Serotype replacement in disease after pneumococcal vaccination

Activation of memory Th17 cells by domain 4 pneumolysin in human nasopharynx-associated lymphoid tissue and its association with pneumococcal carriage

Pneumococcal carriage is common in children that may account for the high incidence of disease in this age group. Recent studies in animals suggest an important role for CD4+ T cells, T helper type 17 (Th17) cells in particular, in pneumococcal clearance. Whether this Th17-mediated mechanism operates in humans and what pneumococcal components activate Th17 are unknown. We investigated the ability of domain 4 pneumolysin (D4Ply) to activate CD4+ T cells including Th17 in human nasopharynx-associated lymphoid tissue (NALT) and peripheral blood. We show that D4Ply elicited a prominent CD4+ T-cell proliferative response. More importantly, D4Ply elicited a significant memory Th17 response in NALT, and a moderate response in peripheral blood mononuclear cells (PBMCs). This D4Ply-elicited memory Th17 response was more marked in carriage- than in carriage+ children in both NALT and PBMCs. In contrast, no difference was shown in D4Ply-induced Th1 response between the two groups. We also show D4Ply activated human monocytes and murine macrophages that was in part dependent on Toll-like receptor 4 (TLR-4). Our results support a protective role of Th17 against pneumococcal carriage in human nasopharynx, and identify a novel property of D4Ply to activate Th17 in NALT that may offer an attractive vaccine candidate in intranasal immunization against pneumococcal infection.

Investigating the effects of probiotics on pneumococcal colonization using an in vitro adherence assay

Adherence of Streptococcus pneumoniae (the pneumococcus) to the epithelial lining of the nasopharynx can result in colonization and is considered a prerequisite for pneumococcal infections such as pneumonia and otitis media. In vitro adherence assays can be used to study the attachment of pneumococci to epithelial cell monolayers and to investigate potential interventions, such as the use of probiotics, to inhibit pneumococcal colonization. The protocol described here is used to investigate the effects of the probiotic Streptococcus salivarius on the adherence of pneumococci to the human epithelial cell line CCL-23 (sometimes referred to as HEp-2 cells). The assay involves three main steps: 1) preparation of epithelial and bacterial cells, 2) addition of bacteria to epithelial cell monolayers, and 3) detection of adherent pneumococci by viable counts (serial dilution and plating) or quantitative real-time PCR (qPCR). This technique is relatively straightforward and does not require specialized equipment other than a tissue culture setup. The assay can be used to test other probiotic species and/or potential inhibitors of pneumococcal colonization and can be easily modified to address other scientific questions regarding pneumococcal adherence and invasion.

Characterization of protective extracellular membrane-derived vesicles produced by Streptococcus pneumoniae

Extracellular vesicles are produced by many pathogenic microorganisms and have varied functions that include secretion and release of microbial factors, which contribute to virulence. Very little is known about vesicle production by Gram-positive bacteria, as well as their biogenesis and release mechanisms. In this work, we demonstrate the active production of vesicles by Streptococcus pneumoniae from the plasma membrane, rather than being a product from cell lysis. We biochemically characterized them by proteomics and fatty acid analysis, showing that these vesicles and the plasma membrane resemble in essential aspects, but have some differences: vesicles are more enriched in lipoproteins and short-chain fatty acids. We also demonstrate that these vesicles act as carriers of surface proteins and virulence factors. They are also highly immunoreactive against human sera and induce immune responses that protect against infection. Overall, this work provides insights into the biology of this important Gram-positive human pathogen and the role of extracellular vesicles in clinical applications.

BIOLOGICAL SIGNIFICANCE

Pneumococcus is one of the leading causes of bacterial pneumonia worldwide in children and the elderly, being responsible for high morbidity and mortality rates in developing countries. The augment of pneumococcal disease in developed countries has raised major public health concern, since the difficulties to treat these infections due to increasing antibiotic resistance. Vaccination is still the best way to combat pneumococcal infections. One of the mechanisms that bacterial pathogens use to combat the defense responses of invaded hosts is the production and release of extracellular vesicles derived from the outer surface. Little is known about this phenomenon in Gram-positives. We show that pneumococcus produces membrane-derived vesicles particularly enriched in lipoproteins. We also show the utility of pneumococcal vesicles as a new type of vaccine, as they induce protection in immunized mice against infection with a virulent strain. This work will contribute to understand the role of these structures in important biological processes such as host-pathogen interactions and prevention of human disease.

A randomized clinical trial of the immunogenicity of 7-valent pneumococcal conjugate vaccine compared to 23-valent polysaccharide vaccine in frail, hospitalized elderly

BACKGROUND

Elderly people do not mount strong immune responses to vaccines. We compared 23-valent capsular polysaccharide (23vPPV) alone versus 7-valent conjugate (PCV7) vaccine followed by 23vPPV 6 months later in hospitalized elderly.

METHODS

Participants were randomized to receive 23vPPV or PCV7-23vPPV. Antibodies against serotypes 3, 4, 6A, 6B, 9V, 14, 18C, 19A, 19F, 23F were measured by enzyme-linked immunosorbent (ELISA) and opsonophagocytic (OPA) assays at baseline, 6 months and 12 months.

RESULTS

Of 312 recruited, between 40% and 72% of subjects had undetectable OPA titres at baseline. After one dose, PCV7 recipients had significantly higher responses to serotypes 9V (both assays) and 23F (OPA only), and 23vPPV recipients had significantly higher responses to serotype 3 (ELISA), 19F and 19A (OPA only). In subjects with undetectable OPA titres at baseline, a proportionately greater rise in OPA titre (P<0.01) was seen for all serotypes after both vaccines. The GMT ratio of OPA was significantly higher at 12 months in the PCV7-23vPPV group for serotypes 6A, 9V, 18C and 23F. OPA titre levels for these serotypes increased moderately after 6 months, whereas immunity waned in the 23vPPV only arm.

CONCLUSION

We did not show overwhelming benefit of one vaccine over the other. Low baseline immunity does not preclude a robust immune response, reiterating the importance of vaccinating the frail elderly. A schedule of PCV7-23vPPV prevents waning of antibody, suggesting that both vaccines could be useful in the elderly. Follow up studies are needed to determine persistence of immunity.

TRIAL REGISTRATION

The Australian Clinical Trials Registry ACTRN12607000387426.

Vaccination with a Streptococcus pneumoniae trivalent recombinant PcpA, PhtD and PlyD1 protein vaccine candidate protects against lethal pneumonia in an infant murine model

Streptococcus pneumoniae infections continue to cause significant worldwide morbidity and mortality despite the availability of efficacious serotype-dependent vaccines. The need to incorporate emergent strains expressing additional serotypes into pneumococcal polysaccharide conjugate vaccines has led to an identified need for a pneumococcal protein-based vaccine effective against a broad scope of serotypes. A vaccine consisting of several conserved proteins with different functions during pathogenesis would be preferred. Here, we investigated the efficacy of a trivalent recombinant protein vaccine containing pneumococcal choline-binding protein A (PcpA), pneumococcal histidine triad D (PhtD), and genetically detoxified pneumolysin (PlyD1) in an infant mouse model. We found the trivalent vaccine conferred protection from lethal pneumonia challenges using serotypes 6A and 3. The observed protection with trivalent PcpA, PhtD, and PlyD1 vaccine in infant mice supports the ongoing study of this candidate vaccine in human infant clinical trials.

Optimising assessments of the epidemiological impact in The Netherlands of paediatric immunisation with 13-valent pneumococcal conjugate vaccine using dynamic transmission modelling

This work is the first attempt to quantify the overall effects of a 13-valent pneumococcal conjugate vaccine (PCV13) vaccination programme in the Dutch population taking into account all the direct and indirect effects of the vaccine on invasive pneumococcal disease. Using available Dutch data, a dynamic transmission model for the spread of pneumococci and potential subsequent invasive pneumococcal disease has been adapted to the Dutch setting. Overall, invasive pneumococcal disease cases in the Netherlands are predicted to decrease from a pre-vaccination level of 2623 cases annually to 2475, 2289, 2185, 2179, and 2178 cases annually 5-, 10-, 20-, 30-, and 40-years, respectively, post-vaccination. Therefore, vaccination with PCV13 in the Netherlands is predicted to lower invasive pneumococcal disease cases per year by up to 445 cases in the medium- to long-term. The results are quite robust for the sensitivity analyses performed on the parameters that regulate herd immunity and competition between vaccine and non-vaccine types.

