Strain Coverage Research Articles

Differences between culture & non-culture confirmed invasive meningococci with a focus on factor H-binding protein distribution

To compare the distribution of capsular groups and factor H-binding protein (fHBP) variants among meningococcal isolates and non-culture clinical specimens and to assess the representativeness of group B isolates amongst group B cases as a whole. A PCR sequencing assay was used to characterise fHBP from non-culture cases confirmed from January 2011 to December 2013. These were compared to genotypic data derived from whole genome analysis of isolates received during the same period. Group W and Y strains were more common among isolates than non-culture strains. The distribution of fHBP variants among group B non-culture cases generally reflected that seen in the corresponding isolates. Nonetheless, the non-culture subset contained a greater proportion of fHBP variant 15/B44, associated with the ST-269 cluster sublineage. Differences in capsular group and fHBP distribution among culture and non-culture cases may be indicative of variation in strain viability, diagnostic practice, disease severity and/or clinical presentation. Future analyses combining clinical case information with laboratory data may help to further explore these differences. Group B isolates provide a good representation of group B disease in E&W and, therefore, can reliably be used in fHBP strain coverage predictions of recently-licensed vaccines.

Predicted Strain Coverage of a New Meningococcal Multicomponent Vaccine (4CMenB) in Spain: Analysis of the Differences with Other European Countries.

BackgroundA novel meningococcal multicomponent vaccine, 4CMenB (Bexsero®), has been approved in Europe, Canada, Australia and US. The potential impact of 4CMenB on strain coverage is being estimated by using Meningococcal Antigen Typing System (MATS), an ELISA assay which measures vaccine antigen expression and diversity in each strain. Here we show the genetic characterization and the 4CMenB potential coverage of Spanish invasive strains (collected during one epidemiological year) compared to other European countries and discuss the potential reasons for the lower estimate of coverage in Spain.Material and MethodsA panel of 300 strains, a representative sample of all serogroup B Neisseria meningitidis notified cases in Spain from 2009 to 2010, was characterized by multilocus sequence typing (MLST) and FetA variable region determination. 4CMenB vaccine antigens, PorA, factor H binding protein (fHbp), Neisseria Heparin Binding Antigen (NHBA) and Neisserial adhesin A (NadA) were molecularly typed by sequencing. PorA coverage was assigned to strain with VR2 = 4. The levels of expression and cross-reactivity of fHbp, NHBA and NadA were analyzed using MATS ELISA.FindingsGlobal estimated strain coverage by MATS was 68.67% (95% CI: 47.77–84.59%), with 51.33%, 15.33% and 2% of strains covered by one, two and three vaccine antigens, respectively. The predicted strain coverage by individual antigens was: 42% NHBA, 36.33% fHbp, 8.33% PorA and 1.33% NadA. Coverage within the most prevalent clonal complexes (cc) was 70.37% for cc 269, 30.19% for cc 213 and 95.83% for cc 32.ConclusionsClonal complexes (cc) distribution accounts for variations in strain coverage, so that country-by-country investigations of strain coverage and cc prevalence are important. Because the cc distribution could also vary over time, which in turn could lead to changes in strain coverage, continuous detailed surveillance and monitoring of vaccine antigens expression is needed in those countries where the multicomponent vaccine is introduced. This is really important in countries like Spain where most of the strains are predicted to be covered by only one vaccine antigen and the chance for escape mutants to emerge with vaccine use is higher. Based on the observed data, cc213 should receive special attention as it is associated with low predicted strain coverage, and has recently emerged in Spain.

High predicted strain coverage by the multicomponent meningococcal serogroup B vaccine (4CMenB) in Poland

