The immunogenicity of pneumococcal polysaccharides in infants and children: a meta-regression

Glycovaccinology: The design and engineering of carbohydrate-based vaccine components

Vaccines remain one of the most important pillars in preventative medicine, providing protection against a wide array of diseases by inducing humoral and/or cellular immunity. Of the many possible candidate antigens for subunit vaccine development, carbohydrates are particularly appealing because of their ubiquitous presence on the surface of all living cells, viruses, and parasites as well as their known interactions with both innate and adaptive immune cells. Indeed, several licensed vaccines leverage bacterial cell-surface carbohydrates as antigens for inducing antigen-specific plasma cells secreting protective antibodies and the development of memory T and B cells. Carbohydrates have also garnered attention in other aspects of vaccine development, for example, as adjuvants that enhance the immune response by either activating innate immune responses or targeting specific immune cells. Additionally, carbohydrates can function as immunomodulators that dampen undesired humoral immune responses to entire protein antigens or specific, conserved regions on antigenic proteins. In this review, we highlight how the interplay between carbohydrates and the adaptive and innate arms of the immune response is guiding the development of glycans as vaccine components that act as antigens, adjuvants, and immunomodulators. We also discuss how advances in the field of synthetic glycobiology are enabling the design, engineering, and production of this new generation of carbohydrate-containing vaccine formulations with the potential to prevent infectious diseases, malignancies, and complex immune disorders.

Neutrophils Are Required During Immunization With the Pneumococcal Conjugate Vaccine for Protective Antibody Responses and Host Defense Against Infection

Neutrophils can shape adaptive immunity; however, their role in vaccine-induced protection against infections in vivo remains unclear. Here, we tested their role in the clinically relevant polysaccharide conjugate vaccine against Streptococcus pneumoniae (pneumococcus). We antibody depleted neutrophils during vaccination, allowed them to recover, and 4 weeks later challenged mice with pneumococci. We found that while isotype-treated vaccinated controls were protected against an otherwise lethal infection in naive mice, full protection was lost upon neutrophil depletion. Compared to vaccinated controls, neutrophil-depleted mice had higher lung bacterial burdens, increased incidence of bacteremia, and lower survival rates. Sera from neutrophil-depleted mice had less antipneumococcal IgG2c and IgG3, were less efficient at inducing opsonophagocytic killing of bacteria by neutrophils in vitro, and were worse at protecting naive mice against pneumococcal pneumonia. In summary, neutrophils are required during vaccination for optimal host protection, which has important implications for future vaccine design against pneumococci and other pathogens.

Circulating innate and adaptive immunity against anti-Haemophilus influenzae type b

Haemophilus influenzae type b (Hib) are one of most dangerous microbes that occupies the paediatric nasopharyngeal as a commensal opportunistic bacterium, which may lead to meningitis in uncontrolled infection. Colonisation of pharyngeal tissues is the starting point for most H. influenzae infections, which may develop into invasive diseases, such meningitis. The vaccination against Hib in specific, as well as against most of vaccines preventable diseases; in general, play a major role in reducing children (< 5 years old) Hib meningitis from 57/100,000 to the lowest known Hib meningitis incidents in the history. First invented Hib vaccine was licensed in 1985 and contained Hib capsular polysaccharide (CPS); afterward, conjugate vaccines have been innovated and licensed on the road to improve Hib vaccine efficacy. Polyribosylribitol phosphate (PRP) is the main vaccine unite structure. Since anti-CPS antibodies in the serum reflect the extent of the acquired immunity against Hib infections, the concentration of ⩾ 0.15 g/ml of anti-CPS is believed to be an indicator for short-term protection from invasive Hib diseases, whereas one-month post-completion of primary Hib immunization concentration of ⩾ 1.0 g/ml is trusted to be immunological protective. As considered that serum anti-CPS antibodies are effectively linked to protection, the evaluation of antibodies concentration and reconsideration of published worldwide populations antibodies concentration are consider vital strides on the way to accurate valuation of Hib immunity that induced by vaccination; either direct or herd. As documented, some populations; worldwide, still susceptible to invasive Hib infections. Several populations worldwide remain vulnerable to Hib-related infections. We believe that up-to-date review article regarding circulated Hib immunology, represented in anti-Hib antibodies and worldwide Hib incidences will provide a precious information for microbiologists, public health officials, epidemiologists, immunologists, and strategic preventive healthcare executives.