Early impact of sequential introduction of 7-valent and 13-valent pneumococcal conjugate vaccine on IPD in Israeli children <5 years: an active prospective nationwide surveillance

BACKGROUND

The 7-valent pneumococcal conjugated vaccine (PCV7) was introduced to the Israeli national immunization plan (NIP) in July 2009 (administered at age 2, 4 and 12 months), with a fast reduction of invasive pneumococcal disease (IPD) caused by PCV7 serotypes. Starting in November 2010, PCV13 gradually replaced PCV7.

AIM

To report the impact of PCV7/PCV13 sequential introduction on IPD in Israeli children <5 years.

METHODS

An ongoing nationwide, prospective, population-based, active surveillance. All IPD episodes (Streptococcus pneumoniae isolated from blood and/or cerebrospinal fluid) from July 2004 through June 2013 were included.

RESULTS

Overall, 2670 IPD episodes were recorded. Incidence of IPD caused by PCV7+6A serotypes during the PCV13 period vs. pre-PCV period decreased by 95% (Incidence Rate Ratio [IRR]=0.05; 95% CI=0.03-0.09). This reduction was observed in a two-step manner: 90% in the PCV7-period and further 5% in the PCV13-period. The rates of IPD caused by the 5 additional PCV13-serotypes (1, 3, 5, 7F, 19A; 5VT) increased initially by 47%, but subsequently decreased by 79%, resulting in an overall 70% reduction during the entire study period (IRR=0.30; 0.21-0.44). A two-fold increase in non-PCV13 serotypes IPD was observed (IRR=2.43; 1.73-3.66). In total, a 63% reduction of all-serotype IPD episodes was observed in children <5 years (69% and 48% in children <2 and 2-4 years old, respectively).

CONCLUSIONS

After initiation of PCV NIP, a rapid and substantial 2-step IPD reduction was observed in children <5 years. The serotype-specific rate reduction reflected the sequential introduction of PCV7/PCV13.

Reduced incidence of invasive pneumococcal disease after introduction of the 13-valent conjugate vaccine in Navarre, Spain, 2001-2013

Pneumococcal conjugate vaccines (PCVs) were licensed for use in children and became available for private purchase in Spain in 2001 (PCV7), 2009 (PCV10) and 2010 (PCV13). This study evaluates changes in the incidence of invasive pneumococcal disease (IPD) and the pattern of serotypes isolated in Navarre, Spain, between the period of use of PCV7 (2004-2009) and that of PCV13 (2010-2013). The percentage of children <2 years who received at least one dose of PCV in these periods ranged from 25 to 61% and 61 to 78%, respectively. Between the periods 2004-2009 and 2010-2013 IPD incidence declined by 37%, from 14.9 to 9.4 cases/100,000 inhabitants (p<0.001). In children <5 years it fell by 69% (p<0.001), in persons aged 5-64 years, by 34% (p<0.001), and in those ≥ 65, by 23% (p=0.024). The incidence of cases due to PCV13 serotypes declined by 81% (p<0.001) in children <5 years and by 52% (p<0.001) in the whole population. No significant changes were seen in the distribution of clinical presentations or in disease severity. The incidence of IPD has declined and the pattern of serotypes causing IPD has changed notably in children and moderately in adults following the replacement of PCV7 by PCV13.

Invasive pneumococcal diseases in children and adolescents--a single centre experience

Background

S. pneumoniae is a major cause of meningitis, pneumonia and sepsis in children. In 2006 universal pneumococcal vaccination was recommended in Germany for all children up to their second birthday. We have compared the prevalence and outcome of IPD at a single hospital before and after the introduction of vaccination.

Findings

55 cases of IPD were identified over an 11 year period. Almost half of the patients were younger than 2 years of age. Most of the children were affected by pneumonia. The second highest incidence seen was for meningitis and sepsis. 17 patients exhibited additional complications. Significant pre-existing and predisposing disorders, such as IRAK 4 defect, ALPS or SLE were identified in 4 patients. Complete recovery was seen in 78% of affected children; 11% had a fatal outcome and 11% suffered from long term complications. Only 31% overall had been vaccinated. The most common serotype was 14. Serotypes not covered by any of the current vaccines were also found. Antibiotic treatment commenced with cephalosporins in over 90%.

Conclusion

Frequency of IPD in our hospital did not decrease after initiation of the pneumococcal vaccination. This might be due to vaccinations not being administered satisfactorily as well as to poor education about the need of the vaccination. Pre-existing diseases must be monitored and treated accordingly and rare deficiencies taken into account when IPD takes a foudroyant course. In addition, antibiotic stewardship has been initiated at this hospital centre as a consequence of the high cephalosporin use detected in this study.

Toll-like receptor 2-dependent protection against pneumococcal carriage by immunization with lipidated pneumococcal proteins

Infections with Streptococcus pneumoniae cause substantial morbidity and mortality, particularly in children in developing nations. Polysaccharide-conjugate vaccines provide protection against both invasive disease and colonization, but their use in developing countries is limited by restricted serotype coverage and expense of manufacture. Using proteomic screens, we recently identified several antigens that protected mice from pneumococcal colonization in a CD4(+) T cell- and interleukin-17A (IL-17A)-dependent manner. Since several of these proteins are lipidated, we hypothesized that their immunogenicity and impact on colonization are in part due to activation of Toll-like receptor 2 (TLR2), a receptor for lipoproteins. Here we show that lipidated versions of the antigens elicited significantly higher activation of both human embryonic kidney cells engineered to express TLR2 (HEK-TLR2) and wild-type (WT) murine macrophages than nonlipidated mutant antigens. Lipoprotein-stimulated secretion of proinflammatory cytokines was ∼10× to ∼100× lower in murine TLR2-deficient macrophages than in WT macrophages. Subcutaneous immunization of C57BL/6 mice with protein subunit vaccines containing one or two of these lipoproteins or protein fusion constructs bearing N-terminal lipid adducts elicited a robust IL-17A response and a significant reduction in colonization compared with immunization with alum alone. In contrast, immunization of Tlr2(-/-) mice elicited no detectable IL-17A response and no protection against pneumococcal colonization. These experiments suggest that the lipid moieties enhance the immunogenicity and protective efficacy of pneumococcal TH17 antigens through activation of TLR2. Thus, triggering TLR2 with an antigen-specific protein subunit formulation is a possible strategy for the development of a serotype-independent pneumococcal vaccine that would reduce pneumococcal carriage.

On the nature of pleural involvement in necrotizing pneumonia: a report of two cases of life threatening late complications

Suppurative complications of pneumonia such as empyema, lung abscess, pyopneumothorax, and necrotizing pneumonia (NP) are uncommon in children. Over the last decade an increasing incidence of NP has been reported. Streptococcus pneumoniae continues to be the predominant causative organism of NP, and while sporadic cases were reported prior to routine administration of heptavalent pneumococcal vaccine, a marked increase in NP appears to relate to replacement pneumococcal strains. Pleural involvement is almost universal in NP, and the course of pleural disease often determines its duration and outcome, particularly as it relates to complication of bronchopleural fistula. Cavities are formed in NP within the lung parenchyma and in the pleural space as the fibrosing pleural process organizes. The similarity of the radiologic appearance of parenchymal and pleural space cavities often makes the differentiation of pneumatocele versus residua of loculated pneumothorax challenging. The prevailing perception from most reports on childhood NP is of a favorable outcome with conservative approach. We report two pediatric cases with pneumonia who presented with prolonged fever despite antibiotic treatment, eventually diagnosed with NP. After stabilization on prolonged IV antibiotics, and weeks after discharge, they presented with unexpected acute respiratory failure due to a life-threatening tension air collection. In this article we discuss the nature of NP, its typical presentation, benign course and outcome, albeit its potential to cause serious late complications in the light of our recent experiences. Increasing awareness of such complications will result in more careful follow-up and in providing appropriate recommendations to parents of patients recovering from NP.