Neisseria meningitidis of serogroup B (MenB) is currently responsible for more than 70% of cases of invasive meningococcal disease (IMD) in Poland and Europe as a whole. The aim of this study was to estimate strain coverage of a multicomponent meningococcal serogroup B vaccine (4CMenB) in Poland; the meningococcal antigen typing system (MATS) was used to test a panel of 196 invasive MenB strains isolated in Poland in 2010 and 2011. The strains were also characterized by MLST and sequencing of porA, factor H-binding protein (fHbp), Neisserial heparin-binding antigen (nhba) and Neisserial adhesin A (nadA) genes. MATS and molecular data were analyzed independently and in combination. The MATS results predicted that 83.7% (95% CI: 78.6–91.0%) of isolates would be covered by the 4CMenB vaccine; 59.2% by one vaccine antigen, 19.9% by two and 4.6% by three antigens. Coverage by each antigen was as follows: fHbp 73.0% (95% CI: 68.9–77.5%), NHBA 28.6% (95% CI: 13.3–47.4%), NadA 1.0% (95% CI: 1.0–2.0%) and PorA 10.2%. Molecular analysis revealed that the most frequent clonal complexes (ccs) were cc32 (33.2%), cc18 (17.9%) and cc41/44 (15.8%) with estimated coverage of 98.5%, 88.6% and 93.5%, respectively.Consistent with findings for other European countries, our study predicts high coverage by the 4CMenB vaccine in Poland.

Strain Selection for Generation of O-Antigen-Based Glycoconjugate Vaccines against Invasive Nontyphoidal Salmonella Disease.

Nontyphoidal Salmonellae, principally S. Typhimurium and S. Enteritidis, are a major cause of invasive bloodstream infections in sub-Saharan Africa with no vaccine currently available. Conjugation of lipopolysaccharide O-antigen to a carrier protein constitutes a promising vaccination strategy. Here we describe a rational process to select the most appropriate isolates of Salmonella as source of O-antigen for developing a bivalent glycoconjugate vaccine. We screened a library of 30 S. Typhimurium and 21 S. Enteritidis in order to identify the most suitable strains for large scale O-antigen production and generation of conjugate vaccines. Initial screening was based on growth characteristics, safety profile of the isolates, O-antigen production, and O-antigen characteristics in terms of molecular size, O-acetylation and glucosylation level and position, as determined by phenol sulfuric assay, NMR, HPLC-SEC and HPAEC-PAD. Three animal isolates for each serovar were identified and used to synthesize candidate glycoconjugate vaccines, using CRM197 as carrier protein. The immunogenicity of these conjugates and the functional activity of the induced antibodies was investigated by ELISA, serum bactericidal assay and flow cytometry. S. Typhimurium O-antigen showed high structural diversity, including O-acetylation of rhamnose in a Malawian invasive strain generating a specific immunodominant epitope. S. Typhimurium conjugates provoked an anti-O-antigen response primarily against the O:5 determinant. O-antigen from S. Enteritidis was structurally more homogeneous than from S. Typhimurium, and no idiosyncratic antibody responses were detected for the S. Enteritidis conjugates. Of the three initially selected isolates, two S. Typhimurium (1418 and 2189) and two S. Enteritidis (502 and 618) strains generated glycoconjugates able to induce high specific antibody levels with high breadth of serovar-specific strain coverage, and were selected for use in vaccine production. The strain selection approach described is potentially applicable to the development of glycoconjugate vaccines against other bacterial pathogens.

The multicomponent meningococcal serogroup B vaccine (4CMenB): origin, composition, health impact and unknown aspects.

Neisseria meningitidis serogroup B is the main cause for meningococcal invasive disease in many parts of the world. Since 2013, a new multicomponent vaccine against meningococcal serogroup B (4CMenB) has been licensed in Europe, Australia, Canada, Chile, Uruguay, USA and Brazil with different immunization schedules. Clinical trials involving adults, adolescents, children and infants showed 4CMenB has a good immunogenicity and safety profile. Strain coverage estimates are similar to or better than other recently approved vaccines, ranging from 66% in Canada to 91% in Unites States. Some points still remain to be clarified such as the best immunization strategy, the effect of 4CMenB on carriage, the long-term persistence of protective bactericidal antibodies titers, long-term safety outcomes, the possible emergence of N. meningitidis escape mutants and the vaccine cost-effectiveness. In this review, we focus on the vaccine composition, clinical trials and suggested schedules, safety data, potential strain coverage and future challenges.

An Invasive Pneumococcal Infection Due to Streptococcus pneumoniae Serotype 24.

