Development of a group A meningococcal conjugate vaccine, MenAfriVac(TM)

The Bacterial Meningitis Epidemic in Banalia in the Democratic Republic of Congo in 2021

BACKGROUND

The Banalia health zone in the Democratic Republic of Congo reported a meningitis epidemic in 2021 that evolved outside the epidemic season. We assessed the effects of the meningitis epidemic response.

METHODS

The standard case definition was used to identify cases. Care was provided to 2651 in-patients, with 8% of them laboratory tested, and reactive vaccination was conducted. To assess the effects of reactive vaccination and treatment with ceftriaxone, a statistical analysis was performed.

RESULTS

Overall, 2662 suspected cases of meningitis with 205 deaths were reported. The highest number of cases occurred in the 30-39 years age group (927; 38.5%). Ceftriaxone contributed to preventing deaths with a case fatality rate that decreased from 70.4% before to 7.7% after ceftriaxone was introduced (p = 0.001). Neisseria meningitidis W was isolated, accounting for 47/57 (82%), of which 92% of the strains belonged to the clonal complex 11. Reactive vaccination of individuals in Banalia aged 1-19 years with a meningococcal multivalent conjugate (ACWY) vaccine (Menactra®) coverage of 104.6% resulted in an 82% decline in suspected meningitis cases (incidence rate ratio, 0.18; 95% confidence interval, 0.02-0.80; p = 0.041).

CONCLUSION

Despite late detection (two months) and reactive vaccination four months after crossing the epidemic threshold, interventions implemented in Banalia contributed to the control of the epidemic.

Exploring the variables influencing the immune response of traditional and innovative glycoconjugate vaccines

Vaccines are cost-effective tools for reducing morbidity and mortality caused by infectious diseases. The rapid evolution of pneumococcal conjugate vaccines, the introduction of tetravalent meningococcal conjugate vaccines, mass vaccination campaigns in Africa with a meningococcal A conjugate vaccine, and the recent licensure and introduction of glycoconjugates against S. Typhi underlie the continued importance of research on glycoconjugate vaccines. More innovative ways to produce carbohydrate-based vaccines have been developed over the years, including bioconjugation, Outer Membrane Vesicles (OMV) and the Multiple antigen-presenting system (MAPS). Several variables in the design of these vaccines can affect the induced immune responses. We review immunogenicity studies comparing conjugate vaccines that differ in design variables, such as saccharide chain length and conjugation chemistry, as well as carrier protein and saccharide to protein ratio. We evaluate how a better understanding of the effects of these different parameters is key to designing improved glycoconjugate vaccines.

Translating diagnostics and drug delivery technologies to low-resource settings

Diagnostics and drug delivery technologies engineered for low-resource settings aim to meet their technical design specifications using strategies that are compatible with limited equipment, infrastructure, and operator training. Despite many preclinical successes, very few of these devices have been translated to the clinic. Here, we identify factors that contribute to the clinical success of diagnostics and drug delivery systems for low-resource settings, including the need to engage key stakeholders at an early stage, and provide recommendations for the clinical translation of future medical technologies.

Analytical technology development to monitor the stability of Polysaccharide-Protein conjugate vaccines

The covalent attachment of a bacterial-derived capsular polysaccharide to protein is of critical importance in transforming the polysaccharide from an antigen with limited immunogenicity in infants and older adults to an antigen that can prevent potentially fatal disease. For a polysaccharide-protein conjugate vaccine (PCV) candidate to be successful, it must be sufficiently stable. Chemical breakage of carbohydrate bonds in the polysaccharide may result in the reduction of "conjugate dose" and could negatively impact immunogenicity and the ability of the vaccine to prime for memory responses. Therefore, development of analytical tools to monitor the integrity of a polysaccharide-protein conjugate (glycoconjugate) vaccine is of practical significance. In this work, reducing SDS-PAGE, Intrinsic Protein Fluorescence Spectroscopy (IPFS), Differential Scanning Fluorimetry (DSF) were evaluated methods to study the impact of time, temperature, and formulation composition on the stability of a glycoconjugate vaccine prepared by multisite coupling of polysaccharide to a carrier protein. In addition, an automated capillary Western system was also evaluated to study the impact of storage on glycoconjugate vaccine stability. Two streptococcus pneumoniae polysaccharide-protein conjugates (serotype 3 and serotype 19A) were chosen to examine their physicochemical stability when formulated as a single antigen vaccine. While all methods require only a small amount of test article and can test multiple samples per assay run, automated capillary Western has the additional advantage of being highly sensitive even at low concentrations in complex vaccine formulations that contain aluminum adjuvant and multiple antigens. Results suggest that automated capillary Western is stability-indicating and may be an effective analytical technology tool for the formulation development of a multivalent glycoconjugate vaccine.

Development and Immunogenicity of a Brazilian Glycoconjugate vaccine against Meningococcal W in a Pilot Scale

Recent changes in the epidemiology of meningococcal have been reported and meningococcal group W (MenW) has become the third most prevalent group isolated in Brazil in the last 10 years. In this study we have developed a conjugate vaccine for MenW using a modified reductive amination conjugation method through a covalent linkage between periodate-oxidized MenW non-O-acetylated polysaccharide and hydrazide-activated monomeric tetanus toxoid. Process control of bulks was done by physicochemical analysis including polysaccharide and protein quantification, high performance liquid chromatography - size exclusion chromatography, capillary electrophoresis, and hydrogen nuclear magnetic resonance. Conjugate bulks were best produced with concentration of polysaccharide twice as high as protein, at room temperature, and pH approximately 6.0. A scaled-up bulk (100 mg scale) was formulated and inoculated intramuscularly in mice in a dose-response study (0.1, 0.5, 1.0 and 10.0 µg of polysaccharide/dose). The immunogenicity of conjugate bulks was determined by serum bactericidal assay and ELISA assays of serum from immunized mice. ELISA and SBA titers revealed high titers of IgG and demonstrated the functionality of the antibodies produced in all doses studied 15 days after the third dose. However, significant differences were observed among them by ELISA. In conclusion, this study established the best conditions to produce MenW conjugate bulks and showed the efficacy of the obtained conjugate bulk in induce a good immune response in mice. Further experiments will need to be done to scale up the conjugation reaction and then allow the use of this conjugate in clinical trials.

Invasion of the choroid plexus epithelium by Neisseria meningitidis is differently mediated by Arp2/3 signaling and possibly by dynamin dependent on the presence of the capsule

Neisseria meningitis (Nm) is a human-specific bacterial pathogen that can cause sepsis and meningitis. To cause meningitis Nm must enter the central nervous system (CNS) across one of the barriers between the blood and the brain. We have previously shown that a capsule-depleted Serogroup B strain of Nm displays enhanced invasion into human choroid plexus (CP) epithelial papilloma (HIBCPP) cells, which represent an in vitro model of the blood-cerebrospinal fluid barrier (BCSFB). Still, the processes involved during CNS invasion by Nm, especially the role of host cell actin cytoskeleton remodeling, are not investigated in detail. Here, we demonstrate that invasion into CP epithelial cells by encapsulated and capsule-depleted Nm is mediated by distinct host cell pathways. Whereas a Serogroup B wild-type strain enters HIBCPP cells by a possibly dynamin-independent, but actin related protein 2/3 (Arp2/3)-dependent mechanism, invasion by a capsule-depleted mutant is reduced by the dynamin inhibitor dynasore and Arp2/3-independent. Both wild-type and mutant bacteria require Src kinase activity for entry into HIBCPP cells. Our data show that Nm can employ different mechanisms for invasion into the CP epithelium dependent on the presence of a capsule.

