Immunogenicity and reactogenicity of a pneumococcal conjugate vaccine administered combined with a haemophilus influenzae type B conjugate vaccine in United Kingdom infants

Associations between geographic region and immune response variations to pneumococcal conjugate vaccines in clinical trials: A systematic review and meta-analysis

OBJECTIVE

Geographic region can be an important source of variation in the immune response to pneumococcal conjugate vaccines (PCV). The aim of this study was to collate data from available PCV clinical trials in order to characterize the differences in antibody responses in different countries.

METHODS

A systematic review and meta-analysis was conducted to examine the difference in antibody responses after primary series of PCVs in infants, associated with geographic regions, compared with each other and with the different PCVs using random-effects models.

RESULTS

A total of 69 trials were included. Studies conducted in the Western Pacific Region (WPR) showed higher geometric mean concentrations (GMC) compared to studies conducted in Europe. The pooled GMC for serotype 4 after three doses of PCV7 in the WPR was 5.19 μg/ml (95% confidence interval 4.85-5.53 μg/ml), while for studies conducted in Europe this was 2.01 μg/ml (95% confidence interval 1.88-2.14 μg/ml). The IgG GMC ratios among the WPR versus European regions ranged from 1.51 to 2.87 for PCV7, 1.69 to 3.22 for PCV10, and 1.49 to 3.08 for PCV13.

CONCLUSIONS

Studies conducted in the WPR generally showed greater antibody responses than the studies conducted in Europe. Indications of differences among geographic regions highlight the fact that further research is needed to compare the biological factors contributing to immune responses, which may affect vaccination schedules.

Effect of previous vaccination with pneumococcal conjugate vaccine on pneumococcal polysaccharide vaccine antibody responses

During the past 10 years, pneumococcal conjugate vaccine (PCV) has become part of the standard childhood vaccination programme. This may impact upon the diagnosis of polysaccharide antibody deficiency by measurement of anti-polysaccharide immunoglobulin (Ig)G after immunization with unconjugated pneumococcal polysaccharide vaccine (PPV). Indeed, contrary to PPV, PCV induces a T-dependent, more pronounced memory response. The antibody response to PPV was studied retrospectively in patients referred for suspected humoral immunodeficiency. The study population was divided into four subgroups based on age (2-5 years versus ≥ 10 years) and time tested (1998-2005 versus 2010-12). Only 2-5-year-old children tested in 2010-12 had been vaccinated with PCV prior to PPV. The PCV primed group showed higher antibody responses for PCV-PPV shared serotypes 4 and 18C than the unprimed groups. To a lesser extent, this was also found for non-PCV serotype 9N, but not for non-PCV serotypes 19A and 8. Furthermore, PCV-priming elicited a higher IgG2 response. In conclusion, previous PCV vaccination affects antibody response to PPV for shared serotypes, but can also influence antibody response to some non-PCV serotypes (9N). With increasing number of serotypes included in PCV, the diagnostic assessment for polysaccharide antibody deficiency requires careful selection of serotypes that are not influenced by prior PCV (e.g. serotype 8). Further research is needed to identify more serotypes that are not influenced.

Use and clinical interpretation of pneumococcal antibody measurements in the evaluation of humoral immune function

Pneumococcal vaccination is a commonly used technique for assessing the humoral immune status of a patient suspected of having immunodeficiency. Interpretation of what constitutes an adequate response, however, can be challenging. This is due to the complexity of the data generated from serotype-specific assays, historical variations in the assays used to measure pneumococcal antibodies, and varying recommendations on the relevant cut points that define response. In this review, we summarize the historical evolution of assays used for this purpose and discuss the analytical considerations that have influenced published data. We also examine current clinical recommendations for defining an adequate response to vaccination, with a particular focus on the interpretation of serotype-specific data generated by multiplex assays.

The differential impact of coadministered vaccines, geographic region, vaccine product and other covariates on pneumococcal conjugate vaccine immunogenicity

BACKGROUND

Antipneumococcal capsular polysaccharide antibody concentrations are used as predictors of vaccine efficacy against vaccine serotype (ST) pneumococcal disease among infants. While pneumococcal conjugate vaccines (PCV) are recommended globally, factors associated with optimal PCV immune response are not well described. We aimed to systematically assess local setting factors, beyond dosing schedule, which may affect PCV antibody levels.

METHODS

We conducted a literature review of PCV immunogenicity, abstracting data from published reports, unpublished sources, and conference abstracts from 1994 to 2010 (and ad hoc 2011 reports). Studies included in this analysis evaluated ≥ 2 primary doses of PCV before 6 months of age in non-high-risk populations, used 7-valent or higher PCV products (excluding Aventis-Pasteur and Merck products) and provided information on geometric mean concentration (GMC) for STs 1, 5, 6B, 14, 19F or 23F. Using random effects meta-regression, we assessed the impact of geographic region, coadministered vaccines and PCV product on postprimary GMC, adjusting for dosing schedule and ELISA laboratory method.

