Safety and immunogenicity of a heptavalent pneumococcal conjugate vaccine in infants

Pneumococcal conjugate vaccine dose-ranging studies in humans: A systematic review

BACKGROUND

Streptococcus pneumoniae is one of the most common bacterial pathogens of infants and young children. Antibody responses against the pneumococcal polysaccharide capsule are the basis of vaccine-mediated protection. We examined the relationship between the dose of polysaccharide in pneumococcal conjugate vaccines (PCVs) and immunogenicity.

METHODS

A systematic search of English publications that evaluated the immunogenicity of varying doses of pneumococcal conjugate vaccines was performed in Medline and Embase (Ovid Sp) databases in August 2019. We included only articles that involved administration of pneumococcal conjugate vaccine in humans and assessed the immunogenicity of more than one serotype-specific saccharide dose. Results were synthesised descriptively due to the heterogeneity of product valency, product content and vaccine schedule.

RESULTS

We identified 1691 articles after de-duplication; 9 studies met our inclusion criteria; 2 in adults, 6 in children and 1 in both. Doses of polysaccharide evaluated ranged from 0.44 mcg to 17.6 mcg. In infants, all doses tested elicited IgG geometric mean concentrations (GMCs) above the established correlate of protection (COP; 0.35 mcg/ml). A month after completion of the administered vaccine schedule, 95% confidence intervals of only three out of all the doses evaluated had GMCs that crossed below the COP. In the adult studies, all adults achieved GMCs that would be considered protective in children who have received 3 standard vaccine doses.

CONCLUSION

For some products, the mean antibody concentrations induced against some pneumococcal serotypes increased with increasing doses of the polysaccharide conjugate, but for other serotypes, there were no clear dose-response relationships or the dose response curves were negative. Fractional doses of polysaccharide which contain less than is included in currently distributed formulations may be useful in the development of higher valency vaccines, or dose-sparing delivery for paediatric use.

Impact of Pneumococcal Conjugate Vaccines on Selected Head and Neck Infections in Hospitalized Israeli Children

BACKGROUND

Streptococcus pneumoniae is a major pathogen of pediatric head and neck infections (HNIs), for example, acute otitis media (AOM), acute mastoiditis, acute bacterial sinusitis and meningitis. The aim of this study was to characterize the epidemiology of pneumococcal HNIs (pHNIs) before, during and after the introduction of pneumococcal conjugate vaccines (PCVs).

METHODS

Children 0-16 years of age, who were hospitalized with HNIs in the pediatrics department in a general hospital between January 1, 2007, and December 31, 2014, were retrospectively identified. Study years were categorized according to the PCV introduction timeline: 2007-2008: "pre-PCV years"; 2009-2011: "transition years" and 2012-2014: "post-PCV years." pHNIs episodes were defined if pneumococcal culture or urine antigen was positive. Children who received ≥2 doses of PCV7/PCV13 were considered as immunized. All other children were considered as unimmunized.

RESULTS

HNIs accounted for 2.5%-4.7% of the total admissions; 3%-17% of them were pHNIs. Eighty-seven pHNI episodes were identified: AOM (n = 42), acute mastoiditis (n = 28) and meningitis (n = 17). There was a downward trend in the overall incidence of HNIs, and particularly of pHNIs, in the post-PCV years. The average age and hospitalization duration of children with HNIs/pHNIs remained stable during the study years. In 2009-2010, pHNIs incidence sharply decreased, from 7 to 1.74/1000 hospitalized children/year, due to ~55% reduction of pneumococcal AOM episodes. An additional decrease was observed in the post-PCV years (1.62/1000 hospitalized children/year). Immunized children were less likely to present with pHNIs (P = 0.001) but were more likely to undergo surgery (P = 0.042).

CONCLUSION

We observed a reduction in pHNIs incidence after PCV program implementation.

Systematic review of the effect of pneumococcal conjugate vaccine dosing schedules on immunogenicity

BACKGROUND

Despite the breadth of studies demonstrating benefits of pneumococcal conjugate vaccine (PCV), uncertainty remains regarding the optimal PCV dosing schedule in infants.

