An inactivated hepatitis A viral vaccine of cell culture origin

Safety and potency of BIV1-CovIran inactivated vaccine candidate for SARS-CoV-2: A preclinical study

The development of effective and safe COVID‐19 vaccines is a major move forward in our global effort to control the SARS‐CoV‐2 pandemic. The aims of this study were (1) to develop an inactivated whole‐virus SARS‐CoV‐2 candidate vaccine named BIV1‐CovIran and (2) to determine the safety and potency of BIV1‐CovIran inactivated vaccine candidate against SARS‐CoV‐2. Infectious virus was isolated from nasopharyngeal swab specimen and propagated in Vero cells with clear cytopathic effects in a biosafety level‐3 facility using the World Health Organization’s laboratory biosafety guidance related to COVID‐19. After characterisation of viral seed stocks, the virus working seed was scaled‐up in Vero cells. After chemical inactivation and purification, it was formulated with alum adjuvant. Finally, different animal species were used to determine the toxicity and immunogenicity of the vaccine candidate. The study showed the safety profile in studied animals including guinea pig, rabbit, mice and monkeys. Immunisation at two different doses (3 or 5 μg per dose) elicited a high level of SARS‐CoV‐2 specific and neutralising antibodies in mice, rabbits and nonhuman primates. Rhesus macaques were immunised with the two‐dose schedule of 5 or 3 μg of the BIV1‐CovIran vaccine and showed highly efficient protection against 10⁴ TCID50 of SARS‐CoV‐2 intratracheal challenge compared with the control group. These results highlight the BIV1‐CovIran vaccine as a potential candidate to induce a strong and potent immune response that may be a promising and feasible vaccine to protect against SARS‐CoV‐2 infection.

Impact of Protein Glycosylation on the Design of Viral Vaccines

Glycans play crucial roles in various biological processes such as cell proliferation, cell-cell interactions, and immune responses. Since viruses co-opt cellular biosynthetic pathways, viral glycosylation mainly depends on the host cell glycosylation machinery. Consequently, several viruses exploit the cellular glycosylation pathway to their advantage. It was shown that viral glycosylation is strongly dependent on the host system selected for virus propagation and/or protein expression. Therefore, the use of different expression systems results in various glycoforms of viral glycoproteins that may differ in functional properties. These differences clearly illustrate that the choice of the expression system can be important, as the resulting glycosylation may influence immunological properties. In this review, we will first detail protein N- and O-glycosylation pathways and the resulting glycosylation patterns; we will then discuss different aspects of viral glycosylation in pathogenesis and in vaccine development; and finally, we will elaborate on how to harness viral glycosylation in order to optimize the design of viral vaccines. To this end, we will highlight specific examples to demonstrate how glycoengineering approaches and exploitation of different expression systems could pave the way towards better self-adjuvanted glycan-based viral vaccines.

The Discovery of Hepatitis Viruses: Agents and Disease

Discovery of five hepatitis viruses A to E has followed distinctive definable phases. Human experiments at Willowbrook identified two forms of hepatitis namely infectious hepatitis and serum hepatitis. The discovery of Australia antigen in 1965 led to rapid scientific developments in viral hepatitis. SH antigen was detected in sera of patients with serum hepatitis and soon SH antigen and Australia antigen were found to be identical and selectively associated with serum hepatitis. In 1970, 42-nm Dane particles were detected in Australia antigen positive sera and linked to the virus of serum hepatitis. Subsequently, a new antigen-antibody system (e-antigen/antibody) was detected in such patients and associated with infectivity. Then, DNA polymerase was found in concentrated pellets containing Australia antigen. Hepatitis B virus (HBV) DNA cloning and sequencing of HBV followed these developments. In 1973, 27 nm hepatitis A virus (HAV)-like particles were visualized in stool samples obtained during acute phase of illness after inoculation of MS-1 strain in volunteers. Cloning and sequencing of HAV followed. In 1977, a new antigen-antibody system (δ antigen-antibody system) was identified by chance associated with HBV. Based on animal transmission studies, δ agent was found to be another virus called hepatitis D virus that is defective, requires the helper functions of HBV and interferes with HBV replication. The search for hepatitis C virus started when non-A, non-B hepatitis was recognised in multiply transfused patients with subsequent successful animal transmission. HCV was identified by a novel immunoscreening approach involving screening of cDNA libraries from infectious sera. The story of hepatitis E is historically linked to discovery of waterborne epidemic non-A, non-B hepatitis from Kashmir, India. Virus-like-particles of the agent were identified in stool samples of a human volunteer after a self-experimentation. HEV cDNA was detected in bile-enriched infectious samples and full-length HEV RNA genome was subsequently cloned and sequenced.

Cell Culture Systems and Drug Targets for Hepatitis A Virus Infection

Hepatitis A virus (HAV) infection is one of the major causes of acute hepatitis, and this infection occasionally causes acute liver failure. HAV infection is associated with HAV-contaminated food and water as well as sexual transmission among men who have sex with men. Although an HAV vaccine has been developed, outbreaks of hepatitis A and life-threatening severe HAV infections are still observed worldwide. Therefore, an improved HAV vaccine and anti-HAV drugs for severe hepatitis A should be developed. Here, we reviewed cell culture systems for HAV infection, and other issues. This review may help with improving the HAV vaccine and developing anti-HAV drugs.

