Effect of postexposure vaccination in a chimpanzee model of hepatitis A virus infection

The infectivity and pathogenicity of Hepatitis A virus live-attenuated vaccine strain H2 in type I interferon receptor-deficient mice

Hepatitis A virus (HAV) live-attenuated vaccine H2 strain has been approved for clinical use for decades with ideal safety profiles in nonhuman primate models and humans. Recently, type I interferon (IFN) receptor-deficient mice were shown to be susceptible to HAV infection. Herein, we sought to determine the infection and replication dynamics of the H2 in Ifnar^−/− mice that lack type I IFN receptor. Following intravenous injection, the H2 failed to cause obvious clinical symptoms in Ifnar^−/− mice, and no significant upregulation in serum alanine aminotransferase (ALT) levels was observed. Notably, the histopathological examination showed that there were significant focal infiltrations of lymphocytes and neutrophils in the portal area, but no focal necrosis was observed in liver tissues. Viral RNAs sustained in the liver, and the infectious virus could be recovered from the liver tissue until 42 days post-infection. More importantly, H2 infection induced obvious viremia and persistent viral shedding in feces. In addition, robust HAV-specific humoral immune responses were induced in Ifnar^−/− mice. Overall, our study revealed the safety profile of H2 in Ifnar^−/− mice, which not only helps understand the attenuation mechanism of H2, but also expands the application of the Ifnar^−/− mouse model for HAV studies.

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We described the characteristics of Ifnar−/− mice infected by HAV H2 strain infection.

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H2 fails to induce ALT elevationand obvious liver damage in Ifnar−/− mice.

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H2 causes viremia, persistent viral shedding in feces, and replication in mice liver.

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H2 induces robust HAV-specific humoral immune responses in Ifnar^−/− mice.

Adaptive Immune Responses in Hepatitis A Virus and Hepatitis E Virus Infections

Both hepatitis A virus (HAV) and hepatitis E virus (HEV) cause self-limited infections in humans that are preventable by vaccination. Progress in characterizing adaptive immune responses against these enteric hepatitis viruses, and how they contribute to resolution of infection or liver injury, has therefore remained largely frozen for the past two decades. How HAV and HEV infections are so effectively controlled by B- and T-cell immunity, and why they do not have the same propensity to persist as HBV and HCV infections, cannot yet be adequately explained. The objective of this review is to summarize our understanding of the relationship between patterns of virus replication, adaptive immune responses, and acute liver injury in HAV and HEV infections. Gaps in knowledge, and recent studies that challenge long-held concepts of how antibodies and T cells contribute to control and pathogenesis of HAV and HEV infections, are highlighted.

Type A viral hepatitis: A summary and update on the molecular virology, epidemiology, pathogenesis and prevention

Although epidemic jaundice was well known to physicians of antiquity, it is only in recent years that medical science has begun to unravel the origins of hepatitis A virus (HAV) and the unique pathobiology underlying acute hepatitis A in humans. Improvements in sanitation and the successful development of highly efficacious vaccines have markedly reduced the worldwide prevalence and incidence of this enterically-transmitted infection over the past quarter century, yet the virus persists in vulnerable populations and remains a common cause of food-borne disease outbreaks in economically-advantaged societies. Reductions in the prevalence of HAV have led to increases in the median age at which infection occurs, often resulting in more severe disease in affected persons and paradoxical increases in disease burden in some developing nations. Here, we summarize recent advances in the molecular virology of HAV, an atypical member of the Picornaviridae family, survey what is known of the pathogenesis of hepatitis A in humans and the host-pathogen interactions that typify the infection, and review medical and public health aspects of immunisation and disease prevention.

Hepatitis A vaccine versus immune globulin for postexposure prophylaxis

BACKGROUND

Hepatitis A vaccine administered to persons after exposure to the hepatitis A virus has not been compared directly with immune globulin, which is known to be highly effective in preventing hepatitis A when given within 2 weeks after exposure to the virus.

