Safety and immunogenicity of hepatitis A vaccine in healthy children

Prevention of Hepatitis A Virus Infection in the United States: Recommendations of the Advisory Committee on Immunization Practices, 2020

HEPATITIS A IS A VACCINE-PREVENTABLE, COMMUNICABLE DISEASE OF THE LIVER CAUSED BY THE HEPATITIS A VIRUS (HAV). THE INFECTION IS TRANSMITTED VIA THE FECAL-ORAL ROUTE, USUALLY FROM DIRECT PERSON-TO-PERSON CONTACT OR CONSUMPTION OF CONTAMINATED FOOD OR WATER. HEPATITIS A IS AN ACUTE, SELF-LIMITED DISEASE THAT DOES NOT RESULT IN CHRONIC INFECTION. HAV ANTIBODIES (IMMUNOGLOBULIN G [IGG] ANTI-HAV) PRODUCED IN RESPONSE TO HAV INFECTION PERSIST FOR LIFE AND PROTECT AGAINST REINFECTION; IGG ANTI-HAV PRODUCED AFTER VACCINATION CONFER LONG-TERM IMMUNITY. THIS REPORT SUPPLANTS AND SUMMARIZES PREVIOUSLY PUBLISHED RECOMMENDATIONS FROM THE ADVISORY COMMITTEE ON IMMUNIZATION PRACTICES (ACIP) REGARDING THE PREVENTION OF HAV INFECTION IN THE UNITED STATES. ACIP RECOMMENDS ROUTINE VACCINATION OF CHILDREN AGED 12-23 MONTHS AND CATCH-UP VACCINATION FOR CHILDREN AND ADOLESCENTS AGED 2-18 YEARS WHO HAVE NOT PREVIOUSLY RECEIVED HEPATITIS A (HEPA) VACCINE AT ANY AGE. ACIP RECOMMENDS HEPA VACCINATION FOR ADULTS AT RISK FOR HAV INFECTION OR SEVERE DISEASE FROM HAV INFECTION AND FOR ADULTS REQUESTING PROTECTION AGAINST HAV WITHOUT ACKNOWLEDGMENT OF A RISK FACTOR. THESE RECOMMENDATIONS ALSO PROVIDE GUIDANCE FOR VACCINATION BEFORE TRAVEL, FOR POSTEXPOSURE PROPHYLAXIS, IN SETTINGS PROVIDING SERVICES TO ADULTS, AND DURING OUTBREAKS.

Hepatitis A virus infections, immunisations and demographic determinants in children and adolescents, Germany

Hepatitis A is a vaccine-preventable disease with a global distribution. It predominantly occurs in regions with inadequate living conditions, but also affects populations in industrialised countries. Children are frequently involved in the transmission of hepatitis A virus (HAV) and thus play a central role in the epidemiology of hepatitis A. Here, we investigated HAV infections, immunisations, and associated demographic determinants in a nationwide, population-based, cross-sectional survey conducted in Germany from 2003-2006. Out of 17,640 children and adolescents, complete data sets (HAV serology, demographic information and vaccination card) were available for 12,249 (69%), all aged 3-17 years. We found protective antibody levels (>=20 IU/L) in 1,755 (14%) individuals, 1,395 (11%) were vaccinated against hepatitis A, 360 (3%) individuals were HAV seropositive without prior hepatitis A vaccination, thus indicating a previous HAV infection. Antibody prevalence (attributable to vaccination or infection) increased significantly with age. Multivariate logistic regression revealed that predominantly children and adolescents with migration background-even if they were born in Germany-are affected by HAV infections. Our results provide a rationale to emphasise existing vaccination recommendations and, moreover, to consider additional groups with a higher risk of infection for targeted vaccination, especially children with a migration background.

Comparing live attenuated and inactivated hepatitis A vaccines: an immunogenicity study after one single dose

INTRODUCTION

While three types of hepatitis A vaccines are available in China, little data are available to compare them in terms of early antibody response. We conducted a trial to compare antibody response at 7, 14 and 28 days.

METHODS

We randomized primary school children in Gansu and Jilin provinces into four groups to receive either (1) Chinese live attenuated hepatitis A vaccine (H2 strain), (2) domestic inactivated hepatitis A vaccine (Healive(®)), (3) imported inactivated hepatitis A vaccine (Havrix(®)) or (4) hepatitis B vaccine (Control group). We compared groups at 7, 14 and 28 days in terms of proportion of sero-conversions (≥10 mUI/ml), and Geometric Mean Concentration (GMC) of antibodies measured with a Microparticle Enzyme Immunoassay (MEIA). We compared rates of self-reported adverse events following immunization (AEFI) in the first three days.