To the Editors: Levy et al1 report a 67% decrease of pediatric pneumococcal meningitis due to serotypes contained in the 13-valent pneumococcal conjugate vaccine (PCV13). Non-PCV13 serotypes that dominate in their setting are 12F, 24F, 22F and 15B/C. We report the recent case of a previously healthy 9-month-old child who presented with septic shock, purpura fulminans, multiorgan failure and meningitis. He received 2 doses of PCV13 at 2 and 4 months of age. Streptococcus pneumoniae serotype 24 was isolated from blood and cerebrospinal fluid. His clinical course was marked by acute renal failure, rhabdomyolysis and intravascular disseminated coagulation. His skin condition worsened with large areas of necrosis. Amputation of 3 necrotic extremities and prolonged course of antibiotics resulted in a slow recovery. It is yet unclear whether PCV13 will lead to the emergence of new dominant serotypes similarly to what has been observed previously with 19A in the PCV7 era.2 Yet, the present case and the study by Levy et al raise the question of the potential invasiveness and replacement capacity of serotype 24. Levy et al reported that 15% of pneumococcal meningitis was attributed to serotype 24F, in 2012, in France. However, evidence of an increased proportion of serotype 24 IPD has not been documented in the actual post-PCV13 era in other settings. Besides, low prevalence of invasive pneumococcal diseases due to serotype 24 has been reported after PCV7 and before PCV13 implementation.3 In addition, increased incidence of invasive pneumococcal diseases due to non-PCV13 serotypes as observed in many settings is not related to the emergence of clearly dominant serotypes.4 If this trend is confirmed by ongoing microbiologic surveillance, the development of new conjugated vaccines will no longer be the appropriate strategy. Tarahomjoo5 in a recent review article details new potential options for vaccine development, including the use of surface protein vaccines that could be coadministered with conjugated vaccines to reach a wider coverage of invasive strains. We hope that these potential new vaccines will contribute to the disappearance of such devastative infections in properly vaccinated children, in the future. Eugénie Gradoux Department of Paediatrics Sandra Asner, MD, MSc, MER1 Unit of Paediatric Infectious Diseases Department of Paediatrics Marie-Hélène Perez, MD Paediatric Intensive Care Unit Department of Paediatrics Pierre A. Crisinel, MD Unit of Paediatric Infectious Diseases Department of Paediatrics University Hospital Centre Lausanne, Switzerland

An anal cancer screening program for MSM in Italy: Prevalence of multiple HPV types and vaccine-targeted infections

BackgroundElevated HPV infection rates have been described in HIV-positive males, placing these subjects at high risk of anal neoplasia. Bivalent, quadrivalent, and nonavalent vaccines to prevent HPV infection have been developed, and recently proposed for gender-neutral immunization programs. ObjectivesIn order to estimate the benefit that could be obtained by vaccination of HIV-positive men who have sex with men (MSM), we aimed at describing the frequency of multiple and vaccine-targeted HPV infections in MSM enrolled in an anal cancer screening program. Study designThe anal cancer screening program was conducted between July 2009 and October 2012. Mucosal anal samples were tested for HPV DNA using MY09/MY11 PCR primers and, if positive, genotyped using the CLART2HPV Clinical Array (35HPV types). ResultsA total of 220 MSM were screened and 88.6% were positive for HPV DNA: in 86.5% at least one high-risk (HR) type was found and in 13% only low-risk (LR) HPV were found. Multiple infections accounted for 84.5% of HPV DNA-positive cases and overall 160 different HPV genotype combinations were recognized (only three combinations were detected in more than one patient each). Based on strain coverage, at least one vaccine-targeted HPV type was found in 38.9%, 64%, and 78.4% of cases when considering bivalent, quadrivalent and nonavalent vaccines, respectively. At least one HR vaccine-targeted strain was found in 39% of MSM for bivalent and quadrivalent vaccines, and in 64% of cases for nonavalent prevention. ConclusionsAnal HPV infections in unvaccinated mostly HIV-infected MSM are highly prevalent. The majority of this population has multiple infections with an extremely heterogeneous number of genotype combinations. The nonavalent vaccine could theoretically have prevented a minimum of one HR HPV type in two thirds of subjects.

