Herd immunity and pneumococcal conjugate vaccine: A quantitative model

Fostering healthy aging: The interdependency of infections, immunity and frailty

Untangling the interdependency of infections, immunity and frailty may help to clarify their roles in the maintenance of health in aging individuals, and the recent COVID-19 pandemic has further highlighted such priority. In this scoping review we aimed to systematically collect the evidence on 1) the impact of common infections such as influenza, pneumonia and varicella zoster on frailty development, and 2) the role played by frailty in the response to immunization of older adults. Findings are discussed under a unifying framework to identify knowledge gaps and outline their clinical and public health implications to foster a healthier aging. Twenty-nine studies (113,863 participants) selected to answer the first question provided a moderately strong evidence of an association between infections and physical as well as cognitive decline - two essential dimensions of frailty. Thirteen studies (34,520 participants) investigating the second aim, showed that frailty was associated with an impaired immune response in older ages, likely due to immunosenescence. However, the paucity of studies, the absence of tools to predict vaccine efficacy, and the lack of studies investigating the efficacy of newer vaccines in presence of frailty, strongly limit the formulation of more personalized immunization strategies for older adults. The current evidence suggests that infections and frailty repeatedly cross each other pathophysiological paths and accelerate the aging process in a vicious circle. Such evidence opens to several considerations. First, the prevention of both conditions pass through a life course approach, which includes several individual and societal aspects. Second, the maintenance of a well-functioning immune system may be accomplished by preventing frailty, and vice versa. Third, increasing the adherence to immunization may delay the onset of frailty and maintain the immune system homeostasis, beyond preventing infections.

Twenty-Year Public Health Impact of 7- and 13-Valent Pneumococcal Conjugate Vaccines in US Children

Pneumococcal conjugate vaccines (PCVs) have been used in the United States since 2000. To assess the cumulative 20-year effect of PCVs on invasive pneumococcal disease (IPD) incidence among children <5 years of age, we analyzed Active Bacterial Core Surveillance data, conducted a literature review, and modeled expected and observed disease. We found that PCVs have averted >282,000 cases of IPD, including ≈16,000 meningitis, ≈172,000 bacteremia, and ≈55,000 bacteremic pneumonia cases. In addition, vaccination has prevented 97 million healthcare visits for otitis media, 438,914-706,345 hospitalizations for pneumonia, and 2,780 total deaths. IPD cases declined 91%, from 15,707 in 1997 to 1,382 in 2019. Average annual visits for otitis media declined 41%, from 78 visits/100 children before PCV introduction to 46 visits/100 children after PCV13 introduction. Annual pneumonia hospitalizations declined 66%-79%, from 110,000-175,000 in 1997 to 37,000 in 2019. These findings confirm the substantial benefits of PCVs for preventing IPD in children.

Ten year public health impact of 13-valent pneumococcal conjugate vaccination in infants: A modelling analysis

Pneumococcal disease is a substantial contributor to illness and death in young children globally. The introduction of 7-valent pneumococcal conjugate vaccine (PCV7) in 2000 had a significant impact in preventing pneumococcal disease in both vaccinated children and unvaccinated individuals (through herd effect). A higher valent PCV13 replaced PCV7 in late 2009. This analysis was undertaken to assess how many cases and deaths have been averted over the last decade since PCV13 introduction. A model estimated the number of infants vaccinated annually with PCV13, as well as the number of cases and deaths of invasive pneumococcal disease, pneumococcal pneumonia, and acute otitis media cases averted. PCV13 vaccination was estimated to have prevented 175.2 million cases of all pneumococcal diseases and 624,904 deaths globally between 2010 and 2019. These results demonstrate the substantial public health impact of PCV13 and highlight the importance of increasing the global reach of PCV programs.

Distribution of PCV13 and PPSV23 Streptococcus pneumoniae serotypes in Argentinean adults with invasive disease, 2013-2017

Streptococcus pneumoniae is a major cause of severe invasive disease associated with high mortality and morbidity worldwide. To identify the serotypes most commonly associated with infection in adults in Argentina, 791 pneumococcal isolates from 56 hospitals belonging to 16 provinces and Buenos Aires city were serotyped. The isolates were submitted as part of a National Surveillance Program for invasive pneumococcal disease in adults, which started in 2013. Serotypes 3, 8, 12F, 7F and 1 were the most prevalent among adult patients. During the study period there was no significant difference in serotype distribution between the age groups studied (18-64 and ≥65 years old), except for serotype 1, 3 and 23A. Most prevalent serotypes in pneumonia were serotype 7F, 1, 12F, 8, and 3. When the clinical diagnosis was meningitis, serotype 3 and 12F were the most prevalent, whereas when the diagnosis was sepsis/bacteremia the most prevalent was serotype 8. In this work, for the 18-64-year-old group, PPSV23 and PCV13 serotypes accounted for 74.56% and 44.54% respectively of the cases in the studied period. On the other hand, for the ≥65-year-old group, these serotypes represented 72.30% and 41.42% respectively. The aim of this work was to establish the knowledge bases of the serotypes that cause invasive pneumococcal diseases in the adult population in Argentina and to be able to detect changes in their distribution over time in order to explore the potential serotype coverage of the vaccines in current use.

Efficacy and Safety of the Pneumococcal Conjugate-13 Valent Vaccine in Adults

Invasive pneumococcal disease and pneumococcal pneumonia cause substantial morbidity and mortality in the elderly. This review focuses on the immunogenicity, safety, efficacy and effectiveness data on the use of the 13-valent conjugate pneumococcal vaccine (PCV13) in adults. A MEDLINE literature search was performed from January 1946 to December 2017. Additional references were identified from a review of literature citations. All English-language randomized trials, observational studies and meta-analyses assessing the immunogenicity, efficacy, effectiveness and safety of PCV13 in adults were evaluated. Six randomized controlled studies evaluated immunogenicity and safety of PCV13 in adults and showed that the conjugated vaccine elicited a greater immune response to the majority of the 13 serotypes compared to the 23-valent polysaccharide pneumococcal vaccine (PPV23). Administering PCV13 prior to PPV23 elicits greater immune responses and multiple doses of PCV13 demonstrated modest advantage. PCV13 titers declined after a year but remained above baseline. A randomized clinical trial (CAPiTA) showed that PCV13 was effective in preventing community-acquired pneumonia (CAP) and vaccine-type invasive pneumococcal disease, but not any cause pneumonia. Safety data shows PCV13 elicits minor local reactions, such as pain at the injection site. Major side effects that were commonly reported included muscle fatigue and headache. Both local and systemic adverse events were comparable to PPV23. While PCV13 has a well-established immunogenicity and safety profile in adults, there is sparse data on sequential or multiple dosing, efficacy and effectiveness in adults. As there are few countries who have adopted PCV13 for routine adult immunization, there is a need to evaluate the effectiveness of PCV13 in a real-world setting.