METHODS

We randomly assigned household and day-care contacts, 2 to 40 years of age, in Almaty, Kazakhstan, to receive one standard age-appropriate dose of hepatitis A vaccine or immune globulin within 14 days after exposure to patients with hepatitis A. Instances of laboratory-confirmed, symptomatic hepatitis A infection occurring between 15 and 56 days after exposure were then assessed during active follow-up of all susceptible contacts.

RESULTS

Of 4524 contacts who underwent randomization, 1414 (31%) were susceptible to hepatitis A virus and 1090 were eligible for the per-protocol analysis. Among these contacts, 568 received hepatitis A vaccine and 522 received immune globulin. Most contacts were children (average age, 12 years), and most received prophylaxis during the second week after exposure (average interval after exposure, 10 days). The baseline characteristics of the contacts were similar in the two groups. Symptomatic infection with hepatitis A virus was confirmed in 25 contacts receiving vaccine (4.4%) and in 17 contacts receiving immune globulin (3.3%) (relative risk, 1.35; 95% confidence interval, 0.70 to 2.67).

CONCLUSIONS

Low rates of hepatitis A in both groups indicate that hepatitis A vaccine and immune globulin provided good protection after exposure. Although the study's prespecified criterion for noninferiority was met, the slightly higher rates of hepatitis A among vaccine recipients may indicate a true modest difference in efficacy and might be clinically meaningful in some settings. Vaccine has other advantages, including long-term protection, and it may be a reasonable alternative to immune globulin for postexposure prophylaxis in many situations. (ClinicalTrials.gov number, NCT00139139 [ClinicalTrials.gov].).

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 vaccine in the last-minute traveler

Current recommendations state that travelers should receive hepatitis A vaccine 2 to 4 weeks before departure. Such recommendations, however, may dissuade last-minute travelers from receiving the vaccine. A preponderance of evidence exists to support hepatitis A vaccination of the imminent-departure traveler and therefore suggests that these guidelines merit reconsideration. In examining this issue, one of the most important elements to determine is the amount of time required for seroconversion following vaccination. Clinical trials of hepatitis A vaccines measured antibody response at 2 and 4 weeks after vaccination. However, studies investigating early seroconversion found that the vast majority of vaccinees develop antibodies within 2 weeks of vaccination, some as early as 12 days after vaccination. This is relevant information, given that the hepatitis A virus has an average incubation period of 28 days. Seroconversion is predicated on achieving a "protective" antibody level. However, levels of antibody considered protective remain debatable. Evidence suggests that clinical disease does not occur at antibody levels lower than those currently accepted as protective. Furthermore, hepatitis A vaccine has been proved effective in controlling outbreaks worldwide. Research data show that a single dose of vaccine can halt outbreaks if an adequate number of susceptible individuals are vaccinated. Information from rapid-outbreak control studies and those assessing postexposure administration of hepatitis A vaccine suggest that late vaccination provides a significant degree of protection. For these reasons, hepatitis A vaccine may be administered at any time before departure because it will still provide travelers with protection.

Cost-effectiveness of hepatitis A vaccine in prevention of secondary hepatitis A infection

Using a decision-tree based model, we investigated the cost-effectiveness of several vaccination strategies for household, day care center and nursery/primary school contacts of primary cases of hepatitis A in France. Depending on the age groups vaccinated, the cost per symptomatic case avoided varied between 700 and 1,300 Euro (1 Euro = 0.93 US dollars) for household contacts. Vaccination of contacts in day care centers and schools resulted in cost-savings. However, these findings are contingent on the limited and controversial data available on vaccine protective efficacy. In particular, the question of the relative efficacy of vaccination as compared with the use of immunoglobulins needs further study.

Hepatitis A: post-exposure prophylaxis

We report on the findings of an exploratory review of evidence published in English from 1945 to identify the best post-exposure prophylaxis treatment and the longest acceptable interval after exposure for prophylaxis to be effective. We found no evidence that post-exposure administration of currently available immunoglobulins is effective in preventing hepatitis A infection and disease. The use of immunoglobulins for immunoprophylaxis should not be widely recommended until a systematic review of the evidence has been conducted. We recommend that active immunization to secondary contacts of exposed and vaccinated subjects be offered.