Immunogenicity and Immune Memory after a Pneumococcal Polysaccharide Vaccine Booster in a High-Risk Population Primed with 10-Valent or 13-Valent Pneumococcal Conjugate Vaccine: A Randomized Controlled Trial in Papua New Guinean Children

We investigated the immunogenicity, seroprotection rates and persistence of immune memory in young children at high risk of pneumococcal disease in Papua New Guinea (PNG). Children were primed with 10-valent (PCV10) or 13-valent pneumococcal conjugate vaccines (PCV13) at 1, 2 and 3 months of age and randomized at 9 months to receive PPV (PCV10/PPV-vaccinated, n = 51; PCV13/PPV-vaccinated, n = 52) or no PPV (PCV10/PPV-naive, n = 57; PCV13/PPV-naive, n = 48). All children received a micro-dose of PPV at 23 months of age to study the capacity to respond to a pneumococcal challenge. PPV vaccination resulted in significantly increased IgG responses (1.4 to 10.5-fold change) at 10 months of age for all PPV-serotypes tested. Both PPV-vaccinated and PPV-naive children responded to the 23-month challenge and post-challenge seroprotection rates (IgG ≥ 0.35 μg/mL) were similar in the two groups (80⁻100% for 12 of 14 tested vaccine serotypes). These findings show that PPV is immunogenic in 9-month-old children at high risk of pneumococcal infections and does not affect the capacity to produce protective immune responses. Priming with currently available PCVs followed by a PPV booster in later infancy could offer improved protection to young children at high risk of severe pneumococcal infections caused by a broad range of serotypes.

Antibodies prevalence against Haemophilus influenzae type b in Jeddah population, Saudi Arabia. II. Antibodies subclasses

Our previous reported that Jeddah, Saudi Arabia population have a comparable and protective herd immunity represented by IgG, IgA and IgM against Haemophilus influenzae type b (Hib), by using indirect ELISA test was used to evaluate Haemophilus influenzae type b (Hib) anti-polyribosyl-ribitol phosphate (PRP) total antibodies (IgM, IgG, IgA) in 1,003 sera samples. Current report was evaluated the IgG and IgA subclasses responsible about this protection using same methodology. IgG, IgA, and their subclasses are responsible about this circulating protection. Our study will consider the first report evaluate the levels of IgA subclasses and its relation to ages, as well as the relations between anti-Hib antibody subclass and age. The current results demonstrated that the highest levels concentrated in IgG1 and IgG2, while IgG3 and IgG4 showed the lowest levels. So, their concentrations were arranged in IgG1 > IgG2 > IgG3 > IgG4. The results indicated that the age and gender have no effect on both IgG or IgA subclasses in healthy immunized individuals enrolled. While, IgA1 concentrations were significantly higher than IgA2 in all age categories regardless of gender. It seem that the IgG1, IgG2 and IgA1 subclasses were the main constituent of Jeddah herd immunity against Hib. Finally, to the best of our knowledge, there were no previous reports that focusing on the levels of IgA subclasses and its relation to ages, so our study considers the first worldwide.