Modifiable risk factors for community-acquired pneumonia in children under 5 years of age in resource-poor settings: a case-control study

OBJECTIVE

Despite the availability of vaccines and antibiotics, pneumonia remains the leading cause of mortality among children under 5 years of age. The objective of this study was to identify modifiable risk factors for community-acquired pneumonia (CAP) in children under 5 years of age in a vaccinated population.

METHODS

A case-control study was conducted between January and December 2017. The cases included children aged 2-59 months with X-ray-confirmed pneumonia, whereas the controls were children from the community with no history of respiratory infection. A multivariable logistic regression model was used to determine the modifiable risk factors for CAP.

RESULTS

A total of 113 children with X-ray-confirmed pneumonia and 350 healthy children were enrolled in this study. The median ages for the cases and controls were 13.7 (IQR = 7.2-25.3) and 13.4 (IQR = 6.0-24.8) months respectively. One (0.9%) child died after the enrolment. The independent predictors of CAP included a lack of exclusive breastfeeding for 6 months (aOR = 1.7, 95% CI = 1.0-2.9), underweight (aOR = 2.1, 95% CI = 1.0-4.5), unclean cooking fuel (aOR = 1.8, 95% CI = 1.0-3.3) and low income (aOR = 2.9, 95% CI = 1.6-5.4). No association was found between vaccination status and CAP.

CONCLUSION

In addition to a lack of exclusive breastfeeding, children from families of low-economic status were at risk of contracting CAP. Since the risk factors are complex, the study results call for more concerted efforts by and collaboration among the health, agriculture and development sectors to address mortality caused by CAP.

The impact of pneumococcal vaccination on pneumonia mortality among the elderly in Japan: a difference-in-difference study

BACKGROUND

It is plausible that the routine immunization among infants using pneumococcal conjugate vaccine 13 (PCV13) from 2013 and among the elderly using pneumococcal polysaccharide vaccine 23 (PPV23) from 2014 contributed to reducing the pneumonia mortality among the elderly in Japan. The present study aimed to estimate the causal effect of this vaccination on pneumonia mortality, using the available cause-of-death data and employing a difference-in-difference (DID) design.

METHODS

Two types of mortality data, that is, prefecture-dependent and age- and gender-specific mortality data, from 2003 to 2017 were retrieved. We used mortality due to malignant neoplasm and heart disease as control groups and employed a DID design with an assumed parallel mortality trend between pneumonia and control group mortality since 2013 to estimate the causal effect of pneumococcal vaccination from 2014.

RESULTS

Our estimation based on malignant neoplasm and heart disease as controls indicated that the reduced pneumonia mortality in 2017 owing to pneumococcal vaccination was as large as 41.9 (33.2, 50.6) and 31.2 (23.8, 38.6) per 100,000 individuals, respectively. The largest mortality reduction was observed for the oldest group (aged ≥90 years), especially among men.

DISCUSSION

The pneumococcal vaccination program, perhaps mainly represented by high vaccination coverage of PCV13 among children and partly by PPV23 administration with low coverage among the elderly in Japan, was shown to have reduced the pneumonia mortality in the elderly at the population level.

Estimating the distribution of morbidity and mortality of childhood diarrhea, measles, and pneumonia by wealth group in low- and middle-income countries

BACKGROUND

Equitable access to vaccines has been suggested as a priority for low- and middle-income countries (LMICs). However, it is unclear whether providing equitable access is enough to ensure health equity. Furthermore, disaggregated data on health outcomes and benefits gained across population subgroups are often unavailable. This paper develops a model to estimate the distribution of childhood disease cases and deaths across socioeconomic groups, and the potential benefits of three vaccine programs in LMICs.

METHODS

For each country and for three diseases (diarrhea, measles, pneumonia), we estimated the distributions of cases and deaths that would occur across wealth quintiles in the absence of any immunization or treatment programs, using both the prevalence and relative risk of a set of risk and prognostic factors. Building on these baseline estimates, we examined what might be the impact of three vaccines (first dose of measles, pneumococcal conjugate, and rotavirus vaccines), under five scenarios based on different sets of quintile-specific immunization coverage and disease treatment utilization rates.

RESULTS

Due to higher prevalence of risk factors among the poor, disproportionately more disease cases and deaths would occur among the two lowest wealth quintiles for all three diseases when vaccines or treatment are unavailable. Country-specific context, including how the baseline risks, immunization coverage, and treatment utilization are currently distributed across quintiles, affects how different policies translate into changes in cases and deaths distribution.

CONCLUSIONS

Our study highlights several factors that would substantially contribute to the unequal distribution of childhood diseases, and finds that merely ensuring equal access to vaccines will not reduce the health outcomes gap across wealth quintiles. Such information can inform policies and planning of programs that aim to improve equitable delivery of healthcare services.

The Equity Impact Vaccines May Have On Averting Deaths And Medical Impoverishment In Developing Countries

With social policies increasingly directed toward enhancing equity through health programs, it is important that methods for estimating the health and economic benefits of these programs by subpopulation be developed, to assess both equity concerns and the programs' total impact. We estimated the differential health impact (measured as the number of deaths averted) and household economic impact (measured as the number of cases of medical impoverishment averted) of ten antigens and their corresponding vaccines across income quintiles for forty-one low- and middle-income countries. Our analysis indicated that benefits across these vaccines would accrue predominantly in the lowest income quintiles. Policy makers should be informed about the large health and economic distributional impact that vaccines could have, and they should view vaccination policies as potentially important channels for improving health equity. Our results provide insight into the distribution of vaccine-preventable diseases and the health benefits associated with their prevention.

Unaltered pneumococcal carriage prevalence due to expansion of non-vaccine types of low invasive potential 8years after vaccine introduction in Stockholm, Sweden

OBJECTIVE

To evaluate the carriage prevalence, serotype distribution, and antibiotic resistance for pneumococcal carriage isolates collected 4-8years after introduction of pneumococcal conjugate vaccines (PCVs) in Stockholm, Sweden, and to identify risk factors for carriage and calculate the invasive disease potential for emerging serotypes.

METHODS

Nasopharyngeal aspirates were collected from 3024 children aged 0-<5years at regular visits at 23 Child Health Centers in Stockholm County in 2011-2015, and from 787 parents in 2014-2015. The invasive disease potential was calculated for serotypes using invasive disease isolates from 824 patients of all ages identified in the Stockholm County during the same time period as the carriage isolates.

RESULTS

A total carriage prevalence of 30% did not change during the study period. Non-vaccine types (NVT) dominated (94% by 2015) and the most common serotypes in descending order were 11A, 23B, 35F and 21. Risk factors for carriage were: age ⩾3months-<3years, having siblings, attending day-care and having travelled abroad the last 3months. Antibiotic resistance remained low. The invasive disease potential was high for NVT 8, 9N, 12F, and 22F, while low for a majority of emerging NVTs in carriage.

CONCLUSION

The carriage prevalence remained the same 4-8years after vaccine introduction, but serotype replacement became almost complete. A majority of emerging NVTs in carriage showed a low invasive disease potential. Carriage studies are an important complement to invasive disease surveillance to understand the full effect of PCV vaccine programs.