RESULTS

204 children received the H2 vaccine, 208 received Healive(®), 214 received Havrix(®), and 215 received hepatitis B vaccine (no differences across groups in terms of age, sex, weight and height). At seven days, sero-conversion proportions were 25%, 35%, 27% and 2% (p<0.0001) with GMC of 6 mIU/ml, 8 mIU/ml, 6 mIU/ml and 3 mIU/ml, respectively for the four groups. At 28 days, sero-conversion proportions were 98%, 100%, 93% and 3% (p<0.0001) with GMC of 47 mIU/ml, 71 mIU/ml, 67 mIU/ml and 3 mIU/ml, respectively. AEFI were benign and did not differ across groups (p=0.94).

CONCLUSIONS

While our study was not able to identify differences between Havrix(®), Healive(®) and H2 vaccine in terms of sero-conversion proportion and GMC between seven and 28 days, further studies should evaluate non-inferiority or equivalence of the Chinese vaccines, particularly with respect to the GMC concentration for the H2 vaccine since it could affect long-term protection.

Compliance with multiple-dose vaccine schedules among older children, adolescents, and adults: results from a vaccine safety datalink study

OBJECTIVES

We studied compliance with multiple-dose vaccine schedules, assessed factors associated with noncompliance, and examined timeliness of series completion among older children, adolescents, and adults.

METHODS

We conducted a large, multisite, retrospective cohort study of older children, adolescents, and adults in the Vaccine Safety Datalink population from 1996 through 2004. We quantified the rates of completion of all required doses for varicella, hepatitis A, and hepatitis B vaccines according to their recommended schedules.

RESULTS

Among those who received a first dose of varicella (n = 16 075), hepatitis A (n = 594 917), and hepatitis B (n = 590 445) vaccine, relatively few completed the series (55%-65% for hepatitis B vaccine and 40%-50% for hepatitis A and varicella vaccines in most age groups). Compliance was lowest among adolescents (35.9%) and Medicaid recipients (29.7%) who received varicella vaccine and among younger adult age groups who received hepatitis A vaccine (25%-35% across those age groups). Even among series completers, there was a relatively long interval of undervaccination between the first and last doses.

CONCLUSIONS

Compliance with multiple-dose vaccine series among older children, adolescents, and adults is suboptimal. Further evaluations of strategies to improve compliance in these populations are needed.

Virologic and immunologic correlates with the magnitude of antibody responses to the hepatitis A vaccine in HIV-infected children on highly active antiretroviral treatment

BACKGROUND

HIV-infected individuals mount poor antibody responses to vaccines. We sought to identify the immunologic and virologic factors associated with a robust response to hepatitis A virus (HAV) vaccine in children on highly active antiretroviral treatment.

METHODS

One hundred fifty-two pediatric highly active antiretroviral treatment recipients immunized against HAV at weeks 0 and 24 had anti-HAV antibodies, CD4+, CD8+, and CD19+ cell percent assessed at weeks 0 and 32. Subgroups had HIV viremia, B- and T-cell subpopulations, and cell-mediated immunity (CMI) to HAV and other stimulants measured.

RESULTS

Anti-HAV antibodies after complete vaccination correlated positively with CD4+ percent and CD19+ percent and negatively with viremia and CD8+ percent at baseline, but not at 32 weeks. There were no significant correlations between anti-HAV antibodies and B- or T-cell-naïve, memory, or activated subpopulations or non-HAV CMI. Compared with children who remained HAV-CMI-negative, those who mounted HAV-CMI in response to vaccination had higher anti-HAV antibody titers and CD19+ CD21+ CD27+ memory B cell percent at 32 weeks, but no other differences.

CONCLUSIONS

In HIV-infected children on highly active antiretroviral treatment, control of viral replication and conserved or reconstituted CD19+ and CD4+ cell numbers and function determine a robust antibody response to anti-HAV primary immunization. Our data support a bidirectional B- and T-cell cooperation in the response to the HAV vaccine.

Antibody response to hepatitis A immunization among human immunodeficiency virus-infected children and adolescents

Seventy-one of 84 human immunodeficiency virus (HIV)-infected children [84.5% (95% confidence interval: 75-91.5%)] were hepatitis A virus (HAV) seropositive after 2 doses of HAV vaccine. Higher CD4% and HIV suppression were significantly associated with increased HAV seropositivity rate. In multivariate analysis, CD4 >or=25% and young age were independent predictors of HAV seropositivity. Of 7 children given a third HAV vaccine dose because of negative HAV antibody after 2 doses, 2 (29%) became seropositive.

