Effect of a nonavalent conjugate vaccine on carriage of antibiotic-resistant Streptococcus pneumoniae in day-care centers

Pneumococcal Competition Modulates Antibiotic Resistance in the Pre-Vaccination Era: A Modelling Study

The ongoing emergence of antibiotic resistant strains and high frequencies of antibiotic resistance of Streptococcus pneumoniae poses a major public health challenge. How and which ecological and evolutionary mechanisms maintain the coexistence of antibiotic resistant and susceptible strains remains largely an open question. We developed an individual-based, stochastic model expanding on a previous pneumococci modelling framework. We explore how between- and within-host mechanisms of competition can sustain observed levels of resistance to antibiotics in the pre-vaccination era. Our framework considers that within-host competition for co-colonization between resistant and susceptible strains can arise via pre-existing immunity (immunological competition) or intrinsic fitness differences due to resistance costs (ecological competition). We find that beyond stochasticity, population structure or movement, competition at the within-host level can explain observed resistance frequencies. We compare our simulation results to pneumococcal antibiotic resistance data in the European region using approximate Bayesian computation. Our results demonstrate that ecological competition for co-colonization can explain the variation in co-existence of resistant and susceptible pneumococci observed in the pre-vaccination era. Furthermore, we show that within-host pneumococcal competition can facilitate the maintenance of resistance in the pre-vaccination era. Accounting for these competition-related components of pneumococcal dynamics can improve our understanding of drivers for the emergence and maintenance of antibiotic resistance in pneumococci.

Understanding the Evolution of Antibiotic-nonsusceptible Pneumococcal Nasopharyngeal Colonization Following Pneumococcal Conjugate Vaccine Implementation in Young Children

BACKGROUND

Four main processes determine pneumococcal conjugate vaccine (PCV) antibiotic-nonsusceptible Streptococcus pneumoniae (ANSP) carriage: reduction of PCV serotypes, increase of non-PCV serotypes, potential overall reduction in carriage, and within-serotype nonsusceptibility resulting from continuous antibiotic pressure. The post-PCV implementation dynamics of these components were examined in young children from 2 distinct ethnic populations: Jewish and Bedouin.

METHODS

We performed ongoing, prospective, population-based, active surveillance initiated at the time of 7- and 13-valent PCVs (PCV7; PCV13) implementation. Nasopharyngeal cultures for S. pneumoniae were obtained daily from children aged <5 years who visited the only pediatric emergency room in the district during a 6-year period (2009 to 2015).

RESULTS

Of 8446 nasopharyngeal samples, 48.3% were positive (42.0% and 52.8% for Jewish and Bedouin children, respectively; P < .001). Nonsusceptibility was significantly more frequent among PCV serotypes than among non-PCV serotypes and among Bedouin children than among Jewish children. PCV serotype carriage declined by 80%, while that of non-PCV serotypes increased by 140%. The overall (all serotypes) pneumococcal carriage significantly declined (33% and 11% in Bedouin and Jewish children, respectively). Among non-PCV isolates, the proportion of ANSP significantly increased with time in both populations. As a summation of all 4 processes, ANSP carriage significantly decreased among both Bedouin and Jewish children.

CONCLUSIONS

PCV impact on ANSP nasopharyngeal carriage is a dynamic, multicomponent process, highly dependent on antibiotic consumption in the community, which may result in a continuous increase in antibiotic resistance in the replacing serotypes.

Risk Factors for Carriage of Antibiotic-resistant Bacteria in Healthy Children in the Community: A Systematic Review

BACKGROUND

In addition to health care settings, antibiotic resistance has also been increasing in the community. Healthy children represent an important potential reservoir of antibiotic-resistant (AR) bacteria. However, strategies to reduce the spread of AR bacteria often fail to specifically address the factors that promote the carriage of AR bacteria in this population.The objective of this review was to Identify risk factors for carriage of AR bacteria by healthy children.

METHODS

We did a systematic search of MEDLINE, Embase and PubMed for studies in developed (OECD) countries that assessed risk factors for carriage of AR bacteria in healthy children in the community. We excluded studies done before 1998 and studies of AR Streptococcus pneumoniae carriage in the absence of pneumococcal conjugate vaccination.

RESULTS

Of 1234 studies identified, 30 were eligible for inclusion. These studies assessed the impact of 49 risk factors on AR strains of S. pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Streptococcus pyogenes and Escherichia coli. The majority of these risk factors were assessed in 2 or fewer studies per bacteria. Recent antibiotic consumption was associated with carriage of resistant respiratory bacteria (S. pneumoniae, H. influenzae); however, it was not consistently associated with carriage of AR bacteria in skin or stool (S. aureus and E. coli). For AR S. aureus, transmission within households appeared to have a greater impact than individual antibiotic use.

CONCLUSIONS

The factors that promote carriage of AR bacteria by healthy children differed between bacterial species. To reduce reservoirs of AR bacteria in the community, it is essential for intervention strategies to target the specific risk factors for different bacteria.

Upper respiratory tract colonization with Streptococcus pneumoniae in adults

INTRODUCTION

Most of the current evidence regarding pneumococcal upper respiratory colonization in adults suggests that despite high disease burden, carriage prevalence is low. Contemporary studies on adult pneumococcal colonization have largely followed the pediatric approach by which samples are obtained mostly from the nasopharynx and bacterial detection is evaluated by routine culture alone. Recent evidence suggests that the 'pediatric approach' may be insufficient in adults and pneumococcal detection in this population may be improved by longitudinal studies that include samples from additional respiratory sites combined with more extensive laboratory testing.

AREAS COVERED

In this article, relevant literature published in peer review journals on adult pneumococcal colonization, epidemiology, detection methods, and recommendations were reviewed.

EXPERT OPINION

Respiratory carriage of Streptococcus pneumoniae has been underestimated in adults. Contemporary pneumococcal carriage studies in adults that collect samples from alternative respiratory sites such as the oropharynx, saliva, or nasal wash; are culture-enriched for pneumococcus; and use molecular diagnostic methods designed to target two pneumococcal DNA sequences should enhance pneumococcal detection in the adult respiratory tract. This finding may have implications for the interpretation of dynamics of pneumococcal transmission and vaccination.

Vaccination can drive an increase in frequencies of antibiotic resistance among nonvaccine serotypes of Streptococcus pneumoniae

The bacterial pathogen Streptococcus pneumoniae is a major public health concern, being responsible for more than 1.5 million deaths annually through pneumonia, meningitis, and septicemia. Available vaccines target only a subset of serotypes, so vaccination is often accompanied by a rise in the frequency of nonvaccine serotypes. Epidemiological studies suggest that such a change in serotype frequencies is often coupled with an increase of antibiotic resistance among nonvaccine serotypes. Building on previous multilocus models for bacterial pathogen population structure, we have developed a theoretical framework incorporating variation of serotype and antibiotic resistance to examine how their associations may be affected by vaccination. Using this framework, we find that vaccination can result in a rapid increase in the frequency of preexisting resistant variants of nonvaccine serotypes due to the removal of competition from vaccine serotypes.

The relationship between mucosal immunity, nasopharyngeal carriage, asymptomatic transmission and the resurgence of Bordetella pertussis

The incidence of whooping cough in the US has been rising slowly since the 1970s, but the pace of this has accelerated sharply since acellular pertussis vaccines replaced the earlier whole cell vaccines in the late 1990s. A similar trend occurred in many other countries, including the UK, Canada, Australia, Ireland, and Spain, following the switch to acellular vaccines. The key question is why. Two leading theories (short duration of protective immunologic persistence and evolutionary shifts in the pathogen to evade the vaccine) explain some but not all of these shifts, suggesting that other factors may also be important.

In this synthesis, we argue that sterilizing mucosal immunity that blocks or abbreviates the duration of nasopharyngeal carriage of Bordetella pertussis and impedes person-to-person transmission (including between asymptomatically infected individuals) is a critical factor in this dynamic. Moreover, we argue that the ability to induce such mucosal immunity is fundamentally what distinguishes whole cell and acellular pertussis vaccines and may be pivotal to understanding much of the resurgence of this disease in many countries that adopted acellular vaccines. Additionally, we offer the hypothesis that observed herd effects generated by acellular vaccines may reflect a modification of disease presentation leading to reduced potential for transmission by those already infected, as opposed to inducing resistance to infection among those who have been exposed.

