[Advances in liver immunology in 2018].

The mechanism of innate and adaptive immune responses to chronic infections with hepatotropic viruses (HBV, HCV) was studied in 2018. Its mechanism elucidated the dysregulation of natural killer (NK) cells, monocytes, B cells and T cells. In addition, a new target for immune regulation of HBV infection (TLR3/OX40L) was introduced. The discovery of new NK cell immune checkpoints, the involvement of mononuclear macrophages in liver failure and inflammation, sex hormone affecting intrahepatic-resistant bacterial infection through the regulation of humoral immunity, and the communication mechanism between liver and other immune organs have enriched people's understanding of liver immunology and its clinical significance.

A novel hepatovirus identified in wild woodchuck Marmota himalayana.

Hepatitis A virus (HAV) is a hepatotropic picornavirus that causes acute liver disease worldwide. Here, we report on the identification of a novel hepatovirus tentatively named Marmota Himalayana hepatovirus (MHHAV) in wild woodchucks (Marmota Himalayana) in China. The genomic and molecular characterization of MHHAV indicated that it is most closely related genetically to HAV. MHHAV has wide tissue distribution but shows tropism for the liver. The virus is morphologically and structurally similar to HAV. The pattern of its codon usage bias is also consistent with that of HAV. Phylogenetic analysis indicated that MHHAV groups with known HAVs but forms an independent branch, and represents a new species in the genus Hepatovirus within the family Picornaviridae. Antigenic site analysis suggested MHHAV has a new antigenic property to other HAVs. Further evolutionary analysis of MHHAV and primate HAVs led to a most recent common ancestor estimate of 1,000 years ago, while the common ancestor of all HAV-related viruses including phopivirus can be traced back to 1800 years ago. The discovery of MHHAV may provide new insights into the origin and evolution of HAV and a model system with which to explore the pathogenesis of HAV infection.

Virosomal hepatitis a vaccine: comparing intradermal and subcutaneous with intramuscular administration.

BACKGROUND: Vaccination against hepatitis A virus (HAV) is unaffordable to many developing countries. Substantial reductions in cost occur when vaccines are administered intradermally at low doses. Aluminum-free HAV vaccines are considered more suitable for intradermal use than traditional vaccines which can cause long-lasting local reactions. Thus, we compared the immunogenicity and safety of an aluminum-free virosomal HAV vaccine (Epaxal) administered by different routes: intradermal (i.d.), subcutaneous (s.c.), and intramuscular (i.m.). METHODS: Two open pilot studies were conducted as sub-studies of a large lot consistency trial. Healthy subjects aged 18 to 45 were enrolled. Study 1 compared two i.d. regimens of a lower dose of Epaxal [0.1 mL (4.8 IU), one or two injection sites] with i.m. administration of the standard dose [0.5 mL (24 IU)]. Study 2 compared the s.c. with the i.m. administration of the standard dose. At month 12, subjects in study 1 received a booster dose of 0.1 mL i.d. or 0.5 mL i.m.; subjects in study 2 received 0.5 mL via the respective route (s.c. or i.m.). Serum was tested for antibodies at baseline, 2 weeks (study 1), and 1 and 6 months after the primary vaccination as well as prior and 1 month after the booster dose. Incidences of solicited and unsolicited adverse events were recorded. RESULTS: Seroprotection rates (anti-HAV geometric mean concentration of > or =20 mIU/mL) after 1 month ranged from 93.2% to 100% in all groups and remained high until month 12 (range 85.2&-90.2%). Complete (100%) seroprotection was achieved by all subjects in all groups after booster vaccination. All routes of administration were well tolerated. Local reactions were more common in subjects vaccinated i.d. and s.c. than i.m. CONCLUSIONS: The aluminum-free virosomal HAV vaccine Epaxal is highly immunogenic and well tolerated when administered either via i.d., s.c., or i.m. Vaccination via the i.d. route may confer significant cost savings over the conventional i.m. route.

Principles of vaccination and possible development strategies for rational design.

Historically, apart from hygiene, vaccination can be considered as one of the most successful accomplishments of public health in the 20th century. It has lead to some of the greater public health triumphs ever, including the eradication of naturally occurring smallpox and in the control of diseases such as polio. In addition there has been a significant reduction in disease burden imposed by measles, mumps, hepatitis, influenza, diphtheria, haemophilus influenza B and many other infections.