RESULTS

Of 12,980 citations reviewed, we identified 103 vaccine study arms for this analysis. Children in studies from Asia, Africa and Latin America had significantly higher GMC responses compared with those in studies from Europe and North America. Coadministration with acellular pertussis DTP compared with whole-cell DTP had no effect on PCV immunogenicity except for ST14, where GMCs were higher when coadministered with acellular pertussis DTP. Vaccine product, number of PCV doses, dosing interval, age at first dose and ELISA laboratory method also affected the GMC.

CONCLUSIONS

PCV immunogenicity is associated with geographic region and vaccine product; however, the associations and magnitude varied by ST. Consideration of these factors is essential when comparing PCV immunogenicity results between groups and should be included in the evidence base when selecting optimal PCV vaccine schedules in specific settings.

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

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

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.

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.

Randomised, controlled trial of concomitant pneumococcal and meningococcal conjugate vaccines

A randomised, open-label study compared the immunogenicity and safety of 7-valent pneumococcal conjugate vaccine (PCV7) and meningococcal C conjugate vaccine (MnCC vaccine) administered concomitantly and individually. Infants received PCV7+MnCC vaccine (n=265), PCV7 alone (n=268) or MnCC vaccine alone (n=178). PCV7 was administered at 2, 3½, 6 and 12 months, and MnCC vaccine at 2, 6 and 12 months. For the 7 pneumococcal serotypes tested (4, 6B, 9V, 14, 18C, 19F and 23F), proportions of subjects with pneumococcal serotype-specific immunoglobulin G (IgG) antibody concentrations ≥0.35 μg/mL post-infant series were non-inferior for the PCV7+MnCC vaccine (91.5-99.6%) and PCV7 (89.0-99.6%) groups. Proportions of subjects achieving serogroup C meningococcal serum bactericidal assay titres ≥1:8 post-infant series were non-inferior for the PCV7+MnCC vaccine (99.6%) and MnCC vaccine groups (98.8%). Pneumococcal IgG antibody levels were similar in the PCV7+MnCC vaccine and PCV7 groups at each time point. Post-infant and post-toddler meningococcus C serum bactericidal assay titres and IgG levels were similar in the PCV7+MnCC vaccine and MnCC groups, although pre-toddler, the levels were lower in the PCV7+MnCC vaccine group than the MnCC vaccine group. Immune response rates to diphtheria antigen approached 100% for all vaccine groups. Local reactions were mostly similar among the treatment groups. The MnCC vaccine group had lower rates of some systemic events than the PCV7+MnCC vaccine group. Immune responses to PCV7+MnCC vaccine were non-inferior compared with those seen with each vaccine administered alone.

Safety and immunogenicity of the 23-valent pneumococcal polysaccharide vaccine at 12 months of age, following one, two, or three doses of the 7-valent pneumococcal conjugate vaccine in infancy

Fijian infants aged 6 weeks were stratified by ethnicity and randomized to receive 0, 1, 2, or 3 PCV-7 doses with or without the 23-valent pneumococcal polysaccharide vaccine (PPV-23) at 12 months. Strong booster effects for all 7 PCV-7 serotypes were elicited, and for 4/7 serotypes these responses were highest in the single PCV-7 group. There were fourfold rises in GMC for all non-PCV-7 serotypes. By 17 months the PPV-23 group still had significantly higher GMC (each p<0.001) for all serotypes. The PPV-23 was well tolerated and induced excellent responses for all serotypes which were greatest in the single PCV-7 group.

Immunogenicity of a heptavalent conjugate pneumococcal vaccine administered concurrently with a combination diphtheria, tetanus, five-component acellular pertussis, inactivated polio, and Haemophilus influenzae type B vaccine and a meningococcal group C conjugate vaccine at 2, 3, and 4 months of age

The immunogenicities of conjugate pneumococcal vaccines have been demonstrated when they are administered at 2, 3, and 4 months of age. There is a paucity of data on the immunogenicity of this vaccine when it is administered concurrently with other vaccines in the primary immunization schedule of the United Kingdom. We immunized 55 term infants at 2, 3, and 4 months of age with the seven-valent pneumococcal conjugate vaccine (PCV7), the meningococcal group C conjugate (MCC) vaccine, and the diphtheria, tetanus, five-component acellular pertussis, inactivated polio, and Haemophilus influenzae type b (DTaP(5)/IPV/Hib-TT) vaccine. The immune responses to the H. influenzae type b (Hib), MCC, and tetanus vaccines were measured at 2, 5, and 12 months of age; and the immune responses to PCV7 were measured at 2 and 5 months and then either at 12 months or following a 4th dose of PCV7. There were increases in the geometric mean concentrations (GMCs) of all antigens postimmunization. Greater than or equal to 90% of the infants achieved putatively protective levels postimmunization for all vaccine antigens except pneumococcal serotype 6B and Hib. The GMCs of the PCV7 serotypes increased following a 4th dose, although one infant had not reached putative levels of protection against serotype 6B. In conclusion, when infants were vaccinated according to the schedule described above, they had lower postprimary immunization responses to Hib, meningococcus group C capsular polysaccharide, and pneumococcal serotype 6B than the responses demonstrated by use of the other schedules. Despite this finding, there was a good response following a 4th dose of PCV7.

