Immunogenicity and safety of a new inactivated hepatitis A vaccine in a comparative study

Hepatitis A immunisation in persons not previously exposed to hepatitis A

This review is withdrawn because it is outdated. A new review is to be published by the end of 2019.

Use of hepatitis A vaccine for post-exposure prophylaxis in individuals over 40 years of age: A systematic review of published studies and recommendations for vaccine use

INTRODUCTION

Hepatitis A can cause widespread outbreaks. Until 2018, postexposure prophylaxis (PEP) in the United States for individuals >40 years consisted of immune globulin (IG) administered as soon as possible after exposure, ideally within 14 days whereas those aged ≤40 should receive hepatitis A (HepA) vaccine. However, state health departments reporting difficulty quickly accessing and administering IG, costs of higher IG doses and importance of long-term HAV protection prompted CDC to review immunogenicity data for use of HepA vaccine for PEP in older adults. We reviewed literature on use of HepA vaccine in adults >40 years and existing recommendations for HepA vaccine for use as PEP in other countries.

METHODS

We searched PubMed and EMBASE from January 1, 1992-January 7, 2017 using the terms "hepatitis A vaccine∗" and "HAV vaccine∗." Two reviewers read each abstract and articles were preserved if they included results (seroprotection, mean titers) within 28 days of HepA vaccine administration in adults >40 years. Additionally, we reviewed PEP recommendations from six other jurisdictions.

RESULTS

A total of 1,039 unique articles were identified, of which eight were retained and two added from references. Three studies included direct comparisons between individuals aged >40 years and those ≤40 years and one other study included three age groups over 40 years, finding lowest immunogenicity in the oldest adults. All found higher proportions seroprotected (definition varied by study) in younger age groups (ages varied by study) at 15 days post-vaccination but similar seroprotection at 30 days. Most other jurisdictions reviewed recommended vaccine alone or in conjunction with IG for PEP in older adults.

CONCLUSIONS

Immunogenicity of HepA vaccine may be diminished in older adults, especially in the very oldest age groups. HepA vaccine should be administered as soon as possible within 14 days after exposure to achieve the best possible immune response.

Hepatitis A immunisation in persons not previously exposed to hepatitis A

BACKGROUND

In many parts of the world, hepatitis A infection represents a significant cause of morbidity and socio-economic loss. Whilst hepatitis A vaccines have the potential to prevent disease, the degree of protection afforded against clinical outcomes and within different populations remains uncertain. There are two types of hepatitis A virus (HAV) vaccine, inactivated and live attenuated. It is important to determine the efficacy and safety for both vaccine types.

OBJECTIVES

To determine the clinical protective efficacy, sero-protective efficacy, and safety and harms of hepatitis A vaccination in persons not previously exposed to hepatitis A.

SEARCH METHODS

We searched The Cochrane Hepato-Biliary Group Controlled Trials Register, The Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library, MEDLINE, EMBASE, Science Citation Index Expanded, and China National Knowledge Infrastructure (CNKI) up to November 2011.

SELECTION CRITERIA

Randomised clinical trials comparing HAV vaccine with placebo, no intervention, or appropriate control vaccines in participants of all ages.

DATA COLLECTION AND ANALYSIS

Data extraction and risk of bias assessment were undertaken by two authors and verified by a third author. Where required, authors contacted investigators to obtain missing data. The primary outcome was the occurrence of clinically apparent hepatitis A (infectious hepatitis). The secondary outcomes were lack of sero-protective anti-HAV immunoglobulin G (IgG), and number and types of adverse events. Results were presented as relative risks (RR) with 95% confidence intervals (CI). Dichotomous outcomes were reported as risk ratio (RR) with 95% confidence interval (CI), using intention-to-treat analysis. We conducted assessment of risk of bias to evaluate the risk of systematic errors (bias) and trial sequential analyses to estimate the risk of random errors (the play of chance).