Influence of Childhood Pneumococcal Conjugate Vaccines on Invasive Pneumococcal Disease in Adults With Underlying Comorbidities in Calgary, Alberta (2000-2013)

BACKGROUND

Pneumococcal conjugate vaccine (PCV) was introduced into Alberta, Canada's routine childhood immunization programs in 2002 (7-valent [PCV7]) and 2010 (13-valent [PCV13]). We assessed the effect of these programs on the epidemiology of invasive pneumococcal disease (IPD) to determine if PCV-associated indirect protection was relatively reduced in adults with underlying comorbidities.

METHODS

Demographic and clinical data were collected by a prospective, population-based surveillance system in Calgary, Alberta, Canada, from January 2000 to December 2013. An indirect cohort study design was used to assess for changes in the proportion of IPD cases with underlying comorbidities.

RESULTS

There were 1598 overall and 1346 adult IPD cases from 1 January 2000 to 31 December 2013. Overall IPD incidence decreased 33% (age 0-5 months), 86% (6-23 months), 67% (2-4 years), 26% (5-17 years), 22% (18-64 years), 36% (65-84 years), and 42% (≥85 years) from the prevaccine (January 2000-July 2002) to the post-PCV13 (July 2010-December 2013) period. Over the same timeframe, PCV7 serotype disease incidence declined to ≤1 case per 100 000 persons in all age groups. Neither the proportion of adult cases with immunocompetent comorbidities (relative risk ratio [RRR], 0.93; 95% confidence interval [CI], .62-1.40) nor immunocompromising comorbidities (RRR, 0.99; 95% CI, .61-1.61) differed between the pre-PCV period and post-PCV era.

CONCLUSIONS

Childhood PCV programs have provided considerable benefit, with substantial declines in overall and vaccine-serotype IPD in vaccinated children and in unvaccinated persons. Conjugate vaccine-associated indirect protection for adults with comorbidities was similar to that for healthy adults.

Comparative Genomics of Carriage and Disease Isolates of Streptococcus pneumoniae Serotype 22F Reveals Lineage-Specific Divergence and Niche Adaptation

Streptococcus pneumoniae is a major cause of meningitis, sepsis, and pneumonia worldwide. Pneumococcal conjugate vaccines have been part of the United Kingdom’s childhood immunization program since 2006 and have significantly reduced the incidence of disease due to vaccine efficacy in reducing carriage in the population. Here we isolated two clones of 22F (an emerging serotype of clinical concern, multilocus sequence types 433 and 698) and conducted comparative genomic analysis on four isolates, paired by Sequence Type (ST) with one of each pair being derived from carriage and the other disease (sepsis). The most compelling observation was of nonsynonymous mutations in pgdA, encoding peptidoglycan N-acetylglucosamine deacetylase A, which was found in the carriage isolates of both ST433 and 698. Deacetylation of pneumococcal peptidoglycan is known to enable resistance to lysozyme upon invasion. Althought no other clear genotypic signatures related to disease or carriage could be determined, additional intriguing comparisons between the two STs were possible. These include the presence of an intact prophage, in addition to numerous additional phage insertions, within the carriage isolate of ST433. Contrasting gene repertoires related to virulence and colonization, including bacteriocins, lantibiotics, and toxin-–antitoxin systems, were also observed.

Epidemiology of antimicrobial resistance in bloodstream infections

Antimicrobial resistance in bacterial pathogens is a worldwide challenge leading high morbidity and mortality in clinical settings. Multidrug resistant patterns in gram-positive and -negative bacteria have resulted in difficult-to-treat or even untreatable infections with conventional antimicrobials. Since the early identification of causative microorganisms and their antimicrobial susceptibility patterns in patients with bacteremia and other serious infections is lacking in many healthcare institutions, broad spectrum antibiotics are liberally and mostly unnecessarily used. Such practice has, in turn, caused dramatic increases in emerging resistance and when coupled with poor practice of infection control, resistant bacteria can easily be disseminated to the other patients and the environment. Thus, availability of updated epidemiological data on antimicrobial resistance in frequently encountered bacterial pathogens will be useful not only for deciding on empirical treatment strategies, but also devising an effective antimicrobial stewardship program in hospitals.

A Review of Pneumococcal Vaccines: Current Polysaccharide Vaccine Recommendations and Future Protein Antigens

This review describes development of currently available pneumococcal vaccines, provides summary tables of current pneumococcal vaccine recommendations in children and adults, and describes new potential vaccine antigens in the pipeline. Streptococcus pneumoniae, the bacteria responsible for pneumonia, otitis media, meningitis and bacteremia, remains a cause of morbidity and mortality in both children and adults. Introductions of unconjugated and conjugated pneumococcal polysaccharide vaccines have each reduced the rate of pneumococcal infections caused by the organism S. pneumoniae. The first vaccine developed, the 23-valent pneumococcal polysaccharide vaccine (PPSV23), protected adults and children older than 2 years of age against invasive disease caused by the 23 capsular serotypes contained in the vaccine. Because PPSV23 did not elicit a protective immune response in children younger than 2 years of age, the 7-valent pneumococcal conjugate vaccine (PCV7) containing seven of the most common serotypes from PPSV23 in pediatric invasive disease was developed for use in children younger than 2 years of age. The last vaccine to be developed, the 13-valent pneumococcal conjugate vaccine (PCV13), contains the seven serotypes in PCV7, five additional serotypes from PPSV23, and a new serotype not contained in PPSV23 or PCV7. Serotype replacement with virulent strains that are not contained in the polysaccharide vaccines has been observed after vaccine implementation and stresses the need for continued research into novel vaccine antigens. We describe eight potential protein antigens that are in the pipeline for new pneumococcal vaccines.

Using Standardized Interpretation of Chest Radiographs to Identify Adults with Bacterial Pneumonia--Guatemala, 2007-2012

Background

Bacterial pneumonia is a leading cause of illness and death worldwide, but quantifying its burden is difficult due to insensitive diagnostics. Although World Health Organization (WHO) protocol standardizes pediatric chest radiograph (CXR) interpretation for epidemiologic studies of bacterial pneumonia, its validity in adults is unknown.

Methods

Patients (age ≥15 years) admitted with respiratory infections to two Guatemalan hospitals between November 2007 and March 2012 had urine and nasopharyngeal/oropharyngeal (NP/OP) swabs collected; blood cultures and CXR were also performed at physician clinical discretion. ‘Any bacterial infection’ was defined as a positive urine pneumococcal antigen test, isolation of a bacterial pneumonia pathogen from blood culture, or detection of an atypical bacterial pathogen by polymerase chain reaction (PCR) of nasopharyngeal/oropharyngeal (NP/OP) specimens. ‘Viral infection’ was defined as detection of viral pathogens by PCR of NP/OP specimens. CXRs were interpreted according to the WHO protocol as having ‘endpoint consolidation’, ‘other infiltrate’, or ‘normal’ findings. We examined associations between bacterial and viral infections and endpoint consolidation.

