Safety and immunogenicity of hepatitis A vaccine in infants: a candidate for inclusion in the childhood vaccination programme

Vaccination proposal for patients on onasemnogene abeparvovec therapy

The approval of disease-modifying treatment in spinal muscular atrophy made the condition less severe. The course of the disease changed, but some new concerns occurred with the different new therapies. The side effects of onasemnogene aboparvovec therapy can raise differential diagnostic challenges and necessitate immune therapy, leading to immunosuppression affecting response to vaccines. We provide a pretherapy screening proposal from an infectological point of view separately for newborns treated presymptomatically and children diagnosed with symptoms at any age. Furthermore, we summarise the guidelines on the vaccination before, during, and after immune therapy (steroids) in onasemnogene aboparvovec-treated patients.

Hepatitis A vaccination

Hepatitis A is an important public health issue worldwide. Hepatitis A vaccine (HepA) was first licensed in 1992. Both inactivated HepA (HepA-I) and live attenuated HepA (HepA-L) are highly immunogenic and well tolerated, and immune protection postvaccination can persist for at least 20 y. HepA is effective for both preexposure and postexposure prophylaxis, especially among children and young adults. The strategy of HepA vaccination varies in different countries and mainly includes vaccination among high-risk populations, regional childhood vaccination and universal childhood vaccination. The incidence of hepatitis A has decreased greatly in many countries in the last 30 y, but hepatitis A outbreaks frequently occur among high-risk populations and those who have not been covered by universal child vaccination programs in recent years. Disease surveillance and serosurveys are suggested to clarify the shift in the epidemiology of hepatitis A. The long-term persistence of immune protection after one dose of HepA should be further studied, as well as the cost-effective evaluation of different strategies of HepA vaccination. Based on this evidence, the recommendation on HepA vaccination should be put forward scientifically and updated in a timely and well-implemented manner.

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.

Persistence of seropositivity among persons vaccinated for hepatitis A during infancy by maternal antibody status: 15-year follow-up

The effect of passively transferred maternal antibody to hepatitis A virus (anti-HAV) on the duration of seropositivity after hepatitis A vaccination during infancy and early childhood is unclear. We obtained levels of anti-HAV at intervals through age 15-16 years among three groups of Alaskan Native children who initiated a two-dose inactivated hepatitis A vaccination series at ages 6 months (group 1), 12 months (group 2), and 15 months (group 3), each group randomized according to maternal anti-HAV status. Seropositivity (anti-HAV ≥20 mIU/mL) 30 years after the second vaccine dose among the three groups was predicted using a random effects model. One hundred eighty-three children participated in the study; follow-up did not differ significantly by vaccine group or maternal anti-HAV status. Although the frequency of seropositivity among all participants through age 10 years was high (100% among groups 2 and 3 and >90% among group 1), there was a decrease thereafter through age 15-16 years among group 1 children, who initiated vaccination at age 6 months (50%-75%), and among maternal anti-HAV-positive children in groups 2 and 3 (67%-87%), who initiated vaccination at ages 12 months and 15 months, respectively. Nonetheless, the model indicated that anti-HAV seropositivity should persist for ≥30 years after vaccination in 64% of all participants; among those seropositive at age 15-16 years, 84% were predicted to remain so for ≥30 years.

CONCLUSION

Most children vaccinated during early childhood available for sampling maintained seropositivity through age 15-16 years; however, seropositivity was less frequent among those starting vaccination at age 6 months and among maternal antibody-positive participants who started vaccination at age 12 months or 15 months; overall, our findings support current vaccine recommendations and continued follow-up of this cohort.

Kinetics of maternally acquired anti-hepatitis A antibodies: prediction of waning based on maternal or cord blood antibody levels

BACKGROUND

Timing is critical for efficient hepatitis A vaccination in high endemic areas as high levels of maternal IgG antibodies against the hepatitis A virus (HAV) present in the first year of life may impede the vaccine response.

OBJECTIVES

To describe the kinetics of the decline of anti-HAV maternal antibodies, and to estimate the time of complete loss of maternal antibodies in infants in León, Nicaragua, a region in which almost all mothers are anti-HAV seropositive.