Tailoring the Immune Response via Customization of Pathogen Gene Expression

The majority of studies focused on the construction and reengineering of bacterial pathogens have mainly relied on the knocking out of virulence factors or deletion/mutation of amino acid residues to then observe the microbe's phenotype and the resulting effect on the host immune response. These knockout bacterial strains have also been proposed as vaccines to combat bacterial disease. Theoretically, knockout strains would be unable to cause disease since their virulence factors have been removed, yet they could induce a protective memory response. While knockout strains have been valuable tools to discern the role of virulence factors in host immunity and bacterial pathogenesis, they have been unable to yield clinically relevant vaccines. The advent of synthetic biology and enhanced user-directed gene customization has altered this binary process of knockout, followed by observation. Recent studies have shown that a researcher can now tailor and customize a given microbe's gene expression to produce a desired immune response. In this commentary, we highlight these studies as a new avenue for controlling the inflammatory response as well as vaccine development.

Capsular serotyping of Streptococcus pneumoniae using the Quellung reaction

There are over 90 different capsular serotypes of Streptococcus pneumoniae (the pneumococcus). As well as being a tool for understanding pneumococcal epidemiology, capsular serotyping can provide useful information for vaccine efficacy and impact studies. The Quellung reaction is the gold standard method for pneumococcal capsular serotyping. The method involves testing a pneumococcal cell suspension with pooled and specific antisera directed against the capsular polysaccharide. The antigen-antibody reactions are observed microscopically. The protocol has three main steps: 1) preparation of a bacterial cell suspension, 2) mixing of cells and antisera on a glass slide, and 3) reading the Quellung reaction using a microscope. The Quellung reaction is reasonably simple to perform and can be applied wherever a suitable microscope and antisera are available.

Efficacy and effectiveness of extended-valency pneumococcal conjugate vaccines

The 7-valent pneumococcal protein conjugate vaccine (PCV7) has been shown to be highly efficacious against invasive pneumococcal diseases and effective against pneumonia and in reducing otitis media. The introduction of PCV7 has resulted in major changes in the epidemiology of pneumococcal diseases. However, pneumococcal vaccines induce serotype-specific immunity, and a relative increase in non-vaccine serotypes has been reported following the widespread use of PCV7, leading to a need for extended serotype coverage for protection. PCV10 and PCV13 have been licensed on the basis of noninferiority of immunogenicity compared to a licensed conjugate vaccine. In this article, we aimed to review important data regarding the efficacy and effectiveness of the extended-coverage PCVs published or reported thus far and to discuss future implications for pneumococcal vaccines in Korea. After the introduction of PCV10 and PCV13, within a short period of time, evidence of protection conferred by these vaccines against invasive and mucosal infections caused by most of the serotypes included in the vaccines is accumulating. The choice of vaccine should be based on the changes in the dynamics of pneumococcal serotype distribution and diseases in the region where the vaccines are to be used. Continuous surveillance is essential for the appropriate use of pneumococcal vaccines and evaluation of the impact of PCVs on pneumococcal diseases.

Optimal serotype compositions for Pneumococcal conjugate vaccination under serotype replacement

Pneumococcal conjugate vaccination has proved highly effective in eliminating vaccine-type pneumococcal carriage and disease. However, the potential adverse effects of serotype replacement remain a major concern when implementing routine childhood pneumococcal conjugate vaccination programmes. Applying a concise predictive model, we present a ready-to-use quantitative tool to investigate the implications of serotype replacement on the net effectiveness of vaccination against invasive pneumococcal disease (IPD) and to guide in the selection of optimal vaccine serotype compositions. We utilise pre-vaccination data on pneumococcal carriage and IPD and assume partial or complete elimination of vaccine-type carriage, its replacement by non-vaccine-type carriage, and stable case-to-carrier ratios (probability of IPD per carriage episode). The model predicts that the post-vaccination IPD incidences in Finland for currently available vaccine serotype compositions can eventually decrease among the target age group of children <5 years of age by 75%. However, due to replacement through herd effects, the decrease among the older population is predicted to be much less (20–40%). We introduce a sequential algorithm for the search of optimal serotype compositions and assess the robustness of inferences to uncertainties in data and assumptions about carriage and IPD. The optimal serotype composition depends on the age group of interest and some serotypes may be highly beneficial vaccine types in one age category (e.g. 6B in children), while being disadvantageous in another. The net effectiveness will be improved only if the added serotype has a higher case-to-carrier ratio than the average case-to-carrier ratio of the current non-vaccine types and the degree of improvement in effectiveness depends on the carriage incidence of the serotype. The serotype compositions of currently available pneumococcal vaccines are not optimal and the effectiveness of vaccination in the population at large could be improved by including new serotypes in the vaccine (e.g. 22 and 9N).

The bacterial pathogen Streptococcus pneumoniae (pneumococcus) is a major contributor to child mortality worldwide. Hence, effective pneumococcal vaccination programmes are globally among the most cost-effective public health interventions. Three different conjugate vaccine compositions, targeting 7, 10 or 13 pneumococcal serotypes, have been used in infant vaccination programmes. The use of these vaccines has both decreased the disease burden and changed the patterns of pneumococcal carriage in locations where they have been in use. However, due to serotype replacement, where the lost vaccine serotype carriage is replaced by carriage of the non-vaccine serotypes, the net effect of vaccination on the disease burden has generally been milder than expected. Here, we apply a concise model for serotype replacement and present a ready-to-use tool for the prediction of patterns in post-vaccination pneumococcal incidence of carriage and invasive disease. We introduce a sequential algorithm for the identification of the most optimal additional serotypes to current vaccine formulations and demonstrate how differences in the invasiveness across serotypes imply that the disease incidence may either decrease or increase after vaccination. The methods we outline have direct relevance in decision making while reviewing the performance of the current pneumococcal vaccination programmes.

Respiratory infection and otitis media visits in relation to pneumococcal conjugate vaccine use in Saskatchewan

BACKGROUND

In Saskatchewan, pneumococcal conjugate vaccination (PCV) was offered to high-risk children in 2002 and to all infants in 2005.

OBJECTIVE

To describe trends in the frequency of medical visits for lower respiratory tract infection (LRI) and otitis media (OM) in relation to PCV use during the period 1990 to 2008.

METHODS

Statistics regarding the number of children covered by the health insurance plan, PCV administration, and medical visits with a diagnostic code associated with LRI and OM were provided by Saskatchewan Health. Monthly rates were analyzed using dynamic state space models.

RESULTS

In all series, there was a marked seasonal cycle and some higher-than-expected winter peak values, possibly associated with epidemics of specific respiratory viruses. Three abrupt decreases in baseline rate were observed for LRI and the final one, in February 2007, could be related to the increased proportion of children vaccinated with PCV. There was no statistical correlation between PCV use and OM visit frequency.

CONCLUSION

Many environmental, biological and administrative factors may influence health services use, and an effect of low magnitude of a particular vaccine pertaining to nonspecific outcomes could be obscured in time-series analyses.

Identification of potential vaccine candidates against Streptococcus pneumoniae by reverse vaccinology approach

In the past few decades, genome-based approaches have contributed significantly to vaccine development. Our aim was to identify the most conserved and immunogenic antigens of Streptococcus pneumoniae, which can be potential vaccine candidates in the future. BLASTn was done to identify the most conserved antigens. PSORTb 3.0.2 was run to predict the subcellular localization of the proteins. B cell epitope prediction was done for the immunogenicity testing. Finally, BLASTp was done for verifying the extent of similarity to human proteome to exclude the possibility of autoimmunity. Proteins failing to comply with the set parameters were filtered at each step. Based on the above criteria, out of the initial 22 pneumococcal proteins selected for screening, pavB and pullulanase were the most promising candidate proteins.

Impact of 2+1 pneumococcal conjugate vaccine program in the province of Quebec, Canada

BACKGROUND

Quebec was the first jurisdiction in the world to recommend a 3-dose (2+1) pneumococcal conjugate vaccine (PCV) schedule. The program was implemented in December 2004 with a catch-up for children <5 years. PCV-7 was first used and replaced, respectively, by PCV-10 in 2009 and by PCV-13 in 2011.