Findings

Urine antigen and/or blood culture results were available for 721 patients with CXR interpretations; of these, 385 (53%) had endpoint consolidation and 253 (35%) had other infiltrate. Any bacterial infection was detected in 119 (17%) patients, including 106 (89%) pneumococcal infections. Any bacterial infection (Diagnostic Odds Ratio [DOR] = 2.9; 95% confidence Interval (CI): 1.3–7.9) and pneumococcal infection (DOR = 3.4; 95% CI: 1.5–10.0) were associated with ‘endpoint consolidation’, but not ‘other infiltrate’ (DOR = 1.7; 95% CI: 0.7–4.9, and 1.7; 95% CI: 0.7–4.9 respectively). Viral infection was not significantly associated with ‘endpoint consolidation’, ‘other infiltrate,’ or ‘normal’ findings.

Interpretation

‘Endpoint consolidation’ was associated with ‘any bacterial infection,’ specifically pneumococcal infection. Therefore, endpoint consolidation may be a useful surrogate for studies measuring the impact of interventions, such as conjugate vaccines, against bacterial pneumonia.

Immunogenicity and safety of a 13-valent pneumococcal conjugate vaccine administered to older infants and children naïve to pneumococcal vaccination

BACKGROUND

Streptococcus pneumoniae infections are a major cause of morbidity and mortality in children <5 years old worldwide. To increase serotype coverage globally, a 13-valent pneumococcal conjugate vaccine (PCV13) has been developed and approved in many countries worldwide.

OBJECTIVE

Assess the safety and immunogenicity of PCV13 in healthy older infants and children naïve to previous pneumococcal vaccination.

METHODS

This was a phase 3, open-label, multicenter study conducted in Polish children (N=354) who were vaccinated according to 3 age-appropriate catch-up schedules: Group 1 (aged 7 to <12 months) received two PCV13 doses with a booster at 12-16 months of age; Group 2 (aged 12 to <24 months) received two vaccine doses only; and Group 3 (aged 24 to <72 months) received a single dose of PCV13. Statistical analyses were descriptive. The proportion of immunological "responders" achieving serotype-specific antipneumococcal polysaccharide concentrations ≥0.35μg/mL, 1-month after the last dose of vaccine, was determined for each vaccine serotype. In addition, antipolysaccharide immunoglobulin (Ig) G geometric mean concentrations (GMCs) were calculated. Safety assessments included systemic and local reactions, and adverse events.

RESULTS

The proportion of immunological responders was ≥88% across groups for all serotypes. Antipolysaccharide IgG GMCs were generally similar across groups. Each schedule elicited immune response levels against all 13 serotypes comparable to or greater than levels previously reported in infants after a 3-dose series. The 3 catch-up schedules had similar tolerability and safety profiles; a trend was present towards greater local tenderness with increasing age and subsequent dose administration.

CONCLUSIONS

Immunological responses and safety results support the use of PCV13 for catch-up schedules in older infants and children naïve to pneumococcal vaccination.

Choosing between 7-, 10- and 13-valent pneumococcal conjugate vaccines in childhood: a review of economic evaluations (2006-2014)

BACKGROUND

Seven-valent pneumococcal conjugate vaccines (PCV7) have been used in children for more than a decade. Given the observed increase in disease caused by pneumococcal serotypes not covered by PCV7, an increasing number of countries are switching from 7-valent to 10- and 13-valent PCVs ("PCV10" and "PCV13"). Economic evaluations are important tools to inform decisions and price negotiations to make such a switch.

OBJECTIVE

This review aims to provide a critical assessment of economic evaluations involving PCV10 or PCV13, published since 2006.

METHODS

We searched Scopus, ISI Web of Science (SCI and SSCI) and Pubmed to retrieve, select and review relevant studies, which were archived between 1st January 2006 and 31st January 2014. The review protocol involved standard extraction of assumptions, methods, results and sponsorships from the original studies.

RESULTS

Sixty-three economic evaluations on PCVs published since January 2006 were identified. About half of these evaluated PCV10 and/or PCV13, the subject of this review. At current prices, both PCV13 and PCV10 were likely judged preferable to PCV7. However, the combined uncertainty related to price differences, burden of disease, vaccine effectiveness, herd and serotype replacement effects determine the preference base for either PCV10 or PCV13. The pivotal assumptions and results of these analyses also depended on which manufacturer sponsored the study.

CONCLUSION

A more thorough exploration of uncertainty should be made in future analyses on this subject, as we lack understanding to adequately model herd and serotype replacement effects to reliably predict the population impact of PCVs. The introduction of further improved PCVs in an environment of evolving antibiotic resistance and under the continuing influence of previous PCVs implies that the complexity and data requirements for relevant analyses will further increase. Decision makers using these analyses should not just rely on an analysis from a single manufacturer.

Invasive pneumococcal disease in children can reveal a primary immunodeficiency

BACKGROUND

About 10% of pediatric patients with invasive pneumococcal disease (IPD) die from the disease. Some primary immunodeficiencies (PIDs) are known to confer predisposition to IPD. However, a systematic search for these PIDs has never been carried out in children presenting with IPD.

METHODS

We prospectively identified pediatric cases of IPD requiring hospitalization between 2005 and 2011 in 28 pediatric wards throughout France. IPD was defined as a positive pneumococcal culture, polymerase chain reaction result, and/or soluble antigen detection at a normally sterile site. The immunological assessment included abdominal ultrasound, whole-blood counts and smears, determinations of plasma immunoglobulin and complement levels, and the evaluation of proinflammatory cytokines.

RESULTS

We included 163 children with IPD (male-to-female ratio, 1.3; median age, 13 months). Seventeen children had recurrent IPD. Meningitis was the most frequent type of infection (87%); other infections included pleuropneumonitis, isolated bloodstream infection, osteomyelitis, endocarditis, and mastoiditis. One patient with recurrent meningitis had a congenital cerebrospinal fluid fistula. The results of immunological explorations were abnormal in 26 children (16%), and a PID was identified in 17 patients (10%), including 1 case of MyD88 deficiency, 3 of complement fraction C2 or C3 deficiencies, 1 of isolated congenital asplenia, and 2 of Bruton disease (X-linked agammaglobulinemia). The proportion of PIDs was much higher in children aged >2 years than in younger children (26% vs 3%; P < .001).

CONCLUSIONS

Children with IPD should undergo immunological investigations, particularly those aged >2 years, as PIDs may be discovered in up to 26% of cases.

Infectious Disease Epidemiology

Most textbooks dealing with the epidemiology of infectious diseases address the epidemiological features (also named biology) of specific infectious diseases. In this chapter, the focus is placed on the concepts and methods more specific to the general epidemiological study of infectious diseases. At a later stage, implementation of these methods must be adapted to the specific infectious disease under consideration. Then, detailed knowledge of the disease biology is of capital importance.

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.