Cationic pullulan nanogel as a safe and effective nasal vaccine delivery system for respiratory infectious diseases

The mucosal surfaces of the respiratory and gastrointestinal tracts are continuously exposed to countless beneficial and pathologic antigens. These mucosal surfaces are thus equipped with an immune system that is unique from those elsewhere in the body; this unique system provides the first line of immune surveillance and defense against pathogen invasion. The sophisticated immune induction machinery in the aero–digestive tract involves mucosa-associated lymphoid tissues, including nasopharyngeal- and gut-associated lymphoid tissues, for the generation of antigen-specific humoral and cellular immune responses. Consequently, nasal or oral immunization with an appropriate vaccine delivery vehicle prompts the induction of protective immunity in both the mucosal and systemic compartments, leading to a double layer of protection against pathogens. To harness the benefits of mucosal vaccines, various mucosal antigen delivery vehicles are under development, and a cationic cholesteryl-group-bearing pullulan nanogel (cCHP nanogel) has emerged as a potent nasal vaccine delivery system for the induction of protective immunity against respiratory infections.

Interplay of Carbohydrate and Carrier in Antibacterial Glycoconjugate Vaccines

Bacterial infections are a serious health concern and are responsible for millions of illnesses and deaths each year in communities around the world. Vaccination is an important public health measure for reducing and eliminating this burden, and regions with comprehensive vaccination programs have achieved significant reductions in infection and mortality. This is often accomplished by immunization with bacteria-derived carbohydrates, typically in conjunction with other biomolecules, which induce immunological memory and durable protection against bacterial human pathogens. For many species, however, vaccines are currently unavailable or have suboptimal efficacy characterized by short-lived memory and incomplete protection, especially among at-risk populations. To address this challenge, new tools and techniques have emerged for engineering carbohydrates and conjugating them to carrier molecules in a tractable and scalable manner. Collectively, these approaches are yielding carbohydrate-based vaccine designs with increased immunogenicity and protective efficacy, thereby opening up new opportunities for this important class of antigens. In this chapter we detail the current understanding of how carbohydrates interact with the immune system to provide immunity; how glycoengineering, especially in the context of glycoconjugate vaccines, can be used to modify and enhance immune responses; and current trends and strategies being pursued for the rational design of next-generation glycosylated antibacterial vaccines. Graphical Abstract.

Rationale and methods of a randomized controlled trial of immunogenicity, safety and impact on carriage of pneumococcal conjugate and polysaccharide vaccines in infants in Papua New Guinea

BACKGROUND

Children in third-world settings including Papua New Guinea (PNG) experience early onset of carriage with a broad range of pneumococcal serotypes, resulting in a high incidence of severe pneumococcal disease and deaths in the first 2 years of life. Vaccination trials in high endemicity settings are needed to provide evidence and guidance on optimal strategies to protect children in these settings against pneumococcal infections.

METHODS

This report describes the rationale, objectives, methods, study population, follow-up and specimen collection for a vaccination trial conducted in an endemic and logistically challenging setting in PNG. The trial aimed to determine whether currently available pneumococcal conjugate vaccines (PCV) are suitable for use under PNG's accelerated immunization schedule, and that a schedule including pneumococcal polysaccharide vaccine (PPV) in later infancy is safe and immunogenic in this high-risk population.

RESULTS

This open randomized-controlled trial was conducted between November 2011 and March 2016, enrolling 262 children aged 1 month between November 2011 and April 2014. The participants were randomly allocated (1:1) to receive 10-valent PCV (10vPCV) or 13-valent PCV (13vPCV) in a 1-2-3-month schedule, with further randomization to receive PPV or no PPV at age 9 months, followed by a 1/5th PPV challenge at age 23 months. A total of 1229 blood samples were collected to measure humoral and cellular immune responses and 1238 nasopharyngeal swabs to assess upper respiratory tract colonization and carriage load. Serious adverse events were monitored throughout the study. Of the 262 children enrolled, 87% received 3 doses of PCV, 79% were randomized to receive PPV or no PPV at age 9 months, and 67% completed the study at 24 months of age with appropriate immunization and challenge.

CONCLUSION

Laboratory testing of the many samples collected during this trial will determine the impact of the different vaccine schedules and formulations on nasopharyngeal carriage, antibody production and function, and immune memory. The final data will inform policy on pneumococcal vaccine schedules in countries with children at high risk of pneumococcal disease by providing direct comparison of an accelerated schedule of 10vPCV and 13vPCV and the potential advantages of PPV following PCV immunization.