Recent advances on smart glycoconjugate vaccines in infections and cancer

Vaccination is one of the greatest achievements in biomedical research preventing death and morbidity in many infectious diseases through the induction of pathogen-specific humoral and cellular immune responses. Currently, no effective vaccines are available for pathogens with a highly variable antigenic load, such as the human immunodeficiency virus or to induce cellular T-cell immunity in the fight against cancer. The recent SARS-CoV-2 outbreak has reinforced the relevance of designing smart therapeutic vaccine modalities to ensure public health. Indeed, academic and private companies have ongoing joint efforts to develop novel vaccine prototypes for this virus. Many pathogens are covered by a dense glycan-coat, which form an attractive target for vaccine development. Moreover, many tumor types are characterized by altered glycosylation profiles that are known as "tumor-associated carbohydrate antigens". Unfortunately, glycans do not provoke a vigorous immune response and generally serve as T-cell-independent antigens, not eliciting protective immunoglobulin G responses nor inducing immunological memory. A close and continuous crosstalk between glycochemists and glycoimmunologists is essential for the successful development of efficient immune modulators. It is clear that this is a key point for the discovery of novel approaches, which could significantly improve our understanding of the immune system. In this review, we discuss the latest advancements in development of vaccines against glycan epitopes to gain selective immune responses and to provide an overview on the role of different immunogenic constructs in improving glycovaccine efficacy.

Carbohydrate based meningococcal vaccines: past and present overview

Neisseria meningitidis is a major cause of bacterial meningitidis worldwide. Children less than five years and adolescents are particularly affected. Nearly all invasive strains are surrounded by a polysaccharide capsule, based on which, 12 N. meningitidis serogroups are differentiated. Six of them, A, B, C, W, X, and Y, cause the vast majority of infections in humans. Mono- and multi-valent carbohydrate-based vaccines against meningococcal infections have been licensed or are currently in clinical development. In this mini-review, an overview of the past and present approaches for producing meningococcal glycoconjugate vaccines is provided.

A stabilized glycomimetic conjugate vaccine inducing protective antibodies against Neisseria meningitidis serogroup A

Neisseria meningitidis serogroup A capsular polysaccharide (MenA CPS) consists of (1 → 6)-2-acetamido-2-deoxy-α-D-mannopyranosyl phosphate repeating units, O-acetylated at position C3 or C4. Glycomimetics appear attractive to overcome the CPS intrinsic lability in physiological media, due to cleavage of the phosphodiester bridge, and to develop a stable vaccine with longer shelf life in liquid formulation. Here, we generate a series of non-acetylated carbaMenA oligomers which are proven more stable than the CPS. An octamer (DP8) inhibits the binding of a MenA specific bactericidal mAb and polyclonal serum to the CPS, and is selected for further in vivo testing. However, its CRM197 conjugate raises murine antibodies towards the non-acetylated CPS backbone, but not the natural acetylated form. Accordingly, random O-acetylation of the DP8 is performed, resulting in a structure (Ac-carbaMenA) showing improved inhibition of anti-MenA CPS antibody binding and, after conjugation to CRM197, eliciting anti-MenA protective murine antibodies, comparably to the vaccine benchmark.

Safety profile of the meningococcal conjugate vaccine (Menafrivac™) in clinical trials and vaccination campaigns: a review of published studies

The study aimed to assess the capacity of AEFI surveillance during vaccination campaigns with the new conjugate meningitis vaccine (MenAfrivac). A systematic review of studies on MenAfrivac™ published in English during 2001-2016 was done.AEFIs incidence (I) was estimated and compared between MenAfrivac™ clinical trials and immunization campaigns using incidence difference (Id). Nine studies were included with an overall local AEFI I of 11,496/100,000 doses administered per week in clinical trials and 0.72/100,000 doses in immunization campaigns. An Id of 11,497.92 [11,497.91-11,497.93] and 17,243.20 [17,241.80-17,245.90] per 100,000 doses administered per week for overall local and systemic AEFI, respectively, were observed with highest from clinical trials. The incidence of AEFIs after MenAfrivac™ vaccination was far lower in campaigns than in clinical trial studies. Current capacity of AEFI surveillance during vaccination campaigns requires extensive re-assessment of its structure and capacity.

MenAfriNet: A Network Supporting Case-Based Meningitis Surveillance and Vaccine Evaluation in the Meningitis Belt of Africa

Meningococcal meningitis remains a significant public health threat, especially in the African meningitis belt where Neisseria meningitidis serogroup A historically caused large-scale epidemics. With the rollout of a novel meningococcal serogroup A conjugate vaccine (MACV) in the belt, the World Health Organization recommended case-based meningitis surveillance to monitor MACV impact and meningitis epidemiology. In 2014, the MenAfriNet consortium was established to support strategic implementation of case-based meningitis surveillance in 5 key countries: Burkina Faso, Chad, Mali, Niger, and Togo. MenAfriNet aimed to develop a high-quality surveillance network using standardized laboratory and data collection protocols, develop sustainable systems for data management and analysis to monitor MACV impact, and leverage the surveillance platform to perform special studies. We describe the MenAfriNet consortium, its history, strategy, implementation, accomplishments, and challenges.

Understanding immunogenicity assessments for meningococcal serogroup B vaccines

Invasive meningococcal disease (IMD) is a potentially devastating infection associated with high mortality and long-term sequelae; however, vaccines are available to protect against the five common disease-causing serogroups (A, B, C, W, and Y). Because traditional field efficacy clinical trials were not feasible due to low IMD incidence that necessitates a very large number of participants, serum bactericidal antibody (SBA) assays using rabbit (rSBA) or human (hSBA) complement were established as in vitro surrogates of meningococcal vaccine efficacy and are now routinely used to support vaccine licensure. Specifically, rSBA assays have been used to evaluate responses to meningococcal capsular polysaccharide-protein conjugate vaccines against serogroups A, C, W, and Y; the accepted correlate of protection for rSBA assays is a titer ≥1:8. Importantly, because the bacterial capsular polysaccharide antigen is conserved across strains, only one test strain that expresses an invariant polysaccharide capsule for each serogroup is required to assess coverage. rSBA assays are unsuitable for subcapsular protein-based serogroup B (MenB) vaccines, and therefore, hSBA assays have been used for licensure; titers ≥1:4 are considered the correlate of protection against IMD for hSBA. In contrast to MenACWY vaccines, because bacterial surface proteins are antigenically variable, MenB vaccines must be tested with hSBA assays using multiple test strains that represent the antigenic diversity of disease-causing isolates. As this complexity regarding SBA assessment methods can make data interpretation difficult, herein we describe the use of hSBA assays to evaluate MenB vaccine efficacy and to support licensure. In addition, we highlight how the two recently approved MenB vaccines differ in their use of hSBA assays in clinical studies to demonstrate broad protection against MenB IMD.