Successful Vaccines

Vaccines are considered one of the most important advances in modern medicine and have greatly improved our quality of life by reducing or eliminating many serious infectious diseases. Successful vaccines have been developed against many of the most common human pathogens, and this success has not been dependent upon any one specific class of vaccine since subunit vaccines, non-replicating whole-virus or whole-bacteria vaccines, and attenuated live vaccines have all been effective for particular vaccine targets. After completing the initial immunization series, one common aspect of successful vaccines is that they induce long-term protective immunity. In contrast, several partially successful vaccines appear to induce protection that is relatively short-lived and it is likely that long-term protective immunity will be critical for making effective vaccines against our most challenging diseases such as AIDS and malaria.

Chemical Attenuation in the Development of a Whole-Organism Malaria Vaccine

Malaria vaccine development has been dominated by the subunit approach; however, many subunit vaccine candidates have had limited efficacy in settings of malaria endemicity. As our search for an efficacious malaria vaccine continues, the development of a whole-organism vaccine is now receiving much scrutiny. One strategy currently being explored in the development of a whole-organism vaccine involves chemical attenuation of the malaria parasite. In vivo and in vitro chemical attenuation of both liver-stage and blood-stage Plasmodium parasites has been investigated. Here, we discuss both approaches of chemical attenuation in the development of a whole-organism vaccine against malaria.

Inactivated Viral Vaccines

Inactivated vaccines have been used for over a century to induce protection against viral pathogens. This established approach of vaccine production is relatively straightforward to achieve and there is an augmented safety profile as compared to their live counterparts. Today, there are six viral pathogens for which licensed inactivated vaccines are available with many more in development. Here, we describe the principles of viral inactivation and the application of these principles to vaccine development. Specifically emphasized are the manufacturing procedure and the accompanying assays, of which assays used for monitoring the inactivation process and preservation of neutralizing epitopes, are pivotal. Novel inactivated vaccines in development and the hurdles they face for licensure are also discussed as well as the (dis)advantages of inactivation over the other vaccine production methodologies.

History of vaccination

Vaccines have a history that started late in the 18th century. From the late 19th century, vaccines could be developed in the laboratory. However, in the 20th century, it became possible to develop vaccines based on immunologic markers. In the 21st century, molecular biology permits vaccine development that was not possible before.

The development of vaccines: how the past led to the future

The history of vaccine development has seen many accomplishments, but there are still many diseases that are difficult to target, and new technologies are being brought to bear on them. Past successes have been largely due to elicitation of protective antibodies based on predictions made from the study of animal models, natural infections and seroepidemiology. Those predictions have often been correct, as indicated by the decline of many infections for which vaccines have been made over the past 200 years.

[Classic vaccinology and advances in vaccine design]

The prevention of many infectious diseases, allergies, autoimmune diseases, and cancer continues to be a challenge in the twenty-first century. Nonetheless, considerable advances have already been made, such as the eradication of certain infectious diseases and effective control of many others, and new technology is being developed in areas related to molecular biology, recombinant DNA, protein biochemistry, microbiology, and immunology. The current trends point to continued progress in coming years. Technical skills will become highly refined, so that any antigen or epitope can be presented in a highly immunogenic form within a vaccine. Modern technology has led to the formulation of a new paradigm in vaccine development, in which the genomic and/or proteomic aspects of diseases are analyzed a priori to identify factors implicated in the immune response that may serve as promising vaccine candidates.

Mutational events during the primary propagation and consecutive passages of hepatitis E virus strain JE03-1760F in cell culture

We recently developed a cell culture system for hepatitis E virus (HEV) in PLC/PRF/5 cells, using a genotype 3 HEV (JE03-1760F strain). Thirteen generations of consecutive passages of culture supernatant were successfully carried out in PLC/PRF/5 cells, with the highest HEV load reaching 10(8) copies/ml in the culture medium. Based on continuous release of progenies into culture medium, 50% tissue culture infectivity doses were estimated to be 2.0 x 10(3) copies for wild-type JE03-1760F and 1.4 x 10(2) copies for p13 (progeny in the thirteenth passage). Earlier appearance and greater increase in the yield of progenies in the culture supernatant were evident in p13 compared with wild-type. The cell culture-produced variants in primary propagation (p0) and consecutive passages (p5 [fifth passage], p10 [tenth], and p13) differed from the wild-type virus by 1, 9, 18, and 19 nucleotides (nt), respectively, over the entire genome of 7226nt, excluding the poly(A) tail. Three of five non-synonymous mutations in p13 were shared by a variant (fifth passage) in another series of passages of JE03-1760F. These results suggest that adaptation of HEV variants to growth in vitro is associated with a limited number of mutations similar to hepatitis A virus.