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.

Immunogenicity of routinely used childhood vaccines when coadministered with the 10-valent pneumococcal non-typeable Haemophilus influenzae protein D conjugate vaccine (PHiD-CV)

BACKGROUND

The choice of non-typeable Haemophilus influenzae Protein D as main carrier protein in the candidate 10-valent pneumococcal conjugate vaccine (PHiD-CV, GlaxoSmithKline Biologicals), was driven in part to avoid carrier-mediated suppression and possible bystander interference with coadministered vaccines. Immunogenicity data from 3 primary and 2 booster vaccination studies were assessed for possible impacts of PHiD-CV coadministration on immune responses to routinely administered childhood vaccines, in comparison to 7-valent pneumococcal conjugate vaccine (7vCRM) coadministration.

METHODS

Randomized, controlled studies in which PHiD-CV or 7vCRM vaccines were coadministered with DTPa-[HBV]-IPV/Hib, DTPa-[HBV]-IPV, DTPw-HBV/Hib, IPV, and OPV, combined Hib-Neisseria meningitidis serogroup C vaccine (Hib-MenC-TT), standalone MenC-TT or MenC-CRM vaccines.

RESULTS

One month after primary vaccination, >96% of PHiD-CV recipients had seroprotective antibody concentrations against diphtheria, tetanus, poliovirus types 1 and 3, Hib (>or=0.15 microg/mL), SBA-MenC (>or=1:8), and >94% were seropositive for antibodies against pertussis antigens. Somewhat lower responses against poliovirus type 2 in study A (compared with poliovirus type 1 and 2 responses) and hepatitis B in the 6-, 10-, and 14-week schedule in the Philippines (compared with hepatitis B responses in the other studies) were observed after coadministration of both PHiD-CV and 7vCRM vaccines. Antitetanus and anti-PRP antibody geometric mean concentrations (GMCs) tended to be higher after PHiD-CV coadministration, probably because of the TT carrier protein for serotype 18C in PHiD-CV. Booster vaccination induced substantial increases in antibody GMCs for all coadministered antigens. These responses were generally within the same range in PHiD-CV and 7vCRM groups. Observed anti-PRP responses remained higher in PHiD-CV recipients after the booster dose.

CONCLUSIONS

Coadministration of PHiD-CV with commonly used childhood vaccines induced high levels of seroprotection/seropositivity against all targeted diseases. No evidence of negative interference on the immune response to any of the coadministered vaccine antigens was observed when compared with the current routine practice of 7vCRM coadministration.

Safety profile of pneumococcal conjugate vaccines: systematic review of pre- and post-licensure data

A 7-valent pneumococcal polysaccharide-protein conjugate vaccine (PCV7) was licensed in the United States of America in 2000, but no comprehensive postmarketing review of safety has been carried out. We conducted a systematic review of the safety of PCV7 and other pneumococcal conjugate vaccines. A total of 42 studies were included in the review. Reactogenicity data from some randomized trials suggest that PCV7 may result in more local reactions and fever than certain comparison vaccines. However, the reactions were mild and self-limited, and PCV7 did not carry an increased risk of severe injection-site reactions or high fever. Some, although not all, of the randomized trials in children found that mild local and systemic reactions associated with PCV7 may increase with the number of doses, at least over the three-dose primary series. In addition, PCV7 and other pneumococcal conjugate vaccines were found to have tolerable reactogenicity in Native American and African populations and in medically high-risk groups for which pneumococcal vaccination is recommended. Two of the largest studies of PCVs, one involving PCV7 and the other, PCV9, found a statistically significant increased risk of hospitalization for reactive airway disease, including asthma. Another large trial of PCV9, however, did not find an increased risk of asthma. In conclusion, this review of the evidence did not identify any major safety problems with PCV7 or any other pneumococcal conjugate vaccine, with the possible exception of reactive airway disease, which may bear further scrutiny as additional data become available.

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.

Immunogenicity, reactogenicity, and safety of a seven-valent pneumococcal conjugate vaccine (PCV7) concurrently administered with a fully liquid DTPa-IPV-HBV-Hib combination vaccine in healthy infants

AIM OF THE STUDY

To evaluate the immunogenicity, safety and reactogenicity of a seven-valent pneumococcal conjugate vaccine (PCV7) when given concomitantly with a fully liquid DTaP-IPV-HBV-Hib combination vaccine.

METHODS

Two hundred and sixty-six healthy infants in France (n=136) and Germany (n=130) were randomized to receive DTaP-IPV-HBV-Hib and PCV7 (test group) at the age of 2, 3 and 4 months (primary series) and 12-15 months (booster dose), or to receive DTaP-IPV-HBV-Hib at the same time points but PCV7 at the ages of 5, 6, 7 and 13-16 months (control group). Antibody levels to all vaccine antigens were measured before dose 1, 1 month after dose 3, at the time of booster, and 1 month later. Safety data were collected after each vaccine dose.

