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Clinical and Vaccine Immunology, January 2007, p. 65-73, Vol. 14, No. 1
1071-412X/07/$08.00+0 doi:10.1128/CVI.00230-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

GlaxoSmithKline Biologicals, Rixensart, Belgium,1 Meningococcal Reference Unit, Health Protection Agency, Manchester, United Kingdom,2 Centro de Salud Nazaret, Valencia, Spain,3 Vaccines Institute of Valencia, Valencia, Spain,4 Grupo de Investigación de Atención Primaria de Castellón, Centro de Salud Pública, Castellón, Spain,5 Centro de Salud Quart de Poblet, Valencia, Spain,6 Centro de Salud Paiporta, Valencia, Spain,7 Centro de Salud Malvarosa, Valencia, Spain,8 Centro de Salud Fuente de San Luis, Valencia, Spain,9 Universidad Rey Juan Carlos, Madrid, Spain,10 Ecole de Santé Publique, Brussels, Belgium,11 Finlay Institute, la Habana, Cuba,12
Received 22 June 2006/ Returned for modification 26 July 2006/ Accepted 13 October 2006
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VA-MENGOC-BC is a vaccine consisting of OMVs (50 µg) from the epidemic strain B:4:P1.19,15 and the capsular polysaccharide of meningococcal serogroup C (50 µg) that was developed by the Finlay Institute in response to a serogroup B epidemic in Cuba. VA-MENGOC-BC was used effectively in a public health campaign in Cuba (9); it has also been shown to be efficacious in subjects of more than 4 years of age in settings in Brazil where heterologous meningococcal strains were circulating (7, 14). Recently, a new vaccine (MeNZB; Chiron) has been tailor-made to control the long-term epidemic of group B meningococcal disease in New Zealand, which has been dominated by subtype P1.7-2,4 (15). This new strain-specific vaccine is an OMV vaccine prepared from the B:4:P1.7-2,4 strain (New Zealand strain) and is licensed in New Zealand for use in all age groups from 6 weeks of age upwards (www.immunise.moh.govt.nz). No protective efficacy trials have been performed with the vaccine, but three vaccine doses given at 6-week intervals induced a seroresponse in approximately 75% of children and 96% of adults (15).
In contrast to N. meningitidis serogroups A, C, W135, and Y, for which immunity is related to the capsular polysaccharides, natural immunity against meningococcal serogroup B strains appears to be related mainly to the different serosubtype- and immunotype-specific protein and lipooligosaccharide (LOS) antigens, which vary from one geographical region to another. Although monovalent vaccines appear to offer some cross-protection against heterologous strains, bivalent or even multivalent vaccines would offer wider protection and would be more useful in routine vaccination programs (4).
The Finlay Institute, Havana, Cuba, in collaboration with GlaxoSmithKline (GSK) Biologicals, has developed an experimental bivalent meningococcal serogroup B vaccine containing OMVs from the B:4:P1.7-2,4 strain (from ST-44 complex/lineage 3) and B:4:P1.19,15 strain (from ST-32 complex/ET-5 complex). The experimental vaccine, which is derived from VA-MENGOC-BC with the addition of OMVs from the B:4:P1.7-2,4 strain (but without serogroup C polysaccharide), will provide wider vaccine coverage than the parent vaccine, particularly for the strains circulating in Europe: data report that the most numerous serogroup B meningococcal strains in 1999/2000 were B:4:P1.4, B:15:P1.7,16, and B:4:P1.15, representing, respectively, 59, 17, and 14% of typed serogroup B samples (13).
The primary objective of the current study was to evaluate the bactericidal immune response induced by the experimental OMV vaccine when it was given to healthy adolescents using two different vaccination schedules. As standardization of the serum bactericidal assay is known to be difficult (3, 11), the assay was performed at two different laboratories to allow interlaboratory comparisons. The secondary objective was to evaluate the safety of this vaccine.
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Adolescents were excluded from the study if they had been immunized with a meningococcal serogroup B vaccine or if they had a history of or exposure to meningococcal serogroup B infection. Acute disease or a temperature of
37.5°C at a vaccination visit resulted in postponement of vaccination or withdrawal from the study.
The study was approved by the ethics review committee of each of the study centers and conducted according to the Declaration of Helsinki and Good Clinical Practices. Written informed consent was obtained from all subjects and their parents or guardians.