Modified opsonization, phagocytosis, and killing assays to measure potentially protective antibodies against pneumococcal surface protein A

The standard opsonophagocytosis killing assay (OPKA) for antibodies to pneumococcal capsular polysaccharide was modified to permit an evaluation of the protection-mediating antibodies to pneumococcal surface protein A (PspA). We found that by increasing the incubation time with the complement and phagocytes from 45 min to 75 min, the protective activity was readily detected. In another modification, we used a capsule type 2 target strain that expressed PspA but not pneumococcal surface protein C (PspC). With these modifications separately or in combination, rabbit antisera to the recombinant α-helical or proline-rich domains of PspA mediated >50% killing of the target strain. The ability of normal human sera to mediate the killing of pneumococci in this modified OPKA correlated with their levels of antibodies to PspA and their ability to protect mice against fatal infection with a type 3 strain. Passive protection of mice against pneumococci and killing in the modified OPKA were lost when normal human sera were adsorbed with recombinant PspA (rPspA) on Sepharose, thus supporting the potential utility of the modified OPKA to detect protective antibodies to PspA. In the standard OPKA, monoclonal antibodies to PspA were strongly protective in the presence of subprotective amounts of anti-capsule. Thus, the currently established high-throughput OPKA for antibodies to capsule could be modified in one of two ways to permit an evaluation of the opsonic efficacy of antibodies to PspA.

Evaluation of serotype-specific immunity to Streptococcus pneumoniae in pregnant women and cord blood of infants: impact of race and ethnicity

BACKGROUND

Although invasive pneumococcal disease (IPD) has significantly decreased in children since the introduction of the pneumococcal conjugate vaccine, instances of IPD from non-PCV7 serotypes have increased. Concerns remain regarding the risk for IPD during the neonatal period. Our objective was to measure quantitative antibody levels to 16 serotypes of Streptococcus pneumoniae in pregnant non-Hispanic black, non-Hispanic white, and Hispanic mothers, and in cord blood samples.

METHODS

Antibody levels were evaluated by Luminex assay.

RESULTS

Forty-two percent of all mothers had protective (-0.35 microg/mL) antibody levels to 16 serotypes. Hispanic mothers were most likely to possess protective antibody levels for 12 serotypes but were less likely to possess protective antibody levels for serotypes 9V, 12F, and 18C, compared to non-Hispanic white or black mothers. Thirty-three percent of cord blood samples demonstrated protective antibody levels. Hispanic infants had a higher prevalence of protective antibodies to all serotypes except 11A, 14, 18C, and 23F. Non-Hispanic black infants had a higher prevalence of protective immunity to serotypes 11A, 14, and 18C, and non-Hispanic white infants to only serotype 23F.

CONCLUSIONS

Hispanic mothers and their infants have a higher prevalence of protective immunity to most serotypes of S pneumoniae, compared to white or black mothers/infants. We found no evidence of a lower prevalence of protective immunity to specific serotypes in non-Hispanic black vs. non-Hispanic white infants that might account for the reported higher incidence of IPDs in blacks. Environmental factors in Hispanic mothers may be responsible for their enhanced level of immunity. A significant number of cord blood samples had inadequate levels of protective immunity to a variety of S pneumoniae serotypes.

Pneumococcal vaccines for children: a global public health priority

Pneumococcal conjugated vaccines have been recommended in children for over a decade in many countries worldwide. Here we review the development of pneumococcal vaccines with a focus on the two types currently available for children and their safety record. We discuss also the effect of vaccines, including the 13-valent pneumococcal conjugate vaccine, on invasive pneumococcal diseases in children, particularly bacteraemia, pneumonia and meningitis, as well as on mucosal disease and carriage. In regions where immunization was implemented in young children, the number of invasive pneumococcal diseases decreased significantly, not only in the target age group, but also in younger and much older subjects. Challenges and future perspectives regarding the development of new 'universal' vaccines, which could bypass the current problem of serotype-specific protection in a context of serotype replacement, are also discussed.

Benefits and effectiveness of administering pneumococcal polysaccharide vaccine with seasonal influenza vaccine: an approach for policymakers

For the influenza pandemic of 2009-2010, countries responded to the direct threat of influenza but may have missed opportunities and strategies to limit secondary pneumococcal infections. Delivering both vaccines together can potentially increase pneumococcal polysaccharide vaccine (PPV23) immunization rates and prevent additional hospitalizations and mortality in the elderly and other high-risk groups. We used PubMed to review the literature on the concomitant use of PPV23 with seasonal influenza vaccines. Eight of 9 clinical studies found that a concomitant program conferred clinical benefits. The 2 studies that compared the cost-effectiveness of different strategies found concomitant immunization to be more cost-effective than either vaccine given alone. Policymakers should consider a stepwise strategy to reduce the burden of secondary pneumococcal infections during seasonal and pandemic influenza outbreaks.

Should patients with chronic obstructive pulmonary disease be vaccinated against pneumococcal diseases?

Over the past 15 years, no fewer than ten meta-analyses or systematic literature reviews of the efficacy of pneumococcal polysaccharide vaccine in adults have been conducted, including one specifically in chronic obstructive pulmonary disease patients. Their general conclusion is that it is effective in preventing invasive infections, but no conclusions can be drawn for high-risk patients (owing to a highly polymorphic population). Opinions are divided as to its efficacy in pneumonia, with the studies being too heterogeneous to carry sufficient statistical weight. Most conclude that there is no impact on mortality. Chronic obstructive pulmonary disease patients are frequently described as an at-risk population, but controlled studies in such patients are very limited, leaving only case-control or cohort studies to provide information on which to base any decision. The aim of this article is first to discuss the place of pneumococcal polysaccharide vaccination in this risk population, which is increasing in prevalence and in which pneumococcal infections play a considerable role. Pending other vaccines, the polysaccharide vaccine is currently the only preventive approach that has demonstrated an effect, even if it does not match up to expectations. The possibilities of alternative vaccines, such as conjugate vaccines in the near future and perhaps protein vaccines at a later date, will be considered.

An evaluation of emerging vaccines for childhood pneumococcal pneumonia

BACKGROUND

Pneumonia is the leading cause of child mortality worldwide. Streptococcus pneumoniae (SP) or pneumococcus is estimated to cause 821,000 child deaths each year. It has over 90 serotypes, of which 7 to 13 serotypes are included in current formulations of pneumococcal conjugate vaccines that are efficacious in young children. To further reduce the burden from SP pneumonia, a vaccine is required that could protect children from a greater diversity of serotypes. Two different types of vaccines against pneumococcal pneumonia are currently at varying stages of development: a multivalent pneumococcal conjugate vaccine covering additional SP serotypes; and a conserved common pneumococcal protein antigen (PPA) vaccine offering protection for all serotypes.

METHODS

We used a modified CHNRI methodology for setting priorities in health research investments. This was done in two stages. In Stage I, we systematically reviewed the literature related to emerging SP vaccines relevant to several criteria of interest: answerability; efficacy and effectiveness; cost of development, production and implementation; deliverability, affordability and sustainability; maximum potential for disease burden reduction; acceptability to the end users and health workers; and effect on equity. In Stage II, we conducted an expert opinion exercise by inviting 20 experts (leading basic scientists, international public health researchers, international policy makers and representatives of pharmaceutical companies). The policy makers and industry representatives accepted our invitation on the condition of anonymity, due to sensitive nature of their involvement in such exercises. They answered questions from CHNRI framework and their "collective optimism" towards each criterion was documented on a scale from 0 to 100%.