Modeling the conformations of Neisseria meningitidis serogroup a CPS and a carba-analogue: Implications for vaccine development

Neisseria meningitidis is a major cause of bacterial meningitis worldwide, especially in Africa. The capsular polysaccharide is the main virulence factor and the target antigen for polysaccharide- and conjugate vaccines. Three tetravalent conjugate vaccines against serogroups A, C, Y and W have been licensed and the monovalent MenAfriVac® was introduced to address the high burden of serogroup A disease in the Meningitis Belt of sub-Saharan Africa. Three of these four vaccines are lyophilized due to the instability of the serogroup A antigen (MenA) in aqueous solution, resulting in a two vial presentation with concomitant additional costs for storage and distribution. Replacement of the saccharide ring oxygen with a methylene group is a promising approach to preparing a stable oligosaccharide MenA analogue (Carba-MenA) vaccine suitable for a liquid formulation. However, to be effective, Carba-MenA must elicit an immune response that is cross-reactive to the native MenA. Here we employ microsecond molecular dynamics simulations of ten repeats of MenA and Carba-MenA to establish that there are significant differences in the conformation and dynamics of these antigens in solution. Carba-MenA has a more random extended, conformation than MenA; MenA has a significant population of compact S-bend conformations that are absent in the analogue. We also find that the disaccharides are poor models of the conformational behaviour of longer chains. This information is relevant for the rational design of optimal analogues for conjugate vaccines.

Cost-Effectiveness of Alternative Uses of Polyvalent Meningococcal Vaccines in Niger: An Agent-Based Transmission Modeling Study

Background. Despite the introduction of an effective serogroup A conjugate vaccine (MenAfriVac™), sporadic epidemics of other Neisseria meningitidis serogroups remain a concern in Africa. Polyvalent meningococcal conjugate (PMC) vaccines may offer alternatives to current strategies that rely on routine infant vaccination with MenAfriVac plus, in the event of an epidemic, district-specific reactive campaigns using polyvalent meningococcal polysaccharide (PMP) vaccines. Methods. We developed an agent-based transmission model of N. meningitidis in Niger to compare the health effects and costs of current vaccination practice and 3 alternatives. Each alternative replaces MenAfriVac in the infant vaccination series with PMC and either replaces PMP with PMC for reactive campaigns or implements a one-time catch up campaign with PMC for children and young adults. Results. Over a 28-year period, replacement of MenAfriVac with PMC in the infant immunization series and of PMP in reactive campaigns would avert 63% of expected cases (95% prediction interval 49%-75%) if elimination of serogroup A is not followed by serogroup replacement. At a PMC price of $4/dose, this would cost $1412 ($81-$3510) per disability-adjusted life-year (DALY) averted. If serogroup replacement occurs, the cost-effectiveness of this strategy improves to $662 (cost-saving, $2473) per DALY averted. Sensitivity analyses accounting for incomplete laboratory confirmation suggest that a catch-up PMC campaign would also meet standard cost-effectiveness thresholds. Limitations. The assumption that polyvalent vaccines offer similar protection against all serogroups is simplifying. Conclusions. The use of PMC vaccines to replace MenAfriVac in routine infant immunization and in district-specific reactive campaigns would have important health benefits and is likely to be cost-effective in Niger. An additional PMC catch-up campaign would also be cost-effective if we account for incomplete laboratory reporting.

A review of complement sources used in serum bactericidal assays for evaluating immune responses to meningococcal ACWY conjugate vaccines

Invasive meningococcal disease is rare and potentially devastating but often vaccine-preventable. Evaluation of meningococcal vaccine effectiveness is impractical owing to relatively low disease incidence; protection is therefore estimated using serum bactericidal antibody (SBA) assays. Original experiments on natural immunity established a titer of ≥4 as the correlate of protection for SBA assays using human complement (hSBA), but human complement is relatively difficult to obtain and standardize. Use of baby rabbit complement (rSBA assays), per standard guidelines for serogroups A and C, generally results in comparatively higher titers. Postlicensure effectiveness data for serogroup C conjugate vaccines support acceptance of rSBA titers ≥8 as the correlate of protection for this serogroup, but no thresholds have been formally established for serogroups A, W, and Y. Studies evaluating MenACWY-TT (Nimenrix®; Pfizer Inc, Sandwich, UK) immunogenicity have used both hSBA and rSBA assays, and ultimately suggest that rSBA may be more appropriate for these measurements.

Conformations of Neisseria meningitidis serogroup A and X polysaccharides: The effects of chain length and O-acetylation

Neisseria meningitidis is a major cause of bacterial meningitis worldwide especially in Africa. The capsular polysaccharide (CPS) is the main virulence factor and the target antigen for polysaccharide and conjugate vaccines. The high burden of serogroup A disease in the Meningitis Belt of sub-Saharan Africa led to the introduction of MenAfriVac^®, which has successfully reduced the number of cases of group A disease. However, several outbreaks caused by other serogroups have been reported, including those due to serogroup X. The capsular polysaccharides of serogroups A and X are both homopolymers of amino sugars (α-D-ManNAc and α-D-GlcNAc) containing phosphodiester linkages at C-6 and C-4, respectively. The similarity of the primary structures of the two polysaccharides suggests that serogroup A vaccination may provide cross-protection against serogroup X disease. Molecular dynamics simulations of a series of serogroup A and X oligosaccharides reveal that the MenA CPS behaves as a flexible random coil which becomes less conformationally defined as the length increases, whereas serogroup X forms a more stable regular helical structure. The presence of the MenX helix is supported by NMR analysis; it has four residues per turn and becomes more stable as the chain length increases. Licensed MenA vaccines are largely O-acetylated at C-3: simulations show that these O-acetyl groups are highly solvent exposed and their presence favors more extended conformations compared to the more compact conformations of MenA without O-acetylation. These findings may have implications for the design of optimal conjugate vaccines.

Vaccination strategies for the prevention of meningococcal disease

Routine prophylactic vaccination and mass vaccination strategies have been used to control both endemic and epidemic disease caused by Neisseria meningitidis globally. This review discusses real-world examples of these vaccination strategies, their implementation, and outcomes of these efforts, with the overall goal of providing insights on how to achieve optimal control of meningococcal disease through vaccination in varied settings. Tailoring immunization programs to fit the needs of the target population has the potential to optimally reduce disease incidence.

Novel approaches to Neisseria meningitidis vaccine design

A range of vaccines is available for preventing life-threatening diseases caused by infection with Neisseria meningitidis (meningococcus, Men). Capsule polysaccharide (CPS)-conjugate vaccines are successful prophylactics for serogroup MenA, MenC, MenW and MenY infections, and outer membrane vesicle (OMV) vaccines have been used successfully for controlling clonal serogroup MenB infections. MenB vaccines based on recombinant proteins identified by reverse vaccinology (Bexsero™) and proteomics (Trumenba™) approaches have recently been licensed and Bexsero™ has been introduced into the UK infant immunisation programme. In this review, we chart the development of these licensed vaccines. In addition, we discuss the plethora of novel vaccinology approaches that have been applied to the meningococcus with varying success in pre-clinical studies, but which provide technological platforms for application to other pathogens. These strategies include modifying CPS, lipooligosaccharide and OMV; the use of recombinant proteins; structural vaccinology approaches of designing synthetic peptide/mimetope vaccines, DNA vaccines and engineered proteins; epitope presentation on biological and synthetic particles; through vaccination with live-attenuated pathogen(s), or with heterologous bacteria expressing vaccine antigens, or to competitive occupation of the nasopharyngeal niche by commensal bacterial spp. After close to a century of vaccine research, it is possible that meningococcal disease may be added, shortly, to the list of diseases to have been eradicated worldwide by rigorous vaccination campaigns.