MAIN RESULTS

We included a total of 11 clinical studies, of which only three were considered to have low risk of bias; two were quasi-randomised studies in which we only addressed harms. Nine randomised trials with 732,380 participants addressed the primary outcome of clinically confirmed hepatitis A. Of these, four trials assessed the inactivated hepatitis A vaccine (41,690 participants) and five trials assessed the live attenuated hepatitis A vaccine (690,690 participants). In the three randomised trials with low risk of bias (all assessing inactivated vaccine), clinically apparent hepatitis A occurred in 9/20,684 (0.04%) versus 92/20,746 (0.44%) participants in the HAV vaccine and control groups respectively (RR 0.09, 95% CI 0.03 to 0.30). In all nine randomised trials, clinically apparent hepatitis A occurred in 31/375,726 (0.01%) versus 505/356,654 (0.18%) participants in the HAV vaccine and control groups respectively (RR 0.09, 95% CI 0.05 to 0.17). These results were supported by trial sequential analyses. Subgroup analyses confirmed the clinical effectiveness of both inactivated hepatitis A vaccines (RR 0.09, 95% CI 0.03 to 0.30) and live attenuated hepatitis A vaccines (RR 0.07, 95% CI 0.03 to 0.17) on clinically confirmed hepatitis A. Inactivated hepatitis A vaccines had a significant effect on reducing the lack of sero-protection (less than 20 mIU/L) (RR 0.01, 95% CI 0.00 to 0.03). No trial reported on a sero-protective threshold less than 10 mIU/L. The risk of both non-serious local and systemic adverse events was comparable to placebo for the inactivated HAV vaccines. There were insufficient data to draw conclusions on adverse events for the live attenuated HAV vaccine.

AUTHORS' CONCLUSIONS

Hepatitis A vaccines are effective for pre-exposure prophylaxis of hepatitis A in susceptible individuals. This review demonstrated significant protection for at least two years with the inactivated HAV vaccine and at least five years with the live attenuated HAV vaccine. There was evidence to support the safety of the inactivated hepatitis A vaccine. More high quality evidence is required to determine the safety of live attenuated vaccines.

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

BACKGROUND

Vaccination against hepatitis A virus (HAV) is unaffordable to many developing countries. Substantial reductions in cost occur when vaccines are administered intradermally at low doses. Aluminum-free HAV vaccines are considered more suitable for intradermal use than traditional vaccines which can cause long-lasting local reactions. Thus, we compared the immunogenicity and safety of an aluminum-free virosomal HAV vaccine (Epaxal) administered by different routes: intradermal (i.d.), subcutaneous (s.c.), and intramuscular (i.m.).

METHODS

Two open pilot studies were conducted as sub-studies of a large lot consistency trial. Healthy subjects aged 18 to 45 were enrolled. Study 1 compared two i.d. regimens of a lower dose of Epaxal [0.1 mL (4.8 IU), one or two injection sites] with i.m. administration of the standard dose [0.5 mL (24 IU)]. Study 2 compared the s.c. with the i.m. administration of the standard dose. At month 12, subjects in study 1 received a booster dose of 0.1 mL i.d. or 0.5 mL i.m.; subjects in study 2 received 0.5 mL via the respective route (s.c. or i.m.). Serum was tested for antibodies at baseline, 2 weeks (study 1), and 1 and 6 months after the primary vaccination as well as prior and 1 month after the booster dose. Incidences of solicited and unsolicited adverse events were recorded.

RESULTS

Seroprotection rates (anti-HAV geometric mean concentration of > or =20 mIU/mL) after 1 month ranged from 93.2% to 100% in all groups and remained high until month 12 (range 85.2&-90.2%). Complete (100%) seroprotection was achieved by all subjects in all groups after booster vaccination. All routes of administration were well tolerated. Local reactions were more common in subjects vaccinated i.d. and s.c. than i.m.

CONCLUSIONS

The aluminum-free virosomal HAV vaccine Epaxal is highly immunogenic and well tolerated when administered either via i.d., s.c., or i.m. Vaccination via the i.d. route may confer significant cost savings over the conventional i.m. route.

Immunogenicity, safety, and interchangeability of two inactivated hepatitis A vaccines in Chilean children

OBJECTIVES

To compare the immunogenicity, safety, and interchangeability of two pediatric hepatitis A vaccines, Avaxim 80U-Pediatric and Havrix 720, in Chilean children.

METHODS

In this randomized trial, 332 hepatitis A virus (HAV) seronegative children from 1 to 15 years of age received two doses of Avaxim, two doses of Havrix, or Havrix followed by Avaxim, 6 months apart. Anti-HAV antibody titers were measured before and 14 days after the first dose of vaccine, and before and 28 days after the second dose of vaccine. Immediate reactions were monitored; reactogenicity was evaluated from parental reports.