Interferon-lambda contributes to innate immunity of mice against influenza A virus but not against hepatotropic viruses.

Virus-infected cells secrete a broad range of interferon (IFN) subtypes which in turn trigger the synthesis of antiviral factors that confer host resistance. IFN-alpha, IFN-beta and other type I IFNs signal through a common universally expressed cell surface receptor, whereas IFN-lambda uses a distinct receptor complex for signaling that is not present on all cell types. Since type I IFN receptor-deficient mice (IFNAR1(0/0)) exhibit greatly increased susceptibility to various viral diseases, it remained unclear to which degree IFN-lambda might contribute to innate immunity. To address this issue we performed influenza A virus infections of mice which carry functional alleles of the influenza virus resistance gene Mx1 and which, therefore, develop a more complete innate immune response to influenza viruses than standard laboratory mice. We demonstrate that intranasal administration of IFN-lambda readily induced the antiviral factor Mx1 in mouse lungs and efficiently protected IFNAR1(0/0) mice from lethal influenza virus infection. By contrast, intraperitoneal application of IFN-lambda failed to induce Mx1 in the liver of IFNAR1(0/0) mice and did not protect against hepatotropic virus infections. Mice lacking functional IFN-lambda receptors were only slightly more susceptible to influenza virus than wild-type mice. However, mice lacking functional receptors for both IFN-alpha/beta and IFN-lambda were hypersensitive and even failed to restrict usually non-pathogenic influenza virus mutants lacking the IFN-antagonistic factor NS1. Interestingly, the double-knockout mice were not more susceptible against hepatotropic viruses than IFNAR1(0/0) mice. From these results we conclude that IFN-lambda contributes to inborn resistance against viral pathogens infecting the lung but not the liver.

Cost-effectiveness analyses of hepatitis A vaccine: a systematic review to explore the effect of methodological quality on the economic attractiveness of vaccination strategies.

Hepatitis A vaccines have been available for more than a decade. Because the burden of hepatitis A virus has fallen in developed countries, the appropriate role of vaccination programmes, especially universal vaccination strategies, remains unclear. Cost-effectiveness analysis is a useful method of relating the costs of vaccination to its benefits, and may inform policy. This article systematically reviews the evidence on the cost effectiveness of hepatitis A vaccination in varying populations, and explores the effects of methodological quality and key modelling issues on the cost-effectiveness ratios.Cost-effectiveness/cost-utility studies of hepatitis A vaccine were identified via a series of literature searches (MEDLINE, EMBASE, HSTAR and SSCI). Citations and full-text articles were reviewed independently by two reviewers. Reference searching, author searches and expert consultation ensured literature saturation. Incremental cost-effectiveness ratios (ICERs) were abstracted for base-case analyses, converted to $US, year 2005 values, and categorised to reflect various levels of cost effectiveness. Quality of reporting, methodological issues and key modelling issues were assessed using frameworks published in the literature.Thirty-one cost-effectiveness studies (including 12 cost-utility analyses) were included from full-text article review (n = 58) and citation screening (n = 570). These studies evaluated universal mass vaccination (n = 14), targeted vaccination (n = 17) and vaccination of susceptibles (i.e. individuals initially screened for antibody and, if susceptible, vaccinated) [n = 13]. For universal vaccination, 50% of the ICERs were <$US20 000 per QALY or life-year gained. Analyses evaluating vaccination in children, particularly in high incidence areas, produced the most attractive ICERs. For targeted vaccination, cost effectiveness was highly dependent on the risk of infection.Incidence, vaccine cost and discount rate were the most influential parameters in sensitivity analyses. Overall, analyses that evaluated the combined hepatitis A/hepatitis B vaccine, adjusted incidence for under-reporting, included societal costs and that came from studies of higher methodological quality tended to have more attractive cost-effectiveness ratios. Methodological quality varied across studies. Major methodological flaws included inappropriate model type, comparator, incidence estimate and inclusion/exclusion of costs.

[Hepatitis viruses infection situation in Mianyang of the Sichuan province].

