Changes in serogroup and genotype prevalence among carried meningococci in the United Kingdom during vaccine implementation

Modelling evolutionary pathways for commensalism and hypervirulence in Neisseria meningitidis

Neisseria meningitidis, the meningococcus, resides exclusively in humans and causes invasive meningococcal disease (IMD). The population of N. meningitidis is structured into stable clonal complexes by limited horizontal recombination in this naturally transformable species. N. meningitidis is an opportunistic pathogen, with some clonal complexes, such as cc53, effectively acting as commensal colonizers, while other genetic lineages, such as cc11, are rarely colonizers but are over-represented in IMD and are termed hypervirulent. This study examined theoretical evolutionary pathways for pathogenic and commensal lineages by examining the prevalence of horizontally acquired genomic islands (GIs) and loss-of-function (LOF) mutations. Using a collection of 4850 genomes from the BIGSdb database, we identified 82 GIs in the pan-genome of 11 lineages (10 hypervirulent and one commensal lineage). A new computational tool, Phaser, was used to identify frameshift mutations, which were examined for statistically significant association with genetic lineage. Phaser identified a total of 144 frameshift loci of which 105 were shown to have a statistically significant non-random distribution in phase status. The 82 GIs, but not the LOF loci, were associated with genetic lineage and invasiveness using the disease carriage ratio metric. These observations have been integrated into a new model that infers the early events of the evolution of the human adapted meningococcus. These pathways are enriched for GIs that are involved in modulating attachment to the host, growth rate, iron uptake and toxin expression which are proposed to increase competition within the meningococcal population for the limited environmental niche of the human nasopharynx. We surmise that competition for the host mucosal surface with the nasopharyngeal microbiome has led to the selection of isolates with traits that enable access to cell types (non-phagocytic and phagocytic) in the submucosal tissues leading to an increased risk for IMD.

Deconvolution of intergenic polymorphisms determining high expression of Factor H binding protein in meningococcus and their association with invasive disease

Neisseria meningitidis is a strictly human pathogen and is the major cause of septicemia and meningitis worldwide. Factor H binding protein (fHbp) is a meningococcal surface-exposed lipoprotein that binds the human Complement factor H allowing the bacterium to evade the host innate immune response. FHbp is also a key antigen in two vaccines against N. meningitidis serogroup B. Although the fHbp gene is present in most circulating meningococcal strains, level of fHbp expression varies among isolates and has been correlated to differences in promoter sequences upstream of the gene. Here we elucidated the sequence determinants that control fHbp expression in globally circulating strains. We analyzed the upstream fHbpintergenic region (fIR) of more than 5800 strains representative of the UK circulating isolates and we identified eleven fIR sequence alleles which represent 88% of meningococcal strains. By engineering isogenic recombinant strains where fHbp expression was under the control of each of the eleven fIR alleles, we confirmed that the fIR sequence determines a specific and distinct level of expression. Moreover, we identified the molecular basis for variation in expression through polymorphisms within key regulatory regions that are known to affect fHbp expression. We experimentally established three expression groups, high–medium–low, that correlated directly with the susceptibility to killing mediated by anti-fHbp antibodies and the ability of the meningococcal strain to survive within human serum. By using this sequence classification and information about the variant, we predicted fHbp expression in the panel of UK strains and we observed that strains with higher expressing fIR alleles are more likely associated with invasive disease. Overall, our findings can contribute to understand and predict vaccine coverage mediated by fHbp as well as to shed light on the role of this virulence factor in determining an invasive phenotype.

Complement plays a key role in the immunity against Neisseria meningitidis. The meningococcus uses the Factor H binding protein (fHbp), to bind a negative regulator of the alternative complement pathway, factor H, to its surface thus preventing complement deposition and lysis. The use of fHbp as an antigen in two licensed vaccines highlights its public health relevance. Therefore the levels of this antigen produced by the bacterium are pivotal on the one hand for the survival of N. meningitidis in blood and on the other hand for the susceptibility to vaccine-induced killing antibodies. Here, we identify the predominant nucleotide sequences that drive distinct levels of the fHbp antigen in circulating meningococcal strains. We cluster them into distinct groups with increasing levels and observe that strains expressing higher fHbp amounts are associated with invasive disease. Our findings show that the nucleotide sequence of the fHbp promoter can be used for the prediction of antigen levels of any given strain and consequently for both the assessment of its sensitivity to killing by fHbp antibodies and its likelihood to cause invasive disease.

Meningococcal carriage in periods of high and low invasive meningococcal disease incidence in the UK: comparison of UKMenCar1-4 cross-sectional survey results

Background

The incidence of invasive meningococcal disease in the UK decreased by approximately four times from 1999 to 2014, with reductions in serogroup C and serogroup B disease. Lower serogroup C invasive meningococcal disease incidence was attributable to implementation of the meningococcal serogroup C conjugate vaccine in 1999, through direct and indirect protection, but no vaccine was implemented against serogroup B disease. UK Meningococcal Carriage surveys 1–3 (UKMenCar1–3), conducted in 1999, 2000, and 2001, were essential for understanding the impact of vaccination. To investigate the decline in invasive meningococcal disease incidence, we did a large oropharyngeal carriage survey in 2014–15, immediately before the changes to meningococcal vaccines in the UK national immunisation schedule.

Methods

UKMenCar4 was a cross-sectional survey in adolescents aged 15–19 years who were enrolled from schools and colleges geographically local to one of 11 UK sampling centres between Sept 1, 2014, and March 30, 2015. Participants provided an oropharyngeal swab sample and completed a questionnaire on risk factors for carriage, including social behaviours. Samples were cultured for putative Neisseria spp, which were characterised with serogrouping and whole-genome sequencing. Data from this study were compared with the results from the UKMenCar1–3 surveys (1999–2001).

Findings

From the 19 641 participants (11 332 female, 8242 male, 67 not stated) in UKMenCar4 with culturable swabs and completed risk-factor questionnaires, 1420 meningococci were isolated, with a carriage prevalence of 7·23% (95% CI 6·88–7·60). Carriage prevalence was substantially lower in UKMenCar4 than in the previous surveys: carriage prevalence was 16·6% (95% CI 15·89–17·22; 2306/13 901) in UKMenCar1 (1999), 17·6% (17·05–18·22; 2873/16 295) in UKMenCar2 (2000), and 18·7% (18·12–19·27; 3283/17 569) in UKMenCar3 (2001). Carriage prevalence was lower for all serogroups in UKMenCar4 than in UKMenCar1–3, except for serogroup Y, which was unchanged. The prevalence of carriage-promoting social behaviours decreased from 1999 to 2014–15, with individuals reporting regular cigarette smoking decreasing from 2932 (21·5%) of 13 650 to 2202 (11·2%) of 19 641, kissing in the past week from 6127 (44·8%) of 13 679 to 7320 (37·3%) of 19 641, and attendance at pubs and nightclubs in the past week from 8436 (62·1%) of 13 594 to 7662 (39·0%) of 19 641 (all p<0·0001).