RESULTS

Seroconversion rates after the first vaccination were 99.4% and 100% for Avaxim and Havrix, respectively. Anti-HAV geometric mean concentrations (GMCs) were 138 mIU/ml for Havrix (95% confidence interval (CI): 120; 159) and 311 mIU/ml for Avaxim (95% CI: 274; 353). GMCs increased to 4008 mIU/ml after two doses of Havrix, 8537 mIU/ml following two doses of Avaxim, and 7144 mIU/ml in children who received Havrix with Avaxim as the second dose. Following the first injection, 36% of subjects given Avaxim and 44% given Havrix reported local reactions; 38% of subjects in the Avaxim group and 40% in the Havrix group reported systemic reactions related to vaccination. Solicited reactions were less frequent after the second dose of Avaxim or Havrix, occurring in 27% to 37% of subjects.

CONCLUSIONS

No significant difference in seroconversion rates was seen 14 days after a single dose of vaccine. A two-dose schedule with either vaccine or with Havrix/Avaxim provided a strong booster response. Both vaccines were well tolerated and can be recommended for routine vaccination of Chilean children. Avaxim 80 may be used to complete a vaccine schedule begun with Havrix 720.

Hepatitis A vaccines and the elderly

Hepatitis A virus (HAV) exposure in unprotected adults may cause severe and serious symptoms, with risk of both morbidity and mortality increasing with age. As seroprevalence of HAV is low in industrialised countries, and an increasing number of people, with an increasing median age, travel from areas of low HAV endemicity to high endemicity, pre-travel vaccination is warranted. Vaccination of the elderly against HAV, however, may be associated with reduced seroprotection, since the immune response decreases with age. Studies with monovalent hepatitis A vaccine or combined hepatitis A and B vaccine show good efficacy in adults in general. Few studies have assessed the immune response in older adults. The only prospective study with monovalent hepatitis A vaccine in the elderly showed a reduced seroprotection of approximately 65% after a single primary dose in subjects over the age of 50 years, while seroprotection was 98% in this age group after receiving a booster dose. The only prospective study with combined hepatitis A and B vaccine in younger subjects or older than 40 years showed similar seroprotection (99-100%) against HAV compared to a monovalent vaccine after receiving three doses. As data on seroprotection for HAV in the elderly are limited, further studies are needed to elucidate how optimal protection in the elderly can be achieved. In the mean time, based on the available data, the suggestion is made to screen elderly travellers to areas endemic for HAV for the presence of naturally acquired immunity, and, if found susceptible, be immunised well in advance of their trip, to allow time for post-vaccination antibody testing and/or administration of a second dose of the vaccine.

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.

Cell mediated and antibody immune response to inactivated hepatitis A vaccine

The humoral and cellular immune response to inactivated hepatitis A vaccine was investigated dynamically in a time elapse study over 1 year. Fourty-five healthy volunteers, seronegative for anti-HAV, were vaccinated with 1440 enzyme-linked immunosorbent assay units (EU) of formalin-inactivated hepatitis A virus following a 0--6-month schedule. Serum anti-HAV levels and HAV-specific proliferation of peripheral blood mononuclear cells were measured at several time points over a 26- and 28-week period after the first and second injection, respectively. Distinct B and T cell responses were determined within 14 days after primary vaccination. The booster vaccination-induced immediate peak levels for the humoral (anti-HAV GMC=5376mIU/ml) as well as the cellular (median Deltacpm=14173cpm) response.

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.

Interchangeability and tolerability of a virosomal and an aluminum-adsorbed hepatitis A vaccine

The interchangeability of virosomal (Epaxal) and aluminum-adsorbed (Havrix 1440) hepatitis A virus (HAV) vaccines was studied in 111 healthy adults who were vaccinated in a randomized, single-blind, crossover clinical trial. Anti-HAV antibody titers were measured at days 0 (first dose), 14, and 28, and months 3, 6, 12 (second dose), 13, 24, 36, 48, 60 and 72. Most subjects (>95%) had sero-converted 14 days after the first dose of either vaccine. The second dose with either vaccine induced a high antibody response in all vaccines, irrespective of the type of vaccine administered as the first dose. Although both vaccines were well tolerated, the incidence of local adverse events (in particular pain) was significantly lower in subjects receiving the virosomal vaccine. Six-year follow-up data did not reveal any significant differences between the vaccination groups.