METHODS

Cases of invasive pneumococcal disease (IPD) notified to public health authorities and isolates submitted to the provincial reference laboratory during the period 2000-2011 were analyzed.

RESULTS

IPD incidence in children <5 years was 67/100,000 in 2001-2004, and decreased to 32/100,000 in 2007-2009 following PCV-7 implementation (p<0.01). A further decrease to 24/100,000 was observed in 2010-2011 following PCV-10 introduction (p<0.01). PCV-7 serotypes represented 82% of the total IPD cases in 2000-2004 and elimination was achieved in 2011. Main emerging serotypes were 19A and 7F. Children exposed to the PCV-10 experienced lower IPD rates and all serotypes contributed to the decline, mainly 7F and 19A. In adults, a decrease of low magnitude was observed in 2005-2006 but rates in 2007-2009 were higher than in the prevaccination period.

CONCLUSIONS

A 3-dose PCV schedule with high uptake is highly effective and should be recommended worldwide. Serotype replacement eroded benefits especially in adults. PCV-10 introduction had an effect and the impact of PCV-13 use remains to be evaluated.

A novel high-throughput method for molecular serotyping and serotype-specific quantification of Streptococcus pneumoniae using a nanofluidic real-time PCR system

Serotype-specific quantification data are essential for elucidating the complex epidemiology of Streptococcus pneumoniae and evaluating pneumococcal vaccine efficacy. Various PCR-based assays have been developed to circumvent the drawback of labour-intensive and time-consuming culture-based procedures for serotype determination and quantification of pneumococcus. Here, we applied a nanofluidic real-time PCR system to establish a novel assay. Twenty-nine primer pairs, 13 of which were newly designed, were selected for the assay to cover 50 serotypes including all currently available conjugate and polysaccharide vaccine serotypes. All primer pairs were evaluated for their sensitivity, specificity, efficiency, repeatability, accuracy and reproducibility on the Fluidigm Biomark HD System, a nanofluidic real-time PCR system, by drawing standard curves with a serial dilution of purified DNA. We applied the assay to 52 nasopharyngeal swab samples from patients with pneumonia confirmed by chest X-ray to validate its accuracy. Minimum detection levels of this novel assay using the nanofluidic real-time PCR system were comparable to the conventional PCR-based assays (between 30 and 300 copies per reaction). They were specific to their targets with good repeatability (sd of copy number of 0.1), accuracy (within ±0.1 fold difference in log10 copy number) and reproducibility (sd of copy number of 0.1). When artificially mixed DNA samples consisting of multiple serotypes in various ratios were tested, all the serotypes were detected proportionally, including a minor serotype of one in 1000 copies. In the nasopharyngeal samples, the PCR system detected all the culture-positive samples and 22 out of 23 serotypes identified by the conventional method were matched with PCR results. We conclude that this novel assay, which is able to differentially quantify 29 pneumococcus groups for 45 test samples in a single run, is applicable to the large-scale epidemiological study of pneumococcus. We believe that this assay will facilitate our understanding of the roles of serotype-specific bacterial loads and implications of multiple serotype detections in pneumococcal diseases.

Age-dependent prevalence of nasopharyngeal carriage of streptococcus pneumoniae before conjugate vaccine introduction: a prediction model based on a meta-analysis

Introduction

Data on the prevalence of nasopharyngeal carriage of S.pneumoniae in all age groups are important to help predict the impact of introducing pneumococcal conjugate vaccines (PCV) into routine infant immunization, given the important indirect effect of the vaccine. Yet most carriage studies are limited to children under five years of age. We here explore the association between carriage prevalence and serotype distribution in children aged ≥5 years and in adults compared to children.

Methods

We conducted a systematic review of studies providing carriage estimates across age groups in healthy populations not previously exposed to PCV, using MEDLINE and Embase. We used Bayesian linear meta-regression models to predict the overall carriage prevalence as well as the prevalence and distribution of vaccine and nonvaccine type (VT and NVT) serotypes in older age groups as a function of that in <5 y olds.

Results

Twenty-nine studies compromising of 20,391 individuals were included in the analysis. In all studies nasopharyngeal carriage decreased with increasing age. We found a strong positive linear association between the carriage prevalence in pre-school childen (<5 y) and both that in school aged children (5–17 y olds) and in adults. The proportion of VT serotypes isolated from carriers was consistently lower in older age groups and on average about 73% that of children <5 y among 5–17 y olds and adults respectively. We provide a prediction model to infer the carriage prevalence and serotype distribution in 5–17 y olds and adults as a function of that in children <5 years of age.

Conclusion

Such predictions are helpful for assessing the potential population-wide effects of vaccination programmes, e.g. via transmission models, and thus assist in the design of future pneumococcal conjugate vaccination strategies.

Serotypes and antibiotic resistance of non-invasive Streptococcus pneumoniae circulating in pediatric hospitals in Moscow, Russia

BACKGROUND

Pneumococcal infections remain a major medical problem associated with high morbidity and mortality. Moreover, the resistance of Streptococcus pneumoniae to conventional antibiotics is constantly growing. The implementation of pneumococcal conjugate vaccines (PCVs) in the last decade has dramatically reduced the incidence of the vaccine type-associated invasive pneumococcal diseases in many countries. However, information on the seroepidemiology of S. pneumoniae in Russia is limited.

METHODS

We report the results of serotyping and antibiotic susceptibility testing performed on 863 non-invasive pneumococcal isolates collected prospectively in 2009-2013 from children (median age 3.5 years) who sought medical care at five pediatric hospitals in Moscow. The isolates were recovered from the nasopharynx (71.2%), middle ear fluid (14.3%), and lower respiratory tract specimens (13.6%).

RESULTS

In total, we identified 45 different serotypes. The six leading serotypes (prevalence >5%) included 19F (21.7%), 6B (12.8%), 23F (10.1%), 14 (9.0%), 6A (8.4%), and 3 (7.5%). Serotype 19A isolates had a prevalence of 2.3%. The proportion of PCV-13 serotypes was 78%; the coverage by PCV-7 was 58.2% and was similar to that of PCV-10 (59.8%). The rate of multidrug-resistant pneumococci (i.e., resistant to ≥3 antimicrobials) was 22%. The majority of the multidrug-resistant isolates were serotype 6B, 14, 19A, and 19F. Penicillin non-susceptibility was displayed by 28% of the isolates. The resistance rate to erythromycin was 26%. Among the examined erythromycin-resistant strains, 54% had the erm(B) gene and 13% had the mef gene as a single resistance determinant, whereas both determinants were found in 31% of these strains.

CONCLUSIONS

Our data predict a good coverage of the circulating S. pneumoniae by the PCVs and could be useful for evaluating the serotype distribution in support of the introduction of PCV in Russia. In addition, the antimicrobial resistance rate of S. pneumoniae in Russia is substantial, and the emergence of pneumococcal strains with a dual macrolide resistance mechanism is alarming.

In vitro biofilm formation by Streptococcus pneumoniae as a predictor of post-vaccination emerging serotypes colonizing the human nasopharynx

The increasing use of the 7-valent pneumococcal conjugate vaccine has been accompanied by the rise of non-vaccine serotypes colonizing the human nasopharynx. The vast majority of infections are caused by microorganisms that grow in biofilms. It has recently been shown that the formation of Streptococcus pneumoniae biofilms in vivo and in vitro is hindered by the presence of capsular polysaccharide. The biofilm-forming capacity of pneumococcal clinical isolates with different types of capsular polysaccharide and various isogenic transformants was examined. Strains of serotypes 19A and 19F, but not 19B and 19C, formed ≥ 80% of the quantity of biofilm associated with a non-encapsulated control strain. Strains of serogroup 6 also showed significant biofilm-forming capacity. The capsules of serotypes 19A and 19F, and serogroup 6 contain the disaccharides α-D-Glcp-(1→2)-α-L-Rhap-(1→ and α-D-Glcp-(1→3)-α-L-Rhap-(1→. Serotype 18A and serotypes 18B/18C have very similar capsular disaccharides: α-D-GlcpNAc-(1→3)-β-L-Rhap-(1→ and α-D-Glcp-(1→3)-β-L-Rhap-(1→ respectively. However, the strains of serogroup 18 showed impaired biofilm formation. These results indicate that the chemical composition/structure of the capsular polysaccharide is crucial to the biofilm-forming capacity of pneumococcal serotypes. Testing of the in vitro biofilm-forming ability of isogenic transformants expressing different capsular polysaccharides may help predict the emergence of colonizing, non-vaccine serotypes.