Vaccines. One 0.5-ml dose of the experimental vaccine contained purified OMVs of N. meningitidis strain B:4:P1.19,15 (CU385) and strain B:4:P1.7-2,4 (NZ228/98) (25 µg of each) and 0.69 mg of aluminum hydroxide. One lot of the vaccine was used.
Control vaccines were Wyeth Lederle's Meningitec (10 µg of capsular serogroup C polysaccharide conjugated to 15 µg of Corynebacterium diphtheriae CRM197 protein with 0.125 mg aluminum phosphate per 0.5-ml dose) and GSK Biologicals' Havrix (720 enzyme-linked immunosorbent assay units of hepatitis A virus, strain HM 175, with 0.05 mg aluminum hydroxide per 0.5 ml dose).
Study design. The study was a randomized, partially unblinded study with three parallel groups. Two groups received three doses of the meningococcal OMV vaccine according to either a 0-2-4 month (MenB 0-2-4m group) or a 0-1-6 month schedule (MenB 0-1-6m group). The control group received Havrix at month 0 and month 6 and Meningitec at month 1 (control 0-1-6m group). The vaccines given to the control group and to the MenB 0-1-6m group were administered in an observer-blinded manner (i.e., subjects, parents/guardians, and personnel in charge of the reactogenicity assessment were all unaware of which vaccines were administered).
Adolescents at each study site were assigned to the three study groups using a computer-generated list of random numbers. Subjects were further stratified by age into two equal strata (12 to 15 years and 16 to 18 years).
All vaccines were administered intramuscularly into the (nondominant) deltoid. Venous blood samples were collected from each subject immediately prior to the first vaccination and at 1 month after the third vaccination. Sera were stored at temperatures between 20°C and 70°C until they were sent to GSK Biologicals (Rixensart, Belgium), where they were divided into aliquots for testing. Sera from all subjects in the MenB groups and from a randomized subset of half of the subjects in the control group were tested at GSK Biologicals. In addition, aliquots of serum from randomly selected subjects from the MenB 0-1-6m group (n = 80) and the control group (n = 40) were also sent to the Health Protection Agency (HPA) laboratory (Meningococcal Reference Unit, Manchester, United Kingdom) for testing.
Serum bactericidal assays. Serum bactericidal antibody assays were performed using MenB wild-type clinical isolates (Table 1). All human sera to be tested were heat inactivated for 30 to 40 min at 56°C. Sera from humans with no SBA activity against the tested strains were used as the complement source.
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TABLE 1. Meningococcal strains used in serum bactericidal assays at the two laboratories
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The strains (50 µl from working seed) were spread on CHSA and incubated overnight at 37°C in 5% CO2. The following morning, bacteria from one plate were scraped with a sterile swab and streaked onto fresh CHSA. After 4 h of culture at 37°C in 5% CO2, the plates were swabbed and bacteria resuspended in phosphate-buffered saline (PBS) with 0.5 mM MgCl2-0.9 mM CaCl2 and 0.1% glucose in order to reach an A600 of 0.4 nm (bacterial suspension).
In wells of sterile flat-bottom 96-well microplates (Nunc), 25 µl of undiluted test serum was mixed with 12.5 µl of human complement and 12.5 µl of bacterial suspension. Serial twofold dilutions of test sera (in PBS-MgCl2-CaCl2-glucose) were treated similarly. Controls included bacteria plus complement, bacteria plus heat-inactivated complement, and test serum samples plus bacteria plus heat-inactivated complement.
The microplates were then sealed and incubated for 75 min at 37°C at 210 rpm without CO2. After this incubation, 50 µl of 0.9% Mueller-Hinton agar were added in each microwell, and a second layer of 50 µl of PBS-0.9% agar was added 30 min later. After an overnight incubation at 33°C in 5% CO2, the colonies were counted. The average number of CFU of the controls corresponding to bacteria plus complement was set at 100%. The lowest dilution of the test is 1:2 (seropositivity).
(ii) HPA assays. Working cultures were prepared by streaking the mother cultures for single-colony isolation on Columbia horse blood agar (CHBA) plates (blood agar base no. 2 [Oxoid] and 10% defibrinated horse blood [Oxoid]) and culturing overnight at 37°C with 5% CO2. Following incubation, cells were harvested into brain heart infusion broth (Oxoid), aliquoted, and stored at 80°C.