RESULTS

The experts expressed very high level of optimism (over 80%) that low-cost polysaccharide conjugate SP vaccines would satisfy each of the 9 relevant CHNRI criteria. The median potential effectiveness of conjugate SP vaccines in reduction of overall childhood pneumonia mortality was predicted to be about 25% (interquartile range 20-38%, min. 15%, max 45%). For low cost, cross-protective common protein vaccines for SP the experts expressed concerns over answerability (72%) and the level of development costs (50%), while the scores for all other criteria were over 80%. The median potential effectiveness of common protein vaccines in reduction of overall childhood pneumonia mortality was predicted to be about 30% (interquartile range 26-40%, min. 20%, max 45%).

CONCLUSIONS

Improved SP vaccines are a very promising investment that could substantially contribute to reduction of child mortality world-wide.

Opsonophagocytic activity following a reduced dose 7-valent pneumococcal conjugate vaccine infant primary series and 23-valent pneumococcal polysaccharide vaccine at 12 months of age

Opsonophagocytic activity (OPA) was measured following reduced infant doses of 7-valent pneumococcal conjugate vaccine (PCV-7) with or without 23-valent pneumococcal polysaccharide vaccine (PPV-23) at 12 months, and subsequent re-exposure to a small dose of pneumococcal polysaccharide antigens (mPPS) at 17 months. Fijian infants were randomized to receive 0, 1, 2, or 3 PCV-7 doses. Half received PPV-23 at 12 months and all received mPPS at 17 months. OPA was performed on up to 14 serotypes. Three and 2 PCV-7 doses resulted in similar OPA for most PCV-7 serotypes up to 9 months and for half of the serotypes at 12 months. A single dose improved OPA compared with the unvaccinated group. PPV-23 significantly improved OPA for all serotypes tested but in general, was associated with diminished responses following re-challenge.

Continued control of pneumococcal disease in the UK – the impact of vaccination

Streptococcus pneumoniae, also known as the pneumococcus, is an important cause of morbidity and mortality in the developed and developing world. Pneumococcal conjugate vaccines were first introduced for routine use in the USA in 2000, although the seven-valent pneumococcal conjugate vaccine (PCV7) was not introduced into the UK's routine childhood immunization programme until September 2006. After its introduction, a marked decrease in the incidence of pneumococcal disease was observed, both in the vaccinated and unvaccinated UK populations. However, pneumococci are highly diverse and serotype prevalence is dynamic. Conversely, PCV7 targets only a limited number of capsular types, which appears to confer a limited lifespan to the observed beneficial effects. Shifts in serotype distribution have been detected for both non-invasive and invasive disease reported since PCV7 introduction, both in the UK and elsewhere. The pneumococcal Haemophilus influenzae protein D conjugate vaccine (PHiD-CV, Synflorix; GlaxoSmithKline) and 13-valent pneumococcal conjugate vaccine (PCV13, Prevenar 13; Pfizer) have been newly licensed. The potential coverage of the 10- and 13-valent conjugate vaccines has also altered alongside serotype shifts. Nonetheless, the mechanism of how PCV7 has influenced serotype shift is not clear-cut as the epidemiology of serotype prevalence is complex. Other factors also influence prevalence and incidence of pneumococcal carriage and disease, such as pneumococcal diversity, levels of antibiotic use and the presence of risk groups. Continued surveillance and identification of factors influencing serotype distribution are essential to allow rational vaccine design, implementation and continued effective control of pneumococcal disease.

Pneumococcal and influenza immunization in asplenic persons: a retrospective population-based cohort study 1990-2002

Background

Splenectomy is associated with increased risk for bacteremia, due to impaired clearance of bloodborne agents and to altered phagocytosis and humoral immunity. We conducted a retrospective cohort study of patients at risk for splenectomy for a 13-year period to determine immunization coverage, and outcomes of those with and without splenectomy, and with or without receipt of influenza or pneumococcal vaccine.

Methods

Data were extracted from the provincial Medical Services Insurance database for insured services rendered by a physician for 1990-2002, and from the Vital Statistics Death database. The eligible cohort was selected based on diagnostic codes for hematologic conditions for which splenectomy might be considered, such as immune thrombocytopenia. Each patient was followed longitudinally from the date of first diagnosis until 31Dec2002, or death, or relocation out-of province. In addition, persons with splenectomy and no hematologic condition were identified and followed for 6 months post-surgery. Infectious illness rates per 100 person-years of observation and death rates were calculated with and without splenectomy. Death rates were determined using splenectomy status as a time-dependent covariate. The relationship between splenectomy and death according to immunization status was examined using Cox proportional hazard ratios.

Results

Of 38,812 persons in the cohort 427 subjects with a hematologic diagnosis had splenectomy and another 452 subjects without a hematologic diagnosis had this surgery. 72% were > 18 years of age. Pneumococcal immunization was recorded in 16.5% of asplenic patients overall, and was not associated with reduced risk of death in these persons (adjusted Hazard Ratio [HR] = 1.07, 95% CI 0.70 - 1.65). Influenza immunization was recorded in 53.1% of asplenic patients overall, and was associated with reduced risk of death (adjusted HR = 0.46, 0.33-0.62). No pneumococcal or influenza immunization was recorded in patients with a hematologic diagnosis without splenectomy. Infectious illness visits were higher among all patients who had a splenectomy than among those without a splenectomy (151 visits/100 person-years of observation in the post-splenectomy period vs. 120 visits/100 person-years; p < 0.0001).

Conclusions

In asplenic patients, influenza immunization is associated with a 54% reduced risk of death compared to unimmunized asplenic persons; no reduction in risk was demonstrated with (polysaccharide) pneumococcal vaccine. Vaccine coverage in the entire cohort was less than routinely recommended. Improved delivery of infection prevention programs to this population is warranted. Conjugate pneumococcal vaccines should be urgently studied in this immunocompromised population.