A randomized, open-label study of the immunogenicity and reactogenicity of three lots of a combined typhoid fever/hepatitis A vaccine in healthy adults

BACKGROUND

Travelers are often advised to receive both the typhoid fever and hepatitis A virus (HAV) vaccines, particularly when going to areas where the 2 diseases are endemic. Thus, combined administration of these vaccines could make immunization more acceptable by reducing the number of injections needed.

OBJECTIVE

This study compared the safety profiles and immunogenicity of 3 batches of a combined typhoid fever/HAV vaccine administered using a dual-chamber bypass syringe.

METHODS

This randomized, open-label study was conducted at 2 university-based travel clinics in Germany and Austria. Subjects received a single IM injection from 1 of 3 batches of the combined vaccine. Blood samples were drawn immediately before and 28 days after vaccination to evaluate the response to the 2 antigens by assessing geometric mean titers (GMTs) and rates of seroconversion and seroprotection. Subjects recorded all adverse events (AEs) occurring during the study period in a diary.

RESULTS

Six hundred ten healthy adults were enrolled in the study. Twenty-eight days after vaccination, 90.6% of the study population had protective typhoid Vi antibody titers (> or = 1 microg/mL) and 100% had protective HAV antibody titers (> or = 20 mIU/mL). Seroconversion rates and GMTs were not significantly different between the 3 batches. There were no differences with regard to local or systemic AEs between the 3 batches of vaccine. There were no immediate adverse reactions (within 30 minutes of vaccination) and no serious AEs related to vaccination. Of 609 evaluable subjects (1 was lost to follow-up after the first visit), 555 (91.1%) experienced > or = 1 local reaction within the first 7 days after vaccination, mainly pain at the injection site (550 [90.3%]), but only 26 (4.3%) described this pain as severe. Vaccine-related headache and mild to moderate asthenia were each reported by 54 subjects (8.9%). Symptoms resolved spontaneously in all cases.

CONCLUSIONS

The 3 batches of the combined typhoid fever/HAV vaccine administered by dual-chamber bypass syringe were equally well tolerated and effective in healthy adults, and did not differ significantly in terms of GMTs or seroconversion rates.

Dose-ranging studies of the safety and immunogenicity of human papillomavirus Type 11 and Type 16 virus-like particle candidate vaccines in young healthy women

Two candidate vaccines to prevent infection with human papillomavirus (HPV) Types 11 and 16 were studied in similar double-blind, placebo-controlled, dose-escalation trials. L1 virus-like particle (VLP) vaccines were made from recombinant L1 capsid protein of HPV11 or HPV16. Participants received 10, 20, 50, or 100 microg of HPV11 L1 VLPs, 10, 40, or 80 microg of HPV16 L1 VLPs, or placebo at Months 0, 2, and 6. Serum geometric mean antibody levels at Month 7 were 258, 644, 647, and 1112 milli-Merck units (mMU)/ml for the 10, 20, 50, and 100 microg doses of the HPV11 L1 VLP vaccine, respectively, and 479, 808, and 732 mMU/ml for the 10, 40, and 80 microg doses of the HPV16 L1 VLP vaccine, respectively. Antibody to HPV11 and 16 was still present at Month 36 in 96.8 and 93.5% of vaccinees, respectively. Both vaccines were well tolerated and were associated with only mild to moderate injection-site reactions.

Long-term immunogenicity of an inactivated virosome hepatitis A vaccine

The aim of this study was to predict the long-term protection induced after immunisation with inactivated, aluminium-free virosome hepatitis A vaccine. The study population consisted of adult volunteers enrolled in four different clinical trials. Lower 95% confidence interval limits and seroconversion rate were calculated by using a linear mixed model to estimate the persistence of serum antibodies over time. To assess the robustness of the mathematical model, several sensitivity analyses were performed with more conservative protective threshold (20 mIU/ml vs. 10 mIU/ml), higher yearly decline rate, and exclusion of volunteers who had increasing titres over time. Based on 190 volunteers with at least two valid assessments of titres from year 3 onward, the median duration of protection was 55.5 years, with a lower limit of the 95% CI of 48.7 years. Duration below 25.3 years was predicted for only 5% of the subjects. Women tended to have higher titres to start with, but their rate of decline was higher, resulting in similar duration of protection overall. The use of a more conservative threshold, higher yearly decline rate, and exclusion of volunteers with increasing titres over time did not affect these results. According to this model, 95% of the volunteers should have anti-HAV titres above the minimum protective threshold for 20 years or more following immunisation with two doses of this aluminium-free vaccine.