Working cultures were streaked for single-colony isolation on CHBA and incubated overnight at 37°C with 5% CO2. The following morning, approximately 50 colonies were picked, streaked on fresh CHBA, and incubated for 4 h at 37°C with 5% CO2. After the incubation, colonies were suspended in bactericidal buffer (Gey's balanced salts solution [Gibco] containing 0.5% bovine serum albumin [Sigma]), and the A650 was adjusted to 0.1 nm. The number of CFU was adjusted to approximately 6 x 104 organisms/ml in bactericidal buffer.
U-bottom 96-well microtiter plates (Grenier) were used in the SBA assay. In wells, test sera (20 µl) were double diluted in bactericidal buffer, followed by the addition of 10 µl of the bacterial suspension (6 x 104 organisms/ml) and 10 µl human complement. The controls were identical to those used in the GSK procedure. Microtiter plates were sealed and incubated for 60 min at 37°C at 65 rpm without CO2. Following the incubation, 10 µl from each well was plated out using the tilt method onto CHBA to determine the number of CFU 60 min after the start (T60). After an overnight incubation at 37°C with 5% CO2, the colonies were counted. The lowest dilution of the test is 1:4 (seropositivity).
At both laboratories, a known positive serum sample was included (either on each plate or at least in each run) in addition to the controls. The acceptable limit of variability was 1 dilution in a twofold-dilution series from the assigned mean from a historical database. The reciprocal of the highest serum dilution yielding at least 50% killing at T60/T75 was reported as the titer.
Monitoring for adverse events. All subjects were closely monitored for at least 30 min after each vaccination. Reactogenicity data were collected from diary cards completed by the subjects or their parents/guardians during the 15 days after each dose for pain, redness, and swelling at the injection site and for fever, fatigue, gastrointestinal symptoms, headache, and rash; other (unsolicited) symptoms were recorded during the 30 days after each dose. All serious adverse events occurring throughout the study period were reported by the investigators.
Statistical analysis.
Immunogenicity analyses were performed for the according-to-protocol (ATP) cohort, defined as vaccinated subjects who met all eligibility criteria, complied with protocol-defined procedures, and had pre- and postvaccination assay results available for at least one bactericidal assay. For each assay, seropositivity rates (defined as an SBA titer of
1:2 for GSK assays and an SBA titer of
1:4 for HPA assays) and response rates (defined at each laboratory as a
4-fold increase in prevaccination SBA titer; for GSK, this was 1 to
4, while for HPA, it was 2 to
8) each with their 95% confidence intervals (CI) and geometric mean titers (GMTs) and their 95% CI were calculated prior to the first vaccine dose and at 1 month after the third vaccine dose. GMTs were calculated by taking the antilog of the mean of the log10 titer transformations. Antibody titers below the cutoff of the assay were given an arbitrary value of half the cutoff value for the purpose of GMT calculation.
An exploratory evaluation of the coprimary endpoints (defined as the SBA-MenB response rates at 1 month after the third dose for each GSK assay) was carried out. The primary objective was considered reached if the immune response rates for each of the two homologous or PorA-related strains were statistically above 40% (one-sided P value < 0.0125 for null hypothesis; P = 40%) and if the immune response for the three heterologous strains was statistically above 20% (one-sided P value < 0.0125 for null hypothesis; P = 20%). Table 1 shows MenB strain characteristics.
The safety analysis was performed with the entire vaccinated cohort. The incidences of any adverse events within the 15 days following vaccination and their exact 95% CI were computed by group according to the type of adverse events, intensity, and relationship to vaccination.
The two-sided Fisher's exact test was used to explore differences between groups.
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FIG. 1. Trial profile.
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TABLE 2. Demographics of subjects enrolled
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Immunogenicity. Prevaccination seropositivity rates were high for most strains (Table 3): for GSK assays, rates ranged from 16.2% for strain B16B6 to 78.8% for strain NZ124/98; for HPA assays, rates ranged from 18.2% for M01 240185 to 90.5% for M01 240101.
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TABLE 3. Percentage of subjects with SBA titers of 1:4 pre- and postvaccinationa
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FIG. 2. Percentage of subjects with a 4-fold increase in serum bactericidal antibody to vaccine-homologous or PorA-related and heterologous strains (assays done at GSK Biologicals). All subjects in the ATP cohort for immunogenicity (156 in the MenB 0-2-4m group, 151 in the MenB 0-1-6m group, and 150 in the control group) with results available for a specific assay were included in the analysis for that assay. See Table 1 for strain typing details. The response rate was statistically higher for BZ10 for the MenB 0-1-6m versus the MenB 0-2-4m group and statistically lower for all strains for the control versus the MenB 0-1-6m group (P < 0.05; two-sided Fisher's exact test).
