Two doses of rMenB initially elicited substantial immune responses against serogroups ACW at month 3, but GMTs were lower than those of the MenABCWY vaccines and decreased to baseline levels by month 12 (group V-2d; Figs. 2 and 3).
Antibody Persistence Against Serogroup B Test Strains After a 2-dose Vaccination Series
At 1 month after the second vaccination (month 3), the percentage of subjects with hSBA titers ≥5 against the fHbp strain was high across the 2-dose MenABCWY groups and the 2-dose rMenB group (90–100%). These percentages rapidly declined by month 6 (48–58%) and then decreased less substantially over the subsequent 6 months (Fig. 4). A similar pattern was observed for the NHBA test strain, with the highest proportion of subjects with hSBA titers ≥5 at month 3 in groups III-2d, IV-2d and V-2d (61–73%), when compared with groups I-2d and II-2d (40–50%). Across groups I-2d, II-2d, III-2d, IV-2d and V-2d, the percentage of subjects with hSBA titers ≥5 against the NHBA test strain declined by month 6 (30–46%) and then decreased less substantially over the subsequent 6 months (Fig. 3A). For the PorA test strain, initial immune responses at month 3 were only evident in the groups that received OMV-containing formulations (III-2d and IV-2d: 70–79%). Percentages in groups III-2d and IV-2d declined by month 6 (19–23%); however, there was no substantial difference in the percentages for these groups between months 6 and 12. For the NadA test strain, 85–100% of subjects in groups I-2d, II-2d, III-2d, IV-2 and V-2d maintained hSBA titers ≥5 through month 12.
GMTs against each of the serogroup B test strains correlated with the proportions of subjects with hSBA titers ≥5 against the respective strains (Fig. 5). At 5 months after the second dose (month 7), GMTs against the fHbp test strain were highest in group IV-2d, with ranges of 3.6 to11 across the 2-dose MenABCWY groups and 2-dose rMenB group; by month 12, GMTs against the fHbp strain declined and ranged from 2.3 to 4.3 across these groups. For the NadA test strain, the highest GMTs at month 7 were observed in group II-2d, with ranges of 44–96 across the 2-dose MenABCWY groups and 2-dose rMenB group; by month 12 GMTs against the NadA strain ranged from 30 to 46 across these groups. The highest GMTs against the NHBA and PorA test strains at 5 months after the 2-dose series (month 7) were observed in groups III-2d and IV-2d (NHBA: 5.2–6.6; PorA: 2.5–2.6), with no substantial difference in GMTs against these strains from months 7 to 12.
Immune Responses to a Third Dose and Antibody Persistence Following a 3-dose Vaccination Series, Serogroups ACWY
At month 6, immediately before the third dose a high proportion of subjects across MenABCWY groups I-3d, II-3d, III-3d and IV-3d had hSBA titers ≥8 against serogroups CWY (92–100%), whereas proportions against serogroup A were lower (52–79%; Fig. 6). One month after the third vaccination (month 7), nearly all subjects in the 3-dose MenABCWY groups had hSBA ≥8 against each of the 4 serogroups. At 6 months after the third dose (month 12), all subjects in the 3-dose MenABCWY groups had hSBA titers ≥8 against serogroups CWY and 76–86% maintained hSBA ≥8 against serogroup A.
A third dose of the MenABCWY vaccine formulations increased hSBA GMTs against each of the 4 serogroups at month 7, with increases relative to month 6 of 8- to 15-fold (A), 3- to 5-fold (C), 3- to 4-fold (W) and 3- to 4-fold (Y). GMTs declined by month 12, but remained well above the level associated with seroprotection (≥8) and were higher than the respective GMTs of the 1-dose MenACWY-CRM group (Fig. 7).
One month after a third dose of rMenB (month 7), 73–91% of subjects in group V-3d achieved hSBA ≥8 against serogroups ACW, compared with 33–55% at month 6 (Fig. 6). By month 12, these percentages declined to 45–65%. Immune responses against the serogroup Y reference strain were low (14% at month 7). Similar patterns were seen when immune responses were measured by GMTs (Fig. 7).