Detection of antibodies to HAV 3C proteinase in experimentally infected chimpanzees and in naturally infected children

Commercial assays for the diagnosis of hepatitis A detect antibody to hepatitis A virus (anti-HAV), but they cannot discriminate between antibody resulting from infection and antibody induced by inactivated vaccine. With the licensing and increasing use of inactivated hepatitis A vaccines, there is a need for a test to distinguish between infection and vaccination. Since antibodies to viral non-structural proteins are elicited by infection but not by vaccination with inactivated vaccine, we developed and evaluated a test for such antibodies. The antibody response to the non-structural 3C proteinase (anti-3C) of virus HAV was studied by ELISA in chimpanzees experimentally infected with virulent (wild type) or with attenuated HAV strains and in children who received inactivated HAV vaccine or placebo during a vaccination trial in Nicaragua. Anti-3C was detected in 89% of 18 chimpanzees infected with wild-type HAV strains and 27% of 26 chimpanzees infected with attenuated HAV strains. There was a direct correlation between severity of hepatitis and magnitude of the anti-3C response. In the vaccine trial, anti-3C was detected only in children who were infected with HAV during the study; IgG anti-3C persisted for at least 15 months after infection in one child. Vaccinated and uninfected children remained negative for anti-3C. The anti-3C response can be regarded as an indicator of viral replication. Its detection should be useful for distinguishing between antibody acquired in response to HAV infection and antibody induced by immunization with inactivated vaccine.

Technologies for the design, discovery, formulation and administration of vaccines

This paper summarizes major technologies, with emphasis on applications to preventive vaccines for infectious diseases. A limited number of examples of each technology are provided.

In vitro potency assay for hepatitis A vaccines: development of a unique economical test

Prior to the official release of each Hepatitis A vaccine lot to the market, a quality control performed by a National Control Authority requires an in vivo or an in vitro potency assay. At the beginning of our work, no standardised in vitro test common to all hepatitis A vaccines was available for both manufacturers and National Control Laboratories. In this study, a unique polyvalent enzyme-linked immunosorbent assay (ELISA) method was developed to appraise all commercially available HAV vaccines. After comparing a direct and an indirect sandwich method with commercial antibodies, the indirect assay was selected and an evaluation of sensitivity, linearity, accuracy and precision was performed before being applied to HAV antigen determination from four different manufacturers. The results are satisfactory and incline us to use routinely this method to release Hepatitis A vaccines.

Personal historical chronicle of six decades of basic and applied research in virology, immunology, and vaccinology

The sciences of vaccinology and of immunology were created just two centuries ago by Jenner's studies of prevention of smallpox by inoculation with cowpox virus. This rudimentary beginning was expanded greatly by the giants of late 19th and early 20th centuries biomedical sciences. The period from 1930 to 1950 was a transitional era with the introduction of chick embryos and minced tissues for propagating viruses and rickettsiae in vitro for vaccines. Modern era vaccinology began about 1950 as a continuum of notable advances made during the 1940s and World War II. Present vaccinology is based largely on breakthroughs in cell culture, bacterial polysaccharide chemistry, molecular biology, and immunology. By invitation, the author, who is a microbe hunter in fact, was asked to chronicle his six decades of pioneering achievements in basic and applied virology, bacteriology, immunology, molecular biology, epidemiology, and cancer, with special reference to the pioneering creation of most of the present day vaccines. Knowledge of the past may guide the present and future. This chronicle will have achieved its legacy if it helps others to understand the why and how of the past that may help to create the substance of the future.

Comparative immunogenicity and tolerance of Vaqta and Havrix

In an open-label, randomised trial, 520 adults of both sexes aged 18-30 years were allocated to receive one of two inactivated hepatitis A vaccines; Vaqta or Havrix, at 0 and 24 weeks. Doses used were 50 or 100 antigen units (U) of Vaqta and 1440 enzyme linked immunosorbent assay U of Havrix given as 1 ml intramuscular injections. For each trial group safety data were available for all subjects and full serological data for more than 80% of randomised volunteers. Local side effects which were mild in most cases were significantly (p < 0.0001) more common with Havrix than with Vaqta, irrespective of dose given. Systemic tolerance was similar for the 3 regimens. From 4 weeks after the first dose, > or =94% of the subjects had seroconverted. The mean antibody titres 4 weeks after the second vaccine dose were 2978, 4346 and 1589 mIU/ml in subjects who were randomised to Vaqta 50 U/dose, Vaqta 100 U/dose and Havrix 1440 U/dose, respectively. The 2 vaccines had similar immunogenicity but local tolerance was better with Vaqta.

Interaction of VP3(110-121) Peptide with Hepatocyte and Erythrocyte Membrane Models

The use of synthetic peptides in the goal of developing a new, inexpensive vaccine against hepatitis A virus is one of the encouraging approaches followed by many laboratories. These peptides have to be well characterized, being their physicochemical properties one of the most relevant points to control. In that sense, one can consider the study of the peptide interaction with lipid monolayers by means of the Wilhelmy plate method, to gain insight into the possible mechanism of action at the membrane level. The peptide chosen corresponds to the lineal epitope of hepatitis A virus VP3(110-121). As far as the lipids used are concerned, they were selected according to the composition of hepatocytes and erythrocytes because these structures seem to play an important role in hepatitis proliferation and infection. The peptide was able to accommodate into lipid monolayers. Interaction was slightly lower in the hepatocyte model than in the erythrocyte model, probably due to the presence of cholesterol in the hepatocyte membrane. Copyright 1999 Academic Press.