Hepatitis A vaccine

Hepatitis A is an infectious disease frequently reported in the United States. An average of 26,000 cases were reported each year during 1980 to 1999; probably 3 times as many occurred. Hepatitis A vaccines provide a powerful new prevention tool. The 2 inactivated hepatitis A vaccines available as pediatric and adult formulations in the United States and in many other countries are safe, immunogenic, and efficacious. A single dose provides excellent short-term protection; the second dose is thought to be important for long-term protection. Because hepatitis A virus (HAV) is excreted in high concentrations in the stool, the principal mode of transmission is person-to-person by the fecal-oral route, most commonly among household and sexual contacts of people with HAV infection. Children can be important in transmission because they frequently have unrecognized or asymptomatic infection. Implementation of recommendations for routine hepatitis A vaccination of children living in areas with consistently elevated hepatitis A rates appears to be resulting in dramatic declines in the overall incidence of the disease. Improved vaccination coverage and continued monitoring of incidence rates are needed to determine the overall long-term impact of this strategy.

Inactivated hepatitis A vaccine: immunogenicity, efficacy, safety and review of official recommendations for use

There is 10 years of marketing experience with the hepatitis A vaccine Havrix. It is highly immunogenic, provides lasting protection in healthy individuals and generates protective levels of antibodies in patients with chronic liver disease or impaired immunity. Postmarketing surveillance data have confirmed the outstanding safety profile of the vaccine. The timing of the booster dose is not critical to effectiveness, which has advantages for the protection of travelers to regions of high endemicity. The vaccine is effective in curbing outbreaks of hepatitis A and also when administered postexposure, due to rapid seroconversion and the long incubation period of the disease. In intermediate endemic regions, an epidemiological shift in hepatitis A infection has driven the development of universal preventive strategies to be added to the targeting of at-risk groups. Existing official recommendations and future directions for vaccine use are reviewed.

Vaccination policy against hepatitis A in Italy

In Italy, improved sanitation and living conditions have led to a decline in the rate of hepatitis A infection among children generating an increasing proportion of adults susceptible to this virus. Shellfish consumption is a major source of infection while person to person transmission is important in the spread of infection and in the maintenance of outbreaks. Thus prevention of secondary HAV infection is a crucial point. A randomised controlled trial of hepatitis A vaccine in household contacts of people with sporadic HAV infection in Italy has shown a protective efficacy of 82% (CI 20-96%). The two secondary infections in the vaccine group were symptomless, suggesting that the disease expression may be weaker in vaccinated subjects.

Hepatitis vaccines

The development of highly effective and safe inactivated HAV vaccines and highly effective and safe recombinant HBsAg subunit HBV vaccines represents major advances in the control of viral hepatitis, but many challenges remain. Because current HAV immunization recommendations target high-risk groups only, infection rates are unlikely to fall dramatically until universal childhood immunization programs are implemented. Routine HBV vaccination of infants, children, adolescents, and individuals at high risk will reduce the incidence of infection, but vaccine nonresponsiveness and escape mutants are important potential challenges. Whether either HAV or HBV vaccine provide lifelong protection remains to be determined. Vaccines for HDV, HEV, and HCV are not yet available.

Travel-related vaccines

Travelers are at increased risk for several infections, including familiar infections such as measles that are widely distributed but more common in developing countries. Vaccines can markedly decrease the risk for many of these infections and are an important part of pretravel preparation. Travel provides an opportunity to review and update routine vaccines in adults and assess risk from unusual infections. Global travel is growing. Persons who are elderly, HIV-infected, and immunocompromised account for many of the travelers. Studies that assess the immunogenicity, efficacy, and adverse effects of some of the special vaccines used primarily in travelers generally have been done in young, healthy populations. Findings in young adults do not apply to other populations in whom immune response can be slower, less effective, and less durable. Recent reports of severe adverse events in elderly persons who have received yellow fever vaccine are a reminder that widely used, old vaccines can have unexpected side effects when used in a new population. It is biologically plausible that adverse effects might be more common in the elderly, and epidemiologically plausible that occasional instances of similar adverse events in the past could have been missed. Studies on special and travel vaccines in the elderly are needed urgently to define how these vaccines should be used in older populations and whether alternative means for protection are needed.