TRIAL REGISTRATION

ClinicalTrials.gov CTN NCT01619462, retrospectively registered on May 28, 2012.

Pneumococcal responses are similar in Papua New Guinean children aged 3-5 years vaccinated in infancy with pneumococcal polysaccharide vaccine with or without prior pneumococcal conjugate vaccine, or without pneumococcal vaccination

Trial design

In an earlier trial, Papua New Guinean (PNG) children at high risk of pneumococcal disease were randomized to receive 0 or 3 doses of 7-valent pneumococcal conjugate vaccine (PCV7), followed by a single dose of 23-valent pneumococcal polysaccharide vaccine (PPV23) at 9 months of age. We here studied in a non-randomized follow-up trial the persistence of pneumococcal immunity in these children at 3–5 years of age (n = 132), and in 121 community controls of a similar age with no prior pneumococcal vaccination.

Methods

Circulating IgG antibody titers to all PCV7 and PPV23-only serotypes 2, 5 and 7F were measured before and after challenge with 1/5^th of a normal PPV23 dose. Serotype-specific memory B-cells were enumerated at 10 months and 3–5 years of age for a subgroup of study children.

Results

Serotype-specific IgG antibody titers before and after challenge were similar for children who received PCV7/PPV23, PPV23 only, or no pneumococcal vaccines. Before challenge, at least 89% and 59% of children in all groups had serotype-specific titers ≥ 0.35μg/ml and ≥ 1.0 μg/ml, respectively. Post-challenge antibody titers were higher or similar to pre-challenge titers for most children independent of pneumococcal vaccination history. The rise in antibody titers was significantly lower when pre-challenge titers were higher. Overall the relative number of serotype-specific memory B-cells remained the same or increased between 10 months and 3–5 years of age, and there were no differences in serotype-specific memory B-cell numbers at 3–5 years of age between the three groups.

Conclusions

Immunity induced by PCV7 and/or PPV23 immunization in infancy does not exceed that of naturally acquired immunity in 3-5-year-old children living in a highly endemic area. Also, there was no evidence that PPV23 immunization in the first year of life following PCV7 priming induces longer-term hypo-responsiveness.

Trial registration

Clinicaltrials.gov NCT01414504 and NCT00219401.

Circulating Antibody 1 and 2 Years After Vaccination With the 13-Valent Pneumococcal Conjugate Vaccine in Preterm Compared With Term Infants

BACKGROUND

Premature infants have lower short-term immune responses to vaccination than term infants, but patterns of antibody persistence in preterm infants over longer periods are not well established. This study assessed the persistence of antibody response to the 13-valent pneumococcal conjugate vaccine (PCV13) in formerly preterm versus term infants.

METHODS

In total, 100 preterm and 100 term infants received PCV13 with routine vaccines at ages 2, 3, 4 and 12 months. Serotype-specific anticapsular immunoglobulin G (IgG)-binding antibodies and opsonophagocytic activity were determined 1 and 2 years after the last PCV13 dose.

RESULTS

At 1 and 2 years after the last vaccination (toddler dose), IgG geometric mean concentrations (GMCs) for all serotypes had declined from levels measured 1 month after the toddler dose but remained above pretoddler dose levels. IgG GMCs were significantly lower in preterm than term subjects for a majority of serotypes at both follow-up time points. IgG GMCs increased in both groups for some serotypes from the 1-year to 2-year follow-up, whereas others declined. Opsonophagocytic activity results supported the IgG results.

CONCLUSIONS

The routine (3 + 1) vaccination schedule is likely to offer long-term protection against invasive pneumococcal disease in preterm infants and should be initiated regardless of gestational age or weight at birth, without delay of the toddler dose.