RESULTS

Two hundred and fifty-seven infants (test group, 131; control group, 126) completed the primary immunization series and two hundred and forty-five received the booster dose (test group, 125; control group, 120). Depending on the serotype, 92.8-100% of subjects in the test group achieved antibody levels >or=0.15 microg/mL for PCV7 antigens at 5 months of age, and 89.7-99.1% of them antibody levels >or=0.50 microg/mL 1 month after booster. For DTaP-IPV-HBV-Hib, there was no statistically significant difference between the two groups in the proportion of infants that achieved pre-defined seroprotective levels for each antigen at 5 months and 1 month after booster. Frequency of local and systemic reactions was similar in both groups except for fever above 38.0 degrees C, which was more frequent in the test group after dose 1, 2 or 4. Fever >39.0 degrees C was only reported from three children in each group.

CONCLUSION

The PCV7 vaccine was highly immunogenic, well tolerated, and safe when coadministered with the DTPa-IPV-HBV-Hib vaccine at 2, 3, and 4 months of age and a booster dose at 12-15 months. In this study, PCV7 did not show any relevant influence on the immunogenicity and safety of the concurrently administered DTPa-IPV-HBV-Hib vaccine.

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.

Immunogenicity and induction of immunological memory of the heptavalent pneumococcal conjugate vaccine in preterm UK infants

Data on the immunogenicity and memory induction of pneumococcal conjugate vaccines in very preterm infants is limited. We vaccinated 69 full term and 68 preterm infants (median gestational age (GA) 30 weeks) with a 7-valent pneumococcal conjugate vaccine (PCV7) at 2/3/4 months of age, followed by a plain polysaccharide booster at 12 months of age. IgG-GMC (ELISA) was significantly lower in preterm infants to six vaccine serotypes (ST) at 2 months and 5 months of age, to five ST at 12 months of age and to three ST at 13 months of age. A significantly lower proportion of preterm infants achieved IgG levels>or=0.35 microg/ml to ST 4, 6B and 9V at 5 months and to ST 4, 6B, 18C, 19F and 23F at 12 months of age. Fold rises following the polysaccharide booster were comparable to those of term infants. At least 93% of both cohorts achieved IgG>or=0.35 microg/ml to all STs following booster vaccination. Pneumococcal conjugate vaccine at an accelerated schedule of 2/3/4 months of age is likely to provide protection against pneumococcal disease for preterm infants. Antibody concentrations wane over the first year of life in both preterm and term infants and booster vaccination is therefore likely to be important.

Combination conjugate vaccines

Increasingly, more diseases are becoming vaccine preventable, but maintaining community and provider acceptance demands that the number of injections does not increase. Combination conjugate vaccines represent an inevitable and important advance. This paper reviews the efficacy and safety of combination conjugate vaccines, including immunological mechanisms underlying interactions among vaccine epitopes, the role of immunological memory, and correlates of immunity. Specific attention is given to the experience with combination vaccines against each of Haemophilus influenzae type b, Streptococcus pneumoniae and Neisseria meningitidis. The implications of these findings for different communities are discussed, key areas for further research identified and implications for post-licensure monitoring addressed.

Priming of immunological memory by pneumococcal conjugate vaccine in children unresponsive to 23-valent polysaccharide pneumococcal vaccine

Pneumococcal polysaccharide vaccine (PPV) is of limited immunogenicity in infants and immunocompromised patients. Our prospective randomized controlled trial investigated whether priming with pneumococcal conjugate vaccine (PCV) induced specific immunological memory in previously nonresponders to PPV. Of a total of 33 children (2 to 18 years) with polysaccharide-specific immunodeficiency (PSI), group A (n = 16) received two doses of 7-valent PCV in a 4- to 6-week interval, and a booster dose of 23-valent PPV after one year. Group B (n = 17) received two doses of PPV in a 1-year interval exclusively. Specific antibody concentrations for serotypes 4, 5, 6B, 9V, 14, 18C, 19F, and 23F were determined (enzyme-linked immunosorbent assay) before and at 7 and 28 days after administration of the PPV booster and compared to an opsonophagocytosis assay. Of group A, 64 to 100% had antibody concentrations of > or = 1 microg/ml on day 28 after the booster versus 25 to 94% of group B. Group A had significantly higher antibody concentrations for all PCV-containing serotypes already on day 7, indicating early memory response. Antibody concentrations were in accordance with functional opsonic activity, although opsonic titers varied among individuals. Pneumococcal vaccination was well tolerated. The incidence of airway infections was reduced after priming with PCV (10/year for group A versus 15/year for group B). Following a PPV booster, even patients primarily not responding to PPV showed a rapid and more pronounced memory response after priming with PCV.

Could a single dose of pneumococcal conjugate vaccine in children be effective? Modeling the optimal age of vaccination

Using incidence rates from CDC's Active Bacterial Core surveillance and immunogenicity data from the Navajo/Apache trial of pneumococcal conjugate vaccine (PCV), we used Markov modeling to predict the optimal age to give a single dose of PCV. Antibody concentration thresholds of 0.35 and 1.0 mcg/ml were considered protective. Our outcome was vaccine serotype-specific invasive pneumococcal disease (IPD) incidence at 24 months. The models predicted the optimal age to vaccinate is 5-7 months with vaccine-induced immunologic memory and 8-10 months without memory. IPD reduction ranged from 15 to 62%, depending on model parameters. A single PCV dose in infants could prevent substantial IPD.