The difficult road to new vaccines for pertussis and serogroup B meningococcal disease

AbstractDevelopment of vaccines should be a well‐trodden path in which possible diversions and roadblocks should be clearly understood. However, challenges and unexpected twists and turns are not uncommon in modern vaccine development. In this perspective the considerable uncertainties for development of third generation pertussis vaccines will be discussed along with related issues in the development of new vaccines for the prevention of serogroup B meningococcal (MenB) disease. Acellular pertussis vaccines developed in the 1980s showed good efficacy in large clinical trials and whooping cough was at historically low levels in the last decade of the 20th century in most countries where the vaccines are used. However, the unexpected resurgence in cases in several countries has questioned the ability of current acellular pertussis vaccines to provide long‐term protection against the disease. For MenB vaccines the initial challenge has been to identify antigens that will induce protection against the diverse collection of isolates that cause disease. Following this there have been significant challenges to determine potential breadth of strain coverage. Furthermore, there has been a drop in the incidence of MenB disease in countries considering implementation of the new MenB vaccines making cost effectiveness a more difficult case to argue. It is likely that lessons learnt in the development and use of both pertussis and MenB vaccines will inform the future of vaccines for these two diseases. © 2015 Crown copyright. Journal of Chemical Technology & Biotechnology © 2015 Society of Chemical Industry

Immunogenicity of porcine P[6], P[7]-specific △VP8* rotavirus subunit vaccines with a tetanus toxoid universal T cell epitope

Currently, commercial porcine rotavirus vaccines remain varied limitations. The objective of this study is to develop an alternative porcine rotavirus subunit vaccine candidate by parenteral administration, which enables to elicit robust immune responses against most prevalence porcine rotavirus strains. The bacterially-expressed porcine rotavirus P[6]- or P[7]-specific truncated VP8* (aa 64–223) recombinant protein with or without a universal tetanus toxoid CD4+ T cell epitope P2 was generated. All the recombinant subunit proteins △VP8*s or P2-△VP8*s were of high solubility and high yields. The immunogenicity of each purified △VP8* and P2-△VP8* was evaluated in mice (10μg/dose) or guinea pigs (20μg/dose) immunized IM with 600μg aluminum hydroxide three times at 2-week interval. The introduction of P2T cell epitope to P[7]-△VP8* elicited significantly higher IgG titer in mice than its absence. Comparatively, P2 epitope slightly enhanced the immunogenicity of P[6]-△VP8*. P2-P[7]△VP8* elicited high titer of neutralizing antibody against heterotypic P[7]-specific rotaviruses with varied G type combination. Our data indicated that two subunit vaccines could be plausible bivalent rotavirus vaccine candidate to provide antigenic coverage of porcine rotavirus strains of global or regional importance.

A large portion of meningococcal antigen typing system-negative meningococcal strains from spain is killed by sera from adolescents and infants immunized with 4CMenB.

A new vaccine (the 4CMenB 4-component protein vaccine [Bexsero], which includes PorA, factor H-binding protein [fHbp], neisserial heparin-binding antigen [NHBA], and Neisseria adhesin A [NadA]) against serogroup B meningococci has recently been approved for use in people older than age 2 months in Europe, Australia, and Canada. Preapproval clinical efficacy studies are not feasible for invasive meningococcal disease because its incidence is low/very low, and the serum bactericidal antibody (SBA) titer (or the human SBA [hSBA] titer when human complement is used in the assay) has been used as a surrogate marker of protection. However, the hSBA assay cannot be used on a large scale, and therefore, a meningococcal antigen typing system (MATS) was developed. MATS combines conventional PorA genotyping with an enzyme-linked immunosorbent assay (ELISA) that quantifies both the expression and the cross-reactivity of antigenic variants. The assay has been used to evaluate the potential of the 4CMenB meningococcal group B vaccine to cover group B strains in several countries. Some recent data suggest that MATS is a conservative predictor of strain coverage. We used pooled sera from adolescents and infants to test by the hSBA assay 10 meningococcal group B strains isolated in Spain that were negative for the 3 antigens (n = 9) or that had very low levels of the 3 antigens (n = 1) by MATS. We found that all strains were killed by sera from adolescents and that 5 of the 10 strains were also killed, although at a low titer, by sera from infants. Our data confirm that MATS underestimates vaccine coverage.

Short Communication on “MATS: Global Coverage Estimates for 4CMenB, a Novel Multicomponent Meningococcal B Vaccine”

Meningococcal antigen typing system (MATS) - the golden standard in many reference labs worldwide–for rapid, reproducible and accurate (conservative nonetheless) prediction of Bexsero strain coverage, can pave the way towards a data-driven decision making of national immunization technical advisory groups (NITAGs), allowing indirect comparison of immunization policies across countries and regions leading to rapid adaptation of public health policy decisions based on worldwide datasets. Нe recent milestone of the UK national infant routine recommendation and reimbursement, paves the way for other nations to follow, bringing closer the pediatric community to the vision of a meningitis free world.