OBJECTIVE: To investigate the seroprevalence of hepatitis viruses in Mianyang of the Sichuan province. METHODS: EIISA was used for detecting anti-HAV IgG, HBsAg/HBsAb, anti-HCV IgG and anti-HEV IgG of the serum samples. All sample were collected in Mianyang areas in 2007. RESULTS: 1352 samples were detected. The positive rates of anti-HAV, HBsAg/HBsAb, anti-HCV,and anti-HEV are 81.07% (1096/1352), 5.40% (73/1352) and 61.32% (829/1352), 0.37% (5/1352) and 49.26% (666/1352), respectively. The positive rate at different age group, for anti-HAV was 38.21% of 10-19 years old, 83% of 20-29 years old, 88% of 30-39 years old, 95.03% of 40-49 years old, 97% of 50-59 years old, 97.77% of 60-69 years old, 97.52% of > or =70 years old. For HBsAg/HBsAb were 5.65% or 50.83%, 10.0% or 68.0%, 5.20% or 78.80%, 5.97% or 78.11%, 6.50% or 62.50%, 1.12% or 51.40%, 4.96% or 30.58% at the same age group, respectively,for anti-HCV, was 0.33% of 10-19 years old, 0.80% of 30-39 years, 0.56% of 60-69 years old, 0.83% of > or =70 years old.For HEV-IgG was 26.58% of 10-19 years old, 42.0% of 20-29 years old, 55.22%-61.0% of 30-> or =70 years old, for anti-HEV IgM, was 10.06% (53/527) in the positive samples of HEV-IgG. CONCLUSION: The inoculation againt HAV and HBV is enhanced in the young population. HBsAg carrier and HCV infection is decreasing. The HEV infection is actually increasing.

Cytokines and chronic liver disease.

From an immunological point of view, the healthy liver has been usually associated with the phenomenon of tolerance. A microenvironment of regulatory cytokines produced by liver Kuppfer cells and liver sinusoidal endothelial cells has contributed, together with resident dendritic cells, to generate a tolerogenic environment in this tissue. In this review we discussed the intrahepatic responses to different sorts of liver injury, such as hepatotrophic viruses, alcohol or putative self-antigens. In each case we analyzed the impact of different cytokines in the clinical outcome of the different pathological situations.

Hepatitis A.

The introduction of hepatitis A vaccines in 1995 led to a drop in the number of reported cases of hepatitis A and a shift to a higher percentage of cases occurring in older age groups. The hepatitis A virus survives for extended periods in the environment. Transmission primarily is fecal-oral, although there have been rare instances of transmission through blood products. The virus appears sporadically and is spread by close personal contact, with occasional food-borne outbreaks. Older persons infected by the virus usually develop a symptomatic infection with abrupt onset, fever, and jaundice lasting two months. Children usually have an asymptomatic infection and rarely develop jaundice. Laboratory diagnosis is made by detection of antihepatitis A virus immunoglobulin M in serum. Ten to 20 percent of symptomatic patients experience a prolonged or relapsing course of illness, but chronic infection has not been reported. Fulminant infection occurs in less than 1 percent of patients and can result in emergent liver transplant or death. Prevention starts with thorough handwashing and careful food handling. Prompt disease reporting, the identification of exposed persons, and expeditious administration of immune globulin prevent secondary transmission of the disease. Physicians should consider routine vaccination of children 12 to 23 months of age based on recommendations from the Centers for Disease Control and Prevention. Vaccination for children two years or older and adults should be included in routine preventive care for those at increased risk of contracting the disease (e.g., travelers to certain countries, men who have sex with men, drug abusers, recipients of clotting factor replacement) and for persons with chronic liver disease.

IgA-coated particles of Hepatitis A virus are translocalized antivectorially from the apical to the basolateral site of polarized epithelial cells via the polymeric immunoglobulin receptor.

Although Hepatitis A virus (HAV) is transmitted by the faecal-oral route, its target for replication is the liver. Little is known of its interactions with cells of the gastrointestinal tract, and it is not known by which mechanisms HAV crosses the intestinal epithelium. In this study, it is shown that HAV associated with IgA is translocated from the apical to the basolateral compartment of polarized epithelial cells via the polymeric immunoglobulin receptor by IgA-mediated reverse transcytosis. The relevance of this mechanism, by which HAV-IgA complexes may overcome the intestinal barrier and contribute to infections of the liver, results from the fact that HAV-IgA complexes are infectious for hepatocytes and that significant amounts of intestinal HAV-IgA are present during acute infections, which are also partly transmitted. Besides supporting the primary infection, this mechanism may play a role in relapsing infections by establishing an enterohepatic cycle for HAV.

[Adenovirus induced acute hepatitis in non-human primates after liver- directed gene therapy].