METHODS

We collected cord blood samples from 99 healthy newborns together with 49 corresponding maternal blood samples, as well as further blood samples at 2 and 7 months of age. Anti-HAV IgG antibody levels were measured by enzyme immunoassay (EIA). We predicted the time when antibodies would fall below 10 mIU/ml, the presumed lowest level of seroprotection.

RESULTS

Seroprevalence was 100% at birth (GMC 8392 mIU/ml); maternal and cord blood antibody concentrations were similar. The maternal antibody levels of the infants decreased exponentially with age and the half-life of the maternal antibody was estimated to be 40 days. The relationship between the antibody concentration at birth and time until full waning was described as: critical age (months)=3.355+1.969 × log(10)(Ab-level at birth). The survival model estimated that loss of passive immunity will have occurred in 95% of infants by the age of 13.2 months.

CONCLUSIONS

Complete waning of maternal anti-HAV antibodies may take until early in the second year of life. The here-derived formula relating maternal or cord blood antibody concentrations to the age at which passive immunity is lost may be used to determine the optimal age of childhood HAV vaccination.

Vaccination of newborns against hepatitis A in the presence of maternally derived antibodies

Infection by hepatitis A virus (HAV) is a significant cause of childhood disease but effective vaccines are available. Naturally acquired anti-HAV antibodies ensure transfer of protective immunity which persists for up to 6 months in the newborn. Such maternal anti-HAV antibodies are able to inhibit the antibody responses in infants vaccinated with inactivated hepatitis A vaccines, although no clinically significant consequences of this are observed. By increasing the number of doses, for example by using a three dose primary vaccination schedule, and by increasing the amount of vaccinal antigen, this interfering effect may be partially overcome.

Epidemiology of severe hepatitis A in Indigenous Australian children

AIMS

To describe the epidemiology of hepatitis A in Indigenous Australian children.

METHODS

Analysis and mapping of national notification and hospitalisation data.

RESULTS

Indigenous Australian children are at far higher risk of clinical hepatitis A than their non-Indigenous counterparts, particularly in the age group 0-4 years. Rates of hospitalisation (15.5 vs. 0.3 per 100,000) and notification (24.4 vs. 1.8 per 100,000) were higher in Indigenous children aged 0-4 years compared with other children in the same age group. In the age group 5-14 years, the rates were 4.4 per 100,000 (Indigenous) versus 0.6 per 100,000 (non-Indigenous) hospitalisations. This excess morbidity falls sharply with age. Rates were the highest in the Northern Territory, South Australia, Western Australia and North Queensland.

CONCLUSIONS

Indigenous children are at risk of hepatitis A, particularly early in life. Mapping shows that rates were the highest in jurisdictions with the largest Indigenous populations. This study presents baseline data against which to measure the success of new hepatitis A vaccination programme for Indigenous Australian children which commenced in 2005.

Immunogenicity of an inactivated hepatitis A vaccine in infants and young children

BACKGROUND

Infants with passively transferred maternal antibody, born to mothers immune to hepatitis A virus (HAV), have a blunted response to hepatitis A (HA) vaccine. We compared HA vaccine immunogenicity among infants born to immune and susceptible mothers, vaccinated on different schedules.

METHODS

Infants were randomized into 3 groups, each receiving 2 doses of 720 EL.U. of HA vaccine (HAVRIX; Glaxo SmithKline): group 1 at ages 6 and 12 months, group 2 at ages 12 and 18 months and group 3 at ages 15 and 21 months. We determined mothers' antibody to HAV (anti-HAV) status and infants' anti-HAV concentrations at the first vaccine dose (baseline) and at 1, 7 and 12 months thereafter. All were tested at age 13 months for responses to recommended routine vaccinations administered during infancy.