Immunogenicity of hepatitis A-inactivated vaccine administered to seronegative infants, and serological follow-up 12 months after second dose

AIM

To evaluate a) the safety and immunogenicity of anti-HAV-inactivated vaccine administered during the first year of life to anti-HAV seronegative babies, and b) the antibody persistence in a low/intermediate endemic area.

METHODS

After having obtained informed written consent from mothers, 92 babies were vaccinated at 4 and 10 mo of age. All babies were seronegative at birth and did not present HAV-RNA shedding in three serial stool samples taken at 1, 2 and 3 mo of age.

RESULTS

No general side effects (fever > 38 degrees C) were observed. After the first dose of vaccine, 70/82 (85.4%) babies developed anti-HAV > 10 mIU/ml and 36/82 (43.9%) > 20 mIU/ml. After the second dose of vaccine, all babies developed a titre > 20 mIU/ml, and GMT was 877 mIU/ml. After 1 y of follow-up, the decreasing rate was similar to that reported for adult populations. Furthermore, three babies doubled the titre observed 1 mo after the second dose, indicating the possible spread of HAV even in a low/intermediate endemic area.

CONCLUSION

Anti-HAV vaccine is safe, immunogenic and able to induce immune memory, and can be integrated into the routine infant immunization schedule during the first year of life.

Immunization issues before and after solid organ transplantation in children

Solid-organ transplant recipients are at risk from various infectious diseases, many of which can be prevented by immunizations that could reduce morbidity and mortality. However, it is not uncommon for children requiring transplantation to have received inadequate or no immunizations pre-transplant. Every effort should be made to immunize transplant candidates early in the course of their disease according to recommended schedules prior to transplantation. It is also important to immunize their household contacts and healthcare workers. In this review, we summarize the major immunization issues for children undergoing transplantation, the data currently available on immunization safety and efficacy, and suggest immunization practices to reduce vaccine-preventable disease. There is a real need for a standardized approach to the administration and evaluation of immunizations in this group of patients.

Hepatitis A vaccination of Argentinean infants: comparison of two vaccination schedules

BACKGROUND

Early immunization to protect infants against hepatitis A (HA) is recommended in intermediate or high endemic areas of the world, but little is known of the effects of maternal antibodies on the immune response. We studied the immunogenicity and reactogenicity of an inactivated HA vaccine administered in two different schedules to 2-month-old infants in an intermediate/high endemic area in Argentina.

METHODS

In this double-blind, randomized study 131 infants received either three doses (at 2, 4, 6 months of age [Group A]) or one dose (at 6 months of age [Group B]) of the pediatric inactivated HA vaccine, Avaxim 80, and a booster dose at 15-18 months. HAV antibodies were measured (ELISA) at 2, 7, 15-18 and 16-19 months of age. Immediate (30 min after injection) and solicited local and systemic reactions were recorded for 7 days after each injection.

RESULTS

Of 107/131 subjects (81.6%) who completed the study and who provided final serum samples after booster dose, 94 (87.8%) were seropositive at enrolment (>20 mIU/mL) with geometric mean concentrations (GMC) of 2989 and 3637 mIU/mL in Groups A and B, respectively. One month post-booster GMCs were 8236 mIU/ml (95% CI; 6304, 10760) and 1687 mIU/ml (1148, 2479) in Groups A and B, respectively, with 100% seroprotection.

CONCLUSIONS

The HA vaccine was well tolerated and induced immunological priming in both groups during the first year of life in spite of the presence of maternal antibodies. Post-booster GMCs achieved after one or three primary doses suggest a long-term protection against HA.

Experience with hepatitis A and B vaccines

The lengthy history of efforts to understand the pathogenesis and means of preventing and controlling both hepatitis A and B is noteworthy for many exceptional scientific achievements. Among these are the development of vaccines to prevent the spread of infection through induction of active immunity to hepatitis A virus (HAV) and hepatitis B virus (HBV). The first plasma-derived hepatitis B vaccine was licensed in the United States in 1981 and was replaced by recombinant hepatitis B vaccines in 1986 and 1989. Vaccines to prevent HAV infection were licensed in the United States in 1995 and 1996. Subsequently, combination vaccines that included both hepatitis A and B vaccine components, or the hepatitis B component in combination with other commonly administered vaccines, were licensed in the United States. Despite significant reductions in hepatitis-related morbidity and mortality that have resulted from widespread use of these vaccines, vaccine-preventable morbidity and mortality still occur. The purposes of this article are to review clinical trial and other experience with hepatitis A and B vaccines in healthy individuals as well as in those with chronic liver disease, infected with the human immunodeficiency virus, or requiring hemodialysis; describe the impact that these vaccines and national recommendations for vaccination have had on reducing the incidence of HAV and HBV infection; and recommend expansion of these recommendations to include universal vaccination of adults as a means of further reducing the burden of viral hepatitis.

