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.     

孩尔来福甲型肝炎灭活疫苗0,12个月免疫程序研究

目的　对孩尔来福 (HealiveR○)甲型肝炎 (甲肝 )灭活疫苗的安全性、免疫原性及适宜儿童的剂量进行研究。方法　在某山区两个农村筛选 4～ 10岁甲肝病毒抗体 (抗 HAV)阴性的 85名易感儿童。以自然村随机分为两组 ,按 0 ,12个月免疫程序分别接种北京科兴生物制品有限公司生产的每剂 2 50U 0 .5ml和 50 0U 1ml甲肝灭活疫苗 ,观察免疫后局部反应和全身反应 ,检测初次免疫 (初免 )后 2 1天、12个月及全程免疫后 1个月抗 HAV阳转率和抗体几何平均滴度 (GMT )。结果　两组均未见严重局部反应和全身反应 ;2 50U 0 .5ml组和 50 0U 1ml组初免后 2 1天 ,抗 HAV阳转率分别为94.4%和 10 0 .0 % ,GMT分别为 195mIU ml和 3 70mIU ml ;初免后 12个月抗 HAV全部阳转 ,GMT分别达 3 61mIU ml和 456mIU ml(P >0 .0 5) ;全程免疫后 1个月 ,GMT分别达 14 893mIU ml和2 1696mIU ml。结论　孩尔来福甲肝灭活疫苗的安全性和免疫原性好 ;每剂 2 50U 0 .5ml适宜儿童 ;0 ,12个月免疫程序更适宜中国儿童     

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.     

Hepatitis A vaccine: immunogenicity following administration of a delayed immunization schedule in infants,children and adults

Current immunization schedules for hepatitis A vaccine specify administration of a booster within 6-12 or 6-18 months of the primary dose. However, there may be circumstances that disrupt this schedule and the efficacy of administering a booster beyond the recommended time is a practical concern for healthcare providers. In this study, a booster was administered to 268 participants (137: <18 years old), an average of 27 months (range 20-31) after the primary dose. In those tested after the booster, the median anti-HAV GMT was 1544 milli-international units per milliliter (mIU/ml). Response to a delayed booster was strong in children over 2 years old (GMT 1500-1960 mIU/ml) and adults (GMT 1622 mIU/ml), but was significantly lower in children under 2 years old (GMT 1109 mIU/ml). Findings suggest a booster administered 20-31 months after the primary dose is immunogenic and GMT in persons >2 years of age were comparable to those seen in adults and children who receive hepatitis A vaccine per schedule.     

国产甲型肝炎灭活疫苗在低龄儿童中应用的安全性和免疫原性研究

目的 探讨国产甲型肝炎灭活疫苗在低龄儿童（1－4岁）中应用的安全性和免疫原性。方法 选1－4岁易感健康儿童63名，随机分为两组，按0，3和0，6程序接种国产甲肝灭活疫苗500U／剂，观察免疫后的局部和全身反应，并检测初免后及全程免疫后的抗－HAV阳转率和抗体GMT。结果 初免和加强免疫后有轻微的过性局部和全身反应，未见肝功异常。初免后1、3、6个月抗体阳转率分别为85.7%、88.5%和83.8%；抗体GMT玢别为182mU/ml、225mU/ml和252mU/ml；0，3和0，6程序全程免疫后1个月抗体阳转率均为100％；抗体GMT分别为2718mU/ml和4683mU/ml。结论 国产甲肝灭活疫苗在低龄儿童中应用具有良好的安全性和免疫原性；接种两剂可获高滴度甲肝抗体；0，6程序优于0，3程序。     

Comparison of immunogenicity of two hepatitis A vaccines--VAQTA and HAVRIX--in young adults.