Interpretation

We show that meningococcal carriage prevalence in adolescents sampled nationally during a low incidence period (2014–15) was less than half of that in an equivalent population during a high incidence period (1999–2001). Disease and carriage caused by serogroup C was well controlled by ongoing vaccination. The prevalence of behaviours associated with carriage declined, suggesting that public health policies aimed at influencing behaviour might have further reduced disease.

Funding

Wellcome Trust, UK Department of Health, and National Institute for Health Research.

Molecular characterization of Neisseria meningitidis isolates recovered from patients with invasive meningococcal disease in Colombia from 2013 to 2016

BACKGROUND

Neisseria meningitidis is a significant cause of morbidity and mortality worldwide. Meningococcal isolates have a highly dynamic population structure and can be phenotypically and genetically differentiated into serogroups and clonal complexes. The aim of this study was to describe the phenotypic and genotypic characteristics of invasive isolates recovered in Colombia from 2013 to 2016.

METHODOLOGY

A total of 193 invasive isolates were analyzed. Phenotypic and genotypic characteristics were determined by serotyping, antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE) and whole-genome sequencing.

RESULTS

Based on the results, meningococcal serogroups C, B and Y were responsible for 47.9%, 41.7%, and 9.4% of cases, respectively, and the distribution of serogroups B and C changed over time. Fifteen clonal groups and 14 clonal complexes (cc) were identified by PFGE and genome sequencing. The main clonal group included serogroup B isolates with sequence type (ST)-9493 and its four single-locus variants, which has only been identified in Colombian isolates. The clonal population structure demonstrates that the isolates in this study mainly belong to four clonal complexes: ST-11 cc, ST-32 cc, ST-35 cc and ST-41/44 cc. Thirty-eight penA alleles were identified, but no correlation between MICs and specific sequences was observed.

CONCLUSION

This study shows that most meningococcal isolates recovered from patients with invasive meningococcal disease in Colombia are strains associated with distinct globally disseminated hyperinvasive clones.

Suspected cluster of Neisseria meningitidis W invasive disease in an elderly care home: do new laboratory methods aid public health action? United Kingdom, 2015

In 2015, a suspected cluster of two invasive meningococcal disease (IMD) cases of serogroup W Neisseria meningitidis (MenW) occurred in elderly care home residents in England over 7 months; case investigations followed United Kingdom guidance. An incident control team reviewed epidemiological information. Phenotyping of case specimens informed public health action, including vaccination and throat swabs to assess carriage. Whole genome sequencing (WGS) was conducted on case and carrier isolates. Conventional phenotyping did not exclude a microbiological link between cases (case 1 W:2a:P1.5,2 and case 2 W:2a:NT). After the second case, 33/40 residents and 13/32 staff were vaccinated and 19/40 residents and 13/32 staff submitted throat swabs. Two MenW carriers and two MenC carriers were detected. WGS showed that MenW case and carrier isolates were closely related and possibly constituted a locally circulating strain. Meningococcal carriage, transmission dynamics and influence of care settings on IMD in older adults are poorly understood. WGS analyses performed following public health action helped to confirm the close relatedness of the case and circulating isolates despite phenotypic differences and supported actions taken. WGS was not sufficiently timely to guide public health practice.

UKMenCar4: A cross-sectional survey of asymptomatic meningococcal carriage amongst UK adolescents at a period of low invasive meningococcal disease incidence

Carriage of Neisseria meningitidis, the meningococcus, is a prerequisite for invasive meningococcal disease (IMD), a potentially devastating infection that disproportionately afflicts infants and children. Humans are the sole known reservoir for the meningococcus, and it is carried asymptomatically in the nasopharynx of ~10% of the population. Rates of carriage are dependent on age of the host and social and behavioural factors. In the UK, meningococcal carriage has been studied through large, multi-centre carriage surveys of adolescents in 1999, 2000, and 2001, demonstrating carriage can be affected by immunisation with the capsular group C meningococcal conjugate vaccine, inducing population immunity against carriage. Fifteen years after these surveys were carried out, invasive meningococcal disease incidence had declined from a peak in 1999.  The UKMenCar4 study was conducted in 2014/15 to investigate rates of carriage amongst the adolescent population during a period of low disease incidence. The protocols and methodology used to perform UKMenCar4, a large carriage survey, are described here.

UKMenCar4: A cross-sectional survey of asymptomatic meningococcal carriage amongst UK adolescents at a period of low invasive meningococcal disease incidence

Carriage of Neisseria meningitidis, the meningococcus, is a prerequisite for invasive meningococcal disease (IMD), a potentially devastating infection that disproportionately afflicts infants and children. Humans are the sole known reservoir for the meningococcus, and it is carried asymptomatically in the nasopharynx of ~10% of the population. Rates of carriage are dependent on age of the host and social and behavioural factors. In the UK, meningococcal carriage has been studied through large, multi-centre carriage surveys of adolescents in 1999, 2000, and 2001, demonstrating carriage can be affected by immunisation with the capsular group C meningococcal conjugate vaccine, inducing population immunity against carriage. Fifteen years after these surveys were carried out, invasive meningococcal disease incidence had declined from a peak in 1999.  The UKMenCar4 study was conducted in 2014/15 to investigate rates of carriage amongst the adolescent population during a period of low disease incidence. The protocols and methodology used to perform UKMenCar4, a large carriage survey, are described here.

The Impact of Nucleotide Sequence Analysis on Meningococcal Vaccine Development and Assessment

Since it became available as a routine tool in biology, the determination and analysis of nucleotide sequences has been applied to the design of vaccines and the investigation of their effectiveness. As vaccination is primarily concerned with the interaction of biological molecules with the immune system, the utility of sequence data is not immediately obvious and, indeed, nucleotide sequence data are most effective when used to complement more conventional immunological approaches. Here, the impact of sequencing on the field of vaccinology will be illustrated with reference to the development and implementation of vaccines against Neisseria meningitidis (the meningococcus) over the 30-year period from the late-1980s to the late-2010s. Nucleotide sequence-based studies have been important in the fight against this aggressive pathogen largely because of its high genetic and antigenic diversity, properties that were only fully appreciated because of sequence-based studies. Five aspects will be considered, the use of sequence data to: (i) discover vaccine antigens; (ii) assess the diversity and distribution of vaccine antigens; (iii) determine the evolutionary and population biology of the organism and their implications for immunization; and (iv) develop molecular approaches to investigate pre- and post-vaccine pathogen populations to assess vaccine impact. One of the great advantages of nucleotide sequence data has been its scalability, which has meant that increasingly large data sets have been available, which has proved invaluable in the investigation of an organism as diverse and enigmatic as the meningococcus.