METHODS

We conducted a systematic literature review of PCV immunogenicity published from 1994 to 2010 (supplemented post hoc with studies from 2011). Studies included for analysis evaluated ≥2 doses of 7-valent or higher product (excluding Aventis-Pasteur PCV11) administered to nonhigh-risk infants ≤6 months of age. Impact of PCV schedule on geometric mean antibody concentration (GMC) and proportion of subjects over 0.35 mcg/mL were assessed at various time points; the GMC 1 month postdose 3 (for various dosing regimens) for serotypes 1, 5, 6B, 14, 19F and 23F was assessed in detail using random effects linear regression, adjusted for product, acellular diphtheria-tetanus-pertussis/whole-cell diphtheria- tetanus-pertussis coadministration, laboratory method, age at first dose and geographic region.

RESULTS

From 61 studies, we evaluated 13 two-dose (2+0) and 65 three-dose primary schedules (3+0) without a booster dose, 11 "2+1" (2 primary plus booster) and 42 "3+1" schedules. The GMC after the primary series was higher following 3-dose schedules compared with 2-dose schedules for all serotypes except for serotype 1. Pre- and postbooster GMCs were generally similar regardless of whether 2 or 3 primary doses were given. GMCs were significantly higher for all serotypes when dose 3 was administered in the second year (2+1) compared with ≤6 months of age (3+0).

CONCLUSIONS

While giving the third dose in the second year of life produces a higher antibody response than when given as part of the primary series in the first 6 months, the lower GMC between the 2-dose primary series and booster may result in less disease protection for infants in that interval than those who completed the 3-dose primary series. Theoretical advantages of higher antibodies induced by giving the third dose in the second year of life, such as increased protection against serotype 1 disease, longer duration of protection or more rapid induction of herd effects, need to be evaluated in practice.

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.

Use and interpretation of diagnostic vaccination in primary immunodeficiency: a working group report of the Basic and Clinical Immunology Interest Section of the American Academy of Allergy, Asthma & Immunology

A major diagnostic intervention in the consideration of many patients suspected to have primary immunodeficiency diseases (PIDDs) is the application and interpretation of vaccination. Specifically, the antibody response to antigenic challenge with vaccines can provide substantive insight into the status of human immune function. There are numerous vaccines that are commonly used in healthy individuals, as well as others that are available for specialized applications. Both can potentially be used to facilitate consideration of PIDD. However, the application of vaccines and interpretation of antibody responses in this context are complex. These rely on consideration of numerous existing specific studies, interpolation of data from healthy populations, current diagnostic guidelines, and expert subspecialist practice. This document represents an attempt of a working group of the American Academy of Allergy, Asthma & Immunology to provide further guidance and synthesis in this use of vaccination for diagnostic purposes in consideration of PIDD, as well as to identify key areas for further research.

Randomized, single blind, controlled trial to evaluate the prime-boost strategy for pneumococcal vaccination in renal transplant recipients

Renal transplant recipients are at increased risk of developing invasive pneumococcal diseases but may have poor response to the 23-valent pneumococcal polysaccharide vaccine (PPV). It may be possible to enhance immunogenicity by priming with 7-valent pneumococcal conjugate vaccine (7vPnC) and boosting with PPV 1 year later. In a randomized single-blind, controlled study, adult recipients of renal transplants received either 7nPVC or PPV followed by PPV 1 year later. The vaccine response was defined as 2-fold increase in antibody concentration from baseline and an absolute post-vaccination values ≥1 µg/ml. The primary endpoint was vaccine response of the primed group (7vPnC/PPV) compared with single PPV vaccination. Antibody concentrations for 10 serotypes were measured at baseline, 8 weeks after first vaccination, before second vaccination, and 8 weeks after second vaccination. Of 320 screened patients, 80 patients were randomized and 62 completed the study. Revaccination with PPV achieved no significant increase of immune response in the 7vPnC/PPV group compared with the single PPV recipients A response to at least 1 serotype was seen in 77.1% of patients who received 7vPnC and 93.1% of patients who received PPV (P = 0.046). After second vaccination response to at least 1 serotype was seen in 87.5% patients of 7vPnC/PPV group and 87.1% patients of PPV group (non significant p). The median number of serotypes eliciting a response was 3.5 (95% CI 2.5–4.5) in the 7vPnC/PPV group versus 5 (95% CI 3.9–6.1) in the PPV group (non-significant p). Immunogenicity of pneumococcal vaccination was not enhanced by the prime–boost strategy compared with vaccination with PPV alone. Administration of a single dose of PPV should continue to be the standard of care for adult recipients of renal transplants.