Recombinant protein truncation strategy for inducing bactericidal antibodies to the macrophage infectivity potentiator protein of Neisseria meningitidis and circumventing potential cross-reactivity with human FK506-binding proteins.

A recombinant macrophage infectivity potentiator (rMIP) protein of Neisseria meningitidis induces significant serum bactericidal antibody production in mice and is a candidate meningococcal vaccine antigen. However, bioinformatics analysis of MIP showed some amino acid sequence similarity to human FK506-binding proteins (FKBPs) in residues 166 to 252 located in the globular domain of the protein. To circumvent the potential concern over generating antibodies that could recognize human proteins, we immunized mice with recombinant truncated type I rMIP proteins that lacked the globular domain and the signal leader peptide (LP) signal sequence (amino acids 1 to 22) and contained the His purification tag at either the N or C terminus (C-term). The immunogenicity of truncated rMIP proteins was compared to that of full (i.e., full-length) rMIP proteins (containing the globular domain) with either an N- or C-terminal His tag and with or without the LP sequence. By comparing the functional murine antibody responses to these various constructs, we determined that C-term His truncated rMIP (-LP) delivered in liposomes induced high levels of antibodies that bound to the surface of wild-type but not Δmip mutant meningococci and showed bactericidal activity against homologous type I MIP (median titers of 128 to 256) and heterologous type II and III (median titers of 256 to 512) strains, thereby providing at least 82% serogroup B strain coverage. In contrast, in constructs lacking the LP, placement of the His tag at the N terminus appeared to abrogate bactericidal activity. The strategy used in this study would obviate any potential concerns regarding the use of MIP antigens for inclusion in bacterial vaccines.

Economic evaluation of meningococcal serogroup B childhood vaccination in Ontario, Canada

ObjectiveInvasive Neisseria meningitidis serogroup B (MenB) disease is a low incidence but severe infection (mean annual incidence 0.19/100,000/year, case fatality 11%, major long-term sequelae 10%) in Ontario, Canada. This study assesses the cost-effectiveness of a novel MenB vaccine from the Ontario healthcare payer perspective. MethodsA Markov cohort model of invasive MenB disease based on high quality local data and data from the literature was developed. A 4-dose vaccination schedule, 97% coverage, 90% effectiveness, 66% strain coverage, 10-year duration of protection, and vaccine cost of C$75/dose were assumed. A hypothetical Ontario birth cohort (n=150,000) was simulated to estimate expected lifetime health outcomes, quality-adjusted life years (QALYs), and costs, discounted at 5%. ResultsA MenB infant vaccination program is expected to prevent 4.6 invasive MenB disease cases over the lifetime of an Ontario birth cohort, equivalent to 10 QALYs gained. The estimated program cost of C$46.6 million per cohort (including C$318,383 for treatment of vaccine-associated adverse events) were not offset by healthcare cost savings of C$150,522 from preventing MenB cases, resulting in an incremental cost of C$4.76 million per QALY gained. Sensitivity analyses showed the findings to be robust. ConclusionsAn infant MenB vaccination program significantly exceeds commonly used cost-effectiveness thresholds and thus is unlikely to be considered economically attractive in Ontario and comparable jurisdictions.

Preventing secondary cases of invasive meningococcal capsular group B (MenB) disease using a recently-licensed, multi-component, protein-based vaccine (Bexsero®)

To assess the potential use of a protein-based meningococcal group B (MenB) vaccine (Bexsero(®)) in addition to antibiotic chemoprophylaxis for preventing secondary cases. Published studies on the risk of secondary meningococcal infections were used to estimate the numbers needed to vaccinate (NNV) with Bexsero(®) to prevent a secondary case in household and educational settings. Most secondary cases occur within a few days of diagnosis in the index case. Unlike conjugate vaccines, early protection offered after a single dose of Bexsero(®) is likely to be low, particularly in young children, who are at higher risk of secondary infection. NNV was dependent on predicted meningococcal strain coverage, estimated onset of protection after one Bexsero(®) dose and estimated vaccine efficacy. Even in the most favourable scenario where we assume the vaccine is administered within 4 days of the index case and prevents 90% of cases occurring after 14 days, the NNV for household contacts was >1000. NNV in educational settings was much higher. The estimated NNV should be taken into account when deciding policy to recommend Bexsero(®) for close contacts of single cases in household or educational settings. Bexsero(®) may have a protective role in clusters and outbreaks.