Impact of meningococcal C conjugate vaccination programs with and without catch-up campaigns in adolescents: Lessons learned from Bahia, Brazil

The significant increase in the incidence rates and ongoing outbreaks of serogroup C meningococcal (MenC) disease, associated with the sequence type-103 complex, motivated the incorporation of the meningococcal C conjugate (MCC) vaccine in the routine immunization program in the State of Bahia, Brazil in early 2010, targeting children younger than 5 years of age. In its capital, Salvador, the program also included a catch-up campaign for individuals 10-24 years of age. We performed an observational, ecological study, analyzing data collected from 2007 to 2015, to compare the impact of these two immunization strategies on meningococcal disease incidence and mortality rates. In Salvador, following the vaccination program, a dramatic early impact on MenC disease and mortality rates could be observed, with significant reductions in incidence rates of MenC disease in all age groups, including individuals that were too old to have been vaccinated, indicating the presence of herd protection. Compared to the pre-vaccine period, a virtual disappearance of MenC disease was observed in 2015. However, in the state of Bahia (excluding the city of Salvador), no herd protection could be observed, with significant impact only among vaccine-eligible children within 5 years of introduction of the MCC vaccination program. These results highlight the importance of catch-up campaigns, including adolescents and young adults, to induce herd protection compared to immunization strategies restricted to infants and young children. This information is crucial for identifying optimal immunization policies and future strategies, focused on adolescents, to optimize the impact of MCC vaccination programs.

Molecular characterization of invasive capsule null Neisseria meningitidis in South Africa

Background

The meningococcal capsule is an important virulence determinant. Unencapsulated meningococci lacking capsule biosynthesis genes and containing the capsule null locus (cnl) are predominantly non-pathogenic. Rare cases of invasive meningococcal disease caused by cnl isolates belonging to sequence types (ST) and clonal complexes (cc) ST-845 (cc845), ST-198 (cc198), ST-192 (cc192) and ST-53 (cc53) have been documented. The clinical significance of these isolates however remains unclear. We identified four invasive cnl meningococci through laboratory-based surveillance in South Africa from 2003 through 2013, which we aimed to characterize using whole genome data.

Results

One isolate [NG: P1.7-2,30: F1-2: ST-53 (cc53)] contained cnl allele 12, and caused empyema in an adult male with bronchiectasis from tuberculosis, diabetes mellitus and a smoking history. Three isolates were NG: P1.18-11,42-2: FΔ: ST-192 (cc192) and contained cnl allele 2. One patient was an adolescent male with meningitis. The remaining two isolates were from recurrent disease episodes (8 months apart) in a male child with deficiency of the sixth complement component, and with the exception of two single nucleotide polymorphisms, contained identical core genomes. The ST-53 (cc53) isolate possessed alleles for NHBA peptide 191 and fHbp variant 2; whilst the ST-192 (cc192) isolates contained NHBA peptide 704 and fHbp variant 3. All four isolates lacked nadA. Comparison of the South African genomes to 61 additional cnl genomes on the PubMLST Neisseria database (http://pubmlst.org/neisseria/), determined that most putative virulence genes could be found in both invasive and carriage phenotypes.

Conclusions

Although rare, invasive disease by cnl meningococci may be associated with host immunodeficiency and such patients may benefit from protein-based meningococcal vaccines.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-017-0942-5) contains supplementary material, which is available to authorized users.

Genomic analysis of urogenital and rectal Neisseria meningitidis isolates reveals encapsulated hyperinvasive meningococci and coincident multidrug-resistant gonococci

Objective

Invasive meningococcal disease (IMD) outbreaks in men who have sex with men (MSM) have been associated with meningococcal colonisation of the urethra and rectum, but little is known about this colonisation or co-colonisation with the closely related gonococcus. Whole genome sequencing (WGS) was employed to explore these phenomena.

Methods

Meningococci isolated from the urogenital tract and rectum (n=23) and coincident gonococci (n=14) were analysed by WGS along with contemporary meningococci from IMD (n=11). All isolates were obtained from hospital admissions in Brighton, UK, 2011–2013. Assembled WGS were deposited in the PubMLST/neisseria database (http://pubmlst.org/neisseria) and compared at genomic loci common to gonococci or meningococci.

Results

As expected, most meningococci from IMD were encapsulated and belonged to hyperinvasive lineages. So too were meningococci found in the urogenital tract and rectum, contrasting to those asymptomatically carried in the nasopharynx where such meningococci are rare. Five hyperinvasive meningococcal lineages and four distinct gonococcal genotypes were recovered, including multiresistant ST-1901 (NG MAST-1407) gonococci.

Conclusions

These data were consistent with a predisposition for potentially virulent encapsulated hyperinvasive meningococci to colonise the urethra and rectum, which suggests their involvement in MSM IMD outbreaks. The coincidence of multiresistant gonococci raises wider public health concerns.

Serogroup and Clonal Characterization of Czech Invasive Neisseria meningitidis Strains Isolated from 1971 to 2015

Background

This study presents antigenic and genetic characteristics of Neisseria meningitidis strains recovered from invasive meningococcal disease (IMD) in the Czech Republic in 1971–2015.

Material and Methods

A total of 1970 isolates from IMD, referred to the National Reference Laboratory for Meningococcal Infections in 1971–2015, were studied. All isolates were identified and characterized by conventional biochemical and serological tests. Most isolates (82.5%) were characterized by multilocus sequence typing method.

Results

In the study period 1971–2015, the leading serogroup was B (52.4%), most often assigned to clonal complexes cc32, cc41/44, cc18, and cc269. A significant percentage of strains were of serogroup C (41.4%), with high clonal homogeneity due to hyperinvasive complex cc11, which played an important role in IMD in the Czech Republic in the mid-1990s. Serogroup Y isolates, mostly assigned to cc23, and isolates of clonally homogeneous serogroup W have also been recovered more often over the last years.