Trial Registration

EudraCT 2007-004590-25.

Immunogenicity and safety of heptavalent conjugate vaccine against Streptococcus pneumoniae in pre-term Polish infants

The purpose of the study was to assess post-vaccination immune response and occurrence of adverse events in the group of prematurely born infants. The study included 40 pre-term infants. Each child was vaccined four times (2, 4, 6 and 16 months) with the heptavalent conjugated pneumococcal vaccine (PCV7). Assessing of the level of antibodies was performed before vaccination, 4 weeks after primary series, before and 4 weeks after the booster dose. The research participants were qualified into 2 groups: group I - 19 children born before 30th gestational week, group II - 21 children born between the 30th and 34th gestational week. After the basic vaccination, an increase in the average antibody concentration in the area of all serotypes in most of the children tested was registered, with no significant differences observed between the groups. However, differences between individual serotypes were observed. The lowest values were found for serotype 6B. Before administering the booster dose, a significant drop in antibody titre in all of the children tested was noted. The last vaccination caused another significant increase in antibody concentration in both groups and the results obtained were markedly higher than those obtained after administering three vaccine doses. The majority of the children tested (with the exception of three from group II) achieved the preventive antibody level ≥ 0.35 μg/ml. In all of the children, no serious adverse events were observed. Our research showed, that heptavalent pneumococcal conjugate vaccine is immunogenic in children born before the completion of the 34th week of pregnancy. A booster dose of vaccine must be given at the right time to optimal response to the vaccine for all serotypes. Finally, any serious adverse events were observed.

Hyporesponsiveness to re-challenge dose following pneumococcal polysaccharide vaccine at 12 months of age, a randomized controlled trial

BACKGROUND

To evaluate the immunological impact of the 23-valent pneumococcal polysaccharide vaccine (23vPPS) at 12 months, for children who have received zero to three infant doses of seven-valent pneumococcal conjugate vaccine (PCV), on responses to a subsequent exposure to a small dose of 23vPPS (mPPS).

METHODS

Five hundred and fifty-two Fijian infants were stratified by ethnicity and randomized into eight groups to receive zero, one, two, or three PCV doses at 14 weeks, six and 14 weeks, or six, ten, and 14 weeks. Within each group, half received 23vPPS at 12 months and all received mPPS at 17 months. Sera were taken prior and one month post-mPPS.

FINDINGS

By 17 months, geometric mean antibody concentrations (GMC) to all 23 serotypes in 23vPPS were significantly higher in children who had received 23vPPS at 12 months compared to those who had not. Post-mPPS, children who had not received the 12 month 23vPPS had a significantly higher GMC for all PCV serotypes compared with those who had (each p<0.02). For the non-PCV serotypes, children who had not received the 12 month 23vPPS had significantly higher GMC for six of 16 non-PCV serotypes (7F, 9N, 12F, 19A, 22F, 33F) than those who did (each p<0.02). After adjusting for the pre-mPPS level, exposure to 23vPPS was associated with a lower response to mPPS for all serotypes (each p<0.001).

INTERPRETATION

Despite higher antibody concentrations at 17 months in children who had received 23vPPS at 12 months, the response to a re-challenge was poor for all 23 serotypes compared to children who had not received the 12 month 23vPPS.

Genome-wide dissection of globally emergent multi-drug resistant serotype 19A Streptococcus pneumoniae

BACKGROUND

Emergence of multi-drug resistant (MDR) serotype 19A Streptococcus pneumoniae (SPN) is well-documented but causal factors remain unclear. Canadian SPN isolates (1993-2008, n = 11,083) were serotyped and in vitro susceptibility tested. A subset of MDR 19A were multi-locus sequence typed (MLST) and representative isolates' whole genomes sequenced.

RESULTS

MDR 19A increased in the post-PCV7 era while 19F, 6B, and 23F concurrently declined. MLST of MDR 19A (n = 97) revealed that sequence type (ST) 320 predominated. ST320 was unique amongst MDR 19A in that its minimum inhibitory concentration (MIC) values for penicillin, amoxicillin, ceftriaxone, and erythromycin were higher than for other ST present amongst post-PCV7 MDR 19A. DNA sequencing revealed that alleles at key drug resistance loci pbp2a, pbp2x, pbp2b, ermB, mefA/E, and tetM were conserved between pre-PCV7 ST 320 19F and post-PCV7 ST 320 19A most likely due to a capsule switch recombination event. A genome wide comparison of MDR 19A ST320 with MDR 19F ST320 identified 822 unique SNPs in 19A, 61 of which were present in antimicrobial resistance genes and 100 in virulence factors.