Two new hepatitis A vaccines have been developed, and their immunogenicity tested using different immunoassays. The present study was designed to compare the immunogenicity of these two hepatitis A virus (HAV) vaccines--VAQTA and HAVRIX--as determined by seroconversion rates and anti-HAV titers, and using the same immunoassay. Healthy volunteers (15-30 y), seronegative for anti-HAV, were randomized in an open single center study to four groups of 20-21 vaccinees each, to receive either a 25 U or a 50 U dose of VAQTA, or HAVRIX at 720 EU or 1440 EU/dose, administered at 0, 1 and 6 m or at 0 and 6 m, respectively. Four weeks after primary immunization, seroconversion rates were 100% for VAQTA and 95% for HAVRIX, following injection of 50 U or 1440 EU, respectively (p = NS) and anti-HAV GMTs were 40 and 37 mIU/ml for VAQTA and HAVRIX, respectively. At 6 months, prior to the booster dose, seroconversion rates were 100% for both vaccines, with anti-HAV GMTs of 111 and 70 mIU/ml for VAQTA and HAVRIX, respectively (P < 0.05). At month 7, four weeks after the only booster injection, using the two dose regimen, anti-HAV titers were 2212 and 1511 mIU/ml for VAQTA and HAVRIX, respectively (P < NS). Using three doses of 25 U/dose of VAQTA or 720 EU/dose of HAVRIX at 0, 1 and 6 m did not produce any clinically evaluable advantage over the two dose regimen for either vaccine. No significant adverse events were observed using either vaccine. In summary, both vaccines have similar immunogenicity demonstrated using identical immunoassays for evaluation. These results also confirm the outstanding immunogenicity of a single dose of either of the HAV vaccines and support their use in pre- and possibly postexposure prophylaxis against hepatitis A virus infection.     

Safety and immunogenicity of a new formulation of an inactivated hepatitis A vaccine

The safety and immunogenicity of a new formulation of the inactivated hepatitis A vaccine, Avaxim, was evaluated in 189 children, aged 18 months to 15 years in a monocentric, open trial. Two vaccinations were given six months apart. Enrollment was balanced within three age groups: 18 months to 3 years, 4-8 years and 9-15 years. Antibody titers were measured blindly by an independent laboratory using a modified radioimmunoassay. Two weeks after the first dose, seroconversion was achieved by 94.6, 94.3 and 96.4% of initially HAV-seronegative subjects (antibody titre <20 mIU/ml) in each age group (youngest to oldest, respectively), with corresponding geometric mean titre concentrations (GMC) of 72.2, 54.3 and 47.1 mIU/ml. Just before the booster dose, the seroconversion rate was 100% in all groups, and the corresponding GMC values were 163, 169 and 111 mIU/ml. All groups included, a 22.6-fold rise in GMC from prebooster levels was observed four weeks after the booster dose. An explanatory analysis suggested a tendency for higher antibody levels in younger children at all vaccination time points. Local reactions were noted in 18.2% of the vaccinees after the first dose and in 8.5% after the booster dose. The rates of systemic reactions were 23.8% after the first dose and 11.4% after the booster dose. Overall, this trial demonstrated the good safety and immunogenicity profile of this vaccine in children aged 18 months to 15 years of age.     

Interchangeability of Hepatitis A boosters, Avaxim and Vaqta, in healthy adults following a primary dose of the combined typhoid/Hepatitis A vaccine Viatim

This study investigated the suitability of Avaxim and Vaqta as Hepatitis A booster vaccines 6 months after priming with the combined Hepatitis A/typhoid vaccine, Viatim. One hundred and twenty adults were randomly assigned to one of the three groups. Group A (reference group) received Avaxim then Avaxim (n = 40), Group B received Viatim then Avaxim (n = 41) and Group C received Viatim then Vaqta (n = 39). One month after booster vaccination, anti-Hepatitis A virus (anti-HAV) antibodies geometric mean concentrations (GMC) of subjects primed with Viatim were non-inferior to the group primed and boosted with the monovalent Hepatitis A vaccine Avaxim. Anti-Salmonella typhi capsular polysaccharide virulence antigen (anti-Vi) GMCs in groups primed with Viatim were protective and all vaccines were well-tolerated. Therefore, Viatim may be used as a primary HAV vaccine with either Avaxim or Vaqta as Hepatitis A boosters and it will provide the same protection as two doses of Avaxim.     

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

Forty-eight infants received a single dose (720 ELISA units = 0.5 ml) of inactivated hepatitis A vaccine at the fifth month of age with booster at the 11th month of age, together with the second and third doses of the vaccines compulsory under Italian law (diphtheria, tetanus, oral polio and hepatitis B). Overall, the seroconversion rate was 100%. The anti-HAV geometric mean titre (GMT) reached 3,021 mIU/ml in infants born to anti-HAV-negative mothers, but only 399 mIU/ml in infants born to anti-HAV-positive mothers. Hepatitis A vaccine was immunogenic, safe and well tolerated without significant side-effects. There seems to be no reason for not including it in childhood vaccination programmes particularly in low endemic HAV areas.     