Serotype and genotype distribution among invasive Streptococcus pneumoniae isolates in Colombia, 2005-2010

In Colombia, a laboratory-based surveillance of invasive Streptococcus pneumoniae isolates as part of SIREVA II PAHO has been conducted since 1994. This study describes the serotype distribution, antimicrobial resistance, and genetic relationships of pneumococcal isolates recovered in Colombia from 2005 to 2010. In this study, demographic data of invasive S. pneumoniae isolates were analyzed, and antimicrobial susceptibility patterns were determined. Pulse field gel electrophoresis (n = 629) and multilocus sequence typing (n = 10) were used to determine genetic relationship of isolates with minimal inhibitory concentration to penicillin ≥0.125 µg/mL. A total of 1775 isolates of S. pneumoniae were obtained. Fifteen serotypes accounted for 80.7% of isolates. Serotype 14 (23.1%) was the most frequent in the general population. Penicillin resistance was 30.7% in meningitis and 9.0% in non-meningitis. Clones Spain^6BST90, Spain^9VST156, Spain^23FST81, and Colombia^23FST338 were associated to isolates. Additionally, serotype 6A isolates were associated with ST460 and ST473, and 19A isolates with ST276, ST320, and ST1118. In conclusion, the surveillance program provided updated information of trends in serotype distribution, antimicrobial resistance and the circulation of clones in invasive pneumococcal diseases. These results could be helpful to understand the epidemiology of S. pneumoniae in Colombia, and provide a baseline to measure the impact of vaccine introduction.

Development of Streptococcus pneumoniae Vaccines Using Live Vectors

Streptococcus pneumoniae still causes severe morbidity and mortality worldwide, especially in young children and the elderly. Much effort has been dedicated to developing protein-based universal vaccines to conquer the current shortcomings of capsular vaccines and capsular conjugate vaccines, such as serotype replacement, limited coverage and high costs. A recombinant live vector vaccine delivering protective antigens is a promising way to achieve this goal. In this review, we discuss the researches using live recombinant vaccines, mainly live attenuated Salmonella and lactic acid bacteria, to deliver pneumococcal antigens. We also discuss both the limitations and the future of these vaccines.

Immunogenicity and safety of 23-valent pneumococcal polysaccharide vaccine as a booster dose in 12- to 18-month-old children primed with 3 doses of 7-valent pneumococcal conjugate vaccine

The current study examined the safety and immunogenicity of 23-valent pneumococcal capsular polysaccharide vaccine (Pneumo23(®) [PPV23], Sanofi Pasteur) as a booster dose in 12- to 18-month-old children primed with heptavalent pneumococcal vaccine (PCV7; Prevnar(®), Pfizer). This was a randomized, observer-blinded, 2-arm, controlled, multicenter phase III study performed in Thailand to assess and describe the immunogenicity and safety of PPV23 as a booster dose in children who had received the 3 primary doses of PCV7, the pneumococcal vaccine available during the study period. Children primed with 3 doses of PCV7 were randomized 1:1 to receive a booster immunization with PPV23 or PCV7. Pneumococcal antibody concentrations were measured by enzyme-linked immunosorbent assay and functional antibody levels by multiplex opsonophagocytosis assay on day 30. A total of 339 children were enrolled. Geometric mean serum antibody concentrations against serotypes common to PCV7 and PPV23 (4, 6B, 9V, 14, 18C, 19F, and 23F) increased in both groups but they were higher for serotypes 4, 9V, 18C, and 19F in the PPV23 group. Opsonization indices increased in both groups for all measured serotypes (1, 6B, 14, 19A, and 23F) and were higher for serotypes 6B, 14, and 23F in the PCV7 group and for serotypes 1 and 19A in PPV23 group. Solicited reactions and unsolicited adverse events were similar in the 2 groups and generally mild and transient. No treatment-related serious adverse events were reported. These results confirm that boosting with PPV23 is immunogenic and well tolerated in healthy toddlers primed with PCV7.

Pneumococcal antibody levels in children with PID receiving immunoglobulin

OBJECTIVES

Clinical data are lacking on optimal levels of specific antipneumococcal antibodies (PnPsAbs) in patients with primary immunodeficiency (PID) receiving intravenous immunoglobulin (IVIG) replacement. Objectives were to conduct a prospective multicenter study providing data on total immunoglobulin G (IgG) and peak/trough levels of PnPsAbs specifically targeting the 16 most prevalent pneumococcal serotypes in IVIG-treated children with PID; to compare trough PnPsAb levels with those measured in healthy adults and the IVIG product; and to evaluate PnPsAb protection correlates with thresholds based on World Health Organization.

METHODS

Patients received 7 consecutive IVIG infusions. Total IgG and PnPsAb levels were determined on plasma samples obtained before and after infusion.

RESULTS

Twenty-two children with PID were treated with IVIG (mean weekly dose: 0.10 g/kg). The mean trough and peak levels of total IgG were 7.77 and 13.93 g/L, respectively. Trough and peak geometric mean concentrations and distribution curves differed between serotypes and showed wide dispersion (0.17-7.96 µg/mL). In patients (89%-100%), antibodies against most serotypes reached trough levels ≥ 0.2 µg/mL, a threshold considered protective against invasive pneumococcal infection. For several serotypes, trough levels reached ≥ 1.0 to 1.3 µg/mL, the level found in adults. Trough geometric mean concentrations correlated well with the PnPsAb contents of the IVIG product.

CONCLUSIONS

In IVIG-treated children with PID, protective PnPsAb levels for most pathogenic serotypes were obtained. A correlation was observed between PnPsAb levels in patients and in the IVIG product. This offers the potential to improve infection prevention by adapting the IVIG product and dose according to epidemiology.

High nasopharyngeal carriage of non-vaccine serotypes in Western Australian aboriginal people following 10 years of pneumococcal conjugate vaccination

BACKGROUND

Invasive pneumococcal disease (IPD) continues to occur at high rates among Australian Aboriginal people. The seven-valent pneumococcal conjugate vaccine (7vPCV) was given in a 2-4-6-month schedule from 2001, with a 23-valent pneumococcal polysaccharide vaccine (23vPPV) booster at 18 months, and replaced with 13vPCV in July 2011. Since carriage surveillance can supplement IPD surveillance, we have monitored pneumococcal carriage in western Australia (WA) since 2008 to assess the impact of the 10-year 7vPCV program.

METHODS

We collected 1,500 nasopharyngeal specimens from Aboriginal people living in varied regions of WA from August 2008 until June 2011. Specimens were cultured on selective media. Pneumococcal isolates were serotyped by the quellung reaction.

RESULTS

Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis were carried by 71.9%, 63.2% and 63.3% respectively of children <5 years of age, and 34.6%, 22.4% and 27.2% of people ≥5 years. Of 43 pneumococcal serotypes identified, the most common were 19A, 16F and 6C in children <5 years, and 15B, 34 and 22F in older people. 7vPCV serotypes accounted for 14.5% of all serotypeable isolates, 13vPCV for 32.4% and 23vPPV for 49.9%, with little variation across all age groups. Serotypes 1 and 12F were rarely identified, despite causing recent IPD outbreaks in WA. Complete penicillin resistance (MIC ≥2µg/ml) was found in 1.6% of serotype 19A (5.2%), 19F (4.9%) and 16F (3.2%) isolates and reduced penicillin susceptibility (MIC ≥0.125µg/ml) in 24.9% of isolates, particularly 19F (92.7%), 19A (41.3%), 16F (29.0%). Multi-resistance to cotrimoxazole, tetracycline and erythromycin was found in 83.0% of 23F isolates. Among non-serotypeable isolates 76.0% had reduced susceptibility and 4.0% showed complete resistance to penicillin.