Immunogenicity and Tolerability of Hepatitis A Vaccine in HIV-Infected Children

The immunogenicity and tolerability of hepatitis A virus vaccine was evaluated in a group of 32 children with human immunodeficiency virus (HIV) infection and 27 children with seroreversion. After 2 doses of vaccine, 100% of children experienced seroconversion with good toleration of the vaccine. There were no differences in variation of virus load between immunized HIV-positive children and a group of 31 nonimmunized HIV-positive children with similar characteristics.

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

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

Vaccines and immunotherapies for the prevention of infectious diseases having cutaneous manifestations

Although the development of antimicrobial drugs has advanced rapidly in the past several years, such agents act against only certain groups of microbes and are associated with increasing rates of resistance. These limitations of treatment force physicians to continue to rely on prevention, which is more effective and cost-effective than therapy. From the use of the smallpox vaccine by Jenner in the 1700s to the current concerns about biologic warfare, the technology for vaccine development has seen numerous advances. The currently available vaccines for viral illnesses include Dryvax for smallpox; the combination measles, mumps, and rubella vaccine; inactivated vaccine for hepatitis A; plasma-derived vaccine for hepatitis B; and the live attenuated Oka strain vaccine for varicella zoster. Vaccines available against bacterial illnesses include those for anthrax, Haemophilus influenzae, and Neisseria meningitidis. Currently in development for both prophylactic and therapeutic purposes are vaccines for HIV, herpes simplex virus, and human papillomavirus. Other vaccines being investigated for prevention are those for cytomegalovirus, respiratory syncytial virus, parainfluenza virus, hepatitis C, and dengue fever, among many others. Fungal and protozoan diseases are also subjects of vaccine research. Among immunoglobulins approved for prophylactic and therapeutic use are those against cytomegalovirus, hepatitis A and B, measles, rabies, and tetanus. With this progress, it is hoped that effective vaccines soon will be developed for many more infectious diseases with cutaneous manifestations.

Effect of maternal antibody on immunogenicity of hepatitis A vaccine in infants

OBJECTIVE

To determine the effect of maternal antibody on hepatitis A vaccine immunogenicity in infants. Study design Infants of mothers negative for antibody to hepatitis A virus (anti-HAV; group 1) were administered hepatitis A vaccine at 2, 4, and 6 months of age, and infants of anti-HAV-positive mothers were randomized to receive either hepatitis A vaccine (group 2) or hepatitis B vaccine (group 3) on the same schedule. Group 3 infants subsequently received hepatitis A vaccine at 8 and 10 months of age.

RESULTS

At 15 months of age, 100% of infants in group 1, 93% in group 2, and 92% in group 3 had protective levels of antibody. However, there were significant differences in the geometric mean concentration (GMC) of anti-HAV between groups. Group 1 GMC was 231 mIU/mL, compared with 85 mIU/mL for group 2 and 84 mIU/mL for group 3 (P<.001, group 1 vs group 3).

CONCLUSIONS

Passively acquired maternal anti-HAV resulted in a significantly lower final antibody response when infants were administered hepatitis A vaccine at 2, 4, and 6 months of age or at 8 and 10 months of age.

Immunization of children after solid organ transplantation

The array of immunizations commonly used in childhood has risen in an attempt to prevent many of the potentially serious infections of infancy and childhood. In this article, the authors provide rational guidelines for vaccination of these children. The authors briefly review the susceptibilities caused by immunosuppression in these patients, discuss the problems with various immunizations, and make individual recommendations regarding the use of each vaccine. Most recommendations are based on inferences from populations that may not be directly comparable to the transplantation population (patients with HIV or cancer or patients who have undergone bone marrow transplant), from case reports, and from small series of patients. The best recommendations ultimately must await the results of controlled trials of immunization.

Immunological priming of one dose of inactivated hepatitis A vaccine given during the first year of life in presence of maternal antibodies

BACKGROUND

In hepatitis A virus (HAV)-seronegative infants, inactivated hepatitis A vaccines are highly immunogenic. On the contrary, in infants who are HAV-seropositive before vaccination, the interfering effect of passively-transferred maternal anti-HAV antibodies leads to lower post-primary immunization anti-HAV levels, as compared to those achieved by seronegative infants. One possible way to overcome this drawback is to delay hepatitis A vaccination later during the first year of life. The objective of the study was to document the immunogenicity of an inactivated hepatitis A vaccine in 6 months old HAV-seropositive infants, given as two dose regimen consisting of a single primary immunization at 6 months of age, followed by a booster dose 6 months later.