Safety and immunogenicity of a 13-valent pneumococcal conjugate vaccine compared to those of a 7-valent pneumococcal conjugate vaccine given as a three-dose series with routine vaccines in healthy infants and toddlers

A 13-valent pneumococcal conjugate vaccine (PCV13) has been developed to improve protection against pneumococcal disease beyond that possible with the licensed 7-valent vaccine (PCV7). This study compared the safety and immunogenicity of PCV13 with those of PCV7 when given as part of the pediatric vaccination schedule recommended in Italy. A total of 606 subjects were randomly assigned to receive either PCV13 or PCV7 at 3, 5, and 11 months of age; all subjects concomitantly received diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated polio-Haemophilus influenzae type B (DTaP-HBV-IPV/Hib) vaccine. Vaccine reactions were monitored. Antibody responses to DTaP-HBV-IPV/Hib antigens, serotype-specific anticapsular polysaccharide IgG responses, and antipneumococcal opsonophagocytic assay (OPA) activity were measured 1 month after the two-dose primary series and 1 month after the toddler dose. Overall, the safety profile of PCV13 was similar to that of PCV7. The response to DTaP-HBV-IPV/Hib antigens was substantially the same with both PCV13 and PCV7. PCV13 elicited antipneumococcal capsular IgG antibodies to all 13 vaccine serotypes, with notable increases in concentrations seen after the toddler dose. Despite a lower immunogenicity for serotypes 6B and 23F after the primary series of PCV13, responses to the seven common serotypes were comparable between the PCV13 and PCV7 groups when measured after the toddler dose. PCV13 also elicited substantial levels of OPA activity against all 13 serotypes following both the infant series and the toddler dose. In conclusion, PCV13 appeared comparable to PCV7 in safety profile and immunogenicity for common serotypes, demonstrated functional OPA responses for all 13 serotypes, and did not interfere with immune responses to concomitantly administered DTaP-HBV-IPV/Hib vaccine.

Lack of pneumococcal carriage in the hospitalised elderly

There have been few surveys of Streptococcus pneumoniae and Neisseria meningitidis carriage in sick or frail elderly people who, with the very young, comprise the group who are at highest risk for pneumococcal disease. We studied pneumococcal carriage among participants in a pneumococcal immunisation study in the frail elderly.

METHODS

Subjects aged >or=60 years were recruited from a large tertiary referral hospital in Sydney, Australia. Nose and throat swabs were collected at the time of enrolment and 12 months after immunisation.

RESULTS

Before immunisation, only 1 of 315 participants was identified as a nasal carrier of S. pneumoniae; another was identified as throat carrier of N. meningitidis. None of the participants examined after immunisation was carrying either S. pneumoniae or N. meningitidis.

CONCLUSION

The low rate of pneumococcal carriage in this population of hospitalised elderly patients was unexpected. The most likely reason is that long-term carriage is rare in this population and suggests that pneumococcal disease primarily follows recent acquisition of S. pneumoniae types not associated with carriage.

The proline-rich region of pneumococcal surface proteins A and C contains surface-accessible epitopes common to all pneumococci and elicits antibody-mediated protection against sepsis

Pneumococcal surface protein A (PspA) and PspC of Streptococcus pneumoniae are surface virulence proteins that interfere with complement deposition and elicit protective immune responses. The C-terminal halves of PspA and PspC have some structural similarity and contain highly cross-reactive proline-rich (PR) regions. In many PR regions of PspA and PspC, there exists an almost invariant nonproline block (NPB) of about 33 amino acids. Neither the PR regions nor their NPB exhibit the alpha-helical structure characteristic of much of the protection-eliciting N-terminal portions of PspA and PspC. Prior studies of PspA and PspC as immunogens focused primarily on the alpha-helical regions of these molecules that lack the PR and NPB regions. This report shows that immunization with recombinant PR (rPR) molecules and passive immunization with monoclonal antibodies reactive with either NPB or PR epitopes are protective against infection in mice. PR regions of both PspA and PspC were antibody accessible on the pneumococcal surface. Our results indicate that while PspA could serve as a target of these protective antibodies in invasive infections, PspC might not. When antibody responses to rPR immunogens were evaluated by using flow cytometry to measure antibody binding to live pneumococci, it was observed that the mice that survived subsequent challenge produced significantly higher levels of antibodies reactive with exposed PR epitopes than the mice that became moribund. Due to their conservation and cross-reactivity, the PR regions and NPB regions represent potential vaccine targets capable of eliciting cross-protection immunity against pneumococcal infection.

Incorporating herd immunity effects into cohort models of vaccine cost-effectiveness

BACKGROUND

Cohort models are often used in cost-effectiveness analysis (CEA) of vaccination. However, because they cannot capture herd immunity effects, cohort models underestimate the reduction in incidence caused by vaccination. Dynamic models capture herd immunity effects but are often not adopted in vaccine CEA.

OBJECTIVE

The objective was to develop a pseudo-dynamic approximation that can be incorporated into an existing cohort model to capture herd immunity effects.

METHODS

The authors approximated changing force of infection due to universal vaccination for a pediatric infectious disease. The projected lifetime cases in a cohort were compared under 1) a cohort model, 2) a cohort model with pseudo-dynamic approximation, and 3) an age-structured susceptible-exposed-infectious-recovered compartmental (dynamic) model. The authors extended the methodology to sexually transmitted infections.

RESULTS

For average to high values of vaccine coverage (P > 60%) and small to average values of the basic reproduction number (R(0) < 10), which describes school-based vaccination programs for many common infections, the pseudo-dynamic approximation significantly improved projected lifetime cases and was close to projections of the full dynamic model. For large values of R(0) (R(0) > 15), projected lifetime cases were similar under the dynamic model and the cohort model, both with and without pseudo-dynamic approximation. The approximation captures changes in the mean age at infection in the 1st vaccinated cohort.

CONCLUSIONS

This methodology allows for preliminary assessment of herd immunity effects on CEA of universal vaccination for pediatric infectious diseases. The method requires simple adjustments to an existing cohort model and less data than a full dynamic model.

Transmission-dynamic model to capture the indirect effects of infant vaccination with Prevnar (7-valent pneumococcal conjugate vaccine (PCV7)) in older populations

We developed an age-structured, transmission-dynamic, mathematical model to quantify the direct and indirect benefits of infant PCV7 vaccination. The model simulates the acquisition of asymptomatic carriage of Streptococcus pneumoniae and the development of fatal and non-fatal invasive pneumococcal disease (IPD) among vaccinated and unvaccinated individuals aged <2, 2-4, 5-17, 18-49, 50-64, and >or=65 years old. The model was parameterized using published US surveillance data, supplemented with data from published literature. The model predicts the observed incidence of IPD with good agreement and may be used to predict the impact of various vaccination strategies in the US or other populations yet to introduce PCV7.

Biology and pathogenesis of the evolutionarily successful, obligate human bacterium Neisseria meningitidis

For at least two hundred years, Neisseria meningitidis (the meningococcus), the cause of epidemic meningitis and sepsis, has inflicted rapid death, disability and fear on disparate human populations. The meningococcus is also recognized as a highly successful commensal organism exclusively found in humans. The evolution of N. meningitidis as an exclusive human commensal and sometimes a fulminant and fatal pathogen represents an important case study in microbial pathogenesis. We review the general status of our knowledge of pathogenesis of meningococcal carriage, transmission and virulence behavior with particular emphasis on the relevance of research on this topic to vaccine development.

Increase in the prevalence of the newly discovered pneumococcal serotype 6C in the nasopharynx after introduction of pneumococcal conjugate vaccine

BACKGROUND

Because pneumococcal serotype 6C was previously not distinguished from serotype 6A, the impact of the 7-valent pneumococcal conjugate vaccine (PCV7) on the carriage of serotype 6C is unknown.