CONCLUSIONS

Ten years after introduction of 7vPCV for Aboriginal Australian children, 7vPCV serotypes account for a small proportion of carried pneumococci. A large proportion of circulating serotypes are not covered by any currently licensed vaccine.

Serotype distribution of invasive Streptococcus pneumoniae in Canada after the introduction of the 13-valent pneumococcal conjugate vaccine, 2010–2012

The introduction of the 7-valent pneumococcal vaccine (PCV7) in Canada was very effective in reducing invasive pneumococcal disease (IPD) in children; however, increases of non-PCV7 serotypes have subsequently offset some of these reductions. A 13-valent pneumococcal vaccine (PCV13) targeting additional serotypes was implemented between 2010 and 2011, and in 2012 changes in the incidence of disease and the distribution of IPD serotypes began to emerge. The incidence of IPD in children <5 years of age declined from 18.0 to 14.2 cases per 100 000 population between 2010 and 2012; however, the incidence in ages ≥5 years remained relatively unchanged over the 3-year period, at about 9.7 cases per 100 000 population. From 2010 to 2012, PCV13 serotypes declined significantly from 66% (224/339) to 41% (101/244, p < 0.001) in children <5 years of age, and from 54% (1262/2360) to 43% (1006/2353, p < 0.001) in children ≥5 years of age. Serotypes 19A, 7F, 3, and 22F were the most common serotypes in 2012, with 19A decreasing from 19% (521/2727) to 14% (364/2620, p < 0.001), 7F decreasing from 14% (389/2727) to 12% (323/2620, p = 0.04), and 22F increasing from 7% (185/2727) to 11% (279/2620, p < 0.001) since 2010. Serotype 3 increased from 7% (23/339) to 10% (24/244) in <5-year-olds (p = 0.22) over the 3-year period. The highest rates of antimicrobial resistance were observed with clarithromycin (23%), penicillin using meningitis breakpoints (12%), clindamycin (8%), and trimethoprim–sulfamethoxazole (6%). Shifts in the distribution of IPD serotypes and reductions in the incidence of disease suggest that current immunization programs in Canada are effective in reducing the burden of IPD in children. While we acknowledge the limited data on the effectiveness of the PCV13 vaccine, to our knowledge, this study represents one of the first descriptions of the potential impact of the PCV13 vaccine in the Canadian population. Continued surveillance will be important to recognize replacement serotypes, to determine the extent of herd immunity effects in nonpaediatric populations, and to assess the overall effectiveness of PCV13 in reducing IPD in Canada.

The impact of specific and non-specific immunity on the ecology of Streptococcus pneumoniae and the implications for vaccination

More than 90 capsular serotypes of Streptococcus pneumoniae coexist despite competing for nasopharyngeal carriage and a gradient in fitness. The underlying mechanisms for this are poorly understood and make assessment of the likely population impact of vaccination challenging. We use an individual-based simulation model to generalize widely used deterministic models for pneumococcal competition and show that in these models short-term serotype-specific and serotype non-specific immunity could constitute the mechanism governing between-host competition and coexistence. We find that non-specific immunity induces between-host competition and that serotype-specific immunity limits a type's competitive advantage and allows stable coexistence of multiple serotypes. Serotypes carried at low prevalence show high variance in carriage levels, which would result in apparent outbreaks if they were highly pathogenic. Vaccination against few serotypes can lead to elimination of the vaccine types and induces replacement by others. However, in simulations where the elimination of the targeted types is achieved only by a combination of vaccine effects and the competitive pressure of the non-vaccine types, a universal vaccine with similar-type-specific effectiveness can fail to eliminate pneumococcal carriage and offers limited herd immunity. Hence, if vaccine effects are insufficient to control the majority of serotypes at the same time, then exploiting the competitive pressure by selective vaccination can help control the most pathogenic serotypes.

Seasonal drivers of pneumococcal disease incidence: impact of bacterial carriage and viral activity

BACKGROUND

Winter-seasonal epidemics of pneumococcal disease provide an opportunity to understand the drivers of incidence. We sought to determine whether seasonality of invasive pneumococcal disease is caused by increased nasopharyngeal transmission of the bacteria or increased susceptibility to invasive infections driven by cocirculating winter respiratory viruses.

METHODS

We analyzed pneumococcal carriage and invasive disease data collected from children <7 years old in the Navajo/White Mountain Apache populations between 1996 and 2012. Regression models were used to quantify seasonal variations in carriage prevalence, carriage density, and disease incidence. We also fit a multivariate model to determine the contribution of carriage prevalence and RSV activity to pneumococcal disease incidence while controlling for shared seasonal factors.

RESULTS

The seasonal patterns of invasive pneumococcal disease epidemics varied significantly by clinical presentation: bacteremic pneumococcal pneumonia incidence peaked in late winter, whereas invasive nonpneumonia pneumococcal incidence peaked in autumn. Pneumococcal carriage prevalence and density also varied seasonally, with peak prevalence occurring in late autumn. In a multivariate model, RSV activity was associated with significant increases in bacteremic pneumonia cases (attributable percentage, 15.5%; 95% confidence interval [CI], 1.8%-26.1%) but was not associated with invasive nonpneumonia infections (8.0%; 95% CI, -4.8% to 19.3%). In contrast, seasonal variations in carriage prevalence were associated with significant increases in invasive nonpneumonia infections (31.4%; 95% CI, 8.8%-51.4%) but not with bacteremic pneumonia.

CONCLUSIONS

The seasonality of invasive pneumococcal pneumonia could be due to increased susceptibility to invasive infection triggered by viral pathogens, whereas seasonality of other invasive pneumococcal infections might be primarily driven by increased nasopharyngeal transmission of the bacteria.

Pneumococcal bacterial load colonization as a marker of mixed infection in children with alveolar community-acquired pneumonia and respiratory syncytial virus or rhinovirus infection

BACKGROUND

The main aim of this study was to evaluate whether nasopharyngeal Streptococcus pneumoniae colonization in children with alveolar community-acquired pneumonia (CAP) and respiratory syncytial virus (RSV) or rhinovirus (RV) infection indicates a mixed lung infection.

METHODS

The nasopharyngeal secretions of 530 children with radiographically confirmed CAP were tested using the Luminex x TAG respiratory virus panel fast assay. Real-time polymerase chain reaction for the autolysin-A (LytA) and wzg (cpsA) genes of S. pneumoniae was performed on the RSV- and RV-positive samples.

RESULTS

Sixty-five of the 126 RSV-positive children (51.6%) were colonized with S. pneumoniae. Mean bacterial load was significantly higher in the patients with alveolar involvement (4.54±1.47 log10 DNA copies/mL vs. 3.75±1.62 log10 DNA copies/mL; P=0.04). Serotypes 5 and 19A were almost exclusively identified in the children with RSV and alveolar CAP, although the difference was statistically significant only for serotype 19A (P=0.03). Eighty-three of the 134 RV-positive children (61.9%) were colonized with S. pneumoniae and again mean bacterial load was significantly higher in the patients with alveolar involvement (4.21±1.37 log10 DNA copies/mL vs. 3.41±1.47 log10 DNA copies/mL; P=0.03). Serotypes 1, 5 and 19A were more frequently identified in the children with RV and alveolar CAP, although the difference was statistically significant only for serotype 5 (P=0.04).

CONCLUSIONS

In children with alveolar CAP and RSV or RV infection, the determination of nasopharyngeal pneumococcal bacterial load and identification of the serotypes can contribute to the diagnosis of mixed lung infection.