Conclusion

The incidence of IMD and distribution of serogroups and clonal complexes of N. meningitidis in the Czech Republic varied over time, as can be seen from the long-term monitoring, including molecular surveillance data. Data from the conventional and molecular IMD surveillance are helpful in refining the antimeningococcal vaccination strategy in the Czech Republic.

How Can Vaccines Contribute to Solving the Antimicrobial Resistance Problem?

There is a growing appreciation for the role of vaccines in confronting the problem of antimicrobial resistance (AMR). Vaccines can reduce the prevalence of resistance by reducing the need for antimicrobial use and can reduce its impact by reducing the total number of cases. By reducing the number of pathogens that may be responsible for a particular clinical syndrome, vaccines can permit the use of narrower-spectrum antibiotics for empirical therapy. These effects may be amplified by herd immunity, extending protection to unvaccinated persons in the population. Because much selection for resistance is due to selection on bystander members of the normal flora, vaccination can reduce pressure for resistance even in pathogens not included in the vaccine. Some vaccines have had disproportionate effects on drug-resistant lineages within the target species, a benefit that could be more deliberately exploited in vaccine design. We describe the effects of current vaccines in controlling AMR, survey some vaccines in development with the potential to do so further, and discuss strategies to amplify these benefits. We conclude with a discussion of research and policy priorities to more fully enlist vaccines in the battle against AMR.

Population and Functional Genomics of Neisseria Revealed with Gene-by-Gene Approaches

Rapid low-cost whole-genome sequencing (WGS) is revolutionizing microbiology; however, complementary advances in accessible, reproducible, and rapid analysis techniques are required to realize the potential of these data. Here, investigations of the genus Neisseria illustrated the gene-by-gene conceptual approach to the organization and analysis of WGS data. Using the gene and its link to phenotype as a starting point, the BIGSdb database, which powers the PubMLST databases, enables the assembly of large open-access collections of annotated genomes that provide insight into the evolution of the Neisseria, the epidemiology of meningococcal and gonococcal disease, and mechanisms of Neisseria pathogenicity.

Prevalence of meningococcal carriage in children and adolescents aged 10-19 years in Chile in 2013

In 2011, Chile experienced an increase in the number of cases of IMD caused by Neisseria meningitidis group W. This epidemiological scenario prompted authorities to implement prevention strategies. As part of these strategies, the Institute of Public Heath of Chile conducted a cross-sectional study to determine the prevalence of pharyngeal carriage of N. meningitidis in a representative sample of healthy children and adolescents aged 10-19 years. The identification of presumptive N. meningitidis strains was performed by testing carbohydrate utilization in the National Reference Laboratory at the ISP. Association of meningococcal carriage with risk factors was analyzed by calculating the Odds Ratio. Selected variables were included in a logistic model for risk analyses. The prevalence of carriage of N. meningitidis was 6.5% (CI: 5.7-7.3%). Older age (carriers: 14.2±0.29 vs. non-carriers: 13.8±0.08 years old; p=0.009), cohabitation with children (carriers: 0.9±0.13 vs. non-carriers: 0.7±0.03; p=0.028), number of smoking cohabitants (carriers: 0.55±0.13 vs. non-carriers: 0.44±0.03) and frequent attendance to crowded social venues (carriers: 49% vs. non-carriers: 37%; p=0.008) were determined to favor carriage. Statistical modeling showed that meningococcal carriage was associated with older age (OR: 1.077, p-value: 0.002) and cohabitation with children (OR: 1.182, p-value: 0.02).

Impact of vaccination on meningococcal epidemiology

Neisseria meningitidis may cause invasive disease (meningitis and sepsis), leading to considerable disease burden and mortality. However, effective vaccines are available against most pathogenic serogroups. Large-scale vaccination campaigns with the MCC vaccine conducted in UK and with MenAfriVac in the Sahel have clearly demonstrated the direct and indirect effect of immunization programmes on disease and carriage. Moreover, the introduction of novel subcapsular vaccines against serogroup B, which may cross-protect against other serogroups, is likely to have a further effect on trends. Accurate data collection is key to elaborate vaccination strategies able to reduce meningococcal disease burden through direct protection and herd immunity.

Genomic analysis of diversity, population structure, virulence, and antimicrobial resistance in Klebsiella pneumoniae, an urgent threat to public health

Klebsiella pneumoniae is now recognized as an urgent threat to human health because of the emergence of multidrug-resistant strains associated with hospital outbreaks and hypervirulent strains associated with severe community-acquired infections. K. pneumoniae is ubiquitous in the environment and can colonize and infect both plants and animals. However, little is known about the population structure of K. pneumoniae, so it is difficult to recognize or understand the emergence of clinically important clones within this highly genetically diverse species. Here we present a detailed genomic framework for K. pneumoniae based on whole-genome sequencing of more than 300 human and animal isolates spanning four continents. Our data provide genome-wide support for the splitting of K. pneumoniae into three distinct species, KpI (K. pneumoniae), KpII (K. quasipneumoniae), and KpIII (K. variicola). Further, for K. pneumoniae (KpI), the entity most frequently associated with human infection, we show the existence of >150 deeply branching lineages including numerous multidrug-resistant or hypervirulent clones. We show K. pneumoniae has a large accessory genome approaching 30,000 protein-coding genes, including a number of virulence functions that are significantly associated with invasive community-acquired disease in humans. In our dataset, antimicrobial resistance genes were common among human carriage isolates and hospital-acquired infections, which generally lacked the genes associated with invasive disease. The convergence of virulence and resistance genes potentially could lead to the emergence of untreatable invasive K. pneumoniae infections; our data provide the whole-genome framework against which to track the emergence of such threats.

The Diversity of Meningococcal Carriage Across the African Meningitis Belt and the Impact of Vaccination With a Group A Meningococcal Conjugate Vaccine

Background. Study of meningococcal carriage is essential to understanding the epidemiology of Neisseria meningitidis infection.

Methods. Twenty cross-sectional carriage surveys were conducted in 7 countries in the African meningitis belt; 5 surveys were conducted after introduction of a new serogroup A meningococcal conjugate vaccine (MenAfriVac). Pharyngeal swab specimens were collected, and Neisseria species were identified by microbiological and molecular techniques.