METHODS

The immunogenicity of one hepatitis A vaccine (Avaxim pediatric, Aventis Pasteur) was documented in 108 6 months old, HAV-seropositive infants randomly assigned to receive one priming dose of hepatitis A vaccine either concomitantly with (Group 2) or 2 weeks after the third dose of routine diphteria-tetanus-whole cell pertussis reconstituting lyophilized tetanus conjugated Haemophilus influenzae type b (DTwcP//PRP approximately T) vaccine and oral poliomyelitis vaccine (OPV) (Group 1). A booster dose was given 6 months later, concomitantly with MMR vaccine.

RESULTS

The 91 infants who were HAV-seropositive (ELISA titer >20 mIU/ml) at the moment of primo vaccination remained seropositive 1 month later. Geometric mean titers (GMT) decreased from 292 and 278 mIU/ml 1 month after the first dose, to 77.6 and 76.0 mIU/ml 6 months after, in Groups 1 and 2, respectively. Post-booster titers increased markedly in both groups, with GMTs of 1731 and 1866 mIU/ml and geometric mean post/pre-immunization titer ratios of 22.3 and 24.6, respectively.

CONCLUSIONS

These results suggest that immunological priming induced by a single dose of Avaxim pediatric administered to 6 or 6.5 months old, HAV-seropositive infants is present and should not preclude the use of this vaccine in such populations.

Hepatitis A vaccination of infants: effect of maternal antibody status on antibody persistence and response to a booster dose

BACKGROUND

Infants with passively transferred maternal antibody (PMA) to hepatitis A virus (HAV) have lower concentrations of antibody to HAV (anti-HAV) after vaccination. We examined the effect of PMA on persistence of anti-HAV and on immune memory.

METHODS

We measured anti-HAV concentrations of 6-year-old children who had responded to a three dose hepatitis A vaccine series at ages 2, 4 and 6 months. Group 1 children were born to anti-HAV-negative women; Group 2 children had anti-HAV-positive mothers and PMA at 2 months of age. Children without detectable antibody at 6-year follow-up were offered a booster dose [360 enzyme-linked immunosorbent units (ELU)]. An anamnestic response was defined as a postbooster anti-HAV concentration of > or =400 mIU/ml.

RESULTS

At follow-up, before the booster dose, Group 1 subjects had a higher geometric mean concentration (50 mIU/ml vs.18 mIU/ml, P = 0.007), and a larger proportion retained seroprotective concentrations of anti-HAV [21 of 31 (68%) vs.4 of 17 (24%)] compared with Group 2 subjects. The two stage antibody decline curves for the two groups from 8 months old to follow-up testing were parallel. An anamnestic response occurred in all (5 of 5) Group 1 and 67% (4 of 6) of Group 2 children. The geometric mean antibody concentrations after the booster were 1102 and 406 mIU/ml for Groups 1 and 2, respectively (P = 0.10).

CONCLUSIONS

Infants with PMA who receive hepatitis A vaccine have significantly lower concentrations of anti-HAV 6 years later than infants with no PMA who receive hepatitis A vaccine. Immune memory may remain functional despite these lower anti-HAV concentrations.

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.

Immunogenicity of a recombinant human cytomegalovirus gB vaccine in seronegative toddlers

BACKGROUND

Immunization of young children against cytomegalovirus (CMV) might decrease child-to-child and child-to-adult transmission of CMV and thereby reduce maternal infection during pregnancy. We conducted a Phase I trial in CMV-seronegative toddlers to evaluate the reactogenicity and immunogenicity of a CMV gB vaccine administered with MF59, an oil and water adjuvant.

METHODS

Eighteen children between 12 and 35 months of age received either 20 microg of CMV gB/MF59 (n = 15) or a control hepatitis A vaccine (n = 3) at 0, 1 and 6 months. The study was open-label for the first six children and then observer-blinded and randomized. Children were monitored for local and systemic reactions and for the development of antibodies to the envelope protein gB and CMV-neutralizing antibodies.

RESULTS

Adverse reactions were uncommon and mild. Two children were excluded from the immunogenicity analysis because they had serologic evidence of CMV infection. Reciprocal geometric mean neutralizing titers were: 0 preimmunization (n = 18); 90 (range, 53 to 188) after Dose 2 (n = 6); and 638 (range, 210 to 1645) 1 month after Dose 3 (n = 13). The reciprocal geometric mean neutralizing titers of antibody to gB by EIA were: 0 preimmunization (n = 18); 857 (range, 307 to 2073) after Dose 1 (n = 12); 27 457 (range, 9312 to 55,080) after Dose 2 (n = 6); and 98,264 (range, 35,480 to 228,780) 1 month after Dose 3 (n = 5). After Dose 3 antibody responses of toddlers were greater than those of naturally infected adults and were notably higher than among 149 adults given 3 doses of the same vaccine in other trials.