A new accelerated vaccination schedule for rapid protection against hepatitis A and B.

BACKGROUND: Increasing travel stresses the requirement for rapid protection against infections such as hepatitis A and B. METHODS: This randomised, multicentre study investigated an accelerated vaccination schedule using a combined hepatitis A and B vaccine (Twinrix, Smithkline Beecham Biologicals) compared with simultaneous administration of the two corresponding monovalent vaccines. The combined vaccine was administered on days 0, 7 and 21, whereas the comparison group received hepatitis A vaccine on day 0 and hepatitis B vaccine on days 0, 7 and 21. All subjects received booster vaccination at month 12. RESULTS: At month 1, 100% of subjects in the combined group and 99% of the controls were seropositive for anti-HAV antibodies. The corresponding seroprotection rates for anti-HBs antibodies were 82.0 and 83.9%, respectively. Examination of the 95% confidence intervals (CIs) for the treatment differences showed the two vaccines to be equivalent in terms of immunogenicity 1 week after the initial vaccination course. Just prior to the booster, the seropositivity rate for anti-HAV was 96.2% in the combined group and 95% in the control group. For anti-HBs, this was 94 and 91.6%, respectively. All subjects were seropositive for anti-HAV and seroprotected against hepatitis B at month 13. The anti-HAV GMCs were 9571mIU/ml with the combined vaccine and 5206mIU/ml in control subjects. The anti-HBs titre was 26002 and 29,196mIU/ml, respectively. Both groups had a similar reactogenicity profile. CONCLUSIONS: The accelerated schedule of the combined vaccine provides a good immune response against hepatitis A and B antigens and is suitable for last minute immunisation.     

成人和儿童接种国产甲型肝炎灭活疫苗的安全性与免疫原性的初步观察

为了评价国产甲型肝炎 (甲肝 )灭活疫苗的安全性和免疫原性 ,将 176名健康易感儿童和 2 0 6名成人随机分为 4组 ,10 7名儿童 (A组 )和 131名成人 (B组 )接种国产甲肝灭活疫苗 ,另 6 9名儿童 (C组 )和 75名成人 (D组 )作为对照接种史克必成公司生产的甲肝灭活疫苗。国产疫苗剂量为儿童 6 4 0EU/1 0ml,成人 12 80EU/1 0ml;对照疫苗剂量儿童 72 0EIU/1 0ml,成人 14 4 0EIU/1 0ml,均采用 0、6个月免疫程序。观察 72h内局部和全身反应 ,免疫后 1、6、7个月的免疫应答水平。结果显示 :所有接种对象均未出现明显的局部和全身副反应 ,亦未发现免疫后丙氨酸氨基转移酶 (ALT)升高。初次免疫后 1个月 ,A组和B组抗体阳转率分别为 94 8%和 96 7% ,几何平均滴度(GMT)为 75 8 6mIU/ml和 36 30 8mIU/ml。全程免疫后 1个月 ,4个组抗体阳转率均为 10 0 % ,A组和B组抗体GMT升至 10 4 71 2mIU/ml和 12 30 2 7mIU/ml,略高于对照的C组和D组 (分别为 30 90 3mIU/ml和3388 4mIU/ml)。表明国产甲肝灭活疫苗具有良好安全性和免疫原性。     

甲型肝炎减毒活疫苗加强免疫效果的初步研究

目的　观察甲型肝炎 (甲肝 )减毒活疫菌 (10 7.0 TCID50 )加强免疫效果 ,并同活疫苗一针法结果进行比较。方法　在河北省正定县选择 42名经事先检测甲肝抗体阴性的易感儿童 ,分别于0、2和 6个月各接种一剂甲肝减毒活疫苗 ,并于接种后 1、2、6、7、9和 12个月采集血清标本 ,观察免后抗体动态变化。结果　第 1剂接种后 1个月抗体阳转率达 81.4% ,第 2剂免后抗体阳转率达 10 0 % ,抗体水平于第 3剂免后 1个月达高峰 ,为 2 739mIU/ml,以后呈下降趋势 ,免后 12个月抗体阳转率仍为 10 0 % ,抗体水平下降至 979mIU/ml。结论　甲型肝炎减毒活疫苗加强免疫能诱导良好的免疫回忆反应 ,其免疫学效果同史克灭活疫苗相当 ,而明显高于活疫苗一针法。活疫苗加强免疫中 ,初免是基础。活疫苗加强免疫会提高疫苗保护效果 ,并延长疫苗的免疫持久性     