Results. A total of 1687 of 48 490 participants (3.4%; 95% confidence interval [CI], 3.2%–3.6%) carried meningococci. Carriage was more frequent in individuals aged 5–14 years, relative to those aged 15–29 years (adjusted odds ratio [OR], 1.41; 95% CI, 1.25–1.60); in males, relative to females (adjusted OR, 1.17; 95% CI, 1.10–1.24); in individuals in rural areas, relative to those in urban areas (adjusted OR, 1.44; 95% CI, 1.28–1.63); and in the dry season, relative to the rainy season (adjusted OR, 1.54; 95% CI, 1.37–1.75). Forty-eight percent of isolates had genes encoding disease-associated polysaccharide capsules; genogroup W predominated, and genogroup A was rare. Strain diversity was lower in countries in the center of the meningitis belt than in Senegal or Ethiopia. The prevalence of genogroup A fell from 0.7% to 0.02% in Chad following mass vaccination with MenAfriVac.

Conclusions. The prevalence of meningococcal carriage in the African meningitis belt is lower than in industrialized countries and is very diverse and dynamic, even in the absence of vaccination.

Meningococcal carriage in adolescents in the United Kingdom to inform timing of an adolescent vaccination strategy

OBJECTIVES

Recent development of serogroup B meningococcal (MenB) vaccines highlights the importance of pharyngeal carriage data, particularly in adolescents and young adults, to inform implementation strategies. We describe current UK carriage prevalence in this high risk population and compare methods of carriage detection.

METHODS

In this multisite study, pharyngeal swabs were collected on 3-4 occasions over 6-12 months, from 1040 school and university students, aged 10-25 years. Meningococcal carriage was detected by standard culture combined with seroagglutination or PCR of cultured isolates, or by direct PCR from swab. The factor H binding protein (fHBP) variants present in meningococcal isolates were determined.

RESULTS

Meningococcal serogroups B and Y were most common, with carriage up to 6.5% and 5.5% respectively, increasing throughout adolescence. Identification by seroagglutination was often unreliable, and the sensitivity of direct PCR detection was 66% compared to culture combined with PCR. Of MenB isolates, 89.1% had subfamily A variants of fHBP. The acquisition rate of MenB carriage was estimated at 2.8 per 1000 person-months.

CONCLUSIONS

If vaccination is to precede the adolescent rise in MenB carriage, these data suggest it should take place in early adolescence. Studies assessing vaccine impact should use molecular methods to detect carriage.

Neisseria meningitidis; clones, carriage, and disease

Neisseria meningitidis, the cause of meningococcal disease, has been the subject of sophisticated molecular epidemiological investigation as a consequence of the significant public health threat posed by this organism. The use of multilocus sequence typing and whole genome sequencing classifies the organism into clonal complexes. Extensive phenotypic, genotypic and epidemiological information is available on the PubMLST website. The human nasopharynx is the sole ecological niche of this species, and carrier isolates show extensive genetic diversity as compared with hyperinvasive lineages. Horizontal gene exchange and recombinant events within the meningococcal genome during residence in the human nasopharynx result in antigenic diversity even within clonal complexes, so that individual clones may express, for example, more than one capsular polysaccharide (serogroup). Successful clones are capable of wide global dissemination, and may be associated with explosive epidemics of invasive disease.

A native outer membrane vesicle vaccine confers protection against meningococcal colonization in human CEACAM1 transgenic mice

BACKGROUND

The effect of protein-based meningococcal vaccines on prevention of nasopharyngeal colonization has been difficult to investigate experimentally because a reliable animal colonization model did not exist.

METHODS

Human CEACAM1 transgenic mice, which can be colonized by meningococci, were immunized IP with one of two meningococcal native outer membrane vesicle (NOMV) vaccines prepared from mutants with attenuated endotoxin (lpxL1 knockout) and over-expressed sub-family B Factor H-binding proteins (FHbp). Animals were challenged intranasally two weeks after the third dose with wild-type strain H44/76, or were treated IP with anti-NOMV serum before and during the bacterial challenge.

RESULTS

The NOMV-1 vaccine, prepared from the serogroup B H44/76 mutant, elicited ∼40-fold higher serum bactericidal antibody titers against the wild-type H44/76 challenge strain than the NOMV-2 vaccine prepared from a heterologous serogroup W mutant strain with different PorA and FHbp amino acid sequence variants. Compared to aluminum hydroxide-immunized control mice, the efficacy for prevention of any H44/76 colonization was 93% (95% confidence interval, 52-99, P<0.0001) for the NOMV-1 vaccine, and 19% (-3-36, P=0.23) for NOMV-2. NOMV-2-vaccinated mice had a 5.6-fold decrease in geometric mean CFU of bacteria per animal in tracheal washes compared to control mice (P=0.007). The efficacy of passive administration of serum from NOMV-1-vaccinated mice to immunologically naïve mice against colonization was 44% (17-61; P=0.002).

CONCLUSIONS

Both NOMV vaccines protected against meningococcal colonization but there was greater protection by the NOMV-1 vaccine with antigens matched with the challenge strain. Meningococcal vaccines that target protein antigens have potential to decrease colonization.

Clonal analysis of meningococci during a 26 year period prior to the introduction of meningococcal serogroup C vaccines

Meningococcal disease remains a public health burden in the UK and elsewhere. Invasive Neisseria meningitidis, isolated in Scotland between 1972 and 1998, were characterised retrospectively to examine the serogroup and clonal structure of the circulating population. 2607 isolates causing invasive disease were available for serogroup and MLST analysis whilst 2517 were available for multilocus sequence typing (MLST) analysis only. Serogroup distribution changed from year to year but serogroups B and C were dominant throughout. Serogroup B was dominant throughout the 1970s and early 1980s until serogroup C became dominant during the mid-1980s. The increase in serogroup C was not associated with one particular sequence type (ST) but was associated with a number of STs, including ST-8, ST-11, ST-206 and ST-334. This is in contrast to the increase in serogroup C disease seen in the 1990s that was due to expansion of the ST-11 clonal complex. While there was considerable diversity among the isolates (309 different STs among the 2607 isolates), a large proportion of isolates (59.9%) were associated with only 10 STs. These data highlight meningococcal diversity over time and the need for ongoing surveillance during the introduction of new meningococcal vaccines.