CONCLUSION

The CMV gB vaccine is well-tolerated and highly immunogenic in toddlers.

Routine childhood immunizations

The immunizations recommended in the 2001 Childhood Immunization Schedule are safe and effective. Newly approved vaccines, like the pneumococcal conjugate vaccine, hold the promise of eliminating or dramatically reducing persistent causes of childhood morbidity and mortality in the United States.

Vaccination against hepatitis A in children aged 12 to 24 months [corrected]

BACKGROUND

Current hepatitis A vaccines are either licensed for children >2 years of age, as in the U.S. or Chile, or >1 year of age, as in Europe and other parts of the world. Recent recommendations for immunization against hepatitis A have included routine vaccination of children in areas or regions of higher endemicity. However, data on hepatitis A vaccination in toddlers aged between 1 and 2 years are scarce.

METHODS

This open clinical study investigated the reactogenicity and immunogenicity of two doses (0, 6-month schedule) of an inactivated hepatitis A vaccine (Havrix pediatric, Glaxco SmithKline Biologicals, Rixensart, Belgium) in 120 seronegative children aged 12-24 months.

RESULTS

Pain at the injection site and irritability were the most frequently reported local and general symptoms, respectively. No serious adverse events related to the study vaccine were reported. One month after the first dose, all but one subject had antibodies against hepatitis A with a GMT of 159 mIU/mL. After the booster dose, all had antibodies with a GMT of 2,939 mIU/mL.

CONCLUSIONS

Our data show that the inactivated hepatitis A vaccine was well tolerated by these toddlers and that the vaccine elicits a good immune response.

Change in hepatitis A virus seroepidemiology in southern Taiwan: a large percentage of the population lack protective antibody

Hepatitis A, the predominant reported etiologic form of viral hepatitis in Taiwan, continues to be a disease primarily of children and young adults. A seroepidemiologic study was performed to assess the seroprevalence of hepatitis A (HAV) antibodies in the southern Taiwan general population in 1998 and is compared with results of a similar study in 1992. A total of 948 subjects (477 male and 471 female) with ages ranging from 0.3 to 63 years were stratified into 14 age-specific groups. The presence of anti-HAV antibodies was detected using a commercially available radioimmunoassay. Fifteen percent of the subjects were positive for anti-HAV antibodies, which is lower than that in 1992 (P < 0.001). Seroprevalences were 14.1% for males and 22.6% for females (P = 0.006). The pattern of anti-HAV seroprevalence was distinguishable from that found in 1992; minimum seroconversion occurred at ages ranging from 1 to 30 years. Prevalence of seropositive subjects decreased markedly for the < 1, 13-15, 16-19, 20-24, 25-29, and 30-39 year age groups in comparing 1998 with 1992. The current study demonstrates a continuing decline in the prevalence of HAV among children, adolescents, and young adults. The findings can be ascribed to the improvement of socioeconomic status and modernization of environmental sanitation. As a consequence of this changing trend of endemicity and the resulting lack hepatitis A antibodies among the general population in Taiwan, the risk of sudden major outbreaks is increased because of increasing international travel and immigration, particularly during and after natural disasters. HAV vaccination will be important for the prevention and control of HAV outbreaks in the community.

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.

Vaccine recommendations for patients on chronic dialysis. The Advisory Committee on Immunization Practices and the American Academy of Pediatrics

Pediatric patients on dialysis should receive all the vaccines currently recommended by the ACIP and the AAP for healthy children, except the oral polio vaccine (34, 35). Adult patients should receive the hepatitis B vaccine series, pneumococcal vaccine, yearly influenza vaccinations, tetanus-diphtheria toxoids, and varicella vaccine, if they are susceptible (33, 48, 69). Vaccines are well tolerated by these patients (33), but higher doses and/or additional boosters may be required periodically to adequately protect dialysis patients from vaccine-preventable diseases (33, 36, 37, 82, 83). Following vaccination, antibody concentrations for hepatitis B vaccine should be measured annually and booster doses administered when antibody concentrations fall below protective levels (33, 38). Although both children and adults on dialysis may show an impaired and/or delayed immunologic response to certain antigens, particularly hepatitis B virus and S. pneumoniae, appropriate immunizations can significantly reduce the risk of serious complications from vaccine-preventable diseases (11, 84). Because the protection these vaccines provide may be incomplete or transient, infection control strategies at hospitals and other health care facilities should be implemented simultaneously. Health care providers are encouraged to assess each patients need for vaccinations individually and formulate immunization strategies early in the course of progressive renal disease, ideally before the patient requires dialysis.