Pneumococcal conjugate vaccine followed by pneumococcal polysaccharide vaccine; immunogenicity in patients with ataxia-telangiectasia

The immunodeficiency in Ataxia-telangiectasia (A-T) is characterised by low T and B cell counts, low levels of IgE, IgA and/or IgG2, and especially low levels of pneumococcal antibodies. The 23-valent pneumococcal polysaccharide vaccine (PPV23) has previously been shown not to be effective in A-T, but these patients are capable of making protective antibodies to other vaccines such as diphtheria and tetanus toxin, promising effect of the seven-valent pneumococcal conjugated vaccine (PCV7). Nine A-T patients and 25 age and sex matched controls were vaccinated with both PCV7 and PPV23, and three A-T patients were vaccinated with PCV7 only. In the A-T patients, no significant increase in pneumococcal antibody levels were observed after the single PCV7, while the subsequent PPV23 vaccination resulted in a significant increase in antibody levels to the PPV23 mix, as well as to serotype 4, 14, 19F and to the geometric mean of serotype 4, 6B, 14, 18C, 19F, 23F which increased from median 0.2 (range 0.1-0.5) microg/mL to 0.6 (0.2-1.5) microg/mL (P= 0.014). Compared to the patients' baseline levels, the vaccinations induced a 1.5- to 7-fold increase in antibodies to the six different serotypes tested. The increases in pneumococcal antibody titres were lower than those observed in the controls (9- to 34-fold increase). The results are valuable in planning the care of A-T patients, using PCV7 to trigger and PPV23 to booster the immune response and possibly prevent severe pneumococcal disease.

The safety of 7-valent pneumococcal conjugate vaccine

Streptococcus pneumoniae is one of the most important bacterial pathogens of young children. Currently, there are several conjugate vaccines against S. pneumoniae in various stages of laboratory development, clinical evaluation or currently licensed. Heptavalent pneumococcal conjugate vaccine (Wyeth Lederle; PCV-7) is the only currently approved pneumococcal conjugate vaccine indicated against invasive pneumococcal disease for children younger than two years of age. Safety studies have shown that the PCV-7 is acceptably safe when administered alone, simultaneously with other childhood vaccines or in combination with Haemophilus influenzae type b conjugate vaccines. In addition, PCV-7 vaccine was generally safe and immunogenic among infants infected with HIV and those with sickle cell disease. Surveillance studies to monitor the serotype distribution in invasive pneumococcal disease is important to determine that PCV-7 continues to be the optimal vaccination for prevention of pneumococcal invasive disease.

Advances in Pneumococcal Vaccines

The introduction of Haemophilus influenzae type b (Hib) vaccine into the universal immunisation schedules of many industrialised countries and the subsequent remarkable decline in the incidence of invasive Hib disease has further highlighted the impact of invasive pneumococcal diseases. Streptococcus pneumoniae is now the leading cause of bacterial meningitis in children in many settings and a leading cause of vaccine-preventable bacterial disease in children worldwide. The currently marketed 23-valent pneumococcal polysaccharide vaccine provides large serotype coverage at a relatively low cost. However, it is not efficacious in young children. Pneumococcal conjugate vaccines (PCVs) are highly effective in preventing invasive disease in infants and young children, with favourable safety and immunogenicity profiles. These vaccines have also shown efficacy in reducing cases of non-invasive disease (i.e. otitis media), nasopharyngeal acquisition of vaccine-specific serotypes of S. pneumoniae, and protection against pneumococcal disease caused by resistant strains. However, PCV contains a limited number of pneumococcal serotypes and, given adequate ecological pressure, replacement disease by non-vaccine serotypes remains a threat, particularly in areas with very high disease burden. Furthermore, although capsular-specific antibodies have been shown to be highly protective, it remains unclear what concentration of these serotype-specific antibodies protect against disease and, more recently, it has become clear that opsonic activity and avidity of these antibodies are more critical determinants of protection than concentration. Therefore, monitoring disease burden and defining immune correlates of protection after widespread use of conjugate vaccines are crucial for the evaluation of these new generation vaccines. Furthermore, a need exists to develop pneumococcal vaccines with lower cost and larger serotype coverage. Development of one or more protein vaccines that might be easier and, thus, less expensive to manufacture, and which might provide protection against multiple serotypes, is in progress. This article reviews the current state of pneumococcal disease and pneumococcal vaccines in clinical use.

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.