CONCLUSIONS

Our results suggest a complex genetic picture where high-level drug resistance, vaccine selection pressure, and SPN mutational events have created a "perfect storm" for the emergence of MDR 19A.

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.

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.

Update on childhood pneumococcal vaccination

Since the efficacy of pneumococcal conjugate vaccine (PCV) against invasive pneumococcal disease in young children was first demonstrated in clinical trials in California, USA, in the late 1990s, it has been studied in more diverse populations and introduced into infant vaccination programs in the USA, Australia, Canada and several European countries. This review briefly describes the epidemiology of pneumococcal disease, recent literature on PCV trials in various study populations, the impact of 7-valent PCV infant vaccination on the epidemiology of invasive pneumococcal disease, with special reference to indirect effects in older age groups and the emergence of serotype replacement disease. Variations in vaccine administration schedules, effects on noninvasive pneumococcal diseases, and the use of the polysaccharide pneumococcal vaccine or future formulations of pneumococcal conjugate vaccines from the perspective of policy decisions for population-wide childhood pneumococcal vaccination programs are also highlighted.

Combined schedules of pneumococcal conjugate and polysaccharide vaccines: is hyporesponsiveness an issue?

Streptococcus pneumoniae is a major cause of morbidity and mortality in children less than 5 years of age. Prevention of pneumococcal disease and death in children in the developing world through vaccination with recently developed, highly efficacious pneumococcal conjugate vaccines (PCVs) is now possible. Schedules combining PCV with 23-valent pneumococcal polysaccharide vaccine (PPV23) have been studied and proposed as a means to expand disease protection against serotypes not included in the PCVs. Studies of group A and C meningococcal polysaccharide vaccine and repeated doses of PPV23 in adults and children have shown that a state of immune tolerance, or hyporesponsiveness, can develop to repeated polysaccharide vaccine antigen exposures. In this Review, we describe the evidence for and against this hyporesponsiveness and explore the possible mechanisms for such an occurrence.

Randomised revaccination with pneumococcal polysaccharide or conjugate vaccine in asplenic children previously vaccinated with polysaccharide vaccine

OBJECTIVE

Asplenic children are at high risk of invasive pneumococcal infection. In this group, the American Academy of Pediatrics recommends a single revaccination with the 23-valent polysaccharide vaccine (PSV23) 3-5 years after a previous PSV23 dose. Despite potential advantages, there are few data available regarding the safety and immunogenicity of the heptavalent pneumococcal conjugate vaccine (PCV7) in this population. The aim of the study was to prospectively determine and to compare, in asplenic children, the vaccine specific antibody titres against the seven serotypes included in the PCV7 after administration of one dose of PCV7 or of PSV23, 3 years or more after an initial vaccination with PSV23.

PATIENTS AND METHODS

In this randomised, single-centre study, antibody titres were monitored at baseline, at 1 and 6 months after revaccination in 21 children with anatomic or functional asplenia. Response was considered as positive when there was a four-fold increase in antibody titres from baseline.

RESULTS

The most frequently reported adverse events were local reactions in 7/11 of PCV7 subjects and in 5/8 of PSV23 subjects, and general reactions (loss of appetite, sleepiness) in 5/11 of PCV7 subjects and in 1/8 of PSV23 subjects; without any serious adverse events. One child in the PCV7 group had increased temperature (38.4 degrees C). At least half of the PCV7 children responded to four or five serotypes, while more than half of the PSV23 subjects responded to less than 3 serotypes (p=0.285). After 1 month, the immune response for serotype 23F was significantly greater after PCV7 vaccination than after PSV23 vaccination (p=0.036).

CONCLUSIONS

PCV7 revaccination is safe and immunogenic in asplenic children previously vaccinated with PSV23, and could provide appropriate booster response in this high-risk population. The clinical repercussion on invasive pneumococcal diseases remains to be demonstrated.