Travel vaccines and elderly persons: review of vaccines available in the United States

Aging is associated with alterations in immune responses and may lead to clinically significant changes in the safety, immunogenicity, and protective efficacy of certain vaccines. This review summarizes published data regarding the effects of age on responses after immunization with vaccines generally administered before travel. The specific vaccines discussed in detail include hepatitis A, typhoid, yellow fever, Japanese encephalitis, and rabies vaccines. There is some evidence of diminished serological responses to hepatitis A and rabies vaccines in older individuals. In addition, increased toxic effects following yellow fever vaccination in elderly recipients have recently been reported. However, many travel-related vaccines have never been studied specifically in elderly populations. Consideration of potential age-related differences in responses to travel vaccines is becoming increasingly important as elderly persons more frequently venture to exotic destinations.

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

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

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 and reactogenicity of Avaxim (160 AU) as compared with Havrix (1440 EL.U) as a booster following primary immunization with Havrix (1440 EL.U) against hepatitis A

BACKGROUND

Hepatitis A vaccination is recommended for travelers from the UK to areas of moderate or high endemicity. Two licensed hepatitis A vaccines are now available in the UK, and this trial was undertaken to determine whether Avaxim can be used as a booster following a primary course of Havrix.

METHODS

One hundred and eighty-five subjects were randomized to receive a booster dose of either Avaxim (n=92) or Havrix (n=93), 6 to 7 months after a primary dose of Havrix. Subjects were observed for 30 minutes for immediate reactions and subsequently completed a diary card for a further 2 weeks. Serology samples for HAV antibody titers were taken at 28 6 7 days later.

RESULTS

One month following the booster dose, all subjects in both treatment groups achieved HAV antibody titers >= 20 mIU/mL. In the Avaxim group, geometric mean titer (GMT) values increased from 642 mIU/mL (97.5% CI 330-1250 mIU/mL) to 6669 mIU/mL (4566-9740 miu/mL), compared with 739 mIU/mL (379-1443 mIU/mL) at baseline to 4460 mIU/mL (2880-6908 mIU/mL) following the administration of Havrix. The increase in GMT following the administration of Avaxim was significantly greater than that following Havrix (p=.02). Eight percent of subjects reported pain at the injection site following a booster dose of Havrix, compared with none following Avaxim. This difference in reactogenicity was statistically significant (p=.01). In all other respects, both preparations were safe and equally well tolerated.

CONCLUSION

Either Avaxim or Havrix may be given as a booster dose of hepatitis A vaccine when Havrix has been administered as the primary dose.

SPf66 malaria vaccine is safe and immunogenic in malaria naive adults in Thailand

In preparation for an efficacy trial of malaria vaccine SPf66 in Thailand, a series of overlapping Phase I trials were conducted of US-manufactured SPf66. Here, two clinical lots were evaluated for safety and immunogenicity in a combined open-label trial. Eleven healthy, malaria naive, 18-44 year-old Thai men and women received three doses by subcutaneous injection in alternate arms at 0, 1 and 6 months. Safety was assessed by monitoring local and systemic reactogenicity and laboratory parameters. Common side effects were mild erythema, induration and tenderness at the site of injection which resolved within 24-48 h. At third immunization, two volunteers developed acute bilateral reactions with induration, erythema and pruritus limited to the sites of the second and third immunizations. Eight of 11 volunteers sero-converted by ELISA, six of whom would be classified as high responders by Colombian standards. Eight of 11 volunteers developed a lymphoproliferative response to the SPf66 antigen. Side effects were more common and antibody and lymphoproliferative responses greatest, among the four female volunteers. This initial study of SPf66 malaria vaccine in Asia constitutes an essential link between the initial Phase I study in the US and subsequent field studies in a semi-immune population in a malaria endemic area of Thailand. This study further establishes comparability of US-manufactured SPf66 with that of Colombian provenance and substantiates the validity of the subsequent negative efficacy results of SPf66 in a field trial in Thailand.