Immune Responses to a Third Dose and Antibody Persistence After a 3-dose Vaccination Series, Serogroup B Test Strains
At 1 month after a third dose of a MenABCWY vaccine formulation or the investigational rMenB formulation (month 7), a robust response against the fHbp, NHBA and PorA serogroup B test strains was evident, although the percentages of subjects with hSBA titers ≥5 against the NHBA and PorA strains were substantially higher in groups that received an OMV-containing formulation (III-3d and IV-3d), when compared with groups that received formulations without OMV (I-3d, II-3d, V-3d; Fig. 8). By month 12, the proportion of subjects with hSBA titers ≥5 against the fHbp strain declined relative to month 7, with the highest proportion of subjects being in group III-3d (71%), followed by groups II-3d and V-3d (both 52%). Percentages of subjects with hSBA titers ≥5 against the NHBA and PorA strains also declined by month 12, with the highest proportions in groups III-3d and IV-3d (NHBA: 57–60%; PorA: 20–43%). Across all 3-dose MenABCWY groups, as well as the 3-dose rMenB group, the percentage of subjects with hSBA titers ≥5 against the NadA test strain were high before the third dose and remained high at month 12 (96–100%).
The hSBA GMTs against serogroup B test strains correlated with the percentage of subjects with hSBA titers ≥5 against the respective serogroup B test strains (Fig. 9). At 6 months after the third dose (month 12), the highest GMTs against the fHbp, NHBA and PorA test strains were observed in group III-3d; GMT ranges across the 3-dose MenABCWY groups and 3-dose rMenB group were 5.4–22 (fHbp), 2.8–10 (NHBA) and 1.4–5 (PorA). The highest GMTs against the NadA test strain at 6 months after the third dose (month 12) were observed in groups II-3d and V-3d, with ranges of 126–274 across the 3-dose MenABCWY groups and 3-dose rMenB group.
Among 440 enrolled subjects, all received at least 1 study vaccination and were included in the safety analysis, and 439 contributed to the analyses of solicited local and systemic reactions occurring within 7 days of vaccination (Table 2). One subject was excluded from the safety analyses because of pregnancy.
Across all study groups, 71–92% of subjects reported at least 1 solicited reaction, with an overall higher frequency of any reaction in groups receiving an OMV-containing MenABCWY formulation (III-3d and IV-3d: 92% for both groups vs. other study groups: 71–83%; Table 3). Solicited local and systemic reactions were reported by 60–92% and 42–80%, respectively, of subjects across study groups, with the highest frequencies in groups III-3d and IV-3d.
Injection site pain was the most common local reaction, with the highest frequencies in groups administered OMV-containing formulations (III-3d: 92% including 36% severe; IV-3d: 79% including 13% severe; Table 2), when compared with those groups administered MenABCWY formulations without OMV or the group administered rMenB (I-3d, II-3d, V-3d: 63–75% including 8–13% severe) or Tdap (60–73% including 6–14% severe).
The most common systemic reactions across groups were myalgia (38–60%), headache (21–42%) and malaise (16–32%; Table 2). Frequencies of individual systemic reactions were comparable across all groups, with the exception of higher frequencies of arthralgia and myalgia in groups III-3d and IV-3d, when compared with other study groups (arthralgia: 24–33% vs. 6–21%, respectively; myalgia: 58–60% vs. 25–48%, respectively). Fever (≥38°C) was reported by up to 13% of subjects across groups, with the highest rates in groups I-3d, III-3d and IV-3d. The frequencies of subjects who received analgesics/antipyretics within 7 days postvaccination were higher in groups receiving OMV-containing formulations (III-3d and IV-3d: 20–21%) than among groups receiving MenABCWY formulations without OMV or the group administered rMenB (I-3d, II-3d, V-3d: 8–17%) and the groups that received Tdap (6–12%).
During the entire study period, 107 (24%) of subjects reported at least 1 unsolicited AE, with comparable frequencies of AEs between groups. The most commonly reported AEs were nasopharyngitis (5%) and headache (2%).
A total of 5 SAEs were reported by 5 subjects during the study, with all but 1 assessed as unrelated to the study vaccination. In 1 case, a 13-year-old girl in group IV-3d (MenACWY-CRM + rMenB + ¼OMV formulation), experienced severe postvaccination pain, myalgia, headache, chills and fever within 3 hours of vaccination. These events were reported as a SAE that resolved by the following day after outpatient administration of analgesics. There were no reported AEs leading to premature withdrawal from the study, but there was 1 withdrawal because of pregnancy in group I-2d; the pregnancy was identified after the subject received 1 dose of Tdap, and the pregnancy outcome was normal. No deaths were reported in this study.