Prevention of Community-Acquired Pneumonia with Available Pneumococcal Vaccines

Community-acquired pneumonia (CAP) places a considerable burden on society. A substantial number of pediatric and adult CAP cases are due to Streptococcus pneumoniae, but fortunately there are effective vaccines available that have a significant impact on CAP-related medical, social, and economic problems. The main aim of this paper is to evaluate the published evidence concerning the impact of pneumococcal vaccines on the prevention of CAP in children and adults. Available data indicate that pneumococcal conjugate vaccines (PCVs) are effective in children, reducing all-cause CAP cases and bacteremic and nonbacteremic CAP cases. Moreover, at least for PCV7 and PCV13, vaccination of children is effective in reducing the incidence of CAP among adults. Recently use of PCV13 in adults alone or in combination with the pneumococcal polysaccharide vaccine has been suggested and further studies can better define its effectiveness in this group of subjects. The only relevant problem for PCV13 is the risk of a second replacement phenomenon, which might significantly reduce its real efficacy in clinical practice. Protein-based pneumococcal vaccines might be a possible solution to this problem.

Vaccination for the control of childhood bacterial pneumonia - Haemophilus influenzae type b and pneumococcal vaccines

Pneumonia in childhood is endemic in large parts of the world and in particular, in developing countries, as well as in many indigenous communities within developed nations. Haemophilus influenzae type b and Streptococcus pneumoniae conjugate vaccines are currently available against the leading bacterial causes of pneumonia. The use of the vaccines in both industrialised and developing countries have shown a dramatic reduction in the burden of pneumonia and invasive disease in children. However, the greatest threat facing pneumococcal conjugate vaccine effectiveness is serotype replacement. The current vaccines provide serotype-specific, antibody-mediated protection against only a few of the 90+ capsule serotypes. Therefore, there has been a focus in recent years to rapidly advance technologies that will result in broader disease coverage and more affordable vaccines that can be used in developing countries. The next generation of pneumococcal vaccines have advanced to clinical trials.

Response to pneumococcal polysaccharide vaccine in children with asthma, and children with recurrent respiratory infections, and healthy children

BACKGROUND

To analyse specific immune response to the 23-valent pneumococcal polysaccharide vaccine by measuring pneumococcal antibodies in children with asthma and with respiratory recurrent infection (RRI) as compared to healthy children.

METHODS

The study included 60 children, divided into three groups: 20 with asthma, 20 with RRI, and 20 healthy controls. Post-vaccination specific IgG antibodies against 10 pneumococcal serotypes (S1, S3, S4, S5, S6B, S9V, S14, S18C, S19F, and S23F) contained in the 23-valent pneumococcal polysaccharide vaccine (PPV) were measured. A specific IgG concentration ≥1.3μg/mL was considered a protective response to the vaccine. For statistical analysis, levels of specific IgG antibodies against each of the 10 pneumococcal serotypes were compared across the three groups of children using the x(2) test.

RESULTS

All of the children showed antipneumococcal antibody levels >1.3μg/mL for over 70% of the serotypes, considered within the normal range of response. Average IgG antibody levels and percentages of children protected were statistically comparable among the three groups studied.

CONCLUSION

The asthmatic children without RRI had pneumococcal antibody levels and percentages of serotype-specific protection to PPV comparable to those of healthy children. Asthmatic children with recurrent infections should be evaluated for specific antibody deficiency (SAD). Because asthma patients are at high risk for invasive pneumococcal infections, it would be worthwhile to explore systematic administration of PPV in children over the age of two years who have not received a pneumococcal conjugate vaccine, considering the positive response to PPV reported here.

Hib Vaccines: Past, Present, and Future Perspectives

Haemophilus influenzae type b (Hib) causes many severe diseases, including epiglottitis, pneumonia, sepsis, and meningitis. In developed countries, the annual incidence of meningitis caused by bacteria is approximately 5–10 cases per population of 100,000. The Hib conjugate vaccine is considered protective and safe. Adjuvants, molecules that can enhance and/or regulate the fundamental immunogenicity of an antigen, comprise a wide range of diverse compounds. While earlier developments of adjuvants created effective products, there is still a need to create new generations, rationally designed based on recent discoveries in immunology, mainly in innate immunity. Many factors may play a role in the immunogenicity of Hib conjugate vaccines, such as the polysaccharides and proteins carrier used in vaccine construction, as well as the method of conjugation. A Hib conjugate vaccine has been constructed via chemical synthesis of a Hib saccharide antigen. Two models of carbohydrate-protein conjugate have been established, the single ended model (terminal amination-single method) and cross-linked lattice matrix (dual amination method). Increased knowledge in the fields of immunology, molecular biology, glycobiology, glycoimmunology, and the biology of infectious microorganisms has led to a dramatic increase in vaccine efficacy.