METHODS

The nasopharyngeal (NP) prevalence of the 6C serotype was determined using 1326 pneumococcal isolates collected from 7 cohorts of Massachusetts children between 1994 and 2007. Initially, the isolates were serotyped using the quellung reaction; subsequently, stored specimens of all putative 6A isolates were tested for 6C using monoclonal antibodies. The opsonophagocytic and antibiotic susceptibilities of the isolates were determined.

RESULTS

The prevalence of 6A was 9.6% (33/343) before 2001, 8.0% (18/226) in 2004, and 2.9% (12/416) in 2007. In contrast, the prevalence of 6C was 0.6% (2/343) before 2001, 2.2% (5/226) in 2004, and 8.7% (36/416) in 2007 (P<.001 for 2/343 vs. 36/416). 6C isolates from 2007 were more susceptible to antibiotics than were 6A isolates. PCV7 induced a low ability to opsonize different isolates of 6C.

CONCLUSIONS

Among NP isolates, the prevalence of 6C isolates has increased and the prevalence of 6A isolates has decreased since the introduction of PCV7 in Massachusetts in 2000. The observed increase in serotype 6C prevalence may be explained by the induction by PCV7 of low amounts of functional anti-6C antibody, compared with anti-6A and anti-6B antibodies.

Differential effects of pneumococcal vaccines against serotypes 6A and 6C

BACKGROUND

Because classic pneumococcal serotyping methods cannot distinguish between serotypes 6A and 6C, the effects of pneumococcal vaccines against serotype 6C are unknown. Pneumococcal vaccines contain serotype 6B but not serotypes 6A and 6C.

METHODS

We used a phagocytic killing assay to estimate the immunogenicity of the 7-valent conjugate vaccine (PCV7) in children and the 23-valent polysaccharide vaccine (PPV23) in adults against serotypes 6A and 6C. We evaluated trends in invasive pneumococcal disease (IPD) caused by serotypes 6A and 6C in the United States, using active surveillance.

RESULTS

Serum specimens from PCV7-immunized children had median opsonization indices of 150 and < 20 for serotypes 6A and 6C, respectively. Similarly, only 52% of adults (25 of 48) vaccinated with PPV23 showed opsonic indices of > 20 against serotype 6C. During 1999--2006, the incidence of serotype 6A IPD decreased by 91% (from 4.9 to 0.46 cases per 100,000 persons; P < .05) among individuals aged < 5 years and by 58% (from 0.86 to 0.36 cases per 100,000 persons; P < .05) among those aged > or = 5 years. Although the incidence of 6C IPD showed no consistent trend (range, 0-0.6 cases per 100,000 persons) among individuals aged < 5 years, it increased from 0.25 to 0.62 cases per 100,000 persons (P < .05) among those aged > or = 5 years.

CONCLUSIONS

PCV7 introduction has led to reductions in serotype 6A IPD but not serotype 6C IPD in the United States.

Immune response in infants to the heptavalent pneumococcal conjugate vaccine against vaccine-related serotypes 6A and 19A

The currently available 7-valent pneumococcal conjugate vaccine (PCV7) elicits good immune response to and is effective against vaccine serotypes. However, its effectiveness against vaccine-related serotypes is variable. Serum samples were obtained 1 month after the last vaccination from 31 infants immunized with PCV7 at 2, 4, and 6 months of age. The sera were used to determine immunoglobulin G antibody levels to eight serotypes (seven vaccine serotypes and serotype 19A) with enzyme-linked immunosorbent assay (ELISA) and opsonic capacity against 11 serotypes (seven vaccine serotypes, serotypes 19A and 6A, and nonvaccine serotypes 5 and 7F) using a multiplexed opsonization assay. ELISA results showed antibody concentrations varied between 1.84 and 10.49 microg/ml, and all subjects had antibody concentrations of >or=0.35 microg/ml for all serotypes, including serotype 19A. In contrast, the opsonic index was detectable (i.e., opsonic index >or= 8) in all children for the seven vaccine serotypes, 81% for serotype 6A, and merely 19% for serotype 19A. PCV7 shows good immunogenicity for vaccine serotypes in infants after a primary series. PCV7 does not elicit opsonic antibodies to serotype 19A. ELISA may thus be an inadequate surrogate assay for evaluating the response for cross-reactive serotypes in infants.

Herd immunity: recent uses in vaccine assessment

Human communities defend themselves against specific infectious agents in a way that extends beyond the simple sum of the immune status of its individuals. By analogy with individual immunity to specific agents, the community level of immunity may vary from complete susceptibility to full protection. Herd immunity has been used to name this community property, which is the result of evolution through natural selection, leading to relationships between two species, typical of prey-predator systems. Varying uses of the term herd immunity led to the use of other expressions, such as herd protection, herd effect and community immunity. Knowledge derived from observational studies and models on herd immunity has supported decisions on the choice of vaccines and vaccination strategies for the benefit of populations. This knowledge is most likely to be extended in the future, with far-reaching effects.

Bloodstream infections: evolution and trends in the microbiology workload, incidence, and etiology, 1985-2006

Information available on bloodstream infection (BSI) is usually restricted to short periods of time, certain clinical backgrounds, or specific pathogens, or is just outdated. We conducted the current prospective study of patients with BSI in a 1750-bed teaching hospital to evaluate workload trends and the incidence and etiology of BSI in a general hospital during the last 22 years, including the acquired immunodeficiency syndrome (AIDS) era. The main outcome measures were laboratory workload, trends in incidence per 1000 admissions and per 100,000 population of different microorganisms, and the impact of the human immunodeficiency virus (HIV) epidemic in the period 1985-2006.From 1985 to 2006 we had 27,419 episodes of significant BSI (22,626 patients). BSI incidence evolved from 16.0 episodes to 31.2/1000 admissions showing an annual increase of 0.83 episodes/1000 admissions (95% confidence interval, 0.61-1.05; p < 0.0001). The evolution of the incidence per 1000 admissions and per 100,000 population of different groups of microorganisms was as follows: Gram positives 8.2 to 15.7/1000 admissions and 66.8 to 138.3/100,000 population; Gram negatives 7.8 to 16.2/1000 admissions and 63.5 to 141.9/100,000 population; anaerobes 0.5 to 1.3/1000 admissions and 4.1 to 11.7/100,000 population; and fungi 0.2 to 1.5/1000 admissions and 1.7 to 12.5/100,000 population. All those differences were statistically significant. We observed the emergence of multiresistant Gram-positive and Gram-negative microorganisms. At least 2484 episodes of BSI (9.1%) occurred in 1822 patients infected with HIV. The incidence of BSI in HIV-infected patients increased from 1985 and reached a peak in 1995 (17.6% of BSI). Since 1995, the decrease was continuous, and in 2006 only 3.9% of all BSI episodes occurred in HIV-positive patients in our institution. We conclude that the BSI workload has increased in modern microbiology laboratories. Gram-positive pathogens have overtaken other etiologic agents of BSI. Our observation shows the remarkable escalation of some resistant pathogens, and the rise and relative fall of BSI in patients with HIV.