OBJECTIVE: To define the role of lymphocyte subsets and investigate the efficiency of immunosuppression regimen in acute hepatitis in non-human primates after adenovirus mediated gene therapy. METHODS: Six rhesus monkeys were infused with E-1 deleted adenovirus (Ad) expressing E coli lacZ gene or luciferase by various routes. Four of 6 animals were immunosuppressed by cyclophosphamide and predenisone. Two monkeys were transfected with a lacZ containing plasmid with lipofectamine as the control. Lymphocyte subsets CD3, CD4, CD8, CD20 and MHC molecule beta2-microglobulin(beta2-MG) and HLA-DR in liver tissues were studied using immunohistochemical staining. RESULTS: Staining of beta2-MG and HLA-DR on the membranes of hepatocyte and increased numbers of CD3+, CD4+ and CD8+ T-lymphocytes were detected in the livers after gene transfer, while B-lymphocytes were absent. The monkeys developed a mild to moderate transient hepatitis. This was accompanied by adenovirus-mediated T-cell proliferation and neutralizing antibodies to adenovirus. Drug-induced immune suppression enhanced the ability of adenovirus- mediated gene transfer. The development of acute hepatitis and the accompanying immune abnormalities were delayed in immunosuppressed monkeys until after discontinuation of immunosuppressive therapy. Lipofectamine-mediated gene transfer was inefficient and no immune response and liver damage were observed in the livers. CONCLUSIONS: Increased numbers of beta2-MG, HLA-DR, CD3, CD4 and CD8 antigen positive cells are presented in the monkey livers after adenovirus-mediated gene therapy and induce mild to moderate transient hepatic inflammation. Immunosuppression regimen may prolong transgene expression and delay the development of acute adenoviral hepatitis.

An investigation of the potential risk of an HAV outbreak in a prison population following the introduction of cases from a community outbreak.

Increasing Hepatitis A (HAV) infection has been reported in communities in which there is a high level of intravenous drug use. Several cases were identified in a local prison and since the risk of transmission within the prison was felt to be high, it was decided to determine the prevalence of HAV antibodies in the prison population and therefore the number of susceptible inmates. Oral fluid was collected from 269 prisoners for testing for antibodies to HAV. Both IgM and IgG anti-HAV were assessed so that the percentage susceptible and the number recently infected could be ascertained. Eight inmates had evidence of a recent infection. Of the remaining 261, only 56 (21%) were immune to HAV. Therefore vaccination against HAV in addition to HBV should be considered for intravenous drug users and for prisoners remanded from a community where infection is known to be occurring.

Antibody responses to Hepatitis A vaccine in healthy adults.

Hepatitis A vaccination has been used in a number of settings to control community outbreaks of the disease. Yet United Kingdom guidance for post-exposure prophylaxis continues to promote the administration of human normal immunoglobulin, despite concerns about the administration of human derived blood products. Little is known about the time frame of the antibody response to hepatitis A vaccine which, if rapid, could permit the exclusive use of vaccine for post-exposure prophylaxis. We report the findings of a pilot study in healthy adult volunteers given a single dose of Havrix monodose.

Presence of oligoclonal T cells in cerebrospinal fluid of a child with multiphasic disseminated encephalomyelitis following hepatitis A virus infection.

We have investigated the clonality of beta-chain T-cell receptor (TCR) transcripts from the cerebrospinal fluid (CSF) and peripheral blood from a 7-year old child who developed a multiphasic disseminated encephalomyelitis following an infection with hepatitis A virus. We amplified beta-chain TCR transcripts by nonpalindromic adaptor (NPA)-PCR-Vbeta-specific PCR. TCR transcripts from only five Vbeta families (Vbeta13, Vbeta3, Vbeta17, Vbeta8, and Vbeta20) were detected in CSF. The amplified products were combined, cloned, and sequenced. Sequence analysis revealed in the CSF substantial proportions of identical beta-chain of TCR transcripts, demonstrating oligoclonal populations of T cells. Seventeen of 35 (48%) transcripts were 100% identical, demonstrating a major Vbeta13.3 Dbeta2.1 Jbeta1.3 clonal expansion. Six of 35 (17%) transcripts were also 100% identical, revealing a second Vbeta13 clonal expansion (Vbeta13.1 Dbeta2.1 Jbeta1.2). Clonal expansions were also found within the Vbeta3 family (transcript Vbeta3.1 Dbeta2.1 Jbeta1.5 accounted for 5 of 35 transcripts [14%]) and within the Vbeta20 family (transcript Vbeta20.1 Dbeta1.1 Jbeta2.4 accounted for 3 of 35 transcripts [8%]). These results demonstrate the presence of T-cell oligoclonal expansions in the CSF of this patient following infection with hepatitis A virus. Analysis of the CDR3 motifs revealed that two of the clonally expanded T-cell clones exhibited substantial homology to myelin basic protein-reactive T-cell clones. In contrast, all Vbeta TCR families were expressed in peripheral blood lymphocytes. Oligoclonal expansions of T cells were not detected in the peripheral blood of this patient. It remains to be determined whether these clonally expanded T cells are specific for hepatitis A viral antigen(s) or host central nervous system antigen(s) and whether molecular mimicry between hepatitis A viral protein and a host protein is responsible for demyelinating disease in this patient.