Applying Convergent Immunity to Innovative Vaccines Targeting Staphylococcus aureus

Recent perspectives forecast a new paradigm for future “third generation” vaccines based on commonalities found in diverse pathogens or convergent immune defenses to such pathogens. For Staphylococcus aureus, recurring infections and a limited success of vaccines containing S. aureus antigens imply that native antigens induce immune responses insufficient for optimal efficacy. These perspectives exemplify the need to apply novel vaccine strategies to high-priority pathogens. One such approach can be termed convergent immunity, where antigens from non-target organisms that contain epitope homologs found in the target organism are applied in vaccines. This approach aims to evoke atypical immune defenses via synergistic processes that (1) afford protective efficacy; (2) target an epitope from one organism that contributes to protective immunity against another; (3) cross-protect against multiple pathogens occupying a common anatomic or immunological niche; and/or (4) overcome immune subversion or avoidance strategies of target pathogens. Thus, convergent immunity has a potential to promote protective efficacy not usually elicited by native antigens from a target pathogen. Variations of this concept have been mainstays in the history of viral and bacterial vaccine development. A more far-reaching example is the pre-clinical evidence that specific fungal antigens can induce cross-kingdom protection against bacterial pathogens. This trans-kingdom protection has been demonstrated in pre-clinical studies of the recombinant Candida albicans agglutinin-like sequence 3 protein (rAls3) where it was shown that a vaccine containing rAls3 provides homologous protection against C. albicans, heterologous protection against several other Candida species, and convergent protection against several strains of S. aureus. Convergent immunity reflects an intriguing new approach to designing and developing vaccine antigens and is considered here in the context of vaccines to target S. aureus.

Sequence, distribution and chromosomal context of class I and class II pilin genes of Neisseria meningitidis identified in whole genome sequences

Background

Neisseria meningitidis expresses type four pili (Tfp) which are important for colonisation and virulence. Tfp have been considered as one of the most variable structures on the bacterial surface due to high frequency gene conversion, resulting in amino acid sequence variation of the major pilin subunit (PilE). Meningococci express either a class I or a class II pilE gene and recent work has indicated that class II pilins do not undergo antigenic variation, as class II pilE genes encode conserved pilin subunits. The purpose of this work was to use whole genome sequences to further investigate the frequency and variability of the class II pilE genes in meningococcal isolate collections.

Results

We analysed over 600 publically available whole genome sequences of N. meningitidis isolates to determine the sequence and genomic organization of pilE. We confirmed that meningococcal strains belonging to a limited number of clonal complexes (ccs, namely cc1, cc5, cc8, cc11 and cc174) harbour a class II pilE gene which is conserved in terms of sequence and chromosomal context. We also identified pilS cassettes in all isolates with class II pilE, however, our analysis indicates that these do not serve as donor sequences for pilE/pilS recombination. Furthermore, our work reveals that the class II pilE locus lacks the DNA sequence motifs that enable (G4) or enhance (Sma/Cla repeat) pilin antigenic variation. Finally, through analysis of pilin genes in commensal Neisseria species we found that meningococcal class II pilE genes are closely related to pilE from Neisseria lactamica and Neisseria polysaccharea, suggesting horizontal transfer among these species.

Conclusions

Class II pilins can be defined by their amino acid sequence and genomic context and are present in meningococcal isolates which have persisted and spread globally. The absence of G4 and Sma/Cla sequences adjacent to the class II pilE genes is consistent with the lack of pilin subunit variation in these isolates, although horizontal transfer may generate class II pilin diversity. This study supports the suggestion that high frequency antigenic variation of pilin is not universal in pathogenic Neisseria.

The Long Road to an Effective Vaccine for Meningococcus Group B (MenB)

Neisseria meningitidis infection can cause life-threatening meningitis and meningococcal septicaemia. Over the past 40 years, vaccines against most of the main meningococcal serogroups have offered increasingly good protection from disease, with one major exception in the developed world: serogroup B meningococcus (MenB). In the United States, MenB accounts for about a quarter of cases of meningococcal meningitis, with the bulk of the rest caused by meningococcus serogroups C (MenC) and Y (MenY). In the UK, where a vaccine against MenC is widely used, MenB is now responsible for nearly 90% of cases of invasive meningococcal disease. Recent attempts to create a universal MenB vaccine have been thwarted by the variability of the surface proteins of MenB and by the similarity of the MenB capsule to human glycoproteins. This review discusses current meningococcal vaccine strategies and their limitations with regard to MenB, and examines a promising new strategy for the rational design of a MenB vaccine. Thanks to a fusion of a rational reverse genetics approach and a membrane vesicle approach, a MenB vaccine, 4CMenB (Bexsero(®)), has finally gained regulatory approval in Europe and could be in clinical use by the end of 2013.

An epidemiological review of changes in meningococcal biology during the last 100 years

AIM

The aim of this study was to assess changes in trends of meningococcal disease and strain diversity of Neisseria meningitidis in Europe, South America, and Africa over the last 100 years.

METHODS

Healthcare databases and sources of grey literature were searched in 2012 and records were screened against the protocol eligibility criteria using a three-stage sifting process. Studies included in the review were subject to data extraction. Results were summarised using a narrative approach.

RESULTS

Serogroup A was the dominant cause of invasive meningococcal disease in Europe before and during World Wars I and II. Whilst serogroup B has been dominant from the 1970s in Europe and the 1980s in South America, outbreaks have emerged associated with serogroups W135 and Y in the twenty-first century. There has been a shift in the age groups affected by invasive meningococcal disease with an increase in incidence among the elderly associated with serogroup Y and a decline in serogroup C among adolescent populations. Recent outbreaks of serogroup W135 have occurred in some countries in South America. The epidemiological trend of invasive meningococcal disease has remained largely static across Africa and dominated by serogroup A although recently serogroups X and W135 have accounted for a large proportion of morbidity and mortality.

CONCLUSION

The epidemiology of N. meningitidis has been dynamic in Europe and South America especially over the last 30 years. Routine vaccination with serogroup C vaccines has led to reduced carriage and incidence of invasive meningococcal disease and herd immunity.

Prevention of meningococcal infections in the first 2 years of life

The spectrum of disease caused by Neisseria meningitidis includes bacteremia, fulminant sepsis (meningococcemia), meningitis, and pneumonia. The incidence of meningococcal infection has long been higher in infancy than adolescents or adults older than 65 years (a third group with an increased risk based on age). Five meningococcal serogroups (A, B, C, Y, and W135) cause the great majority of human disease. Serogroup B strains cause about two-thirds of disease in children younger than 6 years. For this reason, new meningococcal vaccine formulations have been developed and evaluated in children younger than 2 years. Of four meningococcal vaccines currently licensed in the United States, two conjugate products, (MenACWY-D [Menactra], Sanofi Pasteur; HibMenCY-TT [MenHibrix], GlaxoSmithKline), are recommended for infants and toddlers younger than 2 years who have an increased risk for invasive meningococcal disease. High-risk conditions are complement deficiencies, community outbreaks, functional or anatomic asplenia, and travel to high-risk areas in which serogroup A infection is prevalent. Recommendations vary by age, dosing, and indication between these two products. Both licensed products are immunogenic and have side-effect profiles that are considered safe for use. In most cases, concomitant use with other recommended childhood vaccines does not interfere with responses to these vaccines. As of yet, there has not been universal adoption of this immunization in the infant population by parents or providers. Factors that weigh against the implementation of a national routine infant program include the prevention of only 40 to 50 meningococcal cases, two to four deaths per year, and a relatively low case fatality among infants. Some argue that costs should not be considered a barrier because infant deaths and morbidity would be prevented. The availability of a serogroup B vaccine would improve impact and cost-effectiveness of a routine infant meningococcal vaccine program. Debate over the implementation of routine infant meningococcal vaccination in the United States is ongoing. This review focuses on vaccines for the prevention of N. meningitidis infection in infants and young toddlers in the first 2 years of life.