Safety, immunogenicity and antibody persistence of an inactivated hepatitis A vaccine in 4 to 15 year old children

Among 277 healthy Venezuelan children, aged between 4 and 15 years, who were screened for hepatitis A virus (HAV) antibodies, 118 seronegative children were enrolled in an open study. Each child received one dose of the Pasteur Mérieux Connaught inactivated hepatitis A vaccine (AVAXIM¿trade mark omitted¿, 160 antigen units), followed by a booster dose 24 weeks later. All seronegative subjects seroconverted 2 weeks after immunisation (antibody titres greater, similar20 mIU/ml), and antibody titres were still over greater, similar20 mIU/ml after 24 weeks, at the moment of the booster dose. The anti-HAV antibody geometric mean titre (GMT), as measured by a modified radio-immunoassay (HAVAB(R), Abbott Laboratories, North Chicago, IL, USA), was 73.7 mIU/ml, 2 weeks after the first dose. Four weeks after the booster, the GMT value reached 6999 mIU/ml, representing a 29.6-fold rise from pre-booster levels. One year after the booster dose, the GMT value was 1673 mIU/ml in the 92 subjects who provided blood samples at this time, all of whom were still seroconverted ( greater, similar20 mIU/ml). No serious adverse event related to the vaccination occurred during the study. No immediate systemic reaction occurred. Local reactions were reported by 9.3% of subjects who received the primary injection and 5.5% of those given the booster dose. The systemic reactions were mainly fever and myalgia reported over the 7 days following the injection by 3.4% of subjects after the first dose and 5.5% of subjects after the booster dose. A clinically significant elevation of serum transaminase from pre-immunisation levels was noted in one subject (AST level 2.2 times the upper normal limit) 2 weeks after the first injection, although this was not associated with any clinical signs of impaired liver function. This trial demonstrated that AVAXIM¿trade mark omitted¿ containing 160 antigen units is safe and highly immunogenic in healthy children aged between 4 and 15 years, and could be included in the childhood vaccination schedule to control infection in areas endemic for hepatitis A.

Hepatitis A vaccination in chronic carriers of hepatitis B virus

Because hepatitis A infection may be more severe in patients with chronic liver disease, we vaccinated 33 children who were chronic HBsAg carriers against hepatitis A virus. Anti-hepatitis A virus seroconversion rates after the first, second, and third doses were 90.9%, 96.9%, and 100%, respectively.

Immune globulin and vaccine therapy to prevent hepatitis A infection

The hepatitis A virus is usually transmitted person-to-person due to fecal-oral exchange of virus. Approximately 30,000 infections are reported each year in the United States, with the actual incidence being much greater. Prophylaxis with immune globulin has had a minimal impact on the overall incidence of hepatitis A. The recent availability and proven efficacy of a hepatitis A vaccine offers the hope that the incidence of infection may be substantially reduced. Pre- and postexposure prophylaxis should be targeted to individuals at increased risk of either acquiring infection, transmitting infection, or developing fulminant hepatitis, or to help control epidemics. This article reviews the current literature and discusses recommendations for pre- and postexposure prophylaxis against hepatitis A virus.

Follow-up immunogenicity of an inactivated hepatitis A virus vaccine in healthy children: results after 5 years

Long-term persistence of hepatitis A virus (HAV) serum antibody in vaccinated children has not been demonstrated in previous studies. To study the long-term immunogenicity to HAV vaccine, three doses of strain HM 175 HAV vaccine with 360 enzyme-linked immunosorbent assay units were administered to 107 children, aged from 1.0 to 6.8 years, at 0, 1, and 6 months. The administration of one vaccine dose induced seropositivity (anti-HAV titer > or = 20 mIU ml-1) in 95% of all vaccinees at month 1. All subjects remained seropositive until month 6. The titers of HAV antibody remained above 20 mIU ml-1 in all subjects followed up to 60 months. The geometric mean titer (GMT) reached its peak (3802 mIU ml-1) at month 7, i.e. 1 month after the booster dose, and then declined until the end of follow-up at month 60 (661 mIU ml-1). A trend of higher GMT in female subjects persisted up to month 60. The changes of the GMT over time were best described by the regression equation: log (GMT) = 3.26-0.08 x (age in years) (r = -0.95, P = 0.014). According to this equation, the geometric mean concentration would reach 20 mIU ml-1 at around 24.5 years after the beginning of vaccination. In conclusion, those who completed the recommended three-dose inactivated HAV vaccination series remained seroprotective for at least 5 years. Theoretically, such a vaccination program can provide a protective period of over 20 years in children. This paper may be the first to describe at least 5-year immunogenicity of inactivated HAV vaccination in healthy children.