Hepatitis A vaccine in healthy adults: a comparison of immunogenicity and reactogenicity between two- and three-dose regimens

Inactivated hepatitis A virus (HAV) vaccine was administered to 55 healthy seronegative adult volunteers to evaluate the immunogenicity and adverse reactions of two doses of HAV vaccination (25 units) in comparison with a three-dose regimen. The volunteers were randomly assigned to receive one of the two regimens: 26 were vaccinated with two doses at 0 and 24 weeks (Group 1), and 29 were vaccinated with three doses at 0, 2, and 24 weeks (Group 2). The vaccine was well tolerated and there was no serious adverse reaction. In both groups, the seroconversion rate was 100% at week 28. At week 52, all remained positive for anti-HAV regardless of a two- or three-dose regimen. No statistically significant difference in seroconversion rates and geometric mean titers could be demonstrated between the two groups. Thus, the two-dose regimen may be favorable to save cost and time for active immunization against hepatitis A.

The effect of age and weight on the response to formalin inactivated, alum-adjuvanted hepatitis A vaccine in healthy adults

Formalin-inactivated, alum-adsorbed, hepatitis A vaccine was evaluated in 100 healthy adults who were stratified at enrollment into two age groups: 18-39 years: n = 50; 40-65 years: n = 50. All individuals received vaccine at 25 U of viral antigen. After stratification, both groups were randomized to receive either vaccination at 0 and 24 weeks or vaccination at 0.2 and 24 weeks. Subjects were bled for serology at 0, 2, 4, 24, 28 weeks and 1 year. The seroconversion rate and geometric mean titer (GMT = mIU ml-1) after one dose of vaccine was lower for older subjects [second week: < 40 years: 15/25 (60%) (GMT: 12.9). > 40 years: 5/22 (23%) (GMT: 6.1): fourth week: < 40 years: 20/22 (91%) (GMT: 29.0), > 40 years: 16/23 (70%) (GMT: 14.3)]. After a second dose at 2 weeks the seroresponse improved so that there were no longer differences between age groups [24 weeks: < 40: 21/22 (95%) (GMT: 123.9), > 40: 22/23 (96%) (GMT: 106.1)]. A third dose at 24 weeks resulted in a 20-40-fold increase in GMT in both age groups. As a separate evaluation height, weight, skin fold thickness, and body mass index (BMI) were assessed by logistic regression for their ability to predict serologic response. Serologic response was significantly associated with lower weight (P = 0.032) and BMI (P = 0.024) but not with height or skin fold thickness. Hepatitis A vaccine was well tolerated, with no serious adverse experiences. Adults older than 40 years appear to respond less well than younger adults to a single dose of 25 U of hepatitis A vaccine but equally well after two doses of vaccine. The slower antibody response to hepatitis A vaccine in overweight individuals was not attributable to skin adipose tissue.

Immunogenicity of two versus three injections of inactivated hepatitis A vaccine in adults

AIM

To investigate the immunogenicity of two versus three injections of inactivated strain CR326F-derived hepatitis A vaccine in healthy adults.

METHODS

Healthy adult volunteers (n = 105) at Utrecht University Hospital, The Netherlands, were randomly assigned to receive intramuscular injections (deltoid muscle) of 25 Units (U) at 0 and 6 months (group A, n = 53), or at 0, 2 and 6 months (group B, n = 52). Blood was drawn before and at various time points after vaccination for determination of serum antibody to hepatitis A (anti-HAV).

RESULTS

One month after the first injection, the seroconversion rates (> or = 10 mIU/ml, international units) were 88% for group A and 90% for group B. Only 2/ 103 (one in each group) showed IgM anti-HAV. One month after the second injection, seroconversion rates were 100% in both groups. At months 3, 6 and 7, anti-HAV geometric mean titers were significantly different because of the different vaccination schedules, but they were similar at months 1, 2 and 12. The anti-HAV geometric mean titer increase after the second injection was higher when the interval between the two doses was of longer duration. Anti-HAV titers of females were significantly higher than those of males and vaccinees < or = 30 years had higher titers than those > 30 years.

CONCLUSIONS

Two 25 U doses of the vaccine investigated given at 0 and 6 months, induce adequate anti-HAV titers in all adult healthy vaccinees and are as immunogenic as three doses given at 0, 2 and 6 months.

Good immunogenicity of GBM strain inactivated hepatitis A vaccine in healthy male adults

A formalin-inactivated aluminium hydroxide adsorbed hepatitis A vaccine was evaluated in a dose-response study on 195 healthy male adults (age range: 18-31 years) in two French hospitals (Lyon, Rouen). Four doses (20, 40, 80, 160 RIA antigen units) were administered intramuscularly (i.m.) in two injections over a 6-month period. At the time of the first vaccine injection, 32 subjects (16.4%) were found positive (> 20 mIU ml-1) for HAV antibody (total Ig RIA HAVAB assay, Abbott Laboratories) and were excluded from the analysis of immunogenicity criteria. Fourteen days after the first vaccine injection, 78.1% (95% confidence interval (CI): 62-90) of seronegative subjects who received the 160 RIA antigen unit dose seroconverted with a geometric mean titre (GMT) of 43 mIU ml-1 (95% CI: 33-56). Seroconversion was 100% (95% CI: 91-100) at 1 month with a GMT of 95 mIU ml-1 (95% CI: 79-112). Statistical analysis revealed a significant dose-related effect (p < 0.0001) on GMT by multivariate regression analysis of the results after the first injection. Biological safety was evaluated and alanine aminotransferase and aspartate aminotransferase levels were similar prior to and 14 days after the first injection in the four groups. Reactions after injection were similar in the four dosage groups: 6.2% of subjects reported immediate reactions after first vaccination (feeling sick, spontaneous pain, headache), 8.9% reported local reactions at the site of injection (spontaneous pain, haematoma, local adenopathy) and 13.5% reported general reactions ('flu-like' syndrome, gastrointestinal tract disorders, fatigue, headache).(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitive assays for hepatitis A antibodies