RESULTS

Of 248 participants, 140 were born to HA-susceptible mothers and 108 to immune mothers. At baseline, 34 of 36 (94%) group 1, 5 of 34 (15%) group 2 and one of 38 (3%) group 3 infants born to immune mothers were seropositive. By month 7, all participants in all groups were seropositive except group 1 infants born to immune mothers (34 of 36 [94%], seropositive). In group 1, peak geometric mean concentrations between infants born to immune (794 mIU/mL) and susceptible (2083 mIU/mL) mothers were significantly different. Across groups, peak geometric mean concentrations were similar among infants born to susceptible mothers (3166 mIU/mL, group 2; 3153 mIU/mL, group 3). Among infants born to immune mothers, the difference between groups 1 and 3 (2715 mIU/mL) was significant. There were no differences in responses to routine vaccinations.

CONCLUSIONS

HA vaccine is immunogenic among infants born to HA-susceptible mothers and those born to immune mothers and vaccinated beginning > or =12 months old. Passively transferred maternal antibody persists for at least 6 months and results in a blunted response to HA vaccination.

Universal mass vaccination against hepatitis A

When first introduced in 1992 the hepatitis A vaccine was recommended for individuals at high risk of exposure. This policy was not expected to have a significant impact on disease incidence at population level in view of the epidemiology of the hepatitis A virus (HAV). More recently two countries, Israel and Bahrain, and regions or subpopulations in others (Australia, China, Byelorussia, Italy, Spain, US) have embarked upon more ambitious vaccination programmes that aim to immunize whole birth cohorts. After a brief survey of the virology and epidemiology of HAV, the disease burden it inflicts and a short history of the development of HAV vaccines--both live (in China) and killed vaccines are available--he vaccination programmes introduced in the countries mentioned above are described. The results have been spectacular: disease incidence, not only in the vaccinated cohorts but also in the whole population, have plummeted within a few years of the start of mass vaccination. There is now convincing evidence that the vaccine confers herd immunity if the main spreaders of the virus are targeted for immunization. This finding should encourage other countries to start mass vaccination programmes against HAV, particularly as pharmacoeconomic studies are beginning to show that such a strategy could be a cost-effective way of controlling the disease. It is now even conceivable to eradicate HAV. In fact, this should be easier to achieve than polio eradication as HAV vaccines confer more durable immunity than polio vaccines. However, the global disease burden of HAV is generally thought not to be high enough to justify such an undertaking in the foreseeable future.

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.

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.

Prevention of hepatitis A by Havrix: a review

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

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

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

Hepatitis A: a preventable threat

Hepatitis A is a major public health problem, particularly in the pediatric population. Although hepatitis A infection does not cause chronic liver disease, it is associated with significant morbidity. The virus is transmitted primarily by person-to-person contact via the fecal-oral route. The infection can be inapparent, subclinical, anicteric, or icteric. In general, the severity of the disease is inversely correlated with the age of the child. Occasionally, fulminant hepatitis, which is associated with a high mortality rate, may result. The diagnosis of acute hepatitis A is most commonly made through the detection of immunoglobulin M (IgM) anti-hepatitis A antibody. Treatment is generally supportive. General preventive measures include improved standards of hygiene and sanitation. Universal childhood vaccination is the most effective method for eradicating hepatitis A and preventing its transmission.

Impact of hepatitis A vaccination of Indigenous children on notifications of hepatitis A in north Queensland

OBJECTIVE

To describe the impact of a hepatitis A vaccination program for Indigenous children in north Queensland.

DESIGN

Enhanced surveillance of all notified cases of hepatitis A in north Queensland from 1996 to 2003.

SETTING

North Queensland; population, 596 500 people, including about 6900 Indigenous children aged under five years.

INTERVENTIONS

Hepatitis A vaccine was provided to Indigenous children in north Queensland from February 1999; two doses were recommended (at 18 months and 2 years of age), as was catch-up vaccination up to the sixth birthday.

RESULTS

In the 4 years 1996-1999, 787 cases of hepatitis A were notified in north Queensland, 237 (30%) of which were in Indigenous people. The average annual notification rates in Indigenous and non-Indigenous people during this period were 110 and 25 cases per 100 000 persons, respectively. In the first 4 years after introduction of the vaccination program (2000-2003), 66 cases of hepatitis A were notified. Only nine of the 66 (14%) were in Indigenous people. The average annual notification rates in Indigenous and non-Indigenous people in 2000-2003 were 4 and 2.5 cases per 100 000 persons, respectively.