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FIG. 3. Percentage of subjects with 4-fold increases in serum bactericidal antibody to vaccine-homologous or PorA-related and heterologous strains (assays done at HPA). A randomly selected subset of subjects from the MenB and control 0-1-6m groups in the ATP cohort for immunogenicity (80 in the MenB group, 40 in control group) with results available for a specific assay were included in the analysis for that assay. See Table 1 for strain typing details. The response rate was statistically lower for all strains for the control versus MenB 0-1-6m group (P < 0.05) except for M01240101 (P = 0.194; two-sided Fisher's exact test).
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There was no difference between the two schedules for the two vaccine homologous or PorA-related strains or for two of the three heterologous strains; however, for bactericidal antibodies against the BZ10 heterologous strain, the 0-1-6 month schedule induced a higher response rate (45.3%) than the 0-2-4 month schedule (32.4%) (GSK assays; P value < 0.05).
One month after the third meningococcal OMV vaccine dose, the SBA-MenB GMTs for all strains were higher than before vaccination (range, 1.8-fold to 6.2-fold in GSK assays and 1.6-fold to 5.3-fold in HPA assays) (Table 4).
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TABLE 4. Pre- and postvaccination geometric mean serum bactericidal antibody titersa
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One month after the three vaccine doses, SBA-MenB response rates were lower (P < 0.05) in the control group than in the MenB 0-1-6m groups for each of the strains tested in both GSK and HPA assays, except for M01 240101 (P = 0.194) (Fig. 2 and 3). GMTs in the control group were either lower or very slightly higher (maximum, 1.3-fold increase) after vaccination than before vaccination for all strains (Table 4).
Safety. There were no serious adverse reactions that were related to the administration of the meningococcal OMV vaccine. The safety and reactogenicity profiles of the OMV vaccine were similar for both schedules (Table 5). The incidences of each solicited local symptom and of those graded 3 were higher in the MenB 0-1-6m group than in the control group (P < 0.05 for each symptom).
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TABLE 5. Incidence of local and general solicited symptoms over the three-dose vaccination coursea
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An SBA titer of
1:4 has been proposed as protective (9). In this study, most subjects had a titer of SBA against strain B:4:P1.7-2,4 of at least 1:4 prior to vaccination, which is as described previously for a similar age group (8). A fourfold increase in SBA titer is therefore a more appropriate measure of vaccine response to a meningococcal B vaccine in this population (25). The meningococcal OMV vaccine induced immune response rates of 51% to 66% against the different vaccine-homologous or PorA-related strains tested in this study (GSK assays).
The rates of immune response to the vaccine-homologous or PorA-related strains of serosubtype B:4:P1.19,15 were similar in the European subjects in this study to those reported for the parent vaccine, VA-MENGOC-BC, in subjects in studies in Chile (20) and in Iceland (16).
Clinical studies have estimated the efficacy of VA-MENGOC-BC against the Cuban epidemic strain (from which the vaccine was derived) to be 83% (19) and the efficacy of the OMV vaccine developed at the National Institute of Public Health (Oslo, Norway) against the Norwegian epidemic strain to be 57% in children 12 to 16 years of age (2). In addition, case-control studies have shown VA-MENGOC-BC to be effective (>70%) in subjects older than 4 years of age in epidemiological settings where both vaccine-homologous and heterologous strains were circulating (5, 14); furthermore, no evidence for serotype-specific protection was found in these studies, suggesting that the protection was cross-reactive. From these results, it appears that the bactericidal immune response underestimates the true efficacy of meningococcal serogroup B vaccines for both homologous and heterologous strains. This underestimation is most likely explained by the fact that even though SBA activity is the major mechanism of protection, others, such as opsonic activity, may also confer protection in the absence of complement-mediated bactericidal activity, as observed in the infant rat challenge model (21, 23, 24) and in human volunteers (1).
A correlation between immune responses and protection rates has also been shown for other meningococcal OMV vaccines (5, 9). Furthermore, MeNZB has been licensed in New Zealand on the basis of immune response, as measured by SBA assay, on the grounds that this provides a good indication of a probable protection (15).