Two commercial assay kits for detecting antibody to hepatitis A virus (anti-HAV) have been modified in order to increase their sensitivity. These modifications are made by less dilution of the test serum, in the case of Abbott HAVAB-M assay, or by an increase in the volumetric ratio of the test serum to the labeled anti-HAV in the case of the Abbott HAVAB assay. These modifications result in 5- to 20-fold increases in test sensitivity and enable the detection of anti-HAV at 2-3 weeks following vaccination. The earlier detection of anti-HAV is important to vaccine development in assuring the presence of antibody levels in travelers sooner after vaccination.

Immunogenicity of inactivated hepatitis A vaccine in children

BACKGROUND

Inactivated hepatitis A vaccine is now becoming available in many countries.

METHODS

To evaluate the immunogenicity and safety of inactivated hepatitis A vaccine in healthy children, 99 susceptible schoolchildren from 4 to 15 years of age received 360 enzyme-linked immunosorbent assay units of the inactivated hepatitis A vaccine at months 0, 1, and 6.

RESULTS

Antibody to hepatitis A virus seroconversion (> or = 20 mIU/mL) was 97% (96/99) in vaccinees after the first dose and 100% after the second (99/99) and booster (96/96) doses. The geometric mean titers of antibody to hepatitis A virus were 167, 465, and 4133 mIU/mL after each dose of vaccine, respectively. There were no significant side effects during the vaccination. Levels of antibody to hepatitis A virus were also tested in 9 susceptible children at day 7 and months 1 and 4 after the intramuscular injection of 2 mL of immune serum globulin. All children had measurable titers of antibody to hepatitis A virus 1 week after receiving immune serum globulin by sensitive enzyme immunoassay, but measurable titers had disappeared 1-4 months later.

CONCLUSIONS

The inactivated hepatitis A vaccine is safe and immunogenic in healthy children.

Considerations for the development of recommendations for the use of hepatitis A vaccine

The prevention of hepatitis A virus (HAV) infection should be greatly facilitated with the expected licensure of inactivated hepatitis A vaccines. In countries with a low endemicity of infection a number of high risk groups have been identified in which HAV infection occurs, and include both children and adults. In most other countries HAV infection occurs primarily in children. Thus, selective immunization of high-risk adults or children would not be expected to lower the overall rates of infection in most countries, and the eventual objective should be the integration of hepatitis A vaccine into the routine childhood immunization schedules. This would reduce disease incidence by preventing infections in children and by preventing infections in adults that are acquired from children. The elimination of a population susceptible to HAV infection through immunization could eliminate this well-known human disease, and the epidemiology of HAV infection suggests that eradication could be attainable with effective vaccines.

Preparation and immunogenicity of an inactivated hepatitis A vaccine

A hepatitis A vaccine was prepared by formaldehyde inactivation of purified hepatitis A virus (HAV) LSH/S strain grown on human diploid MRC-5 cells. The vaccine was devoid of residual infectivity in vitro and failed to induce in marmoset monkeys any pathological features or variations of haematological and clinical chemistry values. Infectious HAV particles were not detected in faeces and sera of the vaccinated primates by ELISA or after passages in MRC-5 cells. The immunogenicity of the vaccine was evaluated by injecting guinea-pigs with 0.8, 0.2 or 0.05 micrograms of HAV antigen adsorbed onto 0.5 and 1 mg of Al (OH)3 or 0.3 mg of AlPO4. The antibody response, measured by a competitive radioimmunoassay, was dose- and adjuvant-dependent. One injection of 0.2 micrograms of AlPO4-adsorbed HAV antigen induced seroconversion in 100% of animals and high levels of specific and neutralizing serum antibodies. A further increase of antibody titres was observed after the second and third inoculations. These results show that this vaccine formulation is safe and immunogenic in animal models, and suggest that it should be evaluated further by human clinical studies.

Development of the formalin-inactivated hepatitis A vaccine, VAQTA from the live attenuated virus strain CR326F

The development of the formalin-inactivated hepatitis A vaccine, VAQTA, culminates nearly two decades of the basic science studies of VAQTA in hepatitis A virology at the MRL. The master seed virus for production of VAQTA is derived from the F'(P18) variant of the strain CR326F which has been studied in human clinical trials and shown to the highly attenuated. The antigen is highly purified to make possible the consistency and thoroughness of its inactivation by formalin. Phase I clinical studies of VAQTA were initiated in 1989 and have progressed since that time to the recent Phase III clinical trials which demonstrated efficacy of a single dose of the vaccine in preventing clinical hepatitis A disease in pediatric populations in Monroe, NY.