Pneumococcal conjugate vaccines—a European perspective

Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, and acute otitis media in children and adults worldwide. In the age group of < 2 years the incidence of invasive pneumococcal disease ranges from approximately 14 cases per 100,000 in Germany and the Netherlands and more than 90 per 100,000 children in Spain. The vulnerability of children to S. pneumoniae can also be demonstrated by the high rate of sequelae (> 20% in Germany) and the high mortality (7.5%) in pneumococcal meningitis. Furthermore, antibiotic resistance of S. pneumoniae is increasing in Europe, particularly in France, Spain, and Eastern European countries, whereas Germany and Northern Europe are only marginally affected. A 7-valent pneumococcal conjugate vaccine (7vPCV) that was shown to be highly efficacious in preventing invasive pneumococcal disease in infants in the USA was licensed in Europe in 2001. It is expected that broad usage of the vaccine would reduce the incidence of invasive pneumococcal disease and the levels of pneumococcal resistance significantly. Important questions have been raised regarding the effectiveness of this vaccine in high-risk populations, serotype replacement, the efficacy of this vaccine in otitis media, and the co-administration of the new vaccine with other standard childhood vaccines used in various European countries. France and Spain currently have the most-wide ranging guidelines recommending pneumococcal vaccination for children. Overall, the development of pneumococcal conjugate vaccines is a significant step in the control of pneumococcal disease in children in Europe. Further progress in pneumococcal vaccine development can be expected from conjugate vaccines including more than seven serotypes (9-valent, 11-valent).

Mucosal immune responses to capsular pneumococcal polysaccharides in immunized preschool children and controls with similar nasal pneumococcal colonization rates

BACKGROUND

Immunization with conjugate pneumococcal vaccines induces significant primary and memory IgG anti-polysaccharide (PS) responses in serum. It can also induce mucosal responses in infants especially after a polysaccharide booster. However, it is unclear whether it can prime for mucosal memory responses on nasal exposure to pneumococcus, which may be important in protection against pneumococcal invasion and/or carriage.

METHOD

IgA and IgG to serotypes 4, 6B, 9V, 14, 18C, 19F and 23F (conjugate vaccine serotypes), 1 and 3 (nonvaccine serotypes) capsular PS were measured by immunoassay in saliva from 2- to 5-year-old children previously given three doses of 7-valent pneumococcal conjugate vaccine in infancy, followed by 23-valent PS vaccine at 13 months and from unvaccinated controls of similar age and sex. Salivary antibody responses were analyzed in relation to carriage of pneumococci assessed by bacterial culture of nasopharyngeal swab samples collected in the summer and winter of the year 2000.

RESULTS

Rates of detectable IgG antibodies to all vaccine serotypes except 23F were higher in subjects than in controls. No such differences were observed for IgA antibodies except for serotype 6B. Nasal colonization rates were similar, and in both groups mucosal IgA responses were more common and larger than IgG responses.

CONCLUSIONS

The mucosal anti-capsular IgA responses observed could develop in response to colonization in preschool children, regardless of vaccination status, and contribute to the falling carriage rates observed with increasing age.

Pneumococcal nasopharyngeal carriage in children following heptavalent pneumococcal conjugate vaccination in infancy

AIMS

To ascertain whether the reduction in nasopharyngeal carriage of vaccine serotypes induced by pneumococcal conjugate vaccine (PnCV) administered to infants persists beyond the age of 2 years.

METHODS

Non-randomised, unblinded controlled study of 2-5 year old children who had received three doses of heptavalent PnCV (7VPnCV) in infancy and 23-valent pneumococcal polysaccharide vaccine at 13 months, and unimmunised controls. Nasopharyngeal swabs were taken in summer (150 vaccinated subjects, 126 controls) and winter (143 vaccinated subjects, 188 controls). The swabs were cultured and serotyped for Streptococcus pneumoniae.

RESULTS

Carriage rates (vaccinated subjects: 24.7% and 43.4%; controls: 27.0% and 41.0%, in summer and winter respectively) and carriage of vaccine serotypes (subjects: 10.0% and 30.0%; controls: 13.5% and 31.5%, in summer and winter respectively) were similar in the two groups.

CONCLUSIONS

Effects of vaccination in infancy on rates of nasal carriage of pneumococcus and serotype replacement in children living in a largely unvaccinated population are no longer evident by 2-5 years of age.

Pneumococcal conjugate vaccine (Prevnar; PNCRM7): a review of its use in the prevention of Streptococcus pneumoniae infection