Long-term immunogenicity after single and booster dose of a live attenuated hepatitis A vaccine: results from 8-year follow-up

Live, attenuated hepatitis A vaccines are used widely in China but there is uncertainty regarding the persistence of vaccine-induced anti-HAV antibodies after single dose and booster dose administrated at month 12. A large scale clinical trial to evaluate the live, attenuated hepatitis A vaccine was conducted in Hebei province between 1996 and 1999. Five years after the trials, children in single dose and booster dose groups were bled and followed. Seventy two percent (61/85) of children who received a single trial dose had detectable anti-HAV antibodies for 96 months (GMC at 96 months: 89.0 mIU/mL). In the booster group 98% (48/49) children remained anti-HAV positive with GMC of 262.8 mIU/mL at month 96. The reinjection with live attenuated HAV vaccine can elicit a booster effect. Results from single dose group seems not to support the need for booster doses of live attenuated hepatitis A vaccine in immunocompetent individuals regarding the persisting anti-HAV and anamnestic response of a single dose vaccine. Continued monitoring of anti-HAV antibodies is needed for a rational hepatitis A immunization strategy in China.     

Immunogenicity and safety of a virosomal hepatitis A vaccine in HIV-positive patients

This short report presents results of an open uncontrolled single centre study which evaluated immunogenicity and safety of a virosome-formulated hepatitis A vaccine (Epaxal) in 14 HIV-positive adult patients and 64 healthy adults receiving a primary immunisation and a booster dose 12 months later. Seroconversion rates (> or =20 mIU/mL), geometric mean concentration (GMC) of anti-HAV antibodies, local and systemic adverse events (AEs) were assessed at baseline and at Months 1, 6, 12, and 13. The seroconversion rate was 63.6% at Month 1 and 91.7% at Month 13 in HIV-positive patients versus 93.8 and 100% in healthy adults. The booster dose increased GMCs from 25.5 to 659.2 mIU/mL in HIV-positive patients versus 104 and 2986 mIU/mL in healthy adults. Epaxal was well tolerated by the HIV-positive patients and was at least as immunogenic as reported for aluminium-adsorbed vaccines. In conclusion, Epaxal can be considered an immunogenic and safe hepatitis A vaccine in HIV-positive patients.     

Comparative immunogenicity and safety of two dosing schedules of a combined hepatitis A and B vaccine in healthy adolescent volunteers: an open, randomised study

An open, randomised study was undertaken to demonstrate the equivalence in immunogenicity and to determine the reactogenicity and safety of two dosing schedules (0, 6 or 0, 12 month) of an adult formulation of a combined hepatitis A and B vaccine containing 720 EL.U. of inactivated hepatitis A antigen and 20 μg of hepatitis B surface antigen (Twinrix™, SmithKline Beecham Biologicals, Belgium) in 240 healthy volunteers aged 12–15 years. The vaccine was well tolerated when administered using either vaccination schedule. At month 7, 98.1% of subjects completing the 0, 6 month vaccination schedule were seroprotected against hepatitis B (anti-hepatitis B surface antigen (anti-HBs)10 mIU/ml) and 100% were seropositive for anti-hepatitis A virus (anti-HAV) antibodies (i.e., 33 mIU/ml). The corresponding geometric mean titres (GMTs) were 2791 mIU/ml for anti-HBs and 5992 mIU/ml for anti-HAV antibodies. At month 13, 97% of subjects assigned to the 0, 12 month vaccination schedule were protected against hepatitis B and 99% were seropositive for anti-HAV antibodies. The corresponding GMTs were 4340 and 8472 mIU/ml, respectively. A combined response (i.e., subjects, who were seropositive for anti-HAV antibodies and seroprotected for anti-HBs antibodies) was achieved in 98% of subjects vaccinated according to the 0, 6 month interval and in 96% of subjects vaccinated using the 0, 12 month schedule. The reactogenicity of both vaccination schedules was also equivalent. The results thus show that the combined hepatitis A and B vaccine can be administered using flexible vaccination intervals, which make it suitable for use in large-scale hepatitis immunisation programmes.     