Combined Chemical Synthesis and Tailored Enzymatic Elongation Provide Fully Synthetic and Conjugation-Ready Neisseria meningitidis Serogroup X Vaccine Antigens

Studies on the polymerization mode of Neisseria meningitidis serogroup X capsular polymerase CsxA recently identified a truncated construct that can be immobilized and used for length controlled on-column production of oligosaccharides. Here, we combined the use of a synthetic acceptor bearing an appendix for carrier protein conjugation and the on-column process to a novel chemo-enzymatic strategy. After protein coupling of the size optimized oligosaccharide produced by the one-pot elongation procedure, we obtained a more homogeneous glycoconjugate compared to the one previously described starting from the natural polysaccharide. Mice immunized with the conjugated fully synthetic oligomer elicited functional antibodies comparable to controls immunized with the current benchmark MenX glycoconjugates prepared from the natural capsule polymer or from fragments of it enzymatically elongated. This pathogen-free technology allows the fast total in vitro construction of predefined bacterial polysaccharide fragments. Compared to conventional synthetic protocols, the procedure is more expeditious and drastically reduces the number of purification steps to achieve the oligomers. Furthermore, the presence of a linker for conjugation in the synthetic acceptor minimizes manipulations on the enzymatically produced glycan prior to protein conjugation. This approach enriches the methods for fast construction of complex bacterial carbohydrates.

Household transmission of Neisseria meningitidis in the African meningitis belt: a longitudinal cohort study

BACKGROUND

Information on transmission of meningococcal infection in the African meningitis belt is scarce. We aimed to describe transmission patterns of Neisseria meningitidis (meningococcus) in households in the African meningitis belt.

METHODS

Cross-sectional carriage surveys were done in seven African meningitis belt countries (Chad, Ethiopia, Ghana, Mali, Niger, Nigeria, and Senegal) between Aug 1, 2010, and Oct 15, 2012. Meningococcal carriers identified in these surveys and all available people in their households were recruited into this longitudinal cohort study. We took pharyngeal swabs at first visit and took further swabs twice a month for 2 months and then monthly for a further 4 months. We used conventional bacteriological and molecular techniques to identify and characterise meningococci. We estimated the rates of carriage acquisition and recovery using a multi-state Markov model.

FINDINGS

Meningococci were isolated from 241 (25%) of 980 members of 133 households in which a carrier had been identified in the cross-sectional survey or at the first household visit. Carriage was detected subsequently in another household member who was not an index carrier in 75 households. Transmission within a household, suggested by detection of a further carrier with the same strain as the index carrier, was found in 52 of these 75 households. Children younger than 5 years were the group that most frequently acquired carriage from other household members. The overall individual acquisition rate was 2·4% (95% CI 1·6-4·0) per month, varying by age and household carriage status. The mean duration of carriage was 3·4 months (95% CI 2·7-4·4).

INTERPRETATION

In the African meningitis belt, transmission of meningococci within households is important, particularly for young children, and periods of carriage are usually of short duration.

FUNDING

Bill & Melinda Gates Foundation, Wellcome Trust.

[Impact of Controlled Temperature Chain (CTC) approach on immunization coverage achieved during the preventive vaccination campaign against meningitis A using MenAfriVac in Togo in 2014]

METHOD

We conducted a survey from 9 to 14 March 2015 (for approximately 3 months) after the end of the vaccination campaign in these four regions. Interviewees were selected using two stages cluster sampling stratified according to the regions. MenAfriVac vaccine in Controlled Temperature Chain (CTC) was used in 10 districts, in Togo.

RESULTS

A total of 2707 households were surveyed and 9082 people aged 1-29 years were interviewed. The average age of the individuals surveyed was 11.8±7.7 years and sex-ratio (H/F) was 1.01. The average number of individuals per household was 5.7 and that of persons aged 1-29 years targeted in the campaign was 3.4. Out of 9082 people surveyed 8889 (98%) were vaccinated. Multivariate analysis showed that the factors associated with immunization coverage using MenAfrivac vaccine were: habitual residence in the area at the time of the campaign (AOR = 4.52; 95%CI = [4.07 - 4.97]) and level of information about the campaign before it starts (AOR=2.42; 95%CI = [2.05 - 2.80]). By contrast, there were no differences in vaccination coverage between the areas based on whether the CTC approach was used or not (AOR=0.09; 95%CI = [-0.27 - 0.45]). Two hundred and seven respondents (2.3%) reported that they had Adverse Event Following Immunisation (AEFI) after the administration of the vaccine. These were usually minor AEFI involving fever, abscesses and swelling at the injection site.

CONCLUSION

Survey results show that the use of CTC in a country with limited resources such as Togo doesn't have a negative impact on immunization coverage. Indeed, there was no difference between immunization coverage in CTC and non-CTC areas. It is important to capitalize on the experience gained in order to use vaccines by Expanded Program of Immunization in CTC approach especially in countries with limited resources in terms of cold chain availability.

Emergence and control of epidemic meningococcal meningitis in sub-Saharan Africa

For more than a century, meningitis epidemics have regularly recurred across sub-Saharan Africa, involving 19 contiguous countries that constitute a 'meningitis belt' where historically the causative agent has been serogroup A meningococcus. Attempts to control epidemic meningococcal meningitis in Africa by vaccination with meningococcal polysaccharide (PS) vaccines have not been successful. This is largely because PS vaccines are poorly immunogenic in young children, do not induce immunological memory, and have little or no effect on the pharyngeal carriage. Meningococcal PS-protein conjugate vaccines overcome these deficiencies. Conjugate meningococcal vaccine against serotype A (MenAfriVac) was developed between 2001 and 2009 and deployed in 2010. So far, 262 million individuals have been immunized across the meningitis belt. The public health benefits of MenAfriVac have already been demonstrated by a sharp decline in reported cases of meningococcal disease in the countries where it has been introduced. However, serogroup replacement following mass meningitis vaccination has been noted, and in 2015 an epidemic with a novel strain of serogroup C was recorded in Niger and Nigeria for the first time since 1975. This has posed a serious challenge toward elimination of meningococcal meningitis epidemics in the African. For an effective control of meningococcal meningitis in the African meningitis belt, there is a need for an effective surveillance system, provision of rapid antigen detection kits as well as affordable vaccine that provides protection against the main serogroups causing meningitis in the sub-region.

Towards understanding the epidemiology of Neisseria meningitidis in the African meningitis belt: a multi-disciplinary overview

OBJECTIVES

Neisseria meningitidis is the major cause of seasonal meningitis epidemics in the African meningitis belt. In the changing context of a reduction in incidence of serogroup A and an increase in incidence of serogroups W and C and of Streptococcus pneumoniae, a better understanding of the determinants driving the disease transmission dynamics remains crucial to improving bacterial meningitis control.

METHODS

The literature was searched to provide a multi-disciplinary overview of the determinants of meningitis transmission dynamics in the African meningitis belt.