Conjugating recombinant proteins to Pseudomonas aeruginosa ExoProtein A: a strategy for enhancing immunogenicity of malaria vaccine candidates

Conjugation of polysaccharides to carrier proteins has been a successful approach for producing safe and effective vaccines. In an attempt to increase the immunogenicity of two malarial vaccine candidate proteins of Plasmodium falciparum, apical membrane antigen 1 (AMA1) to a blood stage vaccine candidate and surface protein 25 (Pfs25) a mosquito stage vaccine candidate, were each independently chemically conjugated to the mutant, nontoxic Pseudomonas aeruginosa ExoProtein A (rEPA). AMA1 is a large (66kD) relatively good immunogen in mice; Pfs25 is a poorly immunogenic protein when presented on alum to mice. Mice were immunized on days 0 and 28 with AMA1- or Pfs25-rEPA conjugates or unconjugated AMA1 or Pfs25, all formulated on Alhydrogel. Remarkably, sera from mice 14 days after the second immunization with Pfs25-rEPA conjugates displayed over a 1000-fold higher antibody titers as compared to unconjugated Pfs25. In contrast, AMA1 conjugated under the same conditions induced only a three-fold increase in antibody titers. When tested for functional activity, antibodies elicited by the AMA1-rEPA inhibited invasion of erythrocytes by blood-stage parasites and antibodies elicited by the Pfs25-rEPA conjugates blocked the development of the sexual stage parasites in the mosquito midgut. These results demonstrate that conjugation to rEPA induces a marked improvement in the antibody titer in mice for the poor immunogen (Pfs25) and for the larger protein (AMA1). These conjugates now need to be tested in humans to determine if mice are predictive of the response in humans.

Immunogenicity, efficacy, safety and effectiveness of pneumococcal conjugate vaccines (1998–2006)

In this paper we present an overview of the literature on efficacy and safety trials of the various pneumococcal conjugate vaccines on the market (PCV7) and in development (PCV9, PCV11 and allegedly PCV10 and PCV13), as well as of observations from post-licensure studies. Seven- (PCV7) and nine-valent PCV (PCV9) are reported to be sufficiently immunogenic after administration of a 3+1 schedule in infants in various RCTs. PncOMPC (PCV7 with a protein of N. meningitidis as a carrier) is less immunogenic, though this may have no repercussions for the protective efficacy against clinical disease. PCV7 is 82-97% efficacious against vaccine serotype (VT) IPD, 90% efficacious against (clinically diagnosed) pneumococcal pneumonia, and, like the 11-valent PCV, 57% efficacious against VT acute otitis media. Naturally, it would be of paramount public health interest if the same levels of efficacy and effectiveness could be achieved with fewer doses. Trials studying 2+1 vaccination schedules for PCV7 and PCV9 generally show that the percentage of infants achieving the protective cut-off set by the World Health Organization (WHO) 1 month after the last priming dose, is comparable to that found at the same time point in studies administering 3+1 schedules. PCVs are generally very well tolerated and safe, also when co-administered with other childhood vaccines. As more and more countries are using these vaccines routinely, post marketing surveillance studies will further establish the safety profile of PCVs.

Functional antibodies elicited by two heptavalent pneumococcal conjugate vaccines in the Finnish Otitis Media Vaccine Trial

In the Finnish Otitis Media Vaccine Trial, the now-licensed pneumococcal conjugate vaccine containing polysaccharides conjugated to protein CRM(197) (PncCRM) and the experimental pneumococcal polysaccharide-meningococcal outer membrane protein complex conjugate vaccine (PncOMPC), showed similar efficacy profiles against acute otitis media despite different antibody concentrations in sera. We now report the opsonophagocytic activities (OPA) in these sera. OPA, antibody concentration, and avidity for serotypes 6B, 19F, and 23F were determined in sera of infants who received either pneumococcal conjugate (PCV) or control vaccine at 2, 4, and 6 months of age and either the homologous or pneumococcal polysaccharide vaccine at 12 months of age. OPA varied by vaccine and serotype. The majority of PCV recipients had positive OPA after the fourth dose, while OPA was undetectable in the control group. Coinciding with the efficacy data, the concentration of antibodies required for 50% killing was low for 6B and high for 19F for both PCVs. Contradictory to the efficacy data, PncOMPC induced lower functional capacity to 23F than PncCRM. OPA correlated with antibody concentration, while avidity and functional capacity of antibodies showed no correlation. The OPA data provide valuable additional information for serotype-specific differences in protection and when evaluating serotype-specific immunogenicity and should thus be considered when defining serological correlates of protection.