Immunization of seronegative infants with hepatitis A vaccine (HAVRIX; SKB): a comparative study of two dosing schedules

Hepatitis A virus (HAV) infection is of public health significance among infants and diapered children. Although two licensed HAV vaccines are available, they have not been assessed widely in children under the age of 2 years and are not currently licensed for this age group. The purpose of this study was to evaluate the immunogenicity and reactogenicity of HAV vaccine in seronegative infants. Fifty-three healthy infants were immunized with 360 ELISA Units (EL.U.) of an inactivated HAV vaccine at 2, 4, and 6 (Group 1) or 2, 4, and 15 months of age (Group 2). These injections were not received on the same day that participants received their routine childhood immunizations. HAV serum antibodies were detected using a modified radioimmunoassay procedure and concentrations were calculated using a World Health Organization serum anti-HAV reference standard. No serious-systemic or local reactions were noted among the immunized infants. Three months following the third immunization, seroconversion rates were 100% and 93% in groups 1 and 2, respectively. No significant differences were observed in the geometric mean anti-HAV concentrations between the two groups at comparable time points, i.e. 2 months after the second dose, 3 months after the third dose, and 19 months after the first dose. Three infants, not included in the data presented above, had preexisting maternal antibodies; one never responded to the vaccine and the other two did not respond until maternal antibody levels had become reduced. The results indicate that the inactivated HAV vaccine is highly immunogenic in seronegative infants and could be included in the routine harmonized infant immunization schedule.

Safety and immunogenicity of an inactivated hepatitis A vaccine in children 2 to 5 years old

The reactogenicity and immunogenicity of an inactivated hepatitis A vaccine were assessed. Seventy healthy children aged between 2 and 5 years old, who lacked antibodies against the hepatitis A virus, were enrolled in this study. With a 0-, 1-, and 6-month vaccination schedule, the children received three doses of 360 enzyme-linked immunosorbent assay (ELISA) units of hepatitis A vaccine intramuscularly (deltoid). Safety parameters were recorded in standardized diary cards by the parents on the day of injection and the three following days. Blood tests for liver enzymes and anti-hepatitis A virus antibody analyses were performed the day of screening and 1, 2, 6 and 7 months after the first dose. Anti-hepatitis A virus antibody was tested by ELISA. Titres < 20 mIU/ml were considered negative. For the three hepatitis A vaccine doses administered, 22% (46/210) of the diary cards reported any kinds of signs or symptoms. Soreness at the injection site (9%, 18/210) and malaise (6%, 12/210) were the most common local and systemic reactions reported, respectively. The seroconversion rates were 83, 99 and 100% one month after the 1st, 2nd, and 3rd doses, respectively. The corresponding geometric mean titres were 124, 352, and 2,778 mIU/ml. We conclude that this HAV vaccine is safe and immunogenic in healthy children. As the hepatitis A epidemiology pattern is rapidly changing in our country (and other regions), resulting in an increasing population of susceptible adolescents and young adults, we suggest that the routine vaccination against hepatitis A in pre-school children attending day-care centres should be seriously considered.

Attenuated hepatitis A virus: genetic determinants of adaptation to growth in MRC-5 cells

A live candidate hepatitis A virus vaccine, developed from the HM-175 strain and adapted to growth in primary African green monkey kidney (AGMK) cells, was adapted to growth in MRC-5 cells. The nucleotide sequence of the MRC-5 cell-adapted virus was determined and compared with the known sequence of the AGMK cell-adapted virus. Thirteen unique mutations, which occurred during passage in MRC-5 cells, were identified. Four of the unique mutations were located in a cluster in the 5' noncoding region (NC), and three of the remaining nine mutations encoded amino acid changes. Infectious chimeric cDNAs were constructed from infectious cDNA clones of the AGMK cell-adapted and wild-type HM-175 viruses and PCR-amplified cDNA segments of the MRC-5 cell-adapted virus. The viruses encoded by these plasmids were recovered after transfection of cultured cells with in vitro transcripts, and their growth phenotypes in fetal rhesus kidney 4 (FRhK-4) and MRC-5 cells were determined. The important growth-enhancing mutations could be divided into three sets. Two of these were located in the 5' NC region, and the third was located in the 2C nonstructural gene. The mutations in the 5' NC region that developed during passage in MRC-5 cells were indispensable for efficient growth in MRC-5 cells, but a combination of the two groups in the 5' NC region and one in the 2C gene were required to increase growth dramatically in MRC-5 cells.