PNCRM7 (Prevnar) is a pneumococcal vaccine containing seven capsular polysaccharide antigens from the bacterium Streptococcus pneumoniae, each of which is conjugated to diphtheria protein [cross-reactive material (CRM(197))]. CRM(197) is an inert but immunogenic variant of diphtheria toxoid that is also used as a carrier molecule in one Haemophilus influenzae type b conjugate vaccine. Unlike the 23-valent unconjugated pneumococcal vaccines, PNCRM7 elicits a T cell-dependent response and thus protects young children against pneumococcal disease. The immunogenicity of PNCRM7 has been demonstrated in both healthy children aged <2 years and older children in high-risk groups. Two randomized, double-blind trials conducted in the US demonstrated that all PNCRM7 serotypes were immunogenic in healthy infants and young children when compared with a control vaccine. A booster dose of PNCRM7 elicited an anamnestic response to all seven serotypes. Data from a large, randomized, double-blind study conducted in California (US) have confirmed the protective efficacy of PNCRM7 against invasive pneumococcal disease (e.g. bacteremia, meningitis) caused by serotypes included in the vaccine. The vaccine efficacy in the per-protocol analysis was 97.4% and its efficacy against invasive disease caused by any pneumococcal serotype in the intent-to-treat (ITT) analysis was 89.1%. Indeed, a postlicense surveillance study (n = 211,565) showed that the introduction and routine use of PNCRM7 was associated with a marked reduction in invasive pneumococcal disease in children <5 years of age. In addition, the US trial and another randomized, double-blind trial conducted in Finland, showed that PNCRM7 vaccine efficacy against all otitis media episodes was between 6 and 7%. PNCRM7 vaccine was generally well tolerated and had a similar local and systemic adverse events profile to other pediatric vaccines. The most common local adverse event associated with PNCRM7 administration was inflammation at the injection site, and the most common systemic adverse effect was febrile illness (> or =38 degrees C) that usually resolved without treatment. The limited available pharmacoeconomic data suggest that PNCRM7 could be cost effective depending, in part, on the manufacturer's list price of the vaccine. Results of the base case analysis in a US study showed a cost-effectiveness ratio for PNCRM7 of US dollars 80,000 per life-year saved from a societal perspective compared with US dollars 176,000 from a healthcare payer perspective, assuming a nondiscounted list price of US dollars 58 per dose (1997 costs). Concomitant administration of PNCRM7 vaccine with hepatitis B, oral polio, meningococcal oligosaccharide protein conjugate or H. influenzae type b vaccines did not affect the immunogenicity of these pediatric vaccines to a clinically relevant extent.

CONCLUSION

PNCRM7 vaccine will be of great benefit to those societies that have active immunization programs implemented. In infants and vulnerable children throughout the world, PNCRM7 vaccine has the potential to reduce the mortality and morbidity rates associated with S. pneumoniae infections. In developed countries, the vaccine will be of particular benefit in preventing disabling infections but its impact in developing countries will be more pronounced with the potential to greatly reduce mortality.

Safety and immunogenicity of pneumococcal conjugate vaccine in combination with diphtheria, tetanus toxoid, pertussis and Haemophilus influenzae type b conjugate vaccine

BACKGROUND

Pneumococcal polysaccharide/protein conjugate vaccines (PnCV) are immunogenic and effective in infancy. However, an addition to the nine currently recommended vaccine injections during the first year of life of African children may be a deterrent to participation in a PnCV program. Thus we have evaluated the safety and immunogenicity of a 9-valent PnCV (Wyeth Lederle Pediatrics and Vaccines) mixed with diphtheria, tetanus toxoid, cell pertussis and type b (TETRAMUNE).

METHODS

Healthy Gambian infants were randomized at the age of 2 months to receive three doses 1 month apart of either (1) placebo reconstituted in TETRAMUNE in the right thigh (control) or (2) PnCV in the left thigh and TETRAMUNE in the right thigh (separate) or (3) PnCV reconstituted in TETRAMUNE as a single injection in the right thigh (combined). The vaccines were given together with routine Expanded Program on Immunization vaccines. Adverse reactions were recorded after vaccination, and antibody concentrations were measured by enzyme-linked immunosorbent assays.

RESULTS

Local induration and tenderness were observed more commonly at the site of injection of TETRAMUNE than at the site of injection with PnCV after each dose of vaccination. Swelling at the site of injection was encountered more frequently at the site of administration of TETRAMUNE than at the site of administration PnCV ( P< 0.00001 for Doses 1 and 2 and P< 0.0009 for Dose 3). Swelling at the site of administration of TETRAMUNE mixed with PnCV was comparable with that observed for TETRAMUNE alone. Although most mothers reported that the babies "felt hot" 24 h after each injection, febrile reactions (temperature, >or=38 degrees C) were infrequent and resolved with antipyretics. Geometric mean titer for anti-polyribosylribitol phosphate antibody was 11.6 microg/ml [95% confidence limits (95% CI), 9.2, 14.6] in the control group and comparable with 13.3 microg/ml (95% CI 11.0, 16.0) in the combined group and significantly higher at 17.9 microg/ml (95% CI 14.7, 21.9; P= 0.01) in the separate group. Geometric mean concentrations of serotype-specific pneumococcal antibodies were higher in the combined group than the separate group for all nine serotypes. Antibody responses to diphtheria and pertussis antigens were similar in all groups. Anti-tetanus toxoid antibody concentrations were lowest in the combined group (6.66 IU/ml, 95% CI 5.77, 7.68 in the control group; 5.15 IU/ml, 95% CI 4.39, 6.03 in the combined group; P= 0.02). However, all vaccinees achieved protective antibody values.

CONCLUSION

The combination of TETRAMUNE and PnCV is safe and immunogenic.