Burden of Culture-Confirmed Pediatric Pneumococcal Pneumonia in Latin America and the Caribbean: A Systematic Review and Meta-Analysis

BACKGROUND

Pneumococcal pneumonia (PP) causes almost one in five deaths in children younger than 5 years worldwide. In Latin America and the Caribbean (LAC), pneumonia causes 14% of all deaths. Although pneumococcal disease is a vaccine-preventable disease that accounts for a significant proportion of this burden, the decision-making process to introduce pneumococcal conjugate vaccines in official schedules is still complex in LAC. Confirmed PP cases and epidemiology are the basis for broader projections.

OBJECTIVE

To gather all the information available in the LAC region to assist decision makers.

METHODS

We performed a systematic review of studies of consolidating and culture-confirmed pediatric PP in LAC (2000-2016) using a generic academic Internet search and search engines without language restrictions. Pairs of reviewers independently selected and assessed the studies' methodological quality. We analyzed meta-information on pneumococcal serotypes available from the SIREVA laboratory-based surveillance system.

RESULTS

A total of 35 out of 750 initially identified studies were included. In the age group between 0 and 59 years, the incidence of culture-confirmed PP ranged from 10.2 to 43.0/100,000 children, with a pooled incidence of 20.4/100,000 children (95% confidence interval 0.0-123.2). Mortality ranged from 0.4 to 5.7/100,000 children, and the pooled mortality was 2.9/100,000 children (95% confidence interval 0.3-8.2). The pooled serotype distribution from surveillance data showed that serotypes 14, 1, and 6B were the most frequent serotypes in LAC, all included in licensed vaccines.

CONCLUSIONS

Studies on confirmed pediatric PP were scarce in LAC in 2000 to 2016. Epidemiology indicators and health resource use are still poorly defined.

Pneumococcal nasopharyngeal carriage in children <5 years of age visiting the pediatric emergency room in relation to PCV7 and PCV13 introduction in southern Israel

The 7-valent and the 13-valent pneumococcal conjugate vaccines (PCV7 and PCV13, respectively) were introduced to the Israeli National Immunization plan in July 2009 and November 2010, respectively. Our aim was to assess pneumococcal conjugate vaccines (PCVs) uptake and dynamics in serotype-specific pneumococcal nasopharyngeal (NP) carriage in children <5  years old in southern Israel, during the immediate 5 y following PCV introduction. This was an ongoing, prospective, population-based, active surveillance, from July 2009 through December 2014. PCVs uptake and NP cultures were obtained daily from children seen at the Pediatric Emergency Room for any reason. Overall, 10,702 vaccine status and 7,610 NP swabs were obtained. Both PCV7 and PCV13 uptake were high, reaching ˜90% by July 2012 and December 2013, respectively. All-pneumococcal carriage rates significantly declined by 10%, from 54.3% in the early-PCV7 period, to 49.1% in the PCV13 impact period. The respective declines for PCV7, 6A and additional PCV13 serotypes carriage rates were 76%, 90% and 66%. In contrast, non-PCV13 serotypes carriage rates increased significantly throughout the study by 71%. All-pneumococcal carriage rates in children <12  months old decreased significantly by 15%, with similar trends observed in other age groups. Initially, all-pneumococcal carriage rates were 45.7%, and 61.9% in Jewish and Bedouin children, respectively (P < 0.001), with a significant 17% reduction throughout the study observed only in Bedouins. While early carriage rates were higher in unvaccinated children compared to vaccinated children, PCV impact on carriage were similar in both groups. In conclusion, a relatively moderate decline in pneumococcal carriage rates, facilitated by a substantial decrease of vaccine-serotypes and increase of non-vaccine serotypes was observed in the immediate period following PCVs introduction in southern Israel.

MLVA Typing of Streptococcus pneumoniae Isolates with Emphasis on Serotypes 14, 9N and 9V: Comparison of Previously Described Panels and Proposal of a Novel 7 VNTR Loci-Based Simplified Scheme

Streptococcus pneumoniae remains as an important cause of community-acquired bacterial infections, and the nasopharynx of asymptomatic carriers is the major reservoir of this microorganism. Pneumococcal strains of serotype 14 and serogroup 9 are among the most frequently isolated from both asymptomatic carriers and patients with invasive disease living in Brazil. Internationally disseminated clones belonging to such serotypes have been associated with the emergence and spread of antimicrobial resistance in our setting, highlighting the need for epidemiological tracking of these isolates. In this scenario, Multiple Loci VNTR Analysis (MLVA) has emerged as an alternative tool for the molecular characterization of pneumococci, in addition to more traditional techniques such as Multi-Locus Sequence Typing (MLST) and Pulsed-Field Gel Electrophoresis (PFGE). In the present study, 18 VNTR loci, as well as other previously described reduced MLVA panels (7 VNTR loci), were evaluated as tools to characterize pneumococcal strains of serotypes 14, 9N and 9V belonging to international and regional clones isolated in Brazil. The 18 VNTR loci panel was highly congruent with MLST and PFGE, being also useful for indicating the genetic relationship with international clones and for discriminating among strains with indistinguishable STs and PFGE profiles. Analysis of the results also allowed deducing a novel shorter 7 VNTR loci panel, keeping a high discriminatory power for isolates of the serotypes investigated and a high congruence level with MLST and PFGE. The newly proposed simplified panel was then evaluated for typing pneumococcal strains of other commonly isolated serotypes. The results indicate that MLVA is a faster and easier to perform, reliable approach for the molecular characterization of S. pneumoniae isolates, with potential for cost-effective application, especially in resource-limited countries.

Serological criteria and carriage measurement for evaluation of new pneumococcal vaccines

The best method of evaluating the efficacy of a vaccine is to compare the incidence of the disease against which it is prepared in randomized, placebo-controlled clinical trials involving vaccinated and unvaccinated subjects. In the case of Streptococcus pneumoniae, the proposed alternatives are evaluations of the so-called "correlates of protection" (i.e. markers of the vaccine-induced immune response that predict protection from infection and disease) and nasopharyngeal carriage. The aim of this paper is to discuss the most important limitations of the immunological criteria suggested for licensing new pneumococcal vaccines, and comment on the use of carriage as an endpoint for evaluating efficacy. Data showed why the use of a single serological correlate of protection cannot be considered the best means of evaluating pneumococcal vaccines and highlighted the importance of using carriage for efficacy evaluation but in the meantime the need to develop new sensitive and specific methods.

A bivalent vaccine based on a replication-incompetent influenza virus protects against Streptococcus pneumoniae and influenza virus infection

Streptococcus pneumoniae is a major causative pathogen in community-acquired pneumonia; together with influenza virus, it represents an important public health burden. Although vaccination is the most effective prophylaxis against these infectious agents, no single vaccine simultaneously provides protective immunity against both S. pneumoniae and influenza virus. Previously, we demonstrated that several replication-incompetent influenza viruses efficiently elicit IgG in serum and IgA in the upper and lower respiratory tracts. Here, we generated a replication-incompetent hemagglutinin knockout (HA-KO) influenza virus possessing the sequence for the antigenic region of pneumococcal surface protein A (PspA). Although this virus (HA-KO/PspA virus) could replicate only in an HA-expressing cell line, it infected wild-type cells and expressed both viral proteins and PspA. PspA- and influenza virus-specific antibodies were detected in nasal wash and bronchoalveolar lavage fluids and in sera from mice intranasally inoculated with HA-KO/PspA virus, and mice inoculated with HA-KO/PspA virus were completely protected from lethal challenge with either S. pneumoniae or influenza virus. Further, bacterial colonization of the nasopharynx was prevented in mice immunized with HA-KO/PspA virus. These results indicate that HA-KO/PspA virus is a promising bivalent vaccine candidate that simultaneously confers protective immunity against both S. pneumoniae and influenza virus. We believe that this strategy offers a platform for the development of bivalent vaccines, based on replication-incompetent influenza virus, against pathogens that cause respiratory infectious diseases.