CONCLUSION

Hepatitis A seems to have been eradicated from Indigenous communities in north Queensland very soon after the vaccination program began. The rapid decline in notifications in non-Indigenous as well as Indigenous people suggests the program quickly interrupted chains of transmission from Indigenous children to the broader community. To our knowledge this is the first evidence that a hepatitis A vaccination program targeting a high-risk population within a community can reduce disease in the broader community. Hepatitis A vaccine should be provided to other high-risk Indigenous children elsewhere in Australia.

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

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

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

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

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.

Hepatitis A booster vaccination: is there a need?

Hepatitis A is one of the most common vaccine-preventable infectious diseases in the world. Effective vaccines against hepatitis A have been available since 1992, and they provide long-term immunity against the infection. However, there is no worldwide consensus on how long protection will last or whether there will be a need for hepatitis A virus (HAV) booster vaccinations in the future. In most countries, booster-vaccination policy is guided by manufacturers' recommendations, national authorities, or both. In June, 2002, a panel of international experts met to review the long-term immunogenicity and protection conferred by HAV vaccine in different population groups. Data have shown that after a full primary vaccination course, protective antibody amounts persist beyond 10 years in healthy individuals, and underlying immune memory provides protection far beyond the duration of anti-HAV antibodies. The group concluded that there is no evidence to lend support to HAV booster vaccination after a full primary vaccination course in a healthy individual. However, further investigations are needed before deciding if boosters can be omitted in special patient-groups.

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.

Prevention of hepatitis A by vaccination

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

Hepatitis vaccines: recent advances

Despite the availability of hepatitis A vaccines that might provide protection for decades, hepatitis B vaccines that provides protection for at least 15 years and the recent introduction of a combined hepatitis A and B vaccine, these infections continue to spread in both the developed and developing world. Hepatitis A vaccine coverage has been limited to high-risk groups: such a selective immunisation policy is unlikely to have a major impact. If adequate immunogenicity in infants is confirmed, dosing schedules can be improved and the costs of vaccination reduced, universal paediatric immunisation with combined hepatitis A and B products is likely to result in the eventual eradication of these infections. In the interim, novel hepatitis A vaccines are being investigated and additional studies on hepatitis A vaccine immunogenicity in infants are in progress. Worldwide use of hepatitis B vaccines for the newborn, young children and high-risk groups should control this infection and obviate the need for a vaccine against hepatitis D. Newer hepatitis B vaccines that may reduce the likelihood of non-responsiveness and have immunotherapeutic value are under study. A recombinant hepatitis E vaccine for use in endemic regions is currently in clinical trials. The development of an effective hepatitis C vaccine has been agonisingly slow and many impediments have been recognised. These include the lack of a susceptible small animal, a high degree of hepatitis C virus (HCV) genomic diversity and failure to produce high quantities of HCV in tissue culture. The development of a novel HCV replicon system may be a major breakthrough. Nonetheless, it may still be exceedingly difficult to produce a vaccine that uniformly provides sterilising immunity; the possibility of developing a hepatitis C vaccine that can prevent chronic infection is an exciting concept that requires further investigation. Advances in recombinant technology, the use of novel genetic (DNA-based) vaccines, expression of hepatitis antigens in plants and improved adjuvants also hold considerable promise.

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.

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.

Active immunization in the United States: developments over the past decade

The Centers for Disease Control and Prevention has identified immunization as the most important public health advance of the 20th century. The purpose of this article is to review the changes that have taken place in active immunization in the United States over the past decade. Since 1990, new vaccines have become available to prevent five infectious diseases: varicella, rotavirus, hepatitis A, Lyme disease, and Japanese encephalitis virus infection. Improved vaccines have been developed to prevent Haemophilus influenzae type b, pneumococcus, pertussis, rabies, and typhoid infections. Immunization strategies for the prevention of hepatitis B, measles, meningococcal infections, and poliomyelitis have changed as a result of the changing epidemiology of these diseases. Combination vaccines are being developed to facilitate the delivery of multiple antigens, and improved vaccines are under development for cholera, influenza, and meningococcal disease. Major advances in molecular biology have enabled scientists to devise new approaches to the development of vaccines against diseases ranging from respiratory viral to enteric bacterial infections that continue to plague the world's population.