Because of the rapid onset and progression of meningococcal disease, persistence of circulating bactericidal antibodies after meningococcal vaccination is important for vaccine effectiveness.24 Here, we report the results of the first study to assess the persistence of immune responses against serogroups ACWY and serogroup B test strains after immunization with investigational MenABCWY vaccine formulations.
Antibody persistence against serogroups ACWY after 2 doses of MenABCWY vaccines was at least comparable with (serogroup A) or higher than (serogroups C, W and Y) that of a single dose of the MenACWY-CRM vaccine. The overall greater persistence against non-B serogroups could be attributed to the receipt of 2 doses of MenABCWY formulations, compared with a single dose of MenACWY-CRM, or to induction, by MenABCWY vaccine, of bactericidal antibodies against subcapsular protein antigens, which contribute to killing of these particular test strains. Comparisons of immune response and antibody persistence after 2 doses of MenABCWY versus 2 doses of MenACWY-CRM are needed to determine which of these mechanisms is responsible for the observed difference in antibody persistence.
Across the 2-dose MenABCWY groups, titers of bactericidal antibodies against most serogroup B test strains declined between 1 and 4 months after the second vaccination (months 3–6) and then decreased less substantially over the next 6 months (months 6–12). Although it is certainly possible that these results reflect limited long-term protection of the vaccine, it is important to recognize that there is no established serocorrelate of protection against serogroup B N. meningitidis strains, and that hSBA is known to underestimate immunity against serogroup B strains.25
Although administration of a third dose of MenABCWY vaccine formulation substantially increased hSBA GMTs and the percentage of subjects with hSBA titers ≥5 against the fHbp, NHBA and PorA test strains 1 month postvaccination, immune responses against these strains declined by 6 months postvaccination. Waning of GMTs against these strains followed a similar pattern to that observed after administration of the 2-dose series, and comparable levels of antibodies against most serogroup B test strains were observed at 5–6 months after completion of either vaccination series. Although this study was not powered to directly compare the immunogenicity of the 2-dose and 3-dose series, these findings indicate that there may not be a significant advantage to administration of a 3-dose primary vaccination series, in terms of antibody persistence. Indeed, analyses of long-term antibody persistence in adolescents following different dosing regimens of 4CMenB demonstrated that 2 doses of 4CMenB, administered 1–6 months apart, provided sustained, high levels of bactericidal antibodies against the evaluated serogroup B test strains.26
Although there were no observed differences between the MenABCWY formulations in terms of immune responses against serogroups ACWY, there were some differences in immunogenicity against the serogroup B test strains. With regards to hSBA GMTs, for all persistence timepoints following either 2 or 3 doses, the highest titers against the fHbp, NHBA and PorA test strains were observed in subjects who received the OMV-containing MenABCWY vaccine formulations. The highest GMTs against the NadA test strain were observed in the group that received the MenABCWY formulation containing 2 doses of rMenB proteins; however, immune responses against this strain were high across all MenABCWY groups. Overall, doubling the dose of rMenB proteins did not appear to offer much added benefit in terms of immunogenicity; a single dose of recombinant proteins is sufficient to achieve maximal immunological response. A further increase in immune response is only afforded by the addition of the OMV, presumably through an adjuvant effect. Persistence data across most serogroup B test strains for both dosing regimens in this study showed a consistent pattern of greater overall immunogenicity with the full OMV MenABCWY formulation over the one-quarter OMV formulation, as well as over the MenABCWY formulations without the OMV components.
In this study, a third dose of rMenB vaccine was found to elicit immune responses against serogroup A, C and W assay strains but not the serogroup Y strain. The susceptibility of any meningococcal strain to the bactericidal activity of antibodies elicited by the recombinant proteins in the rMenB formulation depends on the degree of similarity between each vaccine antigen and the corresponding protein expressed by the target strain, as well as the expression level of the protein.27,28 These factors can be measured using the enzyme-linked immunosorbent assay–based meningococcal antigen typing system, which was developed to relate antigen profiles of different meningococcal strains to killing of the strains by hSBA assay. The test strains used for serogroups A, C and W in this study each express at least 1 protein with similarity to the rMenB antigens, with a meningococcal antigen typing system relative potency level indicative of bactericidal activity.29 Additional analyses would be needed to define rMenB vaccine coverage against circulating non-serogroup B strains and the clinical significance of these antibody responses.