IMPORTANCE

Streptococcus pneumoniae and influenza viruses cause contagious diseases, but no single vaccine can simultaneously provide protective immunity against both pathogens. Here, we used reverse genetics to generate a replication-incompetent influenza virus carrying the sequence for the antigenic region of pneumococcal surface protein A and demonstrated that mice immunized with this virus were completely protected from lethal doses of infection with either influenza virus or Streptococcus pneumoniae. We believe that this strategy, which is based on a replication-incompetent influenza virus possessing the antigenic region of other respiratory pathogens, offers a platform for the development of bivalent vaccines.

Epidemiology of pediatric pneumococcal meningitis and bacteremia in Latin America and the Caribbean: a systematic review and meta-analysis

BACKGROUND

Pneumococcal meningitis and bacteremia pose a significant disease burden in Latin America and the Caribbean (LAC).

METHODS

To perform a systematic review of studies of pediatric pneumococcal meningitis and non-pneumonia, non-meningitis pneumococcal bacteremia in LAC, we conducted an exhaustive search from 2000 to 2010 in electronic databases and grey literature. Pairs of independently selected reviewers assessed the quality and extracted the studies' data. A STROBE-based checklist was used to assess the risk of bias in observational studies. Meta-analyses were performed.

RESULTS

Of 1218 retrieved studies, 39 were included. In children <5 years, the pooled 95% confidence interval (CI) percentage of pneumococcal etiology out of cases studied with cerebrospinal fluid/blood cultures was 6.0% (95% CI: 3.3-9.5) for meningitis and 8.0% (95% CI: 5.3-12.4) for bacteremia. The incidences per 100,000 children were 4.7 (95% CI: 3.2-6.1) and 3.9 (95% CI: 2.0-5.9) for pneumococcal meningitis and non-pneumonia, non-meningitis bacteremia, respectively. The mortality was 8.3 (95% CI: 0.0-21.0) and 0.5 (95% CI: 0.3.0-0.6)/100,000 for meningitis and sepsis, respectively. The case fatality ratio was 33.2% (95% CI: 21.3-46.2) for meningitis and 29.0% (95% CI: 21.9-36.8) for sepsis. The pooled serotype distribution from SIREVA surveillance data showed that 14, 5, 6B (for meningitis) and 14, 6B, 19F (for bacteremia) were the most frequent serotypes, all included in licensed vaccines.

CONCLUSION

Pneumococcal meningitis and bacteremia are important causes of morbidity and mortality in LAC children <5 years of age. This systematic review provided evidence about the burden of pneumococcal disease and the serotype distribution to assess the impact the pneumococcal vaccines and to assist decision makers in the region.

Temporal association of infant immunisation with pneumococcal conjugate vaccine on the ecology of Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus nasopharyngeal colonisation in a rural South African community

BACKGROUND

Immunisation of children with pneumococcal conjugate vaccines (PCV) may affect the bacterial-ecology of the nasopharynx, including colonisation by Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus. The aim of this study was to evaluate the effect of infant PCV-immunisation on the nasopharyngeal ecology of these potentially pathogenic bacteria in a rural African setting.

METHODS

Two cross sectional surveys were undertaken from May to October in 2009 (Period-1) which coincided with the introduction of 7-valent PCV (PCV7) and in May-October 2011 (Period-2). Consenting household members, where there was a child <2 years of age in residence, had nasopharyngeal swabs undertaken for culture.

RESULTS

From Period-1 to Period-2 in children 0-2 years and 3-12 years, prevalence of overall S. pneumoniae colonisation decreased from 74.9% to 67.0% (p<0.001) and H. influenzae declined among children 3-12 years (55.1-45.3%, p<0.001) but not among those <2 years. The prevalence of S. aureus remained unchanged in all children. Competitive associations were found between S. pneumoniae and S. aureus and between H. influenzae and S. aureus among children. In individuals >12 years, the prevalence of colonisation decreased from 11.2% to 6.8%, 16.7% to 8.8% and 31.2% to 23.7% for S. pneumoniae, H. influenzae and S. aureus, respectively; p<0.001 for all comparions. Synergistic relationships for S. aureus with H. influenzae and S. pneumoniae were observed in both periods among this group.

Global control of pneumococcal infections by pneumococcal vaccines

Streptococcus pneumoniae is a major worldwide cause of morbidity and mortality. Pneumococcal carriage is considered to be an important source of horizontal spread of this pathogen within the community. Pneumococcal conjugate vaccine (PCV) is capable of inducing serotype-specific antibodies in sera of infants, and has been suggested to reduce nasopharyngeal carriage of vaccine-type pneumococci in children. PCV is generally immunogenic for pediatric patients with invasive pneumococcal disease, with an exception for the infecting serotypes. Based on evidences from the clinical trials of PCV, the health impact of childhood pneumococcal pneumonia appears to be high in developing countries where most of global childhood pneumonia deaths occur. PCV vaccination may prevent hundreds of deaths per 100,000 children vaccinated in developing countries, while PCV vaccination is expected to prevent less than 10 deaths per 100,000 children vaccinated in the developed countries. Therefore, the WHO has proposed a strategy to reduce the incidence of severe pneumonia by 75% in child less than 5 years of age compared to 2010 levels by 2025.

Serotype distribution and antimicrobial susceptibility of USA Streptococcus pneumoniae isolates collected prior to and post introduction of 13-valent pneumococcal conjugate vaccine

This study evaluated pneumococci cultured from blood or lower respiratory tract specimens from hospitalized patients in the USA (all age groups) during 2011-2012 (N = 1190) and compared findings with those from a similar study performed in 2008 (N = 694). Isolates were tested for susceptibility by broth microdilution and serotypes determined by cpsB sequencing, supplemented with multiplex PCR and capsular swelling assays. Relative percentages of 7-valent pneumococcal conjugate vaccine (PCV7) types were 6.3 and 4.9% in 2008 and 2011-2012, respectively, and the most common PCV7 serotypes (19F and 6B) comprised only 3.7% and 4.0% of all isolates from both periods, respectively. Thirteen-valent pneumococcal conjugate vaccine (PCV13) serotypes represented 42.9% of isolates in 2008 and 30.1% in the second period, and this decrease was driven by 19A and 7F. Non-PCV13 serogroups/serotypes 23A, 15B/15C, 7C, 8, and 31 increased. Penicillin non-susceptibility rates were 9.6-10.0% and 38.9-42.7% when applying the parenteral (i.e. ≥ 4 μg/mL) and oral breakpoints (i.e. ≥ 0.12 μg/mL), respectively. Ceftaroline was the most potent agent tested based on MIC50 and MIC90 values (≤ 0.015 and 0.12 μg/mL, respectively) for both time periods.

Temporal changes in pneumococcal colonization in a rural African community with high HIV prevalence following routine infant pneumococcal immunization

BACKGROUND

Pneumococcal conjugate vaccine (PCV) immunization of children decreases their risk of nasopharyngeal acquisition of vaccine serotypes. We studied the impact of routine infant PCV immunization alone on the epidemiology of nasopharyngeal pneumococcal colonization among a rural African community with high prevalence of HIV positivity.

METHODS

Two cross-sectional surveys were undertaken in a rural South African community from May to October 2009 (period 1) and 2011 (period 2). Seven-valent PCV was introduced into the public immunization program for infants in April 2009, without catch-up campaign for older children. Randomly selected households with at least 1 child<2 years of age were recruited. Nasopharyngeal swabs from all consenting household members were obtained for Streptococcus pneumoniae culture and serotyping by Quellung method.

RESULTS

The median ages (SD) of children enrolled were 4.32 (SD, 3.4) and 3.80 (SD, 3.4) years in periods 1 and 2, respectively. Overall, the prevalence of vaccine serotype colonization declined from 18.3% (368/2010) in period 1 to 11.4% (418/3659) by period 2 (P<0.0001). This included reductions (adjusted risk ratio) of 50% [95% confidence interval (95% CI): 0.42-0.59], 34% (95% CI: 0.48-0.92) and 64% (95% CI: 0.18-0.74) in age groups<2 years, 6-12 years and adults. The prevalence of vaccine serotype colonization among primary caregivers decreased from 10.2% to 5.4% (P≤0.001) by period 2. The prevalence of nonvaccine serotype colonization increased by 35% (95% CI: 1.17-1.56) among <2-year-old children by period 2, while it declined by 45-54% among adolescents and adults.