In the shadow of hemagglutinin: a growing interest in influenza viral neuraminidase and its role as a vaccine antigen.

Despite the availability of vaccine prophylaxis and antiviral therapeutics, the influenza virus continues to have a significant, annual impact on the morbidity and mortality of human beings, highlighting the continued need for research in the field. Current vaccine strategies predominantly focus on raising a humoral response against hemagglutinin (HA)—the more abundant, immunodominant glycoprotein on the surface of the influenza virus. In fact, anti-HA antibodies are often neutralizing, and are used routinely to assess vaccine immunogenicity. Neuraminidase (NA), the other major glycoprotein on the surface of the influenza virus, has historically served as the target for antiviral drug therapy and is much less studied in the context of humoral immunity. Yet, the quest to discern the exact importance of NA-based protection is decades old. Also, while antibodies against the NA glycoprotein fail to prevent infection of the influenza virus, anti-NA immunity has been shown to lessen the severity of disease, decrease viral lung titers in animal models, and reduce viral shedding. Growing evidence is intimating the possible gains of including the NA antigen in vaccine design, such as expanded strain coverage and increased overall immunogenicity of the vaccine. After giving a tour of general influenza virology, this review aims to discuss the influenza A virus neuraminidase while focusing on both the historical and present literature on the use of NA as a possible vaccine antigen.

Genotypic Analysis of Meningococcal Factor H-Binding Protein from Non-Culture Clinical Specimens

Factor H-Binding Protein (fHbp) is an outer membrane protein antigen included in two novel meningococcal group B vaccines and, as such, is an important typing target. Approximately 50% of meningococcal disease cases in England and Wales are confirmed using real-time PCR on non-culture clinical specimens only. Protocols for typing fHbp from this subset of cases have not yet been established. Here we present a nested PCR-based assay designed to amplify and sequence fHbp from non-culture clinical specimens. From analytical sensitivity experiments carried out using diluted DNA extracts, an estimated analytical sensitivity limit of 6 fg/µL of DNA (<3 genome copies/µL) was calculated. The sensitivity of the assay was shown to be comparable to the ctrA-directed real-time PCR assay currently used to confirm invasive disease diagnoses from submitted clinical specimens. A panel of 96 diverse, patient-matched clinical specimen/isolate pairs from invasive disease cases was used to illustrate the breadth of strain coverage for the assay. All fHbp alleles sequenced from the isolates matched those derived from previous whole genome analyses. The first-round PCR primer binding sites are highly conserved, however an exceptional second-round PCR primer site mismatch in one validation isolate prevented amplification. In this case, amplification from the corresponding clinical specimen was achieved, suggesting that the use of a nested PCR procedure may compensate for any minor mismatches in round-two primer sites. The assay was successful at typing 91/96 (94.8%) of the non-culture clinical specimens in this study and exhibits sufficient sensitivity to type fHbp from the vast majority of non-culture clinical specimens received by the Meningococcal Reference Unit, Public Health England.

T-Cell Immunity to Influenza A Viruses

Influenza infection remains a global threat to human health. Influenza viruses are normally controlled by antibodies specific for the surface glycoproteins hemagglutinin (HA) and neuraminidase (NA). Standard influenza vaccines are aimed at inducing these antibodies, but they must be administered annually and can be rendered ineffective since different strains circulate from year to year and vary considerably in their individual HA and NA profiles. Influenza-specific T cells have been shown to be protective in animal models and typically recognize the more conserved internal influenza proteins. Improving our understanding of influenza-specific T-cell responses, including immunodominance, specific epitope sequences, strain-related epitope variation, host/virus interaction, and the balance between immunity versus immunopathology, will be important to improve future T-cell-based vaccines, which promise broader strain coverage and longer-lasting protection than current standard vaccines.

Diversity of Greek meningococcal serogroup B isolates and estimated coverage of the 4CMenB meningococcal vaccine.

