvants that possess the ability to enhance the immunogenicity of a given antigen, preferably with little or no side effects. This paper discusses one of the successes of vaccinology of the past decade: virosomal vaccines. The principles of the concept, immunoadjuvant action and application of virosomes in two currently licensed vaccines are detailed, with specific reference to the induction of both humoral and cellular immunity.