Pneumococcal vaccines and the prevention of community-acquired pneumonia

Community-acquired pneumonia (CAP) is a disease that frequently affects children and adults throughout the world. As it places a considerable burden on society and, particularly, healthcare resources, any means of reducing its incidence and impact arouses great interest. A substantial number of paediatric and adult CAP cases are due to Streptococcus pneumoniae but, fortunately, there are effective vaccines available that are likely to have a significant impact on CAP-related medical, social and economic problems. The main aim of this paper is to evaluate the published evidence concerning the impact of pneumococcal vaccines on CAP in children and adults. The original 7-valent pneumococcal conjugate vaccine (PCV-7) completely modified the total burden of pneumococcal diseases in vaccinated children and unvaccinated contacts of any age. However, the existence of some problems moderately reducing its preventive efficacy has led to the development of PCVs with a larger number of pneumococcal serotypes, including those that were previously of marginal importance but now cause of severe disease. It is reasonable to think that these PCVs (particularly PCV13, which includes all of the most important serotypes emerging since the introduction of PCV7) will further reduce the importance of pneumococcal diseases, although it is still not clear whether the replacement of the 23-valent polysaccharide vaccine with PCV13 would be more protective in adults.

Safety and immunogenicity of 13-valent pneumococcal conjugate vaccine in infants: a meta-analysis

Pneumococcal infections are a major cause of morbidity and mortality worldwide. Pneumococcal conjugate vaccines represent major progress in the prevention of invasive pneumococcal disease in the paediatric population. We performed a meta-analysis, in accordance with the PRISMA statement, in order to assess the immunogenicity and safety of 13-valent pneumococcal conjugate vaccines in infants. A literary search was conducted using electronic databases and specialized journals were searched manually. Inclusion criteria were: clinical trials with infants vaccinated with 13-valent pneumococcal conjugate, compared to 7-valent vaccine. We recorded the results in terms of the immunogenicity and safety of the vaccines. The quality of the studies included was assessed using the CASP and Jadad checklists. We included nine randomized clinical trials of 258 potentially relevant references in the meta-analysis. The studies included had high-moderate quality. Both vaccines were well tolerated in all groups of infants, and most local reactions and systemic events were of mild or medium intensity and typical of any injected vaccine. All studies included in the meta-analysis showed high immunogenicity for both pneumococcal vaccines in all tested serotypes. An anti-polysaccharide antibody concentration of ≥0.35 μg/mL was achieved in at least 89% of the infants. Our results suggest that the 13-valent pneumococcal conjugate vaccine has a similar safety profile, and is as effective as, the 7-valent vaccine in the prevention of invasive pneumococcal disease caused by the seven common serotypes, and could provide expanded protection against the six additional serotypes.

Use of the 13-valent pneumococcal conjugate vaccine in children and adolescents aged 6 - 17 years

INTRODUCTION

The introduction of pneumococcal conjugate vaccines into infant immunization schedules has successfully reduced the incidence of pneumococcal disease caused by vaccine serotypes. Disease incidence is low in healthy 6 - 17-year-old children and young people; however, there are a number of clinical conditions that put individuals in this age group at increased risk. Expansion of the license of a 13-valent pneumococcal conjugate vaccine , PCV-13, to include the 6 - 17 age group has recently been approved by European and American regulatory bodies.