In this study, the frequencies of reactogenicity were higher in groups receiving OMV-containing vaccines, in terms of injection site pain, erythema, myalgia and arthralgia. However, this disadvantage of the OMV-containing formulations is balanced by the benefit of overall higher antibody levels against serogroup B test strains at 10 months after vaccination. Reactogenicity profiles were similar between the full and one-quarter dose OMV formulations and were comparable with those reported previously for the licensed 4CMenB vaccine.17 OMV-containing meningococcal vaccines are associated with higher rates of local pain, myalgia and arthralgia, although they are regarded as being well-tolerated with no identified safety concerns when used across age groups.30,31 In this study, the overall drop-out rate was low (<3% of enrolled subjects), and no safety concerns were identified for any of the investigational MenABCWY vaccines.
This study has a number of limitations that must be acknowledged. In particular, this is the first study to evaluate the persistence of immune responses to MenABCWY vaccine formulations and as such, no formal hypotheses were tested. In addition, immunogenicity results are based on historical thresholds (hSBA titers ≥8 for serogroups ACWY and ≥5 for serogroup B test strains) and not on the strain-specific lower limits of quantitation, which might be a more appropriate measure considering differences between the test strains.22 Moreover, as a serocorrelate of protection has not been established for serogroup B strains, the clinical relevance of the hSBA assay in assessing sustained effectiveness of these formulations must be further evaluated.25,32 For these reasons, the presented data may underestimate bactericidal antibody persistence for certain strains. An additional limitation of this study is that the selected serogroup B test strains do not represent all B strains and, as such, caution may be needed in generalization of the study results. Additional analyses using a larger panel of serogroup B test strains will be needed to define vaccine coverage against circulating serogroup B strains. Finally, given the relatively small numbers of subjects within each vaccination group, as dictated by the number of participants in the primary study, the study was not designed to detect statistically significant differences between groups. Comparison of results across groups must be interpreted with caution given the small sample size and the risk of identifying chance findings in the setting of multiple comparisons. Larger studies are needed to substantiate the results of this study. Moreover, as the rMenB vaccine formulation, which does not contain OMV components, was used as a control investigational formulation for serogroup B in this study, additional studies may be needed to compare MenABCWY formulations to the licensed 4CMenB vaccine, in terms of immune response against serogroup B test strains.
All investigational MenABCWY vaccine formulations were immunogenic against serogroups ACWY and serogroup B test strains, with overall greater immunogenicity observed for the OMV-containing vaccine formulations. A third dose of MenABCWY vaccine formulation increased immune responses against serogroups ACWY and serogroup B test strains, although waning of bactericidal antibody levels following a 2-dose and 3-dose vaccination series followed a similar pattern and comparable antibody levels were observed at 5–6 months after each vaccination series. All of the investigational MenABCWY vaccine formulations were generally well tolerated with no identified safety concerns.
The authors would like to thank the study participants and their parents and the clinicians, nurses and laboratory technicians who were involved in the study. We acknowledge the contributions of Novartis personnel: Esther Heijnen, Francesca Carini, Julie Densmore, Roberta Rossi, Marta Valentini, Christiane Juengst, Ana Cecilia Villarreal, Gordon Brestrich, Victor Sales, Jose Jimeno, Sanne de Ridder, Colin Malcolm and Marcel Bisschop. The authors also wish to thank the following investigators: Drs. Juan Velasquez and Gonzalo Franco (Colombia); Drs. Adriana Chung, Albino Salas, Luis Marquez and Ivonne Abadía de Regalado (Panama) and Dr. Jose Novoa (Chile). Medical writing and editorial assistance in the development of the manuscript was provided by Dr. Julia Oosterom (CHC Europe; funded by Novartis Vaccines) and Jessica Tyler, PhD (Novartis Vaccines).
Author’s contributions: I.S. and P.M.D. designed the study. X.S-.L., D.C.A.V. and K.A. conducted the study and participated in the acquisition of data. All authors participated in the analysis and interpretation of the data. EM provided biostatistic expertise.
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Keywords:Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
meningococcal disease; conjugate vaccine; immunogenicity; persistence; safety; adolescents