A finger-stick assay for determination of immunity to hepatitis A: a preliminary report

A simple and reproducible method for determining immunity to hepatitis A has been developed, using whole blood obtained by finger-stick and fixed on small discs. This method permits screening of large populations of candidates prior to active or passive immunization, avoiding the discomfort and difficulty of venipuncture, especially in children. The technique involves a finger-stick with a blood lancet, collection of 20 microliter whole blood on a paper disc which is then dried at room temperature. Perforated discs are incubated with phosphate buffered saline and the eluate is then tested for anti-HAV using the HAVAB assay. Results of anti-HAV assays from finger-stick samples obtained from adults and from children, showed 100% conformance with the homologous venous serum samples obtained at the same time. The lower threshold for detection of anti-HAV by this method is currently below 100 mIU/ml, as compared to 20 mIU/ml by the modified HAVAB method. In conclusion, we have developed a simple and reliable method for determination of immunity to HAV using whole blood obtained by finger-stick and fixed on paper discs. Samples can be collected under field trial conditions, without immediate need for laboratory facilities for separation and storage of serum samples. This sampling method, which is mainly intended for qualitative determination of anti-HAV in HAV immune subjects, especially under field trial conditions, is rapid, economical, efficient and acceptable to populations that are generally apprehensive of conventional venipuncture specimen collection methods.

Hepatitis and hepatitis A vaccine: a glimpse of history

Human hepatitis has been recognized since the dawn of recorded history, but proof of infectious etiology and delineation of hepatitis A (infectious hepatitis) from hepatitis B (serum hepatitis) were not established until the first half of the present century. Development of the present killed hepatitis A vaccine depended on a series of breakthrough discoveries made during the last 25 years. These were marmoset propagation (1967); definition of virus attributes (1974-1975); development of diagnostic tests and seroepidemiology (1974-1975); and the preparation and proof of efficacy of a prototype killed hepatitis A vaccine (1976). Successful cultivation of hepatitis A virus in cell culture in 1979 quickly led to development of both live and killed hepatitis A vaccines for tests in human beings (1980-1990). The year 1991 marks the initiation of protective efficacy trials of two different killed virus vaccines in human beings. The safety and protective efficacy of the first vaccine (Merck) is reported in this symposium and the findings in tests of a second vaccine (SKB) are awaited. Hepatitis A is clearly a conquerable disease, initially in its elimination as an important disease entity and eventually in its eradication.

Single and booster dose responses to an inactivated hepatitis A virus vaccine: comparison with immune serum globulin prophylaxis

Pre- and postexposure prophylaxis against hepatitis A virus (HAV) infection with immune serum globulin (Ig) is only effective for 4-6 months. We compared the safety, tolerability and immunogenicity of a single i.m. injection of Ig with a single and booster dose of an inactivated hepatitis A virus vaccine (iHAV) in adults. Healthy volunteers (18-50 years) received a single Ig i.m. injection (n = 30), or iHAV i.m. (n = 15) at 0 and 24 weeks, or placebo (n = 4) at the same intervals. Anti-HAV seroconversion was measured by radioimmunoassay (RIA) and neutralizing antibodies by an antigen reduction assay. After Ig injection (0.06 ml/kg), anti-HAV seroconversion occurred in 100% of recipients at week 1, declining to 10% at week 12 and 0% by week 20. In contrast, after a single 25 ng dose, RIA seropositivity in iHAV vaccinees was 80% by week 2, reaching 100% by week 5 and persisted up to week 24, at which time anti-HAV geometric mean titres (GMT) were two fold higher than those seen at week 1 after Ig. Postbooster anti-HAV titres in iHAV recipients rose within 4 weeks to 73-fold greater than the peak GMT seen one week after Ig, and 400-fold higher than GMT at 12 weeks after Ig. Neutralizing antibody titres after iHAV followed a similar pattern, as observed for anti-HAV. iHAV was well tolerated; placebo and vaccine tolerability were indistinguishable, with no serious adverse experiences observed. In conclusion, active vaccination with a single iHAV dose may eventually replace Ig for pre-exposure prophylaxis.(ABSTRACT TRUNCATED AT 250 WORDS)

Anatomy of a trial: a historical view of the Monroe inactivated hepatitis A protective efficacy trial

The performance of vaccine protective efficacy trials is often more complex than reports of final results suggest. The current article reviews the background, planning and preparations for the Monroe, NY, protective efficacy trial of a formalin-inactivated, alum-adjuvanted hepatitis A vaccine (VAQTA, manufactured by Merck Research Laboratories). The vaccine trial was carried out at Kiryas Joel, a Hasidic Jewish community which had experienced numerous annual outbreaks in a local environment with similarities to day-care centers. Careful communication, and cooperation of community leadership, a flexible technical resource team, and knowledge of an epidemic already ongoing in a sister community whose members were due to arrive for summer holidays, permitted rapid and efficient completion of the trial with a striking demonstration of protection after a single vaccine dose.