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.

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.

H2 strain attenuated live hepatitis A vaccines: Protective efficacy in a hepatitis A outbreak

AIM: To investigate the protective efficacy of H2 strain attenuated live hepatitis A vaccines (H2-strain vaccines) in hepatitis A (HA) out breaks.

METHODS: With the permission of their parents, 5551 pre-school and grade 1-3 primary school children were inoculated with 1 dose (10^6.5TCID₅₀) of H2-strain vaccines in a nonrandomized, controlled trial conducted in Fucheng County, Hebei Province in May 1997. Another 6485 children in the same grades and compatible in gender and age were enrolled as controls. Epidemiological and serological survey was conducted to evaluate the protective efficacy of the vaccines. ELISA was used to detect serum IgM anti-HAV.

RESULTS: HA outbreak started in early May 1998, peaked in the middle of the same month, and lasted about 80 d. Overall 302 HA cases were found, 192 (63.58%) were 5-9 years old. One vaccinee and 25 control cases were found to have hepatitis A, which account for 0.28% (1/356) and 5.92% (25/422) of all vaccinees and controls in the 14 villages, respectively. The protective efficacy of vaccines was 95.27% (95%CI: 85.83%-104.72%). In subjects tested for anti-HAV IgM from 13 villages, 1 (0.40%) overt and 11 (4.06%) asymptomatic HAV cases were found in 271 vaccinees，but 21 (6.69%) of overt and asymptomatic ones were found in 314 controls.

CONCLUSION: H2 strain vaccines were excellent in preventing overt hepatitis A, but not so effective in preventing asymptomatic hepatitis A virus infection. A booster dose might be needed to get permanent reliable immunity.

Immunization against hepatitis A in the first year of life: priming despite the presence of maternal antibody

BACKGROUND

Maternal antibodies interfere with hepatitis A vaccination in young infants. We examined the response to a high dose hepatitis A vaccine administered concomitantly with a combination of diphtheria-tetanus toxoids-acellular pertussis-inactivated poliovirus vaccine/Haemophilus influenzae type b vaccine to initially seropositive vs. initially seronegative infants.

METHODS

Three hundred subjects were originally planned to be enrolled at age 6 to 10 weeks and received hepatitis A vaccine (formalin-inactivated vaccine, SB-Bio, 720 enzyme-linked immunosorbent assay units) at 2, 4 and 6 months concomitantly with a diphtheria-tetanus toxoids-acellular pertussis-inactivated poliovirus vaccine/H. influenzae type b vaccine. Children initially seropositive received a booster dose at 12 months of age. An additional 100 twelve-month-old infants previously not vaccinated with hepatitis A vaccine were given 1 dose, to observe the primary response at that age. Reactogenicity was recorded on diary cards for the 3 subsequent days. Immunogenicity was measured at Months 2, 4, 5, 10 and 11 after administration of the first vaccine dose. For the subjects enrolled at 12 months, blood was drawn before and 1 month after the first vaccination.

RESULTS

Of 297 initially enrolled infants 36% were seronegative before vaccination (Group A). The geometric mean concentration (GMC) (milli-International Units/ml) of the seropositive infants (Group B) before immunization was 2587. The GMCs of Group A infants 1 month after each dose and at 12 months of age were 93, 518, 1656 and 786, respectively. For Group B infants, the respective GMCs were 1165, 460, 508 and 167. One hundred subjects of Group B received a booster dose at age 12 months; at Month 13 all were seropositive with a GMC of 1902. For comparison, a third group of 100 not previously immunized 12-month-old infants (Group C) were enrolled and received 1 dose of hepatitis A vaccine with pre- and postimmunization GMCs of 52 and 120, respectively.

CONCLUSIONS

Our results suggest that the initially seropositive infants were primed despite maternal antibody interference. The hepatitis A vaccine was well-tolerated in this population of young infants.