In this study, the vaccine response against heterologous strains was variable (28 to 62% for the six strains tested at the two laboratories), with the lowest response (28% and 33%) being against strain B16B6. As all the strains used in the SBA assays in our study express LOS immunotype 3 except B16B6, which expresses LOS immunotype 2, these results suggest that non-PorA-cross-reactive bactericidal antibodies are induced partly by the conserved OMP and partly by the LOS part of the OMVs. The demonstrated SBA response against strain B16B6 can best be explained via cross-reactive OMPs. The importance of LOS was also demonstrated in a recent study of a meningococcal B vaccine with LOS as its major component (W. D. Zollinger, J. G. Babcock, B. L. Brandt, E. E. Moran, N. M. Wassif, and C. R. Alving, poster no. 200, 14th International Pathogenic Neisseria Conference, Milwaukee, Wis., 5 to 10 September, 2004).
The SBA-MenB assays were performed at two different laboratories using different methods and different strains, although one strain (H44/76) was common to both laboratories. As expected, there were differences in the titers achieved at each laboratory.
Based on responses against the standard strain (H44/76) but also the other strains, HPA SBA titers are on average twice as high as GSK titers, and this was observed for both prevaccination and postvaccination sera. Despite these differences, the measured vaccine responses were similar between laboratories. Additionally, the overall response rates were comparable at both laboratories for the homologous or PorA-related and the heterologous strains, although in the vaccine response against the P1.19,15 strains, the result was slightly lower (41%) for M01 240101 (ST-269 complex) at HPA than that for M97250687 (ST-32 complex) at GSK (61.1%); interlaboratory variability and/or the use of a strain of a different epidemic clone may have played a role. The P1.19,15 strain used at GSK was similar to the Cuban P1.19,15 vaccine strain (both strains belong to the same clonal complex, ST-32), while the P1.19-1,15-11 strain used at HPA is from the ST-269 complex and can be considered to represent a variant from the vaccine strain. These results are similar to those already reported for another interlaboratory comparison of SBA-MenB assays (3, 11).
The relatively high proportion (about 20%) of subjects in the control group with at least a fourfold increase in SBA for half the strains tested by the HPA lab might be explained by the higher sensitivity of the assays developed by HPA than those developed by GSK, as observed by the overall higher GMT obtained by HPA (compared to GSK) for all time points and with all strains. Between the bleedings done before the vaccination and after vaccination, some subjects from the control group may have been exposed to N. meningitidis strains (carriage) and have produced low levels of bactericidal antibodies that were detected only by the HPA assays.
The bivalent meningococcal OMV vaccine was safe, with no serious adverse reactions related to vaccination reported. It has already been recognized that a high rate of local reactions occurs following the administration of meningococcal OMV vaccines containing aluminum hydroxide (17), as in this study. Although adverse reactions were reported frequently, few severe systemic reactions were related to vaccination. As reported for this age group with other meningococcal OMV vaccines and the parent vaccine, pain at the injection site was the most frequently reported adverse event (6, 15, 20). Indeed, the incidence of local pain in this study is similar to that seen in the older age group vaccinated with the new MeNZB vaccine (also aluminum hydroxide adsorbed), which has recently been licensed for use in New Zealand (15); the incidence is also similar to that reported following administration of the parent vaccine, VA-MENGOC-BC, which has now been administered with an acceptable safety profile to approximately 28 million subjects.
The immune responses induced by the bivalent OMV vaccine demonstrated the induction of bactericidal antibodies against both PorA-homologous strains but also against strains with different PorA proteins, indicating the presence of other protective antigens in OMVs and confirming the potential for clinical cross-protection.
We are grateful to all the children and parents that participated in the study, to Sheila Woods for her assistance in preparation of the manuscript and to all those who helped carry out the study, including the collaborating physicians in the Spanish MenB-002 study group (Vicente Cabedo [Grupo de Investigación de Atención Primaria de Castellón {GIAP-CS group}], José Carvajal, Alberto Cortilla [GIAP-CS group], Manuel Enrubia, María Garcés [Vaccines Institute of Valencia {VIVA}], Luis García [VIVA], Mercedes García [VIVA], Josep Marés, Manuel Martínez-Pons [VIVA], Vicente Meneu [GIAP-CS group], Carmen Peidró [VIVA], Angels Ramón, Neus Rodríguez [GIAP-CS group], Nidia Ruiz [VIVA], Blanca Ruiz-Borau [GIAP-CS group], Vicente Santamaría [GIAP-CS group], Isabel Ubeda [VIVA], Pilar Garcia-Corbeira, Sylvie Vandendunghen, Marc Gillet, and Reyes Boceta-Munoz) and the personnel at the HPA laboratory (Rita Barchha, Ewan Harrison, and Ann Lowe).
Published ahead of print on 25 October 2006. ![]()
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