Safety, tolerability, and immunogenicity of an inactivated hepatitis A vaccine: effects of single and booster injections, and comparison to administration of immune globulin

Hepatitis A virus (HAV) infection in adults is often symptomatic and disabling. The present article summarizes our experience with phase 2 studies of an inactivated hepatitis A virus vaccine. Pre- and post-exposure prophylaxis with immune globulin (IG) is only effective for 4-6 months. We compared the safety, tolerability, and immunogenicity of a single i.m. injection of IG with single and booster doses of an inactivated hepatitis A virus vaccine (iHAV) in adults. A total of 75 healthy volunteers (aged 18-50 years) were evaluated in two separate studies. The first included 15 volunteers who received 25 units iHAV i.m. at 0 and 24 weeks. The second, a randomly controlled study, consisted of three groups receiving 25 units iHAV i.m. at 0, 1, and 6 months, or at 0, 2, and 6 months, or 0.06 ml/kg IG i.m. given once. Anti-HAV seroconversion was measured by radioimmunoassay (RIA). After IG injection, anti-HAV seroconversion occurred in 100% of recipients at week 1, declining to 10% at week 12, and 0% by week 20. In contrast, after a single 25-unit dose, RIA seropositivity in iHAV vaccines was 73% by week 2, reaching 100% by week 5, and persisted in all up to week 24, at which time anti-HAV geometric mean titers (GMT) were 2-fold higher than those seen at week 1 after IG. Administration of a booster dose given 1 or 2 months after primary immunization did not significantly improve the quantitative anti-HAV response at 6 months as compared to the effect of the primary dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose response study of an inactivated hepatitis A virus vaccine

In this dose-response study evaluating 3 different doses and 2 time schedules, the highest dose, 25 units of viral protein antigen, induced a seroconversion antibody response against hepatitis A virus (anti-HAV) over 10 mIU in all vaccinees by week 3 after one dose, indicating rapid onset of protective antibody levels. Following the second dose, given 4 weeks later, rising titers were observed for 20 weeks, when the third and final dose of 25 units was given. The GMT of anti-HAV at 24 weeks (before the third vaccine injection) was 398 mIU/ml for the 25-unit dose, compared to 42 and 65 mIU/ml, respectively, for the 12.5 unit and 6.25 unit doses. The third vaccine dose at 24 weeks gave a booster response in all vaccinees, but the increase in titers was most pronounced in the 25 unit group, which had reached a GMT of 6593 mIU/ml when tested 4 weeks later. Side-effects included mainly local reactions and a few cases of mild diarrhoea, and did not differ for the 3 doses studied. In Scandinavia, hepatitis A vaccines will probably be used mainly for vaccination of foreign travellers. This category usually requires a rapid immunization schedule with few doses. Two doses approximately 3-4 weeks apart will probably be accepted by most travellers, and a single dose may provide short-term protection for most individuals. The need and timing for a booster dose will have to be further studied.

Comparison of modified HAVAB and ELISA for determination of vaccine-induced anti-HAV response

An inhibition ELISA was compared with a modification of the HAVAB assay for measuring antibodies induced by a killed HAV vaccine. GMT's expressed in mIU/ml were higher by ELISA than by modified HAVAB, especially after the first and second doses of vaccine but seroconversion rates were very similar and a good correlation was found between both assays. Because of its higher sensitivity and specificity, the ELISA assay was preferred to modified HAVAB for the evaluation of a Hepatitis A vaccine in human volunteers.

A controlled trial of a formalin-inactivated hepatitis A vaccine in healthy children

BACKGROUND

Although inactivated hepatitis A vaccine is known to be well tolerated and immunogenic in healthy children and adults, its efficacy has yet to be established.

METHODS

To evaluate the efficacy of the hepatitis A vaccine in protecting against clinically apparent disease, we conducted a double-blind, placebo-controlled trial in an Hasidic Jewish community in upstate New York that has had recurrent outbreaks of hepatitis A. At the beginning of a summer outbreak, 1037 healthy seronegative children 2 to 16 years of age were randomly assigned to receive one intramuscular injection of a highly purified, formalin-inactivated hepatitis A vaccine or placebo. A case was defined by the presence of typical signs and symptoms, a diagnostic increase in IgM antibody to hepatitis A, and a serum concentration of alanine aminotransferase at least twice the upper limit of normal. Cases occurring greater than or equal to 50 days after the injection were included in the evaluation of efficacy. The children were followed for a mean of 103 days.

RESULTS

A total of 519 children received vaccine, and 518 received placebo. The vaccine was well tolerated, with no serious adverse reactions. From day 50 after the injection, 25 cases of clinically apparent hepatitis A occurred in the placebo group and none in the vaccine group (P less than 0.001), confirming that the vaccine had 100 percent protective efficacy. Before day 21, seven cases occurred in the vaccine group and three cases in the placebo group. After that time, there were no cases among vaccine recipients and 34 cases among placebo recipients.

CONCLUSIONS

The inactivated purified hepatitis A vaccine that we tested is well tolerated, and a single dose is highly protective against clinically apparent hepatitis A.