RESULTS

Seasonal hyperendemicity is likely predominantly caused by increased invasion rates, sporadic localized epidemics by increased transmission rates, and larger pluri-annual epidemic waves by changing population immunity. Carriage likely involves competition for colonization and cross-immunity. The duration of immunity likely depends on the acquisition type. Major risk factors include dust and low humidity, and presumably human contact rates and co-infections; social studies highlighted environmental and dietary factors, with supernatural explanations.

CONCLUSIONS

Efforts should focus on implementing multi-country, longitudinal seroprevalence and epidemiological studies, validating immune markers of protection, and improving surveillance, including more systematic molecular characterizations of the bacteria. Integrating climate and social factors into disease control strategies represents a high priority for optimizing the public health response and anticipating the geographic evolution of the African meningitis belt.

Regulation of capsule in Neisseria meningitidis

Neisseria meningitidis, a devastating pathogen exclusive to humans, expresses capsular polysaccharides that are the major meningococcal virulence determinants and the basis for successful meningococcal vaccines. With rare exceptions, the expression of capsule (serogroups A, B, C, W, X, Y) is required for systemic invasive meningococcal disease. Changes in capsule expression or structure (e.g. hypo- or hyper-encapsulation, capsule "switching", acetylation) can influence immunologic diagnostic assays or lead to immune escape. The loss or down-regulation of capsule is also critical in meningococcal biology facilitating meningococcal attachment, microcolony formation and the carriage state at human mucosal surfaces. Encapsulated meningococci contain a cps locus with promoters located in an intergenic region between the biosynthesis and the conserved capsule transport operons. The cps intergenic region is transcriptionally regulated (and thus the amount of capsule expressed) by IS element insertion, by a two-component system, MisR/MisS and through sequence changes that result in post-transcriptional RNA thermoregulation. Reversible on-off phase variation of capsule expression is controlled by slipped strand mispairing of homo-polymeric tracts and by precise insertion and excision of IS elements (e.g. IS1301) in the biosynthesis operon. Capsule structure can be altered by phase-variable expression of capsular polymer modification enzymes or "switched" through transformation and homologous recombination of different polymerases. Understanding the complex regulation of meningococcal capsule has important implications for meningococcal biology, pathogenesis, diagnostics, current and future vaccine development and vaccine strategies.

Higher Tetanus Toxoid Immunity 2 Years After PsA-TT Introduction in Mali

Background. In 2010, mass vaccination with a then-new meningococcal A polysaccharide–tetanus toxoid protein conjugate vaccine (PsA-TT, or MenAfriVac) was undertaken in 1- to 29-year-olds in Bamako, Mali. Whether vaccination with PsA-TT effectively boosts tetanus immunity in a population with heterogeneous baseline tetanus immunity is not known. We assessed the impact of PsA-TT on tetanus toxoid (TT) immunity by quantifying age- and sex-specific immunity prior to and 2 years after introduction.

Methods. Using a household-based, age-stratified design, we randomly selected participants for a prevaccination serological survey in 2010 and a postvaccination survey in 2012. TT immunoglobulin G (IgG) antibodies were quantified and geometric mean concentrations (GMCs) pre- and postvaccination among all age groups targeted for vaccination were compared. The probability of TT IgG levels ≥0.1 IU/mL (indicating short-term protection) and ≥1.0 IU/mL (indicating long-term protection) by age and sex was determined using logistic regression models.

Results. Analysis of 793 prevaccination and 800 postvaccination sera indicated that while GMCs were low pre–PsA-TT, significantly higher GMCs in all age–sex strata were observed 2 years after PsA-TT introduction. The percentage with short-term immunity increased from 57.1% to 88.4% (31.3-point increase; 95% confidence interval [CI], 26.6–36.0;, P < .0001) and with long-term immunity increased from 20.0% to 58.5% (38.5-point increase; 95% CI, 33.7–43.3; P < .0001) pre- and postvaccination.

Conclusions. Significantly higher TT immunity was observed among vaccine-targeted age groups up to 2 years after Mali's PsA-TT mass vaccination campaign. Our results, combined with evidence from clinical trials, strongly suggest that conjugate vaccines containing TT such as PsA-TT should be considered bivalent vaccines because of their ability to boost tetanus immunity.

Antibody Persistence 1-5 Years Following Vaccination With MenAfriVac in African Children Vaccinated at 12-23 Months of Age

Background. Following mass vaccination campaigns in the African meningitis belt with group A meningococcal conjugate vaccine, MenAfriVac (PsA-TT), disease due to group A meningococci has nearly disappeared. Antibody persistence in healthy African toddlers was investigated.

Methods. African children vaccinated at 12–23 months of age with PsA-TT were followed for evaluation of antibody persistence up to 5 years after primary vaccination. Antibody persistence was evaluated by measuring group A serum bactericidal antibody (SBA) with rabbit complement and by a group A–specific IgG enzyme-linked immunosorbent assay (ELISA).

Results. Group A antibodies measured by SBA and ELISA were shown to decline in the year following vaccination and plateaued at levels significantly above baseline for up to 5 years following primary vaccination.

Conclusions. A single dose of PsA-TT induces long-term sustained levels of group A meningococcal antibodies for up to 5 years after vaccination.

Clinical Trials Registration. ISRTCN78147026.

Antibody Persistence at 1 and 4 Years Following a Single Dose of MenAfriVac or Quadrivalent Polysaccharide Vaccine in Healthy Subjects Aged 2-29 Years

BACKGROUND

Mass vaccination campaigns of the population aged 1-29 years with 1 dose of group A meningococcal (MenA) conjugate vaccine (PsA-TT, MenAfriVac) in African meningitis belt countries has resulted in the near-disappearance of MenA. The vaccine was tested in clinical trials in Africa and in India and found to be safe and highly immunogenic compared with the group A component of the licensed quadrivalent polysaccharide vaccine (PsACWY). Antibody persistence in Africa and in India was investigated.

METHODS

A total of 900 subjects aged 2-29 years were followed up for 4 years in Senegal, Mali, and The Gambia (study A). A total of 340 subjects aged 2-10 years were followed up for 1 year in India (study B). In study A, subjects were randomized in a 2:1 ratio, and in study B a 1:1 ratio to receive either PsA-TT or PsACWY. Immunogenicity was evaluated by measuring MenA serum bactericidal antibody (SBA) with rabbit complement and by a group A-specific immunoglobulin G (IgG) enzyme-linked immunosorbent assay.

RESULTS

In both studies, substantial SBA decay was observed at 6 months postvaccination in both vaccine groups, although more marked in the PsACWY group. At 1 year and 4 years (only for study A) postvaccination, SBA titers were relatively sustained in the PsA-TT group, whereas a slight increasing trend, more pronounced among the youngest, was observed in the participants aged <18 years in the PsACWY groups. The SBA titers were significantly higher in the PsA-TT group than in the PsACWY group at any time point, and the majority of subjects in the PsA-TT group had SBA titers ≥128 and group A-specific IgG concentrations ≥2 µg/mL at any point in time in both the African and Indian study populations.

CONCLUSIONS

Four years after vaccination with a single dose of PsA-TT vaccine in Africa, most subjects are considered protected from MenA disease.

CLINICAL TRIALS REGISTRATION

PsA-TT-003 (ISRCTN87739946); PsA-TT-003a (ISRCTN46335400).