CONCLUSIONS

An indirect effect of PCV7 was realized in a high HIV prevalence setting within 2 years of PCV introduction. The unexpected decline in nonvaccine serotypes colonization among adolescents/adults may indicate lag in replacement colonization by nonvaccine serotypes in this group.

Protein carriers of conjugate vaccines: characteristics, development, and clinical trials

The immunogenicity of polysaccharides as human vaccines was enhanced by coupling to protein carriers. Conjugation transformed the T cell-independent polysaccharide vaccines of the past to T cell-dependent antigenic vaccines that were much more immunogenic and launched a renaissance in vaccinology. This review discusses the conjugate vaccines for prevention of infections caused by Hemophilus influenzae type b, Streptococcus pneumoniae, and Neisseria meningitidis. Specifically, the characteristics of the proteins used in the construction of the vaccines including CRM, tetanus toxoid, diphtheria toxoid, Neisseria meningitidis outer membrane complex, and Hemophilus influenzae protein D are discussed. The studies that established differences among and key features of conjugate vaccines including immunologic memory induction, reduction of nasopharyngeal colonization and herd immunity, and antibody avidity and avidity maturation are presented. Studies of dose, schedule, response to boosters, of single protein carriers with single and multiple polysaccharides, of multiple protein carriers with multiple polysaccharides and conjugate vaccines administered concurrently with other vaccines are discussed along with undesirable consequences of conjugate vaccines. The clear benefits of conjugate vaccines in improving the protective responses of the immature immune systems of young infants and the senescent immune systems of the elderly have been made clear and opened the way to development of additional vaccines using this technology for future vaccine products.

Pneumococcal carriage and invasive disease in children before introduction of the 13-valent conjugate vaccine: comparison with the era before 7-valent conjugate vaccine

BACKGROUND

Nasopharyngeal (NP) carriage and invasive pneumococcal disease (IPD) attributable to serotypes in the 7-valent pneumococcal conjugate vaccine (PCV7) declined dramatically after vaccine introduction, whereas non-PCV7 serotypes increased modestly. Characteristics of pneumococcal carriage and IPD among children in Atlanta, GA, were compared during 2 time periods: before PCV7 introduction and before 13-valent PCV (PCV13) introduction.

METHODS

NP swabs from 231 and 451 children 6-59 months old receiving outpatient medical care were obtained in 1995 and 2009, respectively. A total of 202 and 47 IPD cases were identified in children younger than 5 years of age in 1995 and in 2008 to 2009, respectively, through active, population-based surveillance in Atlanta. Isolates were serotyped, sequence-typed (ST) and tested for antimicrobial susceptibility.

RESULTS

Forty percent (93/231) of children in 1995 and 31% (139/451) in 2009 were colonized with Streptococcus pneumoniae; 60% and 0.7% were PCV7 serotypes, respectively. In 1995, PCV7 serotypes accounted for 83% and 19A accounted for 5% of IPD compared with no PCV7 serotypes and 19A accounting for 49% of IPD in 2009 (P < 0.001). In 2009, PCV13 serotypes accounted for 22% of carriage (mostly 19A) and 60% of invasive isolates (P < 0.001). ST320 accounted for 66% and 52% of 19A carriage and IPD isolates in 2009, respectively; all ST320 isolates were multidrug-resistant. No ST320 NP or IPD isolates were identified before PCV7.

CONCLUSIONS

Serotype distribution among NP and IPD isolates in Atlanta has shifted to non-PCV7 serotypes; 19A was the leading serotype for both. The multidrug-resistant ST320 strain was responsible for two-thirds of 19A carriage isolates and half of IPD isolates. The predominance of serotype 19A in carriage and IPD among children in Atlanta highlights the potential direct and indirect benefits anticipated by implementation of PCV13 in the community.

Macrolide resistance determinants among Streptococcus pneumoniae isolates from carriers in Central Greece

Background

We sought to characterize the temporal trends in nasopharyngeal carriage of macrolide-resistant pneumococci during a period with increased heptavalent pneumococcal conjugate vaccine (PCV7) coverage in Central Greece.

Methods

Streptococcus pneumoniae isolates were recovered from 2649 nasopharyngeal samples obtained from day-care center attendees in Central Greece during 2005–2009. A phenotypic and genotypic analysis of the isolates was performed, including the identification of macrolide resistance genes mef(A), subclasses mef(A) and mef(E), as well as erm(B).

Results

Of the 1105 typeable S. pneumoniae isolates, 265 (24%) were macrolide-resistant; 22% in 2005, 33.3% in 2006, 23.7% in 2007, and 20.5% in 2009 (P=0.398). Among these macrolide-resistant pneumococci, 28.5% possessed erm(B), 24.3% erm(B)+mef(E), 41.8% mef(E), and 5.3% mef(A). A mef gene as the sole resistance determinant was carried by 31% of macrolide-resistant isolates belonging to PCV7 serotypes and 75.8% of the non-PCV7 serotypes. Across the 4 annual surveillances, pneumococci carrying mef(A) gradually disappeared, whereas serotype 19F isolates carrying both erm(B) and mef(E) persisted without significant yearly fluctuations. Among isolates belonging to non-PCV7 serotypes, macrolide-resistance was observed in those of serotypes 6A, 19A, 10A, 15A, 15B/C, 35F, 35A, and 24F. In 2009, ie 5 years after the introduction of PCV7 in our country, 59% of macrolide-resistant pneumococci belonged to non-PCV7 serotypes.

Conclusions

Across the study period, the annual frequency of macrolide-resistant isolates did not change significantly, but in 2009 a marked shift to non-PCV7 serotypes occurred. Overall, more than half of the macrolide-resistant isolates possessed erm(B) either alone or in combination with mef(E). erm(B) dominated among isolates belonging to PCV7 serotypes, but not among those of non-PCV7 serotypes.

Decline in early childhood respiratory tract infections in the Norwegian mother and child cohort study after introduction of pneumococcal conjugate vaccination

BACKGROUND

The 7-valent pneumococcal conjugate vaccine (PCV7) was introduced into the Norwegian Childhood Immunization Program in 2006. A substantial effectiveness of PCV7 immunization against invasive pneumococcal disease has been demonstrated, whereas evidence of its impact on respiratory tract infections are less consistent.

METHODS

This study included children participating in the Norwegian Mother and Child Cohort Study, which recruited pregnant women between 1999 and 2008. Maternal report of acute otitis media (AOM), lower respiratory tract infections (LRTIs) and asthma in the child was compared by PCV7 immunization status, as obtained from the Norwegian Immunization Registry. Generalized linear models with the log-link function were used to report adjusted relative risks (RRs) and 95% confidence intervals (CIs).

RESULTS

For children who had received 3 or more PCV7 immunizations by 12 months of age, the adjusted RRs of AOM and LRTIs between 12 and 18 months were 0.86 (95% CI: 0.81, 0.91) and 0.78 (95% CI: 0.70, 0.87) respectively, when compared with nonimmunized children. A reduced risk of AOM, RR 0.92 (95% CI: 0.90, 0.94), and LRTIs, RR 0.75 (95% CI: 0.71, 0.80), between 18 and 36 months of age was also identified among children who had received 3 or more immunizations by 18 months of age. No association was seen between PCV7 immunization and asthma at 36 months of age.

CONCLUSION

Reduced incidences of AOM and LRTIs before 36 months of age were observed among children immunized with PCV7 through the childhood immunization program.

Cost-effectiveness of 2 + 1 dosing of 13-valent and 10-valent pneumococcal conjugate vaccines in Canada

Background

Thirteen-valent pneumococcal conjugate vaccine (PCV13) and 10-valent pneumococcal conjugate vaccine (PCV10) are two recently approved vaccines for the active immunization against Streptococcus pneumoniae causing invasive pneumococcal disease in infants and children. PCV13 offers broader protection against Streptococcus pneumoniae; however, PCV10 offers potential protection against non-typeable Haemophilus influenza (NTHi). We examined public health and economic impacts of a PCV10 and PCV13 pediatric national immunization programs (NIPs) in Canada.