The impact of protein-conjugate polysaccharide vaccines: an endgame for meningitis?

The development and implementation of conjugate polysaccharide vaccines against invasive bacterial diseases, specifically those caused by the encapsulated bacteria Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae, has been one of the most effective public health innovations of the last 25 years. These vaccines have resulted in significant reductions in childhood morbidity and mortality worldwide, with their effectiveness due in large part to their ability to induce long-lasting immunity in a range of age groups. At the population level this immunity reduces carriage and interrupts transmission resulting in herd immunity; however, these beneficial effects can be counterbalanced by the selection pressures that immunity against carriage can impose, potentially promoting the emergence and spread of virulent vaccine escape variants. Studies following the implementation of meningococcal serogroup C vaccines improved our understanding of these effects in relation to the biology of accidental pathogens such as the meningococcus. This understanding has enabled the refinement of the implementation of conjugate polysaccharide vaccines against meningitis-associated bacteria, and will be crucial in maintaining and improving vaccine control of these infections. To date there is little evidence for the spread of virulent vaccine escape variants of the meningococcus and H. influenzae, although this has been reported in pneumococci.

The changing epidemiology of meningococcal disease in Quebec, Canada, 1991-2011: potential implications of emergence of new strains

Background

In order to inform meningococcal disease prevention strategies, we analysed the epidemiology of invasive meningococcal disease (IMD) in the province of Quebec, Canada, 10 years before and 10 years after the introduction of serogroup C conjugate vaccination.

Methodology

IMD cases reported to the provincial notifiable disease registry in 1991–2011 and isolates submitted for laboratory surveillance in 1997–2011 were analysed. Serogrouping, PCR testing and assignment of isolates to sequence types (ST) by using multilocus sequence typing (MLST) were performed.

Results

Yearly overall IMD incidence rates ranged from 2.2–2.3/100,000 in 1991–1992 to 0.49/100,000 in 1999–2000, increasing to 1.04/100,000 in 2011. Among the 945 IMD cases identified by laboratory surveillance in 1997–2011, 68%, 20%, 8%, and 3% were due to serogroups B, C, Y, and W135, respectively. Serogroup C IMD almost disappeared following the implementation of universal childhood immunization with monovalent C conjugate vaccines in 2002. Serogroup B has been responsible for 88% of all IMD cases and 61% of all IMD deaths over the last 3 years. The number and proportion of ST-269 clonal complex has been steadily increasing among the identified clonal complexes of serogroup B IMD since its first identification in 2003, representing 65% of serogroup B IMD in 2011. This clonal complex was first introduced in adolescent and young adults, then spread to other age groups.

Conclusion

Important changes in the epidemiology of IMD have been observed in Quebec during the last two decades. Serogroup C has been virtually eliminated. In recent years, most cases have been caused by the serogroup B ST-269 clonal complex. Although overall burden of IMD is low, the use of a vaccine with potential broad-spectrum coverage could further reduce the burden of disease. Acceptability, feasibility and cost-effectiveness studies coupled with ongoing clinical and molecular surveillance are necessary in guiding public policy decisions.

MenACWY-TT vaccine for active immunization against invasive meningococcal disease

Meningococcal disease remains a significant global cause of morbidity and mortality despite the availability of polysaccharide and conjugate vaccines. The implementation of monovalent meningococcal serogroup C vaccine in developed countries has significantly decreased the incidence of meningococcal disease, while the recent introduction of monovalent serogroup A conjugate vaccine in the African meningitis belt aims to reduce the incidence of high endemic disease in this area. Three quadrivalent meningococcal vaccines have already been licensed; a polysaccharide (MenACWY-PS) and two conjugated (MenACWY-DT and MenACWY-CRM) vaccines. An investigational MenACWY-TT vaccine is described in this article. Clinical trials in infants older than 9 months of age, toddlers, children, adolescents and adults have indicated that this vaccine is well tolerated and immunogenic. The inclusion of a spacer molecule coupled with the polysaccharide (for serogroups A and C) and tetanus toxoid as the carrier protein aims to elicit robust immune responses. The tolerability of this vaccine is comparable to that of polysaccharide quadrivalent vaccines and monovalent meningococcal serogroup C vaccines. More importantly, the immunogenicity, antibody persistence and induction of immune memory aim to provide protection to a wide range of susceptible subjects.

Can we, should we, eradicate the meningococcus?

The eradication of infectious agents is an attractive means of disease control that, to date, has been achieved for only one human pathogen, the smallpox virus. The introduction of vaccines against Neisseria meningitidis into immunisation schedules, and particularly the conjugate polysaccharide vaccines which can interrupt transmission, raises the question of whether disease caused by this obligate human bacterium can be controlled, eliminated, or even eradicated. The limited number of meningococcal serogroups, lack of an animal reservoir, and importance of meningococcal disease are considerations in favour of eradication; however, the commensal nature of most infections, the high diversity of meningococcal populations, and the lack of comprehensive vaccines are all factors that suggest that this is not feasible. Indeed, any such attempt might be harmful by perturbing the human microbiome and its interaction with the immune system. On balance, the control and possible elimination of disease caused by particular disease-associated meningococcal genotypes is a more achievable and worthwhile goal.

Laboratory-based surveillance of Neisseria meningitidis isolates from disease cases in Latin American and Caribbean countries, SIREVA II 2006-2010

BACKGROUND

Published data on the epidemiology of meningococcal disease in Latin America and the Caribbean region is scarce and, when available, it is often published in Spanish and/or in non-peer-reviewed journals, making it difficult for the international scientific community to have access.