Population-Level Persistence of Immunity 2 Years After the PsA-TT Mass-Vaccination Campaign in Mali

Background. In 2010, Africa's first preventive meningococcal mass vaccination campaign was launched using a newly developed Neisseria meningitidis group A (NmA) polysaccharide–tetanus toxoid conjugate vaccine, PsA-TT (MenAfriVac), designed specifically for the meningitis belt. Given PsA-TT's recent introduction, the duration of protection against meningococcal group A is unknown.

Methods. We conducted a household-based, age-stratified seroprevalence survey in Bamako, Mali, in 2012, 2 years after the vaccination campaign targeted all 1- to 29-year-olds. Randomly selected participants who had been eligible for PsA-TT provided a blood sample and responded to a questionnaire. Sera were analyzed to assess NmA-specific serum bactericidal antibody titers using rabbit complement (rSBA) and NmA-specific immunoglobulin G (IgG) by enzyme-linked immunosorbent assay. The proportion of participants putatively protected and the age group- and sex-specific rSBA geometric mean titers (GMTs) and IgG geometric mean concentrations (GMCs) were determined.

Results. Two years postvaccination, nearly all of the 800 participants (99.0%; 95% confidence interval [CI], 98.3%–99.7%) maintained NmA-specific rSBA titers ≥8, the accepted threshold for protection; 98.6% (95% CI, 97.8%–99.4%) had titers ≥128, and 89.5% (95% CI, 87.4%–91.6%) had titers ≥1024. The rSBA GMTs were significantly higher in females than in males aged <18 years at vaccination (P < .0001). NmA-specific IgG levels ≥2 µg/mL were found in 88.5% (95% CI, 86.3%–90.7%) of participants.

Conclusions. Two years after PsA-TT introduction, a very high proportion of the population targeted for vaccination maintains high antibody titers against NmA. Assessing the duration of protection provided by PsA-TT is a priority for implementing evidence-based vaccination strategies. Representative, population-based seroprevalence studies complement clinical trials and provide this key evidence.

Technical Development of a New Meningococcal Conjugate Vaccine

Background. Group A Neisseria meningitidis has been a major cause of bacterial meningitis in the sub-Saharan region of Africa in the meningitis belt. Neisseria meningitidis is an encapsulated pathogen, and antibodies against the capsular polysaccharide are protective. Polysaccharide–protein conjugate vaccines have proven to be highly effective against several different encapsulated bacterial pathogens. Purified polysaccharide vaccines have been used to control group A meningococcal (MenA) epidemics with minimal success.

Methods. A monovalent MenA polysaccharide–tetanus toxoid conjugate was therefore developed. This vaccine was developed by scientists working with the Meningitis Vaccine Project, a partnership between PATH and the World Health Organization.

Results. A high-efficiency conjugation method was developed in the Laboratory of Bacterial Polysaccharides in the Center for Biologics Evaluation and Research and transferred to the Serum Institute of India, Ltd, which then developed methods for purification of the group A polysaccharide and used its tetanus toxoid as the carrier protein to produce the now-licensed, highly effective MenAfriVac conjugate vaccine.

Conclusions. Although many years of application of meningococcal polysaccharide vaccines have had minimal success in preventing meningococcal epidemics in the meningitis belt of Africa, our collaborative efforts to develop a MenA conjugate vaccine yielded a safe and highly effective vaccine.

The Global Evolution of Meningococcal Epidemiology Following the Introduction of Meningococcal Vaccines

Invasive meningococcal disease (IMD) caused by Neisseria meningitidis is associated with high morbidity and mortality. Although IMD incidence is highest in infants, a second peak occurs in adolescents/young adults. The incidence of IMD and the predominant disease-causing meningococcal serogroups vary worldwide. Epidemiologic data have guided the development of meningococcal vaccines to reduce the IMD burden. In Europe, serogroup C IMD has been substantially reduced since the introduction of a serogroup C conjugate vaccine. Serogroup B predominates in Europe, although cases of serogroup Y IMD have been increasing in recent years. In the United States, declines in serogroup C and Y disease have been observed in association with the introduction of quadrivalent (serogroups ACWY) meningococcal conjugate vaccines; serogroup B persists and is now the most common cause of outbreak associated disease. In the African meningitis belt, a conjugate vaccine for serogroup A has been effective in decreasing meningitis associated with that serogroup. Outbreaks of the previously rare serogroup X disease have been reported in this region since 2006. In recent years, outbreaks of serogroup B IMD, for which vaccines have only recently been approved by the U.S. Food and Drug Administration and the European Medicines Agency, have occurred in Europe and the United States. Targeting meningococcal vaccination to adolescents/young adults may reduce the morbidity and mortality associated with IMD and has the potential to impact the larger community through herd benefits.

Pharyngeal carriage of Neisseria species in the African meningitis belt

Objectives

Neisseria meningitidis, together with the non-pathogenic Neisseria species (NPNs), are members of the complex microbiota of the human pharynx. This paper investigates the influence of NPNs on the epidemiology of meningococcal infection.

Methods

Neisseria isolates were collected during 18 surveys conducted in six countries in the African meningitis belt between 2010 and 2012 and characterized at the rplF locus to determine species and at the variable region of the fetA antigen gene. Prevalence and risk factors for carriage were analyzed.

Results

A total of 4694 isolates of Neisseria were obtained from 46,034 pharyngeal swabs, a carriage prevalence of 10.2% (95% CI, 9.8–10.5). Five Neisseria species were identified, the most prevalent NPN being Neisseria lactamica. Six hundred and thirty-six combinations of rplF/fetA_VR alleles were identified, each defined as a Neisseria strain type. There was an inverse relationship between carriage of N. meningitidis and of NPNs by age group, gender and season, whereas carriage of both N. meningitidis and NPNs was negatively associated with a recent history of meningococcal vaccination.

Conclusion

Variations in the prevalence of NPNs by time, place and genetic type may contribute to the particular epidemiology of meningococcal disease in the African meningitis belt.

•

A prevalence of 10.2% of Neisseria infection was observed during the study.

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Five Neisseria species were identified in nasopharyngeal samples.

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High level of genetic diversity was observed in carried isolates.

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Inverse relationship between carriage of Neisseria meningitidis and non-pathogenic Neisseria.

Factors contributing to the immunogenicity of meningococcal conjugate vaccines

Various glycoprotein conjugate vaccines have been developed for the prevention of invasive meningococcal disease, having significant advantages over pure polysaccharide vaccines. One of the most important features of the conjugate vaccines is the induction of a T-cell dependent immune response, which enables both the induction of immune memory and a booster response after repeated immunization. The nature of the carrier protein to which the polysaccharides are chemically linked, is often regarded as the main component of the vaccine in determining its immunogenicity. However, other factors can have a significant impact on the vaccine's profile. In this review, we explore the physico-chemical properties of meningococcal conjugate vaccines, which can significantly contribute to the vaccine's immunogenicity. We demonstrate that the carrier is not the sole determining factor of the vaccine's profile, but, moreover, that the conjugate vaccine's immunogenicity is the result of multiple physico-chemical structures and characteristics.