Time course of hepatitis A virus antibody titer after active and passive immunization

To investigate the antibody titer necessary to prevent hepatitis A virus infection, either 15 or 7.5 mg/kg of immune serum globulin was injected into 10 antihepatitis A virus negative volunteers and their serum antihepatitis A virus titers were observed for 28 wk. In addition, antibody titers were observed for 96 wk in a phase 1 clinical trial of a hepatitis A vaccine. The two studies were then compared to assess the immunogenicity of the vaccine and the persistence of the antibody. Serum-neutralizing antibody titers that were greater than or equal to 4 (considered as positive) persisted for 18 wk and 14 wk after the injection of 15 and 7.5 mg/kg of globulin, respectively. Hepatitis A virus vaccine recipients showed adequate neutralizing antibody titers, with the groups receiving 1, 0.5 and 0.25 micrograms/dose showing titers of 4(5.5), 4(4.7) and 4(4), respectively, at 18 mo after the third inoculation. These findings suggested that effective blood antibody titers were likely to be retained in the 1.0 micrograms or 0.5 micrograms/dose groups for at least several years. Moreover, the serum antihepatitis A virus titers demonstrated by a modified radioimmunoassay changed in parallel with the neutralizing antibody titers in the volunteers injected with globulin.

Simultaneous passive and active immunization against hepatitis A

The serum antibody response to simultaneous administration of immune globulin (Ig) and an inactivated hepatitis A vaccine was investigated in healthy volunteers who had been tested and found free of hepatitis A virus. One hundred and forty nine subjects were randomly allocated into three groups. Group 1 received three doses of hepatitis A vaccine at 0, 1 and 6 months, group 2 received 5 ml of Ig and group 3 received a combination of Ig and vaccine. In group 3 the seropositivity rate measured by enzyme-linked immunosorbent assay was 100% at day 5, month 1 and 2, 96% at month 6 and again 100% at month 7. In the group that received vaccine alone the seroconversion rates were 0, 96, 100, 98 and 100 respectively. The geometric mean titres in subjects who received passive/active immunization were about twofold lower than in subjects who received vaccine alone, indicating interference of Ig with the immune response. Despite this, the data show that simultaneous administration of hepatitis A vaccine and Ig confers both immediate protection via Ig administration and long-term vaccine-induced protection. As the antibody levels reached are about twofold lower compared to that after administration of hepatitis A vaccine alone, a booster dose may be required sooner, than if the vaccine were administered alone.

Possible approaches to develop vaccines against hepatitis A

More than a decade ago, successful replication of hepatitis A virus (HAV) in cell culture opened the way to the development of live attenuated and inactivated vaccine candidates. Serial passages of HAV in cell culture led to attenuation as demonstrated by experiments in non-human primates. Several live vaccine candidates obtained through serial passages have been evaluated in volunteers. Significant improvements in the yield of viral antigen from infected cell cultures stimulated the development of killed vaccine candidates. These formalin-inactivated vaccines contain the viral capsid antigens assembled into viral particles. The immunogenic potential of the vaccine candidates depends strongly on the preservation of the configuration of the capsid proteins. Synthetic peptides covering immunogenic sequences of VP1 as well as soluble capsid proteins expressed as fusion proteins in Escherichia coli were therefore only weakly immunogenic when injected at high concentrations in rabbits. On the other hand, tamarin monkeys immunized with a live recombinant vaccinia expressing P1 were protected against virulent challenge. There are, however, considerable drawbacks related to the use of live vaccinia as a carrier virus. Chimeric polio-HAV VP1 viruses have been constructed. These hybrid viruses were not able to induce an immune response, probably because of configurational constraints of poliovirus on the inserted HAV epitopes. More recently, encouraging data on empty virus particles expressed in baculovirus and vaccinia virus systems have been reported.

The main five types of viral hepatitis: an alphabetical update

The rapidly increasing knowledge in the field of viral hepatitis warrants regular updates. Clinical studies with new hepatitis A vaccines have shown that they are safe, well-tolerated, and effective. Several reports on hepatitis B virus (HBV) variants have appeared. Surface antigen mutants may have an important influence on vaccine prophylaxis because existing vaccines may not protect against infection with these variants. Hepatitis D virus is a circular RNA virus that requires the presence of HBV for successful infection. The requirements for the dual expression of these viruses are unknown and their relation is complex. Hepatitis C virus (HCV) is a RNA virus that has homology with the flaviviridae. This is a rather common agent in most populations studied and often causes chronic infection but little is known about its spread. Hepatitis E virus is a RNA virus which is usually spread by contaminated water in developing countries. The disease causes high mortality in pregnant women. The existence of further viral hepatitis agents have been suggested but hard data confirming this is so far lacking.

Immunogenicity of inactivated purified tissue culture vaccine against hepatitis A (HepAvac) assessed in laboratory rodents

Immune response of laboratory rodents (guinea-pigs, CBA and Balb/c mice, Wistar and August rats) to inactivated hepatitis A vaccine was quantitatively assessed. Under comparable conditions of experiment, the mice showed the highest antibody titres and were capable of reacting to the lower doses of immunogen; meanwhile their individual variations in immune response were more pronounced; white rats were the least susceptible to the vaccine, demonstrating the minimal antibody formation; guinea-pigs produced antibody at intermediate levels but the antibody titres were the most homogeneous. The enhancing effect of aluminium hydroxide was observed in guinea-pigs examined at the late postimmunization stage. Differences in immunogenicity of three vaccine lots were essentially similar when these lots were tested as undiluted preparations in guinea-pigs and mice for mean antibody titres and in mice for 50% immune response using serial dilutions of vaccine. All three tests could be routinely employed for vaccine immunogenicity control.