A randomised comparison of two inactivated hepatitis A vaccines, Avaxim and Vaqta, given as a booster to subjects primed with Avaxim.

To investigate whether Vaqta may be used as a booster in subjects primed with Avaxim, 127 adults primed 6 months previously with Avaxim were randomised to receive either Vaqta or Avaxim as a booster. Prior to the booster all subjects were seropositive. Geometric mean antibody titres increased from 496 to 7262 mIU/mL 1 month after receiving Vaqta as a booster and from 325 to 5131 mIU/mL 1 month after receiving Avaxim as a booster. Both vaccines were well tolerated; 20.3% of subjects receiving Vaqta experienced a local reaction, compared to 39.7% of those receiving Avaxim. Systemic reactions were reported by 15.6% of those receiving Vaqta and 14.3% of those receiving Avaxim. Vaqta may be used as a booster in subjects primed with Avaxim.

Immunochemiluminescent focus assays for the quantitation of hepatitis A virus and rotavirus in cell cultures.

Two new immunological methods, the luminescent immunofocus assay (LIFA) and the luminescent immunofocus inhibition assay (LIF-IA), are described for the quantitation of cytopathic and non-cytopathic viruses propagated on cell culture monolayers. These methods use enhanced chemiluminescent detection to identify foci (luminescent immunofoci, LIF) of virus-infected cells. Viruses are propagated in susceptible cells under an agarose overlay, inactivated with ultraviolet irradiation, lifted onto nitrocellulose membranes, and probed with virus-specific monoclonal or polyclonal antibody followed by a second antibody conjugated to horseradish peroxidase. Membranes are then treated with a luminol-based detection reagent and exposed to light sensitive film for up to 10 min. The film is developed and foci appear as dark, discrete spots which are proportional to the dose of each virus. The LIFA detected both cytopathic and non-cytopathic hepatitis A viruses (HAV) and simian rotavirus. For the cytopathic HAV, the LIFA and plaque counts were comparable. The LIF-IA was developed for HAV using virus-specific antiserum which effectively attenuated LIF formation. The LIFA and LIF-IA may be completed 5 days faster than conventional radioimmunofocus assays for HAV and rotavirus and do not require the use of radiolabeled antibodies, offering safety advantages and making these techniques more adaptable for general use. Luminescent immunofocus assays should be useful for the detection and quantitation of virtually any cytopathic or non-cytopathic virus that can be propagated in monolayer cultures when virus-specific antiserum is available.

The presence of hepatitis A antibodies in dental workers. A seroepidemiologic study.

BACKGROUND: The licensing of hepatitis A vaccine in the United States and other countries in the 1990s raised the question of vaccine candidates. The authors undertook a study to evaluate the presence of antibodies against hepatitis A virus, or HAV, in dental workers. METHODS: The authors recruited 115 members of the dental staff of Tel Aviv University: 82 dentists, 21 dental assistants, eight dental hygienists and four laboratory technicians. The subjects completed a structured questionnaire regarding demographic information (such as age, sex, number of siblings, number of children) and occupational characteristics. Venous blood was obtained and examined for presence of immunoglobulin G antibodies to HAV by microparticle enzyme immunoassay. RESULTS: Univariant analysis (chi 2 and Student t test) and multivariate stepwise logistic regression analysis were used to identify variables that were associated with seropositivity. Greater number of years of occupation in dentistry were independently and significantly (P = .0004) associated with seropositivity to HAV. The calculated odds ratio showed that each year of work increased the likelihood of being seropositive by 1.06 (6 percent). Subjects tended to have higher seropositive rates if they were older, had a greater number of children, had a greater number of siblings, had worked in hospitals and worked with children (pediatric dentists and orthodontists). CONCLUSIONS: This study suggests that HAV can be considered a hazard to dental workers, with risk increasing as the number of years in dentistry increases. More studies with larger sample sizes are needed. CLINICAL IMPLICATIONS: As HAV infection is associated with morbidity and mortality, dentists--especially those working in areas of endemic HAV (such as Africa, Asia and Latin America)--are encouraged to consider receiving the active vaccine to prevent HAV infection.