A meningococcal NOMV-FHbp vaccine for Africa elicits broader serum bactericidal antibody responses against serogroup B and non-B strains than a licensed serogroup B vaccine

BACKGROUND

Meningococcal epidemics in Sub-Sahara caused by serogroup A strains are controlled by a group A polysaccharide conjugate vaccine. Strains with serogroups C, W and X continue to cause epidemics. Protein antigens in licensed serogroup B vaccines are shared among serogroup B and non-B strains.

PURPOSE

Compare serum bactericidal antibody responses elicited by an investigational native outer membrane vesicle vaccine with over-expressed Factor H binding protein (NOMV-FHbp) and a licensed serogroup B vaccine (MenB-4C) against African serogroup A, B, C, W and X strains.

METHODS

Human Factor H (FH) transgenic mice were immunized with NOMV-FHbp prepared from a mutant African meningococcal strain containing genetically attenuated endotoxin and a mutant sub-family B FHbp antigen with low FH binding, or with MenB-4C, which contains a recombinant sub-family B FHbp antigen that binds human FH, and three other antigens, NHba, NadA and PorA P1.4, capable of eliciting bactericidal antibody.

RESULTS

The NOMV-FHbp elicited serum bactericidal activity against 12 of 13 serogroup A, B, W or X strains from Africa, and four isogenic serogroup B mutants with sub-family B FHbp sequence variants. There was no activity against a serogroup B mutant with sub-family A FHbp, or two serogroup C isolates from a recent outbreak in Northern Nigeria, which were mismatched for both PorA and sub-family of the FHbp vaccine antigen. For MenB-4C, NHba was expressed by all 16 African isolates tested, FHbp sub-family B in 13, and NadA in five. However, MenB-4C elicited titers ≥ 1:10 against only one isolate, and against only two of four serogroup B mutant strains with sub-family B FHbp sequence variants.

CONCLUSIONS

NOMV-FHbp has greater potential to confer serogroup-independent protection in Africa than the licensed MenB-4C vaccine. However, the NOMV-FHbp vaccine will require inclusion of sub-family A FHbp for coverage against recent serogroup C strains causing outbreaks in Northern Nigeria.

Modeling Long-term Vaccination Strategies With MenAfriVac in the African Meningitis Belt

BACKGROUND

The introduction of MenAfriVac in campaigns targeting people aged 1-29 years across the African meningitis belt has successfully reduced meningitis incidence and carriage due to Neisseria meningitidis group A (MenA). It is important to consider how best to sustain population protection in the long term.

METHODS

We created a mathematical model of MenA transmission and disease to investigate the potential impact of a range of immunization strategies. The model is age structured; includes classes of susceptible, carrier, ill, and immune people (who may be vaccinated or unvaccinated); and incorporates seasonal transmission and a stochastic forcing term that models between year variation in rates of transmission. Model parameters were primarily derived from African sources. The model can describe the typical annual incidence of meningitis in the prevaccine era, with irregular epidemics of varying size. Parameter and structural uncertainty were explored in sensitivity analyses.

RESULTS

Following MenAfriVac introduction at high uptake, the model predicts excellent short-term disease control. With no subsequent immunization, strong resurgences in disease incidence were predicted after approximately 15 years (assuming 10 years' average vaccine protection). Routine immunization at 9 months of age resulted in lower average annual incidence than regular mass campaigns of 1- to 4-year-olds, provided coverage was above approximately 60%. The strategy with the lowest overall average annual incidence and longest time to resurgence was achieved using a combination strategy of introduction into the Expanded Programme on Immunization at 9 months, 5 years after the initial mass campaigns, with a catch-up targeting unvaccinated 1- to 4-year-olds.

CONCLUSIONS

These results can be used to inform policy recommendations for long-term vaccination strategies with MenAfriVac.

The Safety of PsA-TT in Pregnancy: An Assessment Performed Within the Navrongo Health and Demographic Surveillance Site in Ghana

BACKGROUND

Group A meningococcal disease occurs in large epidemics within the meningitis belt of Africa that includes northern Ghana. Major epidemics in the meningitis belt have infection rates ranging from 100 to 800 per 100 000 population. In 2012, a group A meningococcal conjugate vaccine, PsA-TT (MenAfriVac), was introduced into the region in large campaigns.

METHODS

We report here on the safety of this vaccine when used in pregnant women in the Navrongo region of Ghana.

RESULTS

Rates of events in 1730 immunized pregnant women and their infants were compared to the rates of the same events in pregnant women who did not receive the vaccine during the campaign and also to women who were pregnant in the prior year.

CONCLUSIONS

We found no evidence of any safety concerns when this vaccine was administered during pregnancy.

Response thresholds for epidemic meningitis in sub-Saharan Africa following the introduction of MenAfriVac®

BACKGROUND

Since 2010, countries in the African meningitis belt have been introducing a new serogroup A meningococcal conjugate vaccine (MenAfriVac(®)) through mass campaigns. With the subsequent decline in meningitis due to Neisseria meningitidis serogroup A (NmA) and relative increase in meningitis due to other serogroups, mainly N. meningitidis serogroup W (NmW), the World Health Organisation (WHO) initiated a review of the incidence thresholds that guide response to meningitis epidemics in the African meningitis belt.

METHODS

Meningitis surveillance data from African meningitis belt countries from 2002 to 2013 were used to construct a single NmW dataset. The performance of different weekly attack rates, used as thresholds to initiate vaccination response, on preventing further cases was estimated. The cumulative seasonal attack rate used to define an epidemic was also varied.

RESULTS

Considerable variation in effect at different thresholds was observed. In predicting epidemics defined as a seasonal cumulative incidence of 100/10(5) population, an epidemic threshold of 10 cases/10(5) population/week performed well. Based on this same epidemic threshold, with a 6 week interval between crossing the epidemic threshold and population protection from a meningococcal vaccination campaign, an estimated 17 cases per event would be prevented by vaccination. Lowering the threshold increased the number of cases per event potentially prevented, as did shortening the response interval. If the interval was shortened to 4 weeks at the threshold of 10/10(5), the number of cases prevented would increase to 54 per event.

CONCLUSIONS

Accelerating time to vaccination could prevent more cases per event than lowering the threshold. Once the meningitis epidemic threshold is crossed, it is of critical importance that vaccination campaigns, where appropriate, are initiated rapidly.

Molecular shape and immunogenicity of meningococcal polysaccharide group A conjugate vaccine

Neisseria meningitidis is a leading cause of severe bacterial infections in infants and young children. As a major virulence factor, meningococcal capsular polysaccharide (PS) is poorly immunogenic and generally does not induce immunological memory. Conjugation of PS with a carrier protein can significantly increase the PS-specific immunogenicity and induce immunological memory. It is well known that the molecular shape/size of the conjugate vaccine is important for its immunogenicity. However, little is known about the molecular shape/size of the meningococcal conjugate vaccine. A meningococcal PS-ovalbumin (OVA) conjugate vaccine was prepared using cystamine as linker. Four components (P1-P4) with different molecular size were fractionated from the conjugate. Small angle X-ray scattering (SAXS) analysis revealed that the conjugate vaccine exhibited a rod-like shape similar to virus-like particles. PS-specific immunogenicity of the conjugate vaccine was related to its molecular shape and increased as a function of its molecular size. Thus, the present study provides a three-dimensional shape of the conjugate vaccine and helps to identify optimal design of a potent meningococcal conjugate vaccine.