Using pneumococcal carriage data to monitor postvaccination changes in invasive disease

Pneumococcal conjugate vaccines (PCVs) have been introduced worldwide. However, few developing countries have high-quality surveillance systems available for monitoring vaccine impact. We evaluated whether data from nasopharyngeal carriage studies can be used to accurately monitor post-PCV changes in the incidence of invasive pneumococcal disease (IPD) among children under 5 years of age. For various dates during 1991-2010, data on nasopharyngeal pneumococcal carriage and on IPD before and after administration of 7-valent PCV (PCV7) were available from England and Wales, the Netherlands, the Navajo and White Mountain Apache American Indian populations, and the US states of Massachusetts and Alaska. We estimated the change in carriage prevalence for each serotype in each study and then either calculated the average change (inverse variance-weighted) among vaccine and nonvaccine serotypes (model 1) or used mixed-effects models to estimate the change for each serotype individually, pooling serotype data within or between studies (models 2 and 3). We then multiplied these values by the proportion of IPD caused by each serotype during the pre-PCV7 period to obtain an estimate of post-PCV7 disease incidence. Model 1 accurately captured overall changes in IPD incidence following PCV7 introduction for most studies, while the more detailed models, models 2 and 3, were less accurate. Carriage data can be used in this simple model to estimate post-PCV changes in IPD incidence.

Safety, immunogenicity, and antibody persistence following an investigational Streptococcus pneumoniae and Haemophilus influenzae triple-protein vaccine in a phase 1 randomized controlled study in healthy adults

We investigated a protein-based nontypeable Haemophilus influenzae (NTHi) and pneumococcal (HiP) vaccine containing pneumococcal histidine triad D (PhtD), detoxified pneumolysin (dPly), and NTHi protein D (PD) in adults. In a phase I study, 40 healthy 18- to 40-year-old subjects were randomized (2:2:1) to receive two HiP doses administered 60 days apart, with or without AS03 adjuvant (HiP-AS and HiP groups, respectively), or Engerix B (GlaxoSmithKline, Belgium) as a control. Safety, antibodies, and antigen-specific CD4(+) T-cell immune responses were assessed before and until 480 days after vaccination. No serious adverse events were reported, and no subject withdrew due to an adverse event. Local and systemic symptoms were reported more frequently in the HiP-AS group than in the other two groups. The frequency and intensity of local and systemic symptoms appeared to increase after the second dose of HiP-AS or HiP but not Engerix B. Antibody geometric mean concentrations (GMCs) for PhtD, dPly, and PD increased after each dose of HiP-AS or HiP, with higher GMCs being observed in the HiP-AS group (statistically significant for anti-PD after dose 1 and anti-Ply after dose 2). GMCs remained higher at day 420 than prior to vaccination in both the HiP-AS and HiP groups. Antigen-specific CD4(+) T cells increased after each dose but were unmeasurable by day 480. Two doses of an investigational PhtD-dPly-PD protein vaccine induced humoral immunity and antigen-specific CD4(+) T-cell responses after each dose, with generally higher responses when the vaccine was administered with AS03. HiP combined with AS03 appeared to be more reactogenic than the antigens alone. (This study has been registered at ClinicalTrials.gov under registration no. NCT00814489.).

A mathematical model of serotype replacement in pneumococcal carriage following vaccination

A number of childhood vaccination programmes have recently introduced vaccination against Streptococcus pneumoniae, the pneumococcus, a major cause of pneumonia and meningitis. The pneumococcal conjugate vaccines (PCVs) that are currently in use only protect against some serotypes of the bacterium, and there is now strong evidence that those serotypes not included in the vaccine increase in prevalence among most vaccinated populations. We present a mathematical model for the dynamics of nasopharyngeal carriage of S. pneumoniae that allows for carriage with multiple serotypes. The model is used to predict the prevalence of vaccine type (VT) and non-VT (NVT) serotypes following the introduction of PCV. Parameter estimates for the model are obtained by maximum likelihood using pre-vaccination data from The Gambia. The model predicts that low (1, 6A and 9V) and medium (4, 5, 7F, 14, 18C, 19A and 19F) prevalence serotypes can be eliminated through vaccination, but that the overall prevalence of carriage will be reduced only slightly because of an increase in the prevalence of NVT serotypes. Serotype replacement will be sequential, with high and medium prevalence NVT serotypes dominating initially, followed by an increase of serotypes of low prevalence. We examine the impact of a hypothetical vaccine that provides partial protection against all serotypes, and find that this reduces overall carriage, but is unable to eliminate low or medium prevalence serotypes.

Towards the 13-valent pneumococcal conjugate universal vaccination: effectiveness in the transition era between PCV7 and PCV13 in Italy, 2010-2013

Pneumococcal disease epidemiology has changed after introduction of pneumococcal conjugate vaccines. Seven-valent vaccine (PCV7) has been effective in reducing invasive pneumococcal disease (IPD). In Europe, PCV13 effectiveness was estimated at 78% (95% CI: -18-96%) for 2-priming doses. In Italy, PCV7 was introduced in 2006 in the childhood immunization schedule and replaced with PCV13 in 2010. In Apulia, vaccination coverage has reached 95.1% (birth-cohort 2010). We estimated PCV program effectiveness and its impact on S. pneumoniae diseases. PCV EFFECTIVENESS: We used the screening method. We calculated the Proportion of Population Vaccinated from immunization registries and detected cases through a laboratory-confirmed surveillance among hospitalized children≤60 months. A confirmed IPD case was a child with PCR positive for S. pneumoniae. Differences among children were assessed with the Chi-square or the Fisher exact test (P value<0.05). PCV IMPACT: We constructed time series using outcome-specific Poisson regression models: hospitalization rate in pre-PCV era and hospitalization risk ratios (RRs) with 95% CIs for both PCV7 and PCV7/PCV13 shifting era. We calculated hospitalization RR with 95% CIs comparing pre-PCV years with vaccination period. The PCV effectiveness was 84.3% (95% CI: 84.0-84.6%). In May 2010-January 2013, we enrolled 159 suspected IPD of whom 4 were confirmed. Two (fully vaccinated) were caused by serotype 9V, 1 (not vaccinated) by serotype 3, 1 (vaccinated with 2 PCV13 doses) by 15B/C. The most important reduction was for pneumococcal pneumonia (RR: 0.43, 95% CI: 0.21-0.90). The PCV program show promising results in terms of both PCV13 effectiveness and its impact in reducing IPD in children<5 years.

Pneumococcal vaccination programs and the burden of invasive pneumococcal disease in Ontario, Canada, 1995-2011

BACKGROUND

In 1995, a publicly funded pneumococcal vaccination program for 23-valent polysaccharide vaccine (PPV23) was introduced in Ontario. Conjugate vaccines were authorized in 2001 (PCV7), 2009 (PCV10) and 2010 (PCV13).

METHODS

From 1995-2011, active, population-based surveillance for invasive pneumococcal disease (IPD) was conducted in Metropolitan Toronto and Peel Region, Canada.

RESULTS

6404 IPD cases were included. After PPV23 program implementation in 1995, IPD due to PPV23 strains decreased 49% in older adults prior to PCV7 introduction. Estimated PPV23 efficacy in vaccine eligible adults was 42.2% (95% CI; 28.6-53.2%). IPD incidence due to PCV7 serotypes in children <5 years decreased significantly after PCV7 authorization and before introduction of a publicly funded PCV7 program. Seven years after PCV7 program implementation, the incidence of IPD due to PCV7 serotypes decreased to zero in children and by 88% in adults, however, overall IPD incidence remained unchanged in adults. In 2011, the incidence of IPD was 4.5 per 100,000 in adults aged 15-64 and 19.9 per 100,000 in adults aged over 65 years, with 45 serotypes causing disease. Between 1995 and 2011, the case fatality rate of IPD in adults decreased 2% per year (95% CI, -0.9% to -3.2%). In multivariable analysis, predictors of mortality included older age, chronic conditions, nursing home residence, current smoking, bacteraemia, and illness due to serotypes 3,11A, 19A, and 19F.

CONCLUSIONS

While vaccination programs resulted in substantial public health benefits, herd immunity benefits of PCV7 were seen at low pediatric vaccination rates, and the case fatality rate of IPD has decreased, IPD will continue to be a cause of considerable morbidity and mortality in adults.

Pneumococcal carriage in young children one year after introduction of the 13-valent conjugate vaccine in Italy

BACKGROUND

In mid 2010, the 7-valent pneumococcal conjugate vaccine (PCV7) was replaced by the 13-valent conjugate vaccine (PCV13) for childhood immunization in Italy. Our objective in this study was to obtain a snapshot of pneumococcal carriage frequency, colonizing serotypes, and antibiotic resistance in healthy children in two Italian cities one year after PCV13 was introduced.