冻干甲肝减毒活疫苗安全性及免疫原性观察

目的评价国产冻干甲肝减毒活疫苗的安全性和免疫原性。方法选择部分18~24月龄健康儿童接种1剂甲肝减毒活疫苗,使用统一的"疫苗接种日记卡"观察记录疫苗接种后副反应,于免后28 d采集血清检测抗-HAVIgG。结果共接种18~24月龄健康儿童354人,14 d内副反应发生率10.73%,发热反应发生率为7.06%,未观察到严重异常反应;检测有效血清标本333份,免后28 d抗-HAV阳性率为92.79%,抗-HAV GMT为14.60 mIU/ml。结论国产冻干甲肝减毒活疫苗具有良好的安全性和免疫原性。     

Immunogenicity and safety of a pediatric dose virosomal hepatitis A vaccine in Thai HIV-infected children

The immunogenicity and safety of a pediatric dose of a virosomal hepatitis A vaccine (Epaxal?) was evaluated in a group of 45 Thai children with human immunodeficiency virus (HIV) infection, age 2-16 years. Vaccines were administered at 0 and 6 months. Anti-HAV antibody titers were measured at baseline (before injection) 1 and 7 months after primary vaccination. The prevalence of HAV protective antibody in 45 Thai HIV-infected children was 13.6%. The seroprotection rate was 71% at 1 month and 100% at 7 months. The booster dose increased geometric mean concentration (GMC) from 106.5 mIU/ml to 3486.1 mIU/ml. Higher CD4 lymphocyte counts at enrollment was a predictive factor for HAV antibody response. Both doses of Epaxal? were well tolerated. These preliminary data suggest that a pediatric dose of Epaxal? is an effective hepatitis A vaccine for HIV-infected children and should be considered for implementation on a larger scale in the pediatric HIV population.     

威海市新生儿乙肝疫苗初免和低/无应答者再免疫效果分析

[目的]了解新生儿接种乙肝疫苗后的免疫效果和对全程免后低/无应答者的再免疫效果。[方法]2009年,在威海市3个市(区)抽取7～12月龄儿童1 102名,按"0,1,6"程序接种3剂次5μg啤酒酵母重组乙肝疫苗(HepB-SC),对其中低/无应答者分别按上述程序再次接种不同种类和剂量的乙肝疫苗,检测调查对象血清抗-HBs水平,观察变化情况。[结果]检测儿童1 102名,3剂乙肝疫苗接种后,抗-HBs阳性率为98.19%(正常应答率为84.66%、低应答率为13.52%),无应答率为1.81%;GMC为800.94mIU/ml。检测再免疫的低/无应答儿童127名(17名无应答、110名低应答),抗-HBs的GMC,再免疫前为45.72mIU/ml,1剂次再免疫后为1 373.50mIU/ml(P<0.01);3剂次再免疫后检测其中100名(14名无应答、86名低应答),抗-HBs的GMC上升为1 763.33mIU/ml,与1剂次后的差异无统计学意义(P>0.05)。[结论]按现行免疫程序乙肝疫苗全程免疫后,可以取得良好的免疫应答。对低/无应答者按相同免疫程序再次接种3针后,抗-HBs水平有较大幅度提高。     

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.     

Immunogenicity of an inactivated hepatitis A pediatric vaccine: three-year post-booster follow-up

The persistence of anti-hepatitis A virus antibody concentrations was followed over 3 years in 177 healthy children following primary and booster vaccination with an inactivated hepatitis A vaccine, Avaxim 80 pediatric. Seroconversion rates (post-immunization anti-HAV antibody concentration >or=20 mIU/mL) and geometric mean concentrations (GMC) were estimated for each of three age groups: 18 month--3 years, 4--8 years, and 9--15 years. Only subjects who were initially HAV-seronegative at inclusion (<20 mIU/mL) were analyzed. Follow-up visits at years 1, 2, and 3 involved 177, 149, and 135 children, respectively. A decline in GMCs of about 74% occurred during the first year, from 3,060 to 814 mIU/mL overall, but did not continue during years 2 and 3. All subjects remained seropositive (antibody concentration >or=20 mIU/mL), with overall GMCs of 814, 891, and 924 mIU/mL in years 1--3, respectively. The inactivated hepatitis A study-vaccine resulted in sustained seroprotective antibody concentrations in 100% of these children, without a significant decline in antibiotic concentrations over the 3 years following booster injection, thus demonstrating the long-term protection expected with this vaccine.