Continuing effectiveness of serogroup A meningococcal conjugate vaccine, Chad, 2013

In 2011, vaccination with a serogroup A meningococcal polysaccharide conjugate vaccine was implemented in 3 of 23 regions in Chad. Cases of meningitis declined dramatically in vaccinated areas, but an epidemic continued in the rest of Chad. In 2012, the remaining Chad population was vaccinated, and the epidemic was halted.

Serogroup A meningococcal conjugate vaccines in Africa

Serogroup A meningococcal epidemics have been a recurrent public health problem, especially in resource-poor countries of Africa. Recently, the administration in mass vaccination campaigns of a single dose of the monovalent meningococcal conjugate vaccine, MenAfriVac, to the 1-29 year-old population of sub-Saharan Africa has prevented epidemics of meningitis caused by serogroup A Neisseria meningitidis. This strategy has also been shown to provide herd protection of the non-vaccinated population. Development of meningococcal conjugate vaccines covering other serogroups and enhanced use of the pneumococcal and Haemophilus influenzae type b conjugate vaccines must be pursued to fully control bacterial meningitis in sub-Saharan Africa.

Safety and immunogenicity of a quadrivalent meningococcal conjugate vaccine (MenACYW-DT): a multicenter, open-label, non-randomized, phase III clinical trial

OBJECTIVE

To assess the safety and immunogenicity of a quadrivalent meningococcal (groups A,C,Y,W) polysaccharide diphtheria toxoid conjugate vaccine (MenACYW-DT) in India.

DESIGN

Open-label, descriptive, non-randomized study.

SETTING

Three medical college hospitals, one each in New Delhi, Bengaluru and Mumbai, India.

PARTICIPANTS

300 healthy, vaccine-naïve participants (100 children aged 2-11 years, 100 adolescents aged 12-17 years, and 100 adults aged 18-55 years).

INTERVENTION

One dose (0.5 mL) of MenACYW-DT administered intramuscularly.

MAIN OUTCOME MEASURES

Serum bactericidal antibody titers against A, C, Y, and W were measured before and after MenACWY-DT vaccination. Safety data were also collected.

RESULTS

Thirty days post-vaccination, geometric mean titers rose across all serogroups. Most participants had protective titers >8 (1/dil) across the four serogroups. The percentage (95% CI) achieving >8 (1/dil) in the Adolescent Group was typical - A: 96.9% (91.2%; 99.4%); C: 96.9% (91.2%; 99.4%); Y:100% (96.3%; 100%); W:100% (96.3%; 100%). In general, solicited reactions were mild and short-lived. Unsolicited events were uncommon and unrelated to vaccination.

CONCLUSIONS

MenACYW-DT was well tolerated and elicited a robust and protective immune response 30 days post-vaccination against meningococcal serogroups A, C, Y, and W-135 in the Indian study participants aged 2-55 years.

Beyond the bedside: A review of translational medicine in global health

Translational research is a broad field of medicine with several key phases moving from scientific discovery to bench research and the hospital bedside, followed by evidence-based practice and population-level policy and programming. Understanding these phases is crucial when it comes to preventing and treating illness, especially in global health. Communities around the world struggle with a variety of health problems that are at some times similar and at others quite different. Three major world health issues help to outline the phases of translational research: vaccines, human immunodeficiency virus and acquired immunodeficiency syndrome, and non-communicable diseases. Laboratory research has excelled in many of these areas and is struggling in a few. Where successful therapies have been discovered there are often problems with appropriate use or dissemination to groups in need. Also, many diseases would be better prevented from a population health approach. This review highlights successes and struggles in the arena of global health, from smallpox eradication to the impending epidemic of cardiovascular disease, in an attempt to illustrate of the various phases of translational research.

Development and evaluation of a dipstick diagnostic test for Neisseria meningitidis serogroup X

The emergence of Neisseria meningitidis serogroup X (NmX) in the African meningitis belt has urged the development of diagnostic tools and vaccines for this serogroup, especially following the introduction of a conjugate vaccine against N. meningitidis serogroup A (NmA). We have developed and evaluated a new rapid diagnostic test (RDT) for detecting the capsular polysaccharide (cps) antigen of this emerging serogroup. Whole inactivated NmX bacteria were used to immunize rabbits. Following purification by affinity chromatography, the cpsX-specific IgG antibodies were utilized to develop an NmX-specific immunochromatography dipstick RDT. The test was validated against purified cpsX and meningococcal strains of different serogroups. Its performance was evaluated against that of PCR on a collection of 369 cerebrospinal fluid (CSF) samples obtained from patients living in countries within the meningitis belt (Cameroon, Côte d'Ivoire, and Niger) or in France. The RDT was highly specific for NmX strains. Cutoffs of 10(5) CFU/ml and 1 ng/ml were observed for the reference NmX strain and purified cpsX, respectively. Sensitivity and specificity were 100% and 94%, respectively. A high agreement between PCR and RDT (Kappa coefficient, 0.98) was observed. The RDT gave a high positive likelihood ratio and a low negative likelihood (0.07), indicating almost 100% probability of declaring disease or not when the test is positive or negative, respectively. This unique NmX-specific test could be added to the available set of RDT for the detection of meningococcal meningitis in Africa as a major tool to reinforce epidemiological surveillance after the introduction of the NmA conjugate vaccine.

Major Advances in the Development of Synthetic Oligosaccharide-Based Vaccines

Because of their involvement in a variety of different biological processes and their occurrence onto pathogens and malignant cell surface, carbohydrates have been identified as ideal candidates for vaccine formulation. However, as free oligosaccharides are poorly immunogenic and do not induce immunological memory in the most at risk population (infants and young children, elderly and immunocompromised patients), glycoconjugate vaccines containing the same carbohydrate antigen covalently linked to an immunogenic carrier protein have gained a prominent role. Accordingly, a number of glycoconjugate vaccines mostly directed against infections caused by bacterial pathogens have been licensed and are currently available on the market. However, also glycoconjugate vaccines suffer from significant drawbacks. The challenging procedures required for the isolation and purification of the carbohydrate antigen from its natural source often lead to poor homogeneity and presence of biological contaminants, resulting in batch-to-batch variability. Moreover, in some cases, the overwhelming immunogenicity of the carrier protein may induce the carbohydrate epitope suppression, causing hyporesponsiveness. The development of synthetic oligosaccharide-based vaccine candidates, characterized by the presence of pure and well-defined synthetic oligosaccharide structures, is expected to meet the requirement of homogeneous and highly reproducible preparations.

In the present chapter, we report on the major advances in the development of synthetic carbohydrate-based vaccines. First of all, we describe different strategies developed during the last years to circumvent the inherent difficulties of classical oligosaccharide synthesis, such as the one-pot glycosylation and the solid-phase synthesis, and their application to the preparation of carbohydrate antigens apt to conjugation with protein carriers. Next, we discuss the most representative methodologies employed for the chemical ligation of oligosaccharide structures to proteins. Finally, in the last section, we report significant examples of fully synthetic vaccines exploiting the multivalency effect. These constructs are based on the concept that the conjugation of multiple copies of synthetic oligosaccharide antigens to multivalent scaffolds, such as dendrimers, (cyclo)peptides, gold nanoparticles, and calixarenes, raises cooperative interactions between carbohydrates and immune receptors, leading to strong enhancement of the saccharide antigen immunogenicity.