METHODS

Nasopharyngeal swabs were obtained from 571 children aged 0-5 years from November 2011-April 2012. Pneumococcal isolates were serotyped and tested for antimicrobial susceptibility. Penicillin and/or erythromycin non-susceptible isolates were analyzed by Multi Locus Sequence Typing (MLST).

RESULTS

Among the children examined, 81.2% had received at least one dose of PCV7 or PCV13 and 74.9% had completed the recommended vaccination schedule for their age. Among the latter, 57.3% of children had received PCV7, 27.1% PCV13, and 15.6% a combination of the two vaccines. The overall carriage rate was 32.9%, with children aged 6-35 months the most prone to pneumococcal colonization (6-23 months OR: 3.75; 95% CI: 2.19-6.43 and 24-35 months OR: 3.15, 95%CI: 2.36-4.22). A total of 184 pneumococcal isolates were serotyped and divided into PCV7 (5.4%), PCV13 (18.0%), and non-PCV13 (82.0%) serotypes. Serotypes 6C, 24F, and 19A were the most prevalent (10.3%, 8.6%, and 8.1%, respectively). The proportion of penicillin non-susceptible (MIC >0.6 mg/L) isolates was 30.9%, while 42.3% were erythromycin resistant. Non-PCV13 serotypes accounted for 75.4% and 70.8% of the penicillin and erythromycin non-susceptible isolates, respectively.

CONCLUSIONS

Our results revealed low rates of PCV7 and PCV13 serotypes in Italian children, potentially due to the effects of vaccination. As the use of PCV13 continues, its potential impact on vaccine serotypes such as 19A and cross-reactive serotypes such as 6C will be assessed, with this study providing a baseline for further analysis of surveillance isolates.

Surface charge of Streptococcus pneumoniae predicts serotype distribution

Streptococcus pneumoniae (pneumococcus) frequently colonizes the human nasopharynx and is an important cause of pneumonia, meningitis, sinusitis, and otitis media. The outer cell surface of pneumococcus may assume various degrees of negative charge depending on the polysaccharide capsule, of which more than 90 serotypes have been identified. The negative charge of capsular polysaccharides has been proposed to electrostatically repel pneumococci from phagocytic cells, and avoidance of phagocytosis correlates with higher carriage prevalence. We hypothesized that the surface charge of pneumococcus contributes to its success in nasopharyngeal carriage by modulating resistance to phagocyte-mediated killing. Here, we measured the surface charge (zeta potential) of laboratory-constructed strains that share a genetic background but differ in serotype and of clinical strains that differ in serotype and genetic background. A more negative surface charge correlated with higher resistance to nonopsonic killing by human neutrophils in vitro. In addition, a more negative zeta potential was associated with higher carriage prevalence in human populations before and after the widespread use of the pneumococcal conjugate vaccine PCV7. We also confirmed that capsule is the major determinant of net surface charge in clinical isolates with diverse backgrounds. We noted that exceptions exist to the idea that a higher magnitude of negative charge predicts higher prevalence. The results indicated that zeta potential is strongly influenced by pneumococcal capsule type but is unlikely to be the only important mechanism by which capsule interacts with host.

Prospects for prevention of Salmonella infection in children through vaccination

PURPOSE OF REVIEW

Strains of Salmonella enterica subsp. enterica are amongst the most commonly identified invasive bacterial pathogens in resource-poor settings, and cause significant mortality, particularly in children. In this study we review recent progress in the development of vaccines against S. Typhi, S. Paratyphi and nontyphoidal Salmonella for children.

RECENT FINDINGS

Typhoid remains common and S. Paratyphi A is increasingly recognized as a cause of enteric fever in Asia. In rural Africa, nontyphoidal salmonellae are among the most common invasive bacterial infections, although S. Typhi predominates in some urban centres. Licensed vaccines against typhoid have moderate but useful efficacy but neither of the two available vaccines can be used in infants. Although Ty21a may afford some cross-protection against S. Paratyphi B, there are no vaccines that specifically target paratyphoid or any nontyphoidal Salmonella. Several live attenuated vaccines are under development and may offer some advantages over Ty21a. Vi-conjugate vaccines should offer children excellent protection from typhoid once licensed.

SUMMARY

There are few effective vaccines against Salmonella sp. and those that do exist target only one serovar, S. Typhi. Research is urgently needed to combat emerging agents of enteric fever such as S. Paratyphi A as well as nontyphoidal serovars, which commonly cause invasive disease in Africa.

Current concepts in host-microbe interaction leading to pneumococcal pneumonia

PURPOSE OF REVIEW

Infection with Streptococcus pneumoniae (pneumococcus) results in colonization, which can lead to local or invasive disease, of which pneumonia is the most common manifestation. Despite the availability of pneumococcal vaccines, pneumococcal pneumonia is the leading cause of community and inhospital pneumonia in the United States and globally. This article discusses new insights into the pathogenesis of pneumococcal disease.

RECENT FINDINGS

The host-microbe interactions that determine whether pneumococcal colonization will result in clearance or invasive disease are highly complex. This article focuses on new information in three areas that bear on the pathogenesis of pneumococcal disease: factors that govern colonization, the prelude to invasive disease, including effects on colonization and invasion of capsular serotype, pneumolysin, surface proteins that regulate complement deposition, biofilm formation and agglutination; the effect of coinfection with other bacteria and viruses on pneumococcal growth and virulence, including the synergistic effect of influenza virus; and the contribution of the host inflammatory response to the pathogenesis of pneumococcal pneumonia, including the effects of pattern recognition molecules, cells that enhance and modulate inflammation, and therapies that modulate inflammation, such as statins.

SUMMARY

Recent research on pneumococcal pathogenesis reveals new mechanisms by which microbial factors govern the ability of pneumococcus to progress from the state of colonization to disease and host inflammatory responses contribute to the development of pneumonia. These mechanisms suggest that therapies which modulate the inflammatory response could hold promise for ameliorating damage stemming from the host inflammatory response in pneumococcal disease.

Comparison of the prevalence of common bacterial pathogens in the oropharynx and nasopharynx of gambian infants

Background

CRM- based pneumococcal conjugate vaccines generally have little impact on the overall prevalence of pneumococcal carriage because of serotype replacement. In contrast, protein vaccines could substantially reduce the overall prevalence of pneumococcal carriage with potential microbiological and clinical consequences. Therefore, trials of pneumococcal protein vaccines need to evaluate their impact on carriage of other potentially pathogenic bacteria in addition to the pneumococcus.

Methods

As a prelude to a trial of an investigational pneumococcal vaccine containing pneumococcal polysaccharide conjugates and pneumococcal proteins, the prevalence of carriage of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella species and Staphylococcus aureus in the nasopharynx of 1030 Gambian infants (median age 35 weeks) was determined. An oropharyngeal swab was obtained at the same time from the first 371 infants enrolled. Standard microbiological techniques were used to evaluate the bacterial flora of the pharynx and to compare that found in the oropharynx and in the nasopharynx.

Results

The overall pneumococcal carriage rate was high. Isolation rates of S. pneumoniae and Moraxella species were significantly higher using nasopharyngeal rather than oropharyngeal swabs (76.1% [95% CI 73.4%,78.7%] vs. 21.3% [95% CI 17.2%,25.8%] and 48.9% [95% CI 45.8%, 52.0%] vs. 20.5% % [95% CI 16.5%,25.0%] respectively). In contrast, S. aureus and H. influenzae were isolated more frequently from oropharyngeal than from nasopharyngeal swabs (65.0% [95% CI 59.9%, 69.8%] vs. 33.6% [95% CI 30.7%, 36.5%] and 31.8% [95% CI 16.5%, 25.0%] vs. 22.4% [95% CI 19.9%, 25.1%] respectively). No group A β haemolytic streptococci were isolated.

Conclusion

Collection of an oropharyngeal swab in addition to a nasopharyngeal swab will provide little additional information on the impact of a novel pneumococcal vaccine on pneumococcal carriage but it might provide additional, valuable information on the impact of the vaccine on the overall microbiota of the pharynx.