Infection of hepatitis A virus in Japanese haemophiliacs.

OBJECTIVES: Outbreaks of hepatitis A virus (HAV) infection in haemophiliacs have been reported from many countries. The aim of this study was to determine the prevalence of hepatitis A virus antibody (HAVAb) in Japanese haemophiliacs. METHODS: Sixty-seven male haemophiliacs were recruited for this study of HAV infection. We also compared the rate of HAV infection with that of human immunodeficiency virus (HIV), hepatitis C virus (HCV), and hepatitis G virus (HGV). RESULTS: Fifteen of 67 haemophiliacs (22.4%) were positive for HAVAb. Prevalence of HAVAb was significantly higher in haemophiliacs than in Japanese normal subjects previously reported (P= 0.0001). Age, alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin and prevalence of HIV, HCV, and HGV were not statistically different between HAVAb positive and HAVAb negative haemophiliacs. We suggest that the use of clotting factor concentrates is closely associated with HAV infection, but HAV infection does not have an effect on clinical course. CONCLUSIONS: Administration of clotting factor concentrates may increase risk of HAV infection in haemophiliacs.

The cost-saving potential of prevaccination antibody tests when implementing a mass immunization program.

A seroprevalence study of hepatitis A virus (HAV), hepatitis B virus (HBV), and varicella-zoster virus (VZV) was carried out among Saudi Arabian National Guard soldiers with the objective of determining the cost-saving potential of prevaccination antibody tests when implementing an immunization program for the soldiers. A systematic sampling of 450 blood samples from 1,350 soldiers who donated blood at our hospital was carried out. Antibody tests were performed using the enzyme-linked immunosorbent assay method. The seropositivity rates for antibodies to HAV, HBV, and VZV were 97.5, 17.8, and 88.5%, respectively. Comparing the cost of prevaccine screening with that of universal vaccination, it was estimated that savings of 76 and 32% could be effected for HAV and VZV. Conversely, screening for HBV before immunization could increase the cost of vaccinating against the disease by 49%. A seroprevalence study could be a useful cost-saving approach to a mass immunization program against endemic, natural immunity-conferring diseases.

Safety and immunogenicity of a pediatric formulation of inactivated hepatitis A vaccine in Argentinean children.

BACKGROUND: Children are a reservoir of hepatitis A virus and must be considered as primary targets of any immunization strategy. The safety and immunogenicity were evaluated for a new formulation of an inactivated hepatitis A vaccine, Avaxim 80 units, containing one-half the antigen dose of the adult formulation. METHODS: The safety of two doses of this vaccine given 6 months apart was evaluated in an open study in 537 Argentinean children 12 months to 15 years old. Immunogenicity was evaluated at Weeks 0, 2, 24 and 27 in a subgroup of 120 subjects. RESULTS: Two weeks after the first vaccine dose, >99% of initially seronegative children had seroconverted (titers > or =20 mIU/ml), with a geometric mean titer of 98.5 mIU/ml. Before booster at 24 weeks all subjects had seroconverted. A strong anamnestic response was observed after the second dose at which time the geometric mean titer had increased >35-fold, and antibody titers were consistent with long term protection. Immediate adverse reactions were observed in 3 of 537 (0.6%) subjects after the first dose. Local reactions were mild and transient and did not increase with subsequent doses. Among the systemic events reported during the 7-day follow-up period, 37 cases of fever after the first dose and 22 cases after the second dose were reported. Only 3 cases of fever were clearly related to vaccination (< or =38.2 degrees C) after the first injection, all of which subsided in less than 1 day. CONCLUSIONS: This study demonstrated the safety and immunogenicity of a pediatric formulation of hepatitis A vaccine in children ages 12 months to 15 years in healthy children ages 12 to 47 months.