METHODS

Laboratory data on 4,735 Neisseria meningitidis strains was collected and reported by the National Reference Laboratories in 19 Latin American countries and the Caribbean Epidemiology Centre (CAREC) between 2006 and 2010 as part of the work carried out by the SIREVA II network. Serogroup and MIC to penicillin, rifampin and chloramphenicol were determined.

RESULTS

Isolates were mainly obtained from patients <5 years, but each year around 25% of isolates came from adult patients. Serogroup distribution was highly variable among countries. Serogroup C was the main cause of disease in Brazil; the majority of disease seen in the Southern cone was caused by serogroup B, but serogroup W135 strains have increased in recent years. In the Andean and Mexico, Central America and Caribbean regions, serogroups B and C were equally present, and serogroup Y was frequently isolated. Isolates were generally susceptible to chloramphenicol, penicillin and rifampin, but almost 60% of isolates characterized in Southern cone countries presented intermediate resistance to penicillin. Five rifampin-resistant isolates have been isolated in Uruguay and Brazil.

CONCLUSIONS

Serogroup distribution is highly variable among countries, but some geographic structuring can be inferred from these data. Epidemiological and laboratory data are scarce among Andean and Mexico, Central America and Caribbean countries. Evaluation and implementation of corrective measures on disease surveillance and reporting systems and the implementation of molecular diagnostic techniques and molecular characterization on meningococcal isolates are advised.

Serogroup A meningococcal conjugate vaccination in Burkina Faso: analysis of national surveillance data

BACKGROUND

An affordable, highly immunogenic Neisseria meningitidis serogroup A meningococcal conjugate vaccine (PsA-TT) was licensed for use in sub-Saharan Africa in 2009. In 2010, Burkina Faso became the first country to implement a national prevention campaign, vaccinating 11·4 million people aged 1-29 years. We analysed national surveillance data around PsA-TT introduction to investigate the early effect of the vaccine on meningitis incidence and epidemics.

METHODS

We examined national population-based meningitis surveillance data from Burkina Faso using two sources, one with cases and deaths aggregated at the district level from 1997 to 2011, and the other enhanced with results of cerebrospinal fluid examination and laboratory testing from 2007 to 2011. We compared mortality rates and incidence of suspected meningitis, probable meningococcal meningitis by age, and serogroup-specific meningococcal disease before and during the first year after PsA-TT implementation. We assessed the risk of meningitis disease and death between years.

FINDINGS

During the 14 year period before PsA-TT introduction, Burkina Faso had 148 603 cases of suspected meningitis with 17 965 deaths, and 174 district-level epidemics. After vaccine introduction, there was a 71% decline in risk of meningitis (hazard ratio 0·29, 95% CI 0·28-0·30, p<0·0001) and a 64% decline in risk of fatal meningitis (0·36, 0·33-0·40, p<0·0001). We identified a statistically significant decline in risk of probable meningococcal meningitis across the age group targeted for vaccination (62%, cumulative incidence ratio [CIR] 0·38, 95% CI 0·31-0·45, p<0·0001), and among children aged less than 1 year (54%, 0·46, 0·24-0·86, p=0·02) and people aged 30 years and older (55%, 0·45, 0·22-0·91, p=0·003) who were ineligible for vaccination. No cases of serogroup A meningococcal meningitis occurred among vaccinated individuals, and epidemics were eliminated. The incidence of laboratory-confirmed serogroup A N meningitidis dropped significantly to 0·01 per 100 000 individuals per year, representing a 99·8% reduction in the risk of meningococcal A meningitis (CIR 0·002, 95% CI 0·0004-0·02, p<0·0001).

INTERPRETATION

Early evidence suggests the conjugate vaccine has substantially reduced the rate of meningitis in people in the target age group, and in the general population because of high coverage and herd immunity. These data suggest that fully implementing the PsA-TT vaccine could end epidemic meningitis of serogroup A in sub-Saharan Africa.

FUNDING

None.

Resolution of a meningococcal disease outbreak from whole-genome sequence data with rapid Web-based analysis methods

The increase in the capacity and reduction in cost of whole-genome sequencing methods present the imminent prospect of such data being used routinely in real time for investigations of bacterial disease outbreaks. For this to be realized, however, it is necessary that generic, portable, and robust analysis frameworks be available, which can be readily interpreted and used in real time by microbiologists, clinicians, and public health epidemiologists. We have achieved this with a set of analysis tools integrated into the PubMLST.org website, which can in principle be used for the analysis of any pathogen. The approach is demonstrated with genomic data from isolates obtained during a well-characterized meningococcal disease outbreak at the University of Southampton, United Kingdom, that occurred in 1997. Whole-genome sequence data were collected, de novo assembled, and deposited into the PubMLST Neisseria BIGSdb database, which automatically annotated the sequences. This enabled the immediate and backwards-compatible classification of the isolates with a number of schemes, including the following: conventional, extended, and ribosomal multilocus sequence typing (MLST, eMLST, and rMLST); antigen gene sequence typing (AGST); analysis based on genes conferring antibiotic susceptibility. The isolates were also compared to a reference isolate belonging to the same clonal complex (ST-11) at 1,975 loci. Visualization of the data with the NeighborNet algorithm, implemented in SplitsTree 4 within the PubMLST website, permitted complete resolution of the outbreak and related isolates, demonstrating that multiple closely related but distinct strains were simultaneously present in asymptomatic carriage and disease, with two causing disease and one responsible for the outbreak itself.

Evaluation of meningococcal serogroup C conjugate vaccine programs in Canadian children: interim analysis

BACKGROUND

To assess antibody titers afforded by meningococcal C- (MenC) tetanus toxoid conjugate vaccine at 12 months of age in three different immunization schedules.

METHODS

This prospective study included three similar cohorts of healthy infants from 1-dose, 2-dose and 3-dose MenC infant immunization programs. Infants were enrolled at 12 months of age and given the final scheduled dose of MenC-tetanus toxoid conjugate vaccine with sera collected prior to and 1 month after the vaccination. Serum bactericidal activity (SBA) titers ≥ 1:8 were considered protective.

RESULTS

Before the 12 month dose, participants had significantly different protective titers according to the number of prior doses received: 100% (95% CI 97.6-100%) of infants who had 2 prior doses (at 2 and 4 months) were protected compared to 84.0% (76.7-89.3%) of participants with one dose (at 2 months) and 27.6% (21.0-35.4%) of unvaccinated infants. All subjects were protected after the 12 month MenC dose, but titers were higher with prior priming.

CONCLUSIONS

Two MenC doses given in infancy afford optimal protection during the first year of life; however, substantial protection was seen after one dose at 2 months.