Early appearance of neutralizing antibodies after vaccination with an inactivated hepatitis A vaccine

Sera from 30 subjects vaccinated with the Pasteur Merieux Serums & Vaccins (PM) inactivated hepatitis A vaccine, and from 30 subjects vaccinated with the Smithkline Beecham (SB) inactivated hepatitis A vaccine, were tested in two laboratories in order to provide comparative data on neutralizing activities of vaccine-induced antibodies. Sera were also evaluated by a modified radioimmunoassay (mRIA) and results were compared to neutralization assays results. Neutralizing antibody titres provided by the two laboratories correlated well (coefficient or correlation 0.42, P < 0.001). Neutralizing antibodies were detected after vaccination with both vaccines, and the kinetics of neutralizing antibody were the same with both vaccines. The titres gradually increased between the second week after the first dose and the post-booster dose (week 28). A strong booster effect of the booster vaccine dose on neutralizing titres was observed. Significantly higher neutralizing antibody titres with the PM vaccine were observed as early immune response on week 2 titres on both series of results. Vaccine-induced neutralizing antibody titres and vaccine-induced antibody mRIA titres correlated well (coefficient of correlation 0.82 and 0.72, respectively, P < 0.0001 in both cases). These results demonstrate early appearance of neutralizing antibody at high titre with the PM vaccine.

Inactivated hepatitis A vaccine: long-term antibody persistence

During the clinical development of safe, well tolerated and immunogenic vaccines against hepatitis A the persistence of protective antibodies was estimated, based on relatively short observation periods of 18 months to 3 years. We report here on longterm persistence of antibodies in volunteers who participated in one of the early clinical trials on inactivated hepatitis A candidate vaccines. In a randomized trial three groups of altogether 110 healthy adults, initially hepatitis A virus (HAV) seronegative persons were vaccinated with an inactivated hepatitis A vaccine according to the schedule 0-1-2-12 months. One group received 180 ELISA units, one group 360, and one 720 ELISA units per dose. Blood samples were taken prior to the first vaccination and at months 1, 2, 3, 4, 6, 12, 13, 18, 24, 36 and 84. The decrease of antibodies was characterized by two disappearance rates: a rapidly decreasing component and a slower decreasing one becoming predominant ca 12 months after booster vaccination. The disappearance of antibodies could be described by a two-component model which holds for t > or = 13 months. The estimated disappearance rates for the slow component (annual decrease) was found to be 11 and 13% for the 180 and 360 El. U groups, respectively (the 720 El. U group showed no decline, which was probably due to the small sample size). The estimated persistence of antibodies within protective range varied between 24 and 47 years depending on individual titres reached at month 13 and vaccination dose.

Does immunoglobulin interfere with the immunogenicity to Pasteur Mérieux inactivated hepatitis A vaccine?

BACKGROUND/AIMS

The aim of this study was to compare the immunogenicity of Pasteur Mérieux (P.M. s.v.) inactivated hepatitis A vaccine when given alone with its immunogenicity when given in combination with immunoglobulin.

METHODS

We enrolled 80 healthy volunteers who were seronegative for anti-HAV. Forty subjects (group A) were given two doses of vaccine at 0 and 6 months plus 4 ml of immunoglobulin given simultaneously with the first vaccine injection; and 40 subjects (group B) were given vaccine alone. The population characteristics (age, sex, height and weight) of the two groups were comparable.

RESULTS

Anti-HAV antibody was detectable at week 1 in 100% of group A and in 5.7% of group B, and in 100% of both groups at 4 and 8 weeks. Seroconversion rates (> or = 20 mIU/ml) were 97.4% in group A and 100% in group B at week 24 and were 100% in both groups 4 weeks after a booster injection at 6 months. The antibody response level was lower after concomitant administration of vaccine with immunoglobulin. The antibody geometric mean titer was higher at week 1 in subjects who had been given vaccine and immunoglobulin, but nearly 50% lower at week 4 and thereafter, indicating inhibition of the vaccine-induced immune response by immunoglobulin. At week 28, i.e. 4 weeks after the booster injection, geometric mean titers had increased about 13-15 times in both groups, reaching highly protective antibody levels (3351 mIU/ml in group A and 5843 mIU/ml in group B). No serious adverse effects were observed during the follow-up.

CONCLUSIONS

These data indicate that P.M. s.v. hepatitis A vaccine is highly immunogenic and safe, even when given simultaneously with immunoglobulin. Despite the interference of the immunoglobulin with the active immune response, individuals who were immunized passively plus actively also developed high titers of anti-HAV antibody. It is therefore reasonable to expect that this inhibition will not affect the overall protection conferred by the vaccine.