Molecular analysis of monoclonal antibodies to group variant capsular polysaccharide of Neisseria meningitidis: recurrent heavy chains and alternative light chain partners

We determined the molecular sequence of monoclonal antibodies (mAbs) to serogroups B and C capsular polysaccharides (PS) of Neisseria meningitidis. N. meningitidis infections are a leading cause of bacterial septicemia and meningitis in humans. Antibodies to PS are fundamental to host defense and diagnostics. The polysaccharide capsule of group B N. meningitidis is poorly immunogenic and thus is an important model for studying pathogen-host co-evolution through understanding the molecular basis of the host immune response. We used a modified reverse-transcriptase PCR to amplify and sequence the V-genes of murine hybridomas produced against types B and C capsular PS. Databank analysis of the sequences encoding the V-genes of type C capsular PS mAb, 4-2-C, reveal that heavy chain alleles are recurrently used to encode this specificity in mice. Interestingly, a V-gene from the same germline family also encodes the V-domain of mAbs 2-2-B, which targets the antigenically distinct serogroup B capsular PS. Somatic mutation, junctional diversity and alternative light chains collectively impart the specificity for these serologically distinct epitopes. Knowledge of the specific immunoglobulin genes used to target common bacterial virulence factors may lead to insights on pathogen-host co-evolution, and the potential use of this information in pre-symptomatic diagnosis is discussed.

Kinetics and avidity of antibodies evoked by heptavalent pneumococcal conjugate vaccines PncCRM and PncOMPC in the Finnish Otitis Media Vaccine Trial

The licensure of new pneumococcal conjugate vaccines (PCVs) relies on immunogenicity data. When defining correlates of protection, vaccine efficacy data must be included. In the FinOM Vaccine Efficacy Trial, the PncOMPC vaccine showed an efficacy profile similar to that of the licensed PncCRM vaccine despite different antibody responses after primary and booster vaccinations. We determined antibody kinetics and avidities in a subgroup of infants participating in the FinOM trial. A total of 166 infants in three vaccine groups were immunized at 2, 4, 6, and 12 months of age with 7-valent PCV, PncCRM or PncOMPC, or hepatitis B vaccine. Concentrations of serum immunoglobulin G (IgG) against pneumococcal capsular polysaccharides were determined at 2, 4, 6, 7, 12, 13, and 24 months of age, and the avidity index (AI) to serotypes 6B, 19F, and 23F were determined at 7, 12, 13, and 24 months of age by enzyme immunoassay. Both PCVs were highly immunogenic, but they demonstrated different kinetics of antibody response; the concentration of IgG against serotypes 6B, 19F, and 23F declined faster after the third and fourth doses of vaccine in the PncCRM group than in the PncOMPC group. For both PCVs, the mean AI of anti-6B and -23F, but not of anti-19F, increased during the follow-up, which is in line with serotype-specific protection in the FinOM trial. Our data suggest that the kinetics and avidities of antibodies should be considered, in addition to antibody responses, when defining correlates of protection.

Pneumococcal conjugate vaccines for preventing vaccine-type invasive pneumococcal disease and pneumonia with consolidation on x-ray in children under two years of age

BACKGROUND

Pneumonia, most commonly caused by Streptococcus pneumoniae (Pnc), is a major cause of morbidity and mortality among young children especially in developing countries. Recently, the prevalence of antibiotic-resistant Pnc has increased worldwide such that the effectiveness of preventive strategies, like the new pneumococcal conjugate vaccines (PCV) on rates of invasive pneumococcal disease (IPD) and pneumonia, needs to be evaluated.

OBJECTIVES

To determine the efficacy of PCV in reducing the incidence of IPD due to vaccine serotypes (VT) and x-ray confirmed pneumonia with consolidation of unspecified etiology in children who received PCV before 12 months of age.

SEARCH STRATEGY

We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 1 2004), MEDLINE (1990 to March 2004) and EMBASE (1990 to December 2003). Reference list of articles, and books of abstracts of relevant symposia, were hand searched. Researchers in the field were also contacted.

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

Two reviewers independently identified eligible studies, assessed trial quality, and extracted data. Differences were resolved by discussion. The inverse variance method was used to pool effect sizes.