Methods

A decision-analytic model was developed to examine the costs and outcomes associated with PCV10 and PCV13 pediatric NIPs. The model followed individuals over the remainder of their lifetime. Recent disease incidence, serotype coverage, population data, percent vaccinated, costs, and utilities were obtained from the published literature. Direct and indirect effects were derived from 7-valent pneumococcal vaccine. Additional direct effect of 4% was attributed to PCV10 for moderate to severe acute otitis media to account for potential NTHi benefit. Annual number of disease cases and costs (2010 Canadian dollars) were presented.

Results

In Canada, PCV13 was estimated to prevent more cases of disease (49,340 when considering both direct and indirect effects and 7,466 when considering direct effects only) than PCV10. This translated to population gains of 258 to 13,828 more quality-adjusted life-years when vaccinating with PCV13 versus PCV10. Annual direct medical costs (including the cost of vaccination) were estimated to be reduced by $5.7 million to $132.8 million when vaccinating with PCV13. Thus, PCV13 dominated PCV10, and sensitivity analyses showed PCV13 to always be dominant or cost-effective versus PCV10.

Conclusions

Considering the epidemiology of pneumococcal disease in Canada, PCV13 is shown to be a cost-saving immunization program because it provides substantial public health and economic benefits relative to PCV10.

The changing epidemiology of invasive pneumococcal disease at a tertiary children's hospital through the 7-valent pneumococcal conjugate vaccine era: a case for continuous surveillance

BACKGROUND

In 2000, a 7-valent pneumococcal conjugate vaccine (PCV7) was licensed for use among US children. Many sites have since reported changes in invasive pneumococcal disease (IPD). We recognized an opportunity to describe the changes in epidemiology, clinical syndromes, and serotype distribution during a 14-year period including 4 years before vaccine introduction and spanning the entire PCV7 era.

METHODS

Cases were defined as children <18 years of age who were cared for at Primary Children's Medical Center for culture-confirmed IPD. We defined the prevaccine period as the time frame spanning from 1997 to 2000 and the postvaccine period from 2001 to 2010. Demographics, clinical data, and outcomes were collected through electronic query and chart review. Streptococcus pneumoniae serotyping was performed using the capsular swelling method.

RESULTS

The median age of children with IPD increased from 19 months during the prevaccine period to 27 months during postvaccine period (P = 0.02), with a larger proportion of IPD among children older than 5 years. The proportion of IPD associated with pneumonia increased substantially from 29% to 50% (P < 0.001). This increase was primarily attributable to an increase in complicated pneumonia (17% to 33%, P < 0.001). Nonvaccine serotypes 7F, 19A, 22F, and 3 emerged as the dominant serotypes in the postvaccine period. In children with IPD who were younger than 5 years, for whom vaccine is recommended, 67% of the cases were caused by serotypes in 13-valent PCV during 2005 to 2010.

CONCLUSIONS

After PCV7 was introduced, significant changes in IPD were noted. One-third of IPD occurred in children older than 5 years, who were outside the age-group for which PCV is recommended. Continued surveillance is warranted to identify further evolution of the epidemiology, clinical syndromes, and serotype distribution of S. pneumoniae after 13-valent PCV licensure.

The future of pneumococcal disease prevention

Pneumococcal disease (PD) is the leading cause of vaccine preventable deaths in children <5 years of age worldwide, with most of the deaths occurring in the developing world. Prevention of PD in children has been achieved by vaccination with pneumococcal conjugate vaccine (PCV), the basis for which is induction of a protective antibody response against the bacterial polysaccharide capsule. Conjugation of the polysaccharide capsule to a protein carrier enables the generation of an immunologic response to the vaccine in young children, leading to protection against infection. The heptavalent PCV, which contains 7 of the 93 known pneumococcal serotypes (4, 6B, 9V, 14, 18C, 19F, 23F) was the first PCV available, licensed in the US in 2000 and subsequently in many countries worldwide, including Latin American and Caribbean countries. Since its introduction, PCV7 has been documented effective for reducing invasive PD mortality and burden, as well as that of pneumonia and otitis media. Additionally, PD caused by the vaccine serotypes has decreased in the unimmunized population due to herd immunity induced by PCV7. Despite this success, significant disease burden still exists globally due to serotypes not included in PCV7. Currently there are 2 new PCVs that have been approved for use in children, a 10-valent vaccine (includes PCV7 serotypes plus serotypes 1, 5 and 7F) and a 13-valent vaccine (includes PCV7 serotypes plus serotypes 1, 3, 5, 6A, 7F and 19A). The selection of new serotypes to be included was based on importance of these serotypes as causes of PD. An additional 15-valent vaccine (includes PCV 7 serotypes plus serotypes 1, 3, 5, 6A, 7F, 19A, 22F and 33F) is undergoing clinical trial testing. In view of the 93 serotypes that are currently known, it seems clear that vaccines with greater coverage, likely based on proteins common to all serotypes, will be needed in the future. Technical and regulatory challenges to the development and approval of newer PCVs include a need for licensing criteria of common protein vaccines, establishment of correlates of protection for disease manifestations other than invasive disease, comparative efficacy data, and clinical trial testing of concomitant immunization of higher valency PCVs with other vaccines.

7-Valent pneumococcal conjugate vaccination in England and Wales: is it still beneficial despite high levels of serotype replacement?

Background

The UK introduced the 7-valent pneumococcal conjugate vaccine (PCV7) into the national vaccination program in September 2006. Previous modelling assumed that the likely impact of PCV7 on invasive pneumococcal disease (IPD) would be similar to the US experience with PCV7. However, recent surveillance data show a more rapid replacement of PCV7 IPD cases by non-PCV7 IPD cases than was seen in the US.

Methods and Findings

A previous model of pneumococcal vaccination was re-parameterised using data on vaccine coverage and IPD from England and Wales between 2006 and 2009. Disease incidence was adjusted for the increasing trend in reported IPD cases prior to vaccination. Using this data we estimated that individuals carrying PCV7 serotypes have much higher protection (96%;95% CI 72%-100%) against acquisition of NVT carriage than the 15% previously estimated from US data, which leads to greater replacement. However, even with this level of replacement, the annual number of IPD cases may be 560 (95% CI, -100 to 1230) lower ten years after vaccine introduction compared to what it may have been without vaccination. A particularly marked fall of 39% in children under 15 years by 2015/6 is predicted.

Conclusion

Our model suggests that PCV7 vaccination could result in a decrease in overall invasive pneumococcal disease, particularly in children, even in an environment of rapid replacement with non-PCV7 serotypes within 5 years of vaccine introduction at high coverage.

Pneumococcal conjugate vaccination in Canadian infants and children younger than five years of age: Recommendations and expected benefits

INTRODUCTION

Streptococcus pneumoniae infection may result in invasive pneumococcal disease (IPD), such as bacteremia, meningitis and bacteremic pneumonia, or in non-IPD, such as pneumonia, sinusitis and otitis media. In June 2001, a heptavalent pneumococcal conjugate vaccine (PCV7) (Prevnar, Wyeth Pharmaceuticals, Canada) was approved for use in children in Canada. The objective of the present paper is to review S pneumoniae-induced disease incidence and vaccine recommendations in Canadian infants and children younger than five years of age. Particular attention is given to the expected benefits of vaccination in Canada based on postmarketing data and economic modelling.

METHODS

Searches were performed on PubMed and Web of Science databases and specific Canadian journals using the key words 'pneumococc*', 'vaccine', 'conjugate', 'infant' and 'Canadian'.

RESULTS AND DISCUSSION

PCV7 appears to be safe and effective against IPD and non-IPD in children younger than five years of age and, more importantly, in children younger than two years of age (who are at highest risk for IPD). An examination of postmarketing data showed a reduction in incidence of pneumococcal disease in age groups that were vaccinated and in older age groups, indicating the likelihood of herd protection. Concurrently, there was a reduction in the occurrence of antimicrobial-resistant isolates.

CONCLUSIONS

The results from the present review suggest that PCV7 is currently benefiting Canadian children and society by lowering S pneumoniae-associated disease. Additional gains from herd protection and further reductions in antimicrobial resistance will be achieved as more Canadian children younger than five years of age are routinely vaccinated with PCV7.