Efficacy of hepatitis A vaccine in prevention of secondary hepatitis A infection: a randomised trial

BACKGROUND

Hepatitis A vaccination stops outbreaks of hepatitis A infection, but its efficacy against infection after exposure has not been proven. We investigated the use of hepatitis A vaccine to prevent secondary infections with hepatitis A virus (HAV).

METHODS

We did a randomised controlled trial of hepatitis A vaccine in household contacts of people with sporadic HAV infection (index cases). Households (index cases and contacts) were randomly assigned to the vaccine group or unvaccinated group, according to the study week in which they were enrolled. All household contacts in the vaccine group received vaccination at the time of entry to the study.

FINDINGS

During 45 days of follow-up, secondary infection had occurred in ten (13.3%) of 75 households (two families had two cases each) in the untreated group and in two (2.8%) of 71 households in the vaccine group. The protective efficacy of the vaccine was 79% (95% CI 7-95). The number of secondary infections among household contacts was 12 (5.8%) of 207 in the unvaccinated group and two (1.0%) of 197 in the vaccinated group. Therefore, 18 individuals needed to be vaccinated to prevent one secondary infection.

INTERPRETATION

Hepatitis A vaccine is effective in the prevention of secondary infection of HAV and should be recommended for household contacts of primary cases of HAV infection.

The use of non-human primates as animal models for the study of hepatitis viruses

Hepatitis viruses belong to different families and have in common a striking hepatotropism and restrictions for propagation in cell culture. The transmissibility of hepatitis is in great part limited to non-human primates. Enterically transmitted hepatitis viruses (hepatitis A virus and hepatitis E virus) can induce hepatitis in a number of Old World and New World monkey species, while the host range of non-human primates susceptible to hepatitis viruses transmitted by the parenteral route (hepatitis B virus, hepatitis C virus and hepatitis delta virus) is restricted to few species of Old World monkeys, especially the chimpanzee. Experimental studies on non-human primates have provided an invaluable source of information regarding the biology and pathogenesis of these viruses, and represent a still indispensable tool for vaccine and drug testing.

[Inactivated vaccine against hepatitis A: review of the literature and considerations on its use]

A new, safe, highly immunogenic and probably long term effective inactivated hepatitis A virus vaccine has been licensed for clinical use. Clinical trials in developed countries have demonstrated its efficacy in preventing hepatitis A in high risk groups, such as travelers to regions where HAV infection is endemic and day care children and staff, its efficacy in postexposure conditions and in community outbreaks. The authors review the basic and changing features of the disease and its epidemiology in specific geographical regions trying to elucidate its use in the control of the disease in developing countries, especially in Brazil. Taking in consideration its efficacy, safety and immunogenicity, the inactivated hepatitis A vaccine may be of extreme value in terms of individual protection. Because this vaccine is so new, there are no formal recommendations for its use in developing countries, and appropriate public health use of hepatitis A vaccine requires up-to-date epidemiological information.

Postexposure prophylaxis

The timely facilitation of immunologic (immunoglobulin or vaccine) or antimicrobial prophylaxis is used in individuals who have been exposed to certain infectious diseases. Such methodology has been shown to be helpful in infections such as viral hepatitis types A and B, measles, varicella, rabies, and tuberculosis. The data supporting such use in rubella and mumps are not strong and information is still needed in hepatitis C, human immunodeficiency virus, and Lyme borreliosis. This article reviews postexposure prophylaxis in these situations. Preventive strategies for meningococcal disease, group A streptococcus, tetanus, diphtheria, and pertussis are discussed elsewhere in this issue.