MAIN RESULTS

We identified four trials assessing the efficacy of PCV in reducing the incidence of IPD, two on x-ray confirmed pneumonia as outcome, and one on clinical pneumonia, with or without x-ray confirmation. Results from pooling HIV-1 negative children from the South African study with the other studies were as follows: the pooled vaccine efficacy (VE) for vaccine-type IPD was 88% (95% confidence interval (CI) 73% to 94%; fixed effect and random effects models), the effect measure was statistically significant (p <0.00001) and there was no heterogeneity (p = 0.77I2 0%); the pooled VE for all-serotype IPD was 66% (95% CI 46% to 79%; fixed effect model), the effect measure was statistically significant (p <0.00001) and there was no statistical heterogeneity (p = 0.09, I2 51%); the pooled VE for x-ray confirmed pneumonia was 22% (95% CI 11% to 31%; both fixed effect and random effects models) and there was no statistical heterogeneity (p = 0.80, I2 0%). Analyses that included all the children in the South African study (HIV-1 negative and HIV-1 positive children) and pooled with data from the other studies gave very similar results.

REVIEWERS' CONCLUSIONS

PCV is effective in reducing the incidence of IPD from all serotypes but exerts a greater effect in reducing VT IPD. Although PCV is also effective in reducing the incidence of x-ray confirmed pneumonia, there are still uncertainties about the definition of this outcome. Additional randomised controlled trials are currently in progress.

Serotypes and sequence types of pneumococci causing invasive disease in Scotland prior to the introduction of pneumococcal conjugate polysaccharide vaccines

Pneumococcal conjugate polysaccharide (Pnc) vaccines are now available, and the need for an improved understanding of circulating pneumococcal serotypes and sequence types (STs) is recognized. Three hundred sixty-eight pneumococci isolated in cases of invasive disease in Scotland in the first 6 months of 2003 were analyzed. The isolates belonged to 30 serotypes, and there was a strong correlation between serotype and ST, although only nine serotypes consisted of a single ST. The following serotypes coexisted with the following numbers of STs: serotype 14, 10 STs, serotype 8, 8 STs; serotype 4, 6 STs; serotype 22F, 8 STs; serotype 9V, 7 STs; serotype 23F, 6 STs; serotype 6B, 6 STs; serotype 1, 3 STs; serotype 3, 3 STs; and serotype 7F, 3 STs. Our data also showed a strong association between ST and serotype, although 19 STs contained multiple serotypes. Of the 10 most common STs, 6 coexisted with a single serotype each. Vaccine coverage in all age groups was 94.9% for the 23-valent polysaccharide vaccine and 50.7, 55.4, and 64.1% for the 7-, 9-, and 11-valent Pnc vaccines, respectively. For those under the age of 2 years, 79% coverage would be provided by the 7-, 9-, and 11-valent Pnc vaccines.

Heptavalent pneumococcal vaccine conjugated to outer membrane protein of Neisseria meningitidis serogroup b and nasopharyngeal carriage of Streptococcus pneumoniae in infants

BACKGROUND

Streptococcus pneumoniae (Sp) is an important bacterial pathogen in children. Nasopharyngeal (NP) colonization of S. pneumoniae is necessary for person-to-person transmission and often precedes invasive disease.

METHODS

NP carriage of Sp was studied in 49 infants following administration of a heptavalent pneumococcal conjugate vaccine (PCV) conjugated to the outer membrane protein of serogroup b Neisseria meningitidis (vaccine serotypes: 4, 6B, 9V, 14, 18C, 19F, 23F). The vaccine was administered at 2, 4, 6, and 12 months of age and carriage rates were compared to a concurrent group of 32 infants not given PCV and evaluated over the first 15 months of life.

RESULTS

Overall, Sp was isolated in 86/367 (23%) of NP cultures and 49% of infants. Serotype 23F was significantly less prevalent in the PCV group (1.9%) than the control group (16.1%) (P<0.05). Analysis of the proportion of children with prevalent carriage or acquisition of carriage did not differ between groups when evaluated by age or serotype. We noted, however, decreased acquisition and carriage in the vaccine group 1 month following the 12 month dose of PCV for vaccine serotypes (76 and 52% reduction, respectively), but this did not reach statistical significance (P=0.3). Adjustment for age, daycare and antibiotic use by multivariate modeling revealed no difference in carriage of vaccine containing serotypes or non-vaccine serotypes between groups.

CONCLUSION

We did not show a significant effect of this heptavalent PCV on NP carriage. Further study of this issue, including a larger population size, is needed.