Effect of the pneumococcal conjugate vaccine on pneumococcal carriage in Turkish children

BACKGROUND

  The aim of our study was to evaluate the effect of the seven-valent pneumococcal conjugate vaccine which has recently been included in the national immunization schedule on the nasopharyngeal carriage of Streptococcus pneumoniae in a group of healthy Turkish children. This is the first study determining the efficacy of this vaccine in Turkey.

METHODS

  One hundred and thirty-eight children who had completed their pneumococcal vaccination series and 109 unvaccinated control subjects aged 12-59 months were included in the study between October 2007 and April 2008. A single nasopharyngeal swab sample was obtained from each subject.

RESULTS

  S. pneumoniae was isolated in 32 (12.9%) of 247 subjects. No significant differences were detected in pneumococcal carriage rate between the vaccinees and controls (10.1% vs 16.5%). Prevalence of vaccine type (VT) carriage was statistically lower in the vaccinated group than the controls while non-vaccine type carriage (NVT) was similar. Most frequently isolated vaccine serotype was 23F in the vaccinated group and 19F in the non-vaccinated group. Of the isolated S. pneumoniae, 13.3% were penicillin susceptible and 86.7% were non-susceptible. Vaccinees and controls did not differ statistically with respect to carriage rate of penicillin-resistant S. pneumoniae. All the pneumococcal isolates were susceptible to ceftriaxone, vancomycin, rifampicin and quinolones.

CONCLUSION

  Seven-valent conjugate vaccine induces long-term protection against carriage of VT S. pneumoniae in Turkish children. The ability of the conjugate vaccine to reduce transmission of antibiotic resistant S. pneumoniae may be possible if its introduction is coupled with a reduction in inappropriate use of antibiotics.

Microbial communities of the upper respiratory tract and otitis media in children

Streptococcus pneumoniae asymptomatically colonizes the upper respiratory tract of children and is a frequent cause of otitis media. Patterns of microbial colonization likely influence S. pneumoniae colonization and otitis media susceptibility. This study compared microbial communities in children with and without otitis media. Nasal swabs and clinical and demographic data were collected in a cross-sectional study of Philadelphia, PA, children (6 to 78 months) (n=108) during the 2008-2009 winter respiratory virus season. Swabs were cultured for S. pneumoniae. DNA was extracted from the swabs; 16S rRNA gene hypervariable regions (V1 and V2) were PCR amplified and sequenced by Roche/454 Life Sciences pyrosequencing. Microbial communities were described using the Shannon diversity and evenness indices. Principal component analysis (PCA) was used to group microbial community taxa into four factors representing correlated taxa. Of 108 children, 47 (44%) were colonized by S. pneumoniae, and 25 (23%) were diagnosed with otitis media. Microbial communities with S. pneumoniae were significantly less diverse and less even. Two PCA factors were associated with a decreased risk of pneumococcal colonization and otitis media, as follows: one factor included potentially protective flora (Corynebacterium and Dolosigranulum), and the other factor included Propionibacterium, Lactococcus, and Staphylococcus. The remaining two PCA factors were associated with an increased risk of otitis media. One factor included Haemophilus, and the final factor included Actinomyces, Rothia, Neisseria, and Veillonella. Generally, these taxa are not considered otitis media pathogens but may be important in the causal pathway. Increased understanding of upper respiratory tract microbial communities will contribute to the development of otitis media treatment and prevention strategies.

Pneumococcal resistance and serotype 19A in Pittsburgh-area children with acute otitis media before and after introduction of 7-valent pneumococcal polysaccharide vaccine

METHODS

Before and after introduction of pneumococcal conjugate vaccine (PCV7), the authors obtained nasopharyngeal (NP) specimens from 3 groups of children aged 6 to 23 months with acute otitis media (AOM): group 1 (pre-PCV7), group 2 (early post-PCV7), and group 3 (late post-PCV7).

RESULTS

Of the Streptococcus pneumoniae isolates, the proportion that were vaccine serotypes (VTs) declined progressively (60.4% vs 48.6% vs 5.2% in groups 1, 2, and 3, respectively; P < .001). Concurrently, increases occurred in the proportion of penicillin-nonsusceptible isolates (minimum inhibitory concentration >0.1 µg/mL; 26.7% vs 37.8% vs. 38.5%; P = .12); the proportion of isolates that were serotype 19A (4.0% vs 0% vs 25.9%; P < .001); and the proportion of 19A isolates that were penicillin-nonsusceptible (0% in group 1, 68.6% in group 3; P = .004).

CONCLUSION

Shifts in pneumococcal serotype distribution and increases in penicillin nonsusceptibility among pneumococcal isolates from children with AOM underscore the need for continuing bacteriological surveillance for future vaccine development.

The dynamics of nasopharyngeal streptococcus pneumoniae carriage among rural Gambian mother-infant pairs

Background

Streptococcus pneumoniae is an important cause of community acquired pneumonia, sepsis, meningitis and otitis media globally and has been incriminated as a major cause of serious childhood bacterial infections in The Gambia. Better understanding of the dynamics of transmission and carriage will inform control strategies.

Methods

This study was conducted among 196 mother-infant pairs recruited at birth from six villages in the West Kiang region of The Gambia. Nasopharyngeal swabs were collected from mother-infant pairs at birth (within 12 hours of delivery), 2, 5 and 12 months. Standard techniques of culture were used to identify carriage and serotype S. pneumoniae.

Results

Of 46 serotypes identified, the 6 most common, 6A, 6B, 14, 15, 19F and 23F, accounted for 67.3% of the isolates from infants. Carriage of any serotype among infants rose from 1.5% at birth to plateau at approximately 80% by 2 m (prevalence at 2 m = 77%; 5 m = 86%; 12 m = 78%). Likewise, maternal carriage almost doubled in the first 2 months post-partum and remained elevated for the next 10 m (prevalence at birth = 13%; 2 m = 24%; 5 m = 22%; 12 m = 21%). Carriage was significantly seasonal in both infants and mothers with a peak in December and lowest transmission in August. The total number of different serotypes we isolated from each infant varied and less than would be expected had the serotypes assorted independently. In contrast, this variability was much as expected among mothers. The half-life of a serotype colony was estimated to be 1.90 m (CI_95%: 1.66-2.21) in infants and 0.75 m (CI_95%: 0.55-1.19) in mothers. While the odds for a serotype to be isolated from an infant increased by 9-fold if it had also been isolated from the mother, the population attributable fraction (PAF) of pneumococcal carriage in infants due to maternal carriage was only 9.5%. Some marked differences in dynamics were observed between vaccine and non-vaccine serotypes.

Conclusions

Colonisation of the nasopharynx in Gambian infants by S. pneumoniae is rapid and highly dynamic. Immunity or inter-serotype competition may play a role in the dynamics. Reducing mother-infant transmission would have a minimal effect on infant carriage.

Live recombinant Salmonella Typhi vaccines constructed to investigate the role of rpoS in eliciting immunity to a heterologous antigen

We hypothesized that the immunogenicity of live Salmonella enterica serovar Typhi vaccines expressing heterologous antigens depends, at least in part, on its rpoS status. As part of our project to develop a recombinant attenuated S. Typhi vaccine (RASTyV) to prevent pneumococcal diseases in infants and children, we constructed three RASTyV strains synthesizing the Streptococcus pneumoniae surface protein PspA to test this hypothesis. Each vector strain carried ten engineered mutations designed to optimize safety and immunogenicity. Two S. Typhi vector strains (chi9639 and chi9640) were derived from the rpoS mutant strain Ty2 and one (chi9633) from the RpoS(+) strain ISP1820. In chi9640, the nonfunctional rpoS gene was replaced with the functional rpoS gene from ISP1820. Plasmid pYA4088, encoding a secreted form of PspA, was moved into the three vector strains. The resulting RASTyV strains were evaluated for safety in vitro and for immunogenicity in mice. All three RASTyV strains were similar to the live attenuated typhoid vaccine Ty21a in their ability to survive in human blood and human monocytes. They were more sensitive to complement and were less able to survive and persist in sewage and surface water than their wild-type counterparts. Adult mice intranasally immunized with any of the RASTyV strains developed immune responses against PspA and Salmonella antigens. The RpoS(+) vaccines induced a balanced Th1/Th2 immune response while the RpoS(-) strain chi9639(pYA4088) induced a strong Th2 immune response. Immunization with any RASTyV provided protection against S. pneumoniae challenge; the RpoS(+) strain chi9640(pYA4088) provided significantly greater protection than the ISP1820 derivative, chi9633(pYA4088). In the pre-clinical setting, these strains exhibited a desirable balance between safety and immunogenicity and are currently being evaluated in a Phase 1 clinical trial to determine which of the three RASTyVs has the optimal safety and immunogenicity profile in human hosts.