BackgroundSerogroup B meningococcal (MenB) isolates currently account for approximately 90% of invasive meningococcal disease (IMD) in Greece with ST-162 clonal complex predominating. The potential of a multicomponent meningococcal B vaccine (4CMenB) recently licensed in Europe was investigated in order to find whether the aforementioned vaccine will cover the MenB strains circulating in Greece. A panel of 148 serogroup B invasive meningococcal strains was characterized by multilocus sequence typing (MLST) and PorA subtyping. Vaccine components were typed by sequencing for factor H-binding protein (fHbp), Neisserial Heparin Binding Antigen (NHBA) and Neisseria adhesin A (NadA). Their expression was explored by Meningococcal Antigen Typing System (MATS).ResultsGlobal strain coverage predicted by MATS was 89.2% (95% CI 63.5%-98.6%) with 44.6%, 38.5% and 6.1% of strains covered by one, two and three vaccine antigens respectively. NHBA was the antigen responsible for the highest coverage (78.4%), followed by fHbp (52.7%), PorA (8.1%) and NadA (0.7%). The coverage of the major genotypes did not differ significantly. The most prevalent MLST genotype was the ST-162 clonal complex , accounting for 44.6% of the strains in the panel and with a predicted coverage of 86.4%, mainly due to NHBA and fHbp.Conclusions4CMenB has the potential to protect against a significant proportion of Greek invasive MenB strains.

Bactericidal antibody against a representative epidemiological meningococcal serogroup B panel confirms that MATS underestimates 4CMenB vaccine strain coverage

Background4CMenB (Bexsero), a vaccine developed against invasive meningococcal disease caused by capsular group B strains (MenB), was recently licensed for use by the European Medicines Agency. Assessment of 4CMenB strain coverage in specific epidemiologic settings is of primary importance to predict vaccination impact on the burden of disease. The Meningococcal Antigen Typing System (MATS) was developed to predict 4CMenB strain coverage, using serum bactericidal antibody assay with human complement (hSBA) data from a diverse panel of strains not representative of any specific epidemiology. ObjectiveTo experimentally validate the accuracy of MATS-based predictions against strains representative of a specific epidemiologic setting. Methods and resultsWe used a stratified sampling method to identify a representative sample from all MenB disease isolates collected from England and Wales in 2007–2008, tested the strains in the hSBA assay with pooled sera from infant and adolescent vaccinees, and compared these results with MATS. MATS predictions and hSBA results were significantly associated (P=0.022). MATS predicted coverage of 70% (95% CI, 55–85%) was largely confirmed by 88% killing in the hSBA (95% CI, 72–95%). MATS had 78% accuracy and 96% positive predictive value against hSBA. ConclusionMATS is a conservative predictor of strain coverage by the 4CMenB vaccine in infants and adolescents.

Distribution and diversity of the haemoglobin–haptoglobin iron-acquisition systems in pathogenic and non-pathogenic Neisseria

A new generation of vaccines containing multiple protein components that aim to provide broad protection against serogroup B meningococci has been developed. One candidate, 4CMenB (4 Component MenB), has been approved by the European Medicines Agency, but is predicted to provide at most 70–80 % strain coverage; hence there is a need for second-generation vaccines that achieve higher levels of coverage. Prior knowledge of the diversity of potential protein vaccine components is a key step in vaccine design. A number of iron import systems have been targeted in meningococcal vaccine development, including the HmbR and HpuAB outer-membrane proteins, which mediate the utilization of haemoglobin or haemoglobin–haptoglobin complexes as iron sources. While the genetic diversity of HmbR has been described, little is known of the diversity of HpuAB. Using whole genome sequences deposited in a Bacterial Isolate Genome Sequence Database (BIGSDB), the prevalence and diversity of HpuAB among Neisseria were investigated. HpuAB was widely present in a range of Neisseria species whereas HmbR was mainly limited to the pathogenic species Neisseria meningitidis and Neisseria gonorrhoeae. Patterns of sequence variation in sequences from HpuAB proteins were suggestive of recombination and diversifying selection consistent with strong immune selection. HpuAB was subject to repeat-mediated phase variation in pathogenic Neisseria and the closely related non-pathogenic Neisseria species Neisseria lactamica and Neisseria polysaccharea but not in the majority of other commensal Neisseria species. These findings are consistent with HpuAB being subject to frequent genetic transfer potentially limiting the efficacy of this receptor as a vaccine candidate.