Immune responses to novel pneumococcal proteins pneumolysin, PspA, PsaA, and CbpA in adenoidal B cells from children

Studies of mice suggest that pneumococcal proteins, including PspA, pneumolysin, PsaA, and CbpA, are promising vaccine candidates. To determine whether these proteins are good mucosal immunogens in humans, adenoidal lymphocytes from 20 children who had adenoidectomies were isolated and tested by ELISpot for antigen-specific antibody-secreting cells (ASCs). Cells were also cultured for 7 days in the presence of a concentrated culture supernatant (CCS) from a type 14 strain of pneumococcus which contained secreted pneumococcal proteins, including PspA, pneumolysin, PsaA, and CbpA, and then tested by ELISpot. ELISpot assays done on freshly isolated cells detected ASCs to all four antigens in most children studied. However, there were differences both between antigens and between isotypes. The densities of immunoglobulin G (IgG) ASCs against both PsaA and CbpA were significantly higher than those of ASCs for PspA and PdB (pneumolysin toxoid B) (P < 0.001). For all antigens, the numbers of IgA ASCs tended to be lower than those of both IgG and IgM ASCs. The numbers of anti-CbpA and -PsaA IgA ASCs were higher than those of anti-PdB IgA ASCs (P < 0.01). Concentrations of IgA antibodies to PspA and PsaA in saliva correlated with the numbers of IgA ASCs to PspA and PsaA in freshly isolated adenoidal cells, but no such correlation was found between salivary IgG antibody concentrations and IgG ASCs to the four antigens in adenoidal cells. In cultured cells, anti-PspA, -PsaA, and -CbpA IgG ASCs proliferated significantly, but only two of eight samples showed >2-fold increases in anti-CbpA and -PspA IgA ASCs after CCS stimulation. The results suggest that CbpA, PsaA, and PspA may be good upper respiratory mucosal antigens in children. Adenoids may be important inductive sites for memory IgG responses and important sources of salivary IgA. Some protein antigens may also prime for mucosal IgA memory. These data support the effort to explore mucosal immunization against pneumococcal infection.

Current state of pneumococcal vaccines

Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, and acute otitis media in children and adults worldwide. According to World Health Organization estimates, at least 1 million children under 5 years of age die each year from pneumococcal pneumonia. The emergence of resistant strains necessitates the development of an effective vaccine with a large serotype coverage. The 11 most common serotypes cause 72-83% of all serious pneumococcal diseases worldwide. Currently marketed 23-valent pneumococcal polysaccharide vaccine provides large serotype coverage and offers a less expensive option. However, it is efficacious only in adults but not in infants. Conjugate vaccines offer a solution by generating immunological memory already at early age. A recently licensed 7-valent conjugate vaccine is immunogenic and efficacious in infants. Its serotype coverage might be sufficient in Europe and North America, but not in Africa, Asia and Oceania. A need exists to develop pneumococcal vaccines with lower cost and larger serotype coverage. Several 11-valent pneumococcal conjugate vaccines are being evaluated in phase I-III trials. This study reviews the current state of pneumococcal problem and pneumococcal vaccines in clinical use.

Should the new pneumococcal vaccine be used in high-risk children?

A new conjugate 7-valent vaccine to prevent pneumococcal infection (Prevenar, Wyeth) has recently received a European licence for use in young healthy children. The vaccine is not currently included in the universal immunisation schedule in the UK or elsewhere in Europe, although it is being used widely in the USA. Its availability for purchase raises the question whether paediatricians should consider using it in high risk children, including those for whom the polysaccharide 23-valent vaccine was previously recommended, until (or unless) it is introduced into general use-indeed the Chief Medical Officer for England and Wales has recently made a recommendation regarding such children aged less than 2 years. We review the evidence concerning use of the vaccine in such children and make suggestions as to how the vaccine may be used while further information is collected.

Bridging phase 2 and phase 3 pneumococcal immunologic data for future combination vaccines

Pneumococcal conjugate vaccines (PncCs) will be introduced into childhood vaccination programs now that the first PncC has been licensed for use. The next generation of PncCs and possible combination vaccines containing PncC will most probably be approved on the basis of phase 2 immunogenicity and safety data. PncCs are combination vaccines that include, at present, 7-11 components. Immune response to different components may vary. Furthermore, there seem to be population-based differences in immune response. Whether these differences are due to the other vaccines that are given simultaneously or due to the genetic background remains to be seen. Immune response can be evaluated by determining both the quantity and the quality of antibodies after vaccination. However, data are still missing on the minimal protective immune response and serologic correlates or surrogates of protection.

Active immunization in the United States: developments over the past decade

The Centers for Disease Control and Prevention has identified immunization as the most important public health advance of the 20th century. The purpose of this article is to review the changes that have taken place in active immunization in the United States over the past decade. Since 1990, new vaccines have become available to prevent five infectious diseases: varicella, rotavirus, hepatitis A, Lyme disease, and Japanese encephalitis virus infection. Improved vaccines have been developed to prevent Haemophilus influenzae type b, pneumococcus, pertussis, rabies, and typhoid infections. Immunization strategies for the prevention of hepatitis B, measles, meningococcal infections, and poliomyelitis have changed as a result of the changing epidemiology of these diseases. Combination vaccines are being developed to facilitate the delivery of multiple antigens, and improved vaccines are under development for cholera, influenza, and meningococcal disease. Major advances in molecular biology have enabled scientists to devise new approaches to the development of vaccines against diseases ranging from respiratory viral to enteric bacterial infections that continue to plague the world's population.