Bacterial meningitis vaccines: not just for kids

Bacterial meningitis remains a feared diagnosis that may lead to significant mortality and morbidity in both the developed and developing world; case fatality rates range from 10% to 50% among all age groups. Several vaccines are available (including the Haemophilus influenzae type B polysaccharide conjugate vaccine) that have proven effective in reducing the incidence of bacterial meningitis. Although a 23-valent pneumococcal polysaccharide vaccine has been available for some time, use of the 7-valent pneumococcal conjugate vaccine (PCV) has demonstrated a dramatic reduction in the incidence of invasive pneumococcal disease; despite the increase in the disease caused by nonvaccine-serotype strains, the success of the 7-valent PCV is noteworthy. A quadrivalent conjugate meningococcal vaccine has been available in the United States since 2005; although its true efficacy remains to be determined, there have been dramatic results with declining incidence in certain high-risk populations and in endemic areas.

Dynamic models of pneumococcal carriage and the impact of the Heptavalent Pneumococcal Conjugate Vaccine on invasive pneumococcal disease

Background

The 7-valent pneumococcal conjugate vaccine has been introduced in national immunisation programmes of most industrialised countries and recently in two African GAVI eligible countries (Rwanda and The Gambia). However the long term effects of PCV are still unclear, as beneficial direct and herd immunity effects might be countered by serotype replacement.

Method

A dynamic, age-structured, compartmental model of Streptococcus pneumoniae transmission was developed to predict the potential impact of PCV7 on the incidence of invasive disease accounting for both herd immunity and serotype replacement effects. The model was parameterised using epidemiological data from England and Wales and pre and post-vaccination surveillance data from the US.

Results

Model projections showed that serotype replacement plays a crucial role in determining the overall effect of a PCV7 vaccination programme and could reduce, negate or outweigh its beneficial impact. However, using the estimate of the competition parameter derived from the US post-vaccination experience, an infant vaccination programme would prevent 39,000 IPD cases in the 20 years after PCV7 introduction in the UK. Adding a catch-up campaign for under 2 or under 5 year olds would provide a further reduction of 1,200 or 3,300 IPD cases respectively, mostly in the first few years of the programme.

Conclusions

This analysis suggests that a PCV vaccination programme would eradicate vaccine serotypes from circulation. However, the increase in carriage of non-vaccine serotypes, and the consequent increase in invasive disease, could reduce, negate or outweigh the benefit. These results are sensitive to changes in the protective effect of the vaccine, and, most importantly, to the level of competition between vaccine and non-vaccine types. The techniques developed here can be used to assess the introduction of vaccination programmes in developing countries and provide the basis for cost-effectiveness analyses.

New patterns in the otopathogens causing acute otitis media six to eight years after introduction of pneumococcal conjugate vaccine

OBJECTIVE

To describe NP and AOM otopathogens during the time frame 2007 to 2009, 6 to 8 years after the introduction of 7-valent pneumococcal conjugate (PCV7) in the United States and to compare nasopharyngeal (NP) colonization and acute otitis media (AOM) microbiology in children 6 to 36 months of age having first and second AOM episodes with children who are otitis prone.

METHODS

Prospectively, the microbiology of NP colonization and AOM episodes was determined in 120 children with absent or infrequent AOM episodes. NP samples were collected at 7 routine visits between 6 and 30 months of age and at the time of AOM. For first and subsequent AOM episodes, middle ear fluid (MEF) was obtained by tympanocentesis. Eighty otitis prone children were comparatively studied. All 200 children received age-appropriate doses of PCV7.

RESULTS

We found PCV7 serotypes were virtually absent: (0.9% isolated from both NP and MEF) in both study groups. However, non-PCV7 serotypes replaced PCV serotypes such that the frequency of isolation of S. pneumoniae (Spn) was nearly equal to that of non-typeable Haemophilus influenzae (NTHi). M. catarrhalis (Mcat) was less common and Staphylococcus aureus infrequent in the NP and MEF from the 2 groups. The proportion of Spn, NTHi and Mcat causing AOM was similar in children with first and second AOM episodes compared to otitis prone children. However, oxacillin-resistant Spn isolated from the NP and MEF was 19% for the absent/infrequent and 58% for the otitis prone groups, P < 0.0001. Beta-lactamase producing NTHi occurred more frequently in the otitis prone group, P = 0.04.

CONCLUSIONS

Six to 8 years after widespread use of PCV7, Spn strains expressing vaccine-type serotypes have virtually disappeared from the NP and MEF of vaccinated children. NP colonization and AOM has changed to non-PCV7 strains of Spn. NTHi continues to be a major AOM pathogen. The otopathogens in first and second AOM and in otitis prone children are very similar although Spn and NTHi are more often antibiotic resistant in the otitis prone.

Capacity of serotype 19A and 15B/C Streptococcus pneumoniae isolates for experimental otitis media: Implications for the conjugate vaccine

Non-vaccine Streptococcus pneumoniae serotypes are increasingly associated with disease. We evaluated isolates of the same sequence type (ST199) but different serotypes (15B/C, 19A) for growth in vitro, and pathogenic potential in a chinchilla otitis media model. We also developed a quantitative PCR (qPCR) assay to quantitatively assess each isolate, circumventing the need for selectable markers. In vitro studies showed faster growth of serotype 19A over 15B/C. Both were equally capable of colonization and middle ear infection in this model. Serotype 19A is included in new conjugate vaccine formulations while serotype 15B/C is not. Non-capsular vaccine targets will be important in disease prevention efforts.

Nasopharyngeal carriage of Streptococcus pneumoniae in Gambian children who participated in a 9-valent pneumococcal conjugate vaccine trial and in their younger siblings

BACKGROUND

Nasopharyngeal carriage of Streptococcus pneumoniae is extremely prevalent in The Gambia. We studied the effects of vaccination with pneumococcal conjugate vaccines on the carriage of individual serotypes and on antimicrobial resistance in vaccinated children and their younger siblings.

METHODS

A longitudinal study of a subsample of children (n=2342) who participated in a randomized, placebo controlled trial of a 9-valent pneumococcal conjugate vaccines (PCV-9) in The Gambia, and a cross-sectional study of non-PCV-9-vaccinated younger siblings (n=675).

RESULTS

Recipients of PCV-9 were less likely to carry vaccine serotypes 4, 6B, 9V, 14, 19F, and 23F but more likely to carry vaccine-associated 19A and 9 nonvaccine serotypes at approximately 6 months postvaccination (age, 12 months) than were controls (each P<0.05). At approximately 16 months postvaccination, carriage of vaccine-associated-serotype 6A was also significantly reduced (P<0.01) while 3 other nonvaccine serotypes were more prevalent in the PCV-9 recipients (each P<0.05). At 16 months, but not 6 months, postvaccination PCV-9 recipients had lower rate of carrying isolates resistant to tetracycline and trimethoprim-sulfamethoxazole (TMP-SMZ) than controls (risk ratio: 0.90 and 0.95, respectively; each P<0.05). There was no difference in patterns of carriage of pneumococci in younger siblings of PCV-9 or placebo recipients.

CONCLUSIONS

The effects of 9-valent pneumococcal conjugate vaccines on carriage of pneumococci persisted for at least 16 months postvaccination in Gambian children. Vaccination had no indirect effect on carriage in younger siblings and there was limited impact on antibiotic resistance.

Pneumococcal conjugate vaccines for preventing vaccine-type invasive pneumococcal disease and X-ray defined pneumonia in children less than two years of age

BACKGROUND

Pneumonia, caused by Streptococcus pneumoniae, is a major cause of morbidity and mortality among children in low-income countries. The effectiveness of pneumococcal conjugate vaccines (PCVs) against invasive pneumococcal disease (IPD), pneumonia, and mortality needs to be evaluated.

OBJECTIVES

To update the 2004 review on the efficacy of PCVs in preventing vaccine-serotypes IPD (VT-IPD) , X-ray defined pneumonia among HIV-1 negative children, and other new outcomes.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2009, issue 1), which contains the Cochrane Acute Respiratory Infections Group's Specialised Register; MEDLINE (1990 to Week 4 February 2009); and EMBASE (1974 to March 2009).

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing PCV with placebo, or another vaccine, in children under two with IPD and clinical / radiographic pneumonia as outcomes.

DATA COLLECTION AND ANALYSIS

Two review authors independently identified studies, extracted data, and evaluated their corresponding risks of bias. Differences were resolved by discussion. Meta-analysis used the inverse variance method.

MAIN RESULTS

We identified 11 publications from six RCTs conducted in Africa, US, Philippines and Finland where 57,015 children received PCV; while 56,029 received placebo or another vaccine. Seven publications provided high quality evidence on PCV efficacy against IPD and four provided moderate quality evidence against pneumonia. None of the five trials with all-cause mortality data were powered to investigate this outcome. Only two trials have data on all-cause admissions.The main analysis for this review involved HIV-1 negative children and used the pooled results of random-effects model, intent-to-treat analysis (ITT).Pooled vaccine efficacy (VE) for VT-IPD was 80% (95% confidence interval (CI) 58% to 90%, P < 0.0001); all serotypes-IPD, 58% (95% CI 29% to 75%, P = 0.001); World Health Organization X-ray defined pneumonia was 27% (95% CI 15% to 36%, P < 0.0001); clinical pneumonia, 6% (95% CI 2% to 9%, P = 0.0006); and all-cause mortality, 11% (95% CI -1% to 21%, P = 0.08). Analysis involving HIV-1 positive children had similar findings.

AUTHORS' CONCLUSIONS

PCV is effective in preventing IPD, X-ray defined pneumonia, and clinical pneumonia among HIV-1 negative and HIV-1 positive children under two years. The impact was greater for VT-IPD than for all serotypes-IPD, and for X-ray defined pneumonia than for clinical pneumonia. An 11% reduction with a 95% CI of -1% to 21% and a P = 0.08 is compatible with reduction in all-cause mortality.

Continued impact of pneumococcal conjugate vaccine on carriage in young children

OBJECTIVES

The goals were to assess serial changes in Streptococcus pneumoniae serotypes and antibiotic resistance in young children and to evaluate whether risk factors for carriage have been altered by heptavalent pneumococcal conjugate vaccine (PCV7).

METHODS

Nasopharyngeal specimens and questionnaire/medical record data were obtained from children 3 months to <7 years of age in primary care practices in 16 Massachusetts communities during the winter seasons of 2000-2001 and 2003-2004 and in 8 communities in 2006-2007. Antimicrobial susceptibility testing and serotyping were performed with S pneumoniae isolates.

RESULTS

We collected 678, 988, and 972 specimens during the sampling periods in 2000-2001, 2003-2004, and 2006-2007, respectively. Carriage of non-PCV7 serotypes increased from 15% to 19% and 29% (P < .001), with vaccine serotypes decreasing to 3% of carried serotypes in 2006-2007. The relative contribution of several non-PCV7 serotypes, including 19A, 35B, and 23A, increased across sampling periods. By 2007, commonly carried serotypes included 19A (16%), 6A (12%), 15B/C (11%), 35B (9%), and 11A (8%), and high-prevalence serotypes seemed to have greater proportions of penicillin nonsusceptibility. In multivariate models, common predictors of pneumococcal carriage, such as child care attendance, upper respiratory tract infection, and the presence of young siblings, persisted.

CONCLUSIONS

The virtual disappearance of vaccine serotypes in S pneumoniae carriage has occurred in young children, with rapid replacement with penicillin-nonsusceptible nonvaccine serotypes, particularly 19A and 35B. Except for the age group at highest risk, previous predictors of carriage, such as child care attendance and the presence of young siblings, have not been changed by the vaccine.

Novel type of Streptococcus pneumoniae causing multidrug-resistant acute otitis media in children

A new multidrug-resistant strain of serotype 19A has been characterized in upstate New York.

After our recent discovery of a Streptococcus pneumoniae 19A “superbug” (Legacy strain) that is resistant to all Food and Drug Administration–approved antimicrobial drugs for treatment of acute otitis media (AOM) in children, other S. pneumoniae isolates from children with AOM were characterized by multilocus sequence typing (MLST). Among 40 isolates studied, 16 (40%) were serotype 19A, and 9 (23%) were resistant to multiple antimicrobial drugs. Two others had unreported sequence types (STs) that expressed the 19A capsule, and 8 (88%) of the 9 multidrug-resistant strains were serotype 19A, including the Legacy strain with the new ST-2722. In genetic relatedness, ST-2722 belonged to a cluster of reported strains of S. pneumoniae in which all strains had 6 of the same alleles as ST-156. The multidrug-resistant strains related to ST-156 expressed different capsular serotypes: 9V, 14, 11A, 15C, and 19F.

Evaluation of sequential multiplex PCR for direct detection of multiple serotypes of Streptococcus pneumoniae from nasopharyngeal secretions

Sequential multiplex PCR was evaluated for detection of multiple Streptococcus pneumoniae serotypes directly from nasopharyngeal secretions. A total of 279 nasopharyngeal swab samples were tested blindly. When limited to the 29 serotypes identifiable by the molecular method, the mean number of serotypes identified by the conventional latex/Quellung method was 0.85, which was significantly lower than that by the molecular method (P <0.0001). The multiplex PCR method identified significantly more serotypes than the latex/Quellung method if limited to the 29 serotypes (P=0.001 and P=0.014, respectively).

Effect of pneumococcal conjugate vaccine on pneumococcal meningitis

BACKGROUND

Invasive pneumococcal disease declined among children and adults after the introduction of the pediatric heptavalent pneumococcal conjugate vaccine (PCV7) in 2000, but its effect on pneumococcal meningitis is unclear.

METHODS

We examined trends in pneumococcal meningitis from 1998 through 2005 using active, population-based surveillance data from eight sites in the United States. Isolates were grouped into PCV7 serotypes (4, 6B, 9V, 14, 18C, 19F, and 23F), PCV7-related serotypes (6A, 9A, 9L, 9N, 18A, 18B, 18F, 19B, 19C, 23A, and 23B), and non-PCV7 serotypes (all others). Changes in the incidence of pneumococcal meningitis were assessed against baseline values from 1998-1999.

RESULTS

We identified 1379 cases of pneumococcal meningitis. The incidence declined from 1.13 cases to 0.79 case per 100,000 persons between 1998-1999 and 2004-2005 (a 30.1% decline, P<0.001). Among persons younger than 2 years of age and those 65 years of age or older, the incidence decreased during the study period by 64.0% and 54.0%, respectively (P<0.001 for both groups). Rates of PCV7-serotype meningitis declined from 0.66 case to 0.18 case (a 73.3% decline, P<0.001) among patients of all ages. Although rates of PCV7-related-serotype disease decreased by 32.1% (P=0.08), rates of non-PCV7-serotype disease increased from 0.32 to 0.51 (an increase of 60.5%, P<0.001). The percentages of cases from non-PCV7 serotypes 19A, 22F, and 35B each increased significantly during the study period. On average, 27.8% of isolates were nonsusceptible to penicillin, but fewer isolates were nonsusceptible to chloramphenicol (5.7%), meropenem (16.6%), and cefotaxime (11.8%). The proportion of penicillin-nonsusceptible isolates decreased between 1998 and 2003 (from 32.0% to 19.4%, P=0.01) but increased between 2003 and 2005 (from 19.4% to 30.1%, P=0.03).

CONCLUSIONS

Rates of pneumococcal meningitis have decreased among children and adults since PCV7 was introduced. Although the overall effect of the vaccine remains substantial, a recent increase in meningitis caused by non-PCV7 serotypes, including strains nonsusceptible to antibiotics, is a concern.