AREAS COVERED

Studies assessing the safety, immunogenicity, and efficacy of pneumococcal conjugate vaccines in both healthy and high-risk 6 - 17-year-old children and adolescents are covered and the potential impact of PCV-13 in these populations is discussed. The use of the 23-valent pneumococcal polysaccharide vaccine, PPV-23, in high-risk children and adolescents is also considered.

EXPERT OPINION

Expanding the use of PCV-13 to include high-risk children and adolescents aged 6 - 17 has the potential to prevent additional cases of disease; however, vaccination of this population may no longer be necessary when herd immunity to PCV-13 serotypes becomes fully established. Despite the broader serotype coverage of PPV-23, the benefits of this vaccine in high-risk populations are uncertain.

Immune responses to the O-specific polysaccharide antigen in children who received a killed oral cholera vaccine compared to responses following natural cholera infection in Bangladesh

Current oral cholera vaccines induce lower levels of protective efficacy and shorter durations of protection in young children than in adults. Immunity against cholera is serogroup specific, and immune responses to Vibrio cholerae lipopolysaccharide (LPS), the antigen that mediates serogroup-specific responses, are associated with protection against disease. Despite this, responses against V. cholerae O-specific polysaccharide (OSP), a key component of the LPS responsible for specificity, have not been characterized in children. Here, we report a comparison of polysaccharide antibody responses in children from a region in Bangladesh where cholera is endemic, including infants (6 to 23 months, n = 15), young children (24 to 59 months, n = 14), and older children (5 to 15 years, n = 23) who received two doses of a killed oral cholera vaccine 14 days apart. We found that infants and young children receiving the vaccine did not mount an IgG, IgA, or IgM antibody response to V. cholerae OSP or LPS, whereas older children showed significant responses. In comparison to the vaccinees, young children with wild-type V. cholerae O1 Ogawa infection did mount significant antibody responses against OSP and LPS. We also demonstrated that OSP responses correlated with age in vaccinees, but not in cholera patients, reflecting the ability of even young children with wild-type cholera to develop OSP responses. These differences might contribute to the lower efficacy of protection rendered by vaccination than by wild-type disease in young children and suggest that efforts to improve lipopolysaccharide-specific responses might be critical for achieving optimal cholera vaccine efficacy in this younger age group.

Serologic vaccination response after solid organ transplantation: a systematic review

BACKGROUND

Infectious diseases after solid organ transplantation (SOT) are one of the major complications in transplantation medicine. Vaccination-based prevention is desirable, but data on the response to active vaccination after SOT are conflicting.

METHODS

In this systematic review, we identify the serologic response rate of SOT recipients to post-transplantation vaccination against tetanus, diphtheria, polio, hepatitis A and B, influenza, Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitides, tick-borne encephalitis, rabies, varicella, mumps, measles, and rubella.

RESULTS

Of the 2478 papers initially identified, 72 were included in the final review. The most important findings are that (1) most clinical trials conducted and published over more than 30 years have all been small and highly heterogeneous regarding trial design, patient cohorts selected, patient inclusion criteria, dosing and vaccination schemes, follow up periods and outcomes assessed, (2) the individual vaccines investigated have been studied predominately only in one group of SOT recipients, i.e. tetanus, diphtheria and polio in RTX recipients, hepatitis A exclusively in adult LTX recipients and mumps, measles and rubella in paediatric LTX recipients, (3) SOT recipients mount an immune response which is for most vaccines lower than in healthy controls. The degree to which this response is impaired varies with the type of vaccine, age and organ transplanted and (4) for some vaccines antibodies decline rapidly.

CONCLUSION

Vaccine-based prevention of infectious diseases is far from satisfactory in SOT recipients. Despite the large number of vaccination studies preformed over the past decades, knowledge on vaccination response is still limited. Even though the protection, which can be achieved in SOT recipients through vaccination, appears encouraging on the basis of available data, current vaccination guidelines and recommendations for post-SOT recipients remain poorly supported by evidence. There is an urgent need to conduct appropriately powered vaccination trials in well-defined SOT recipient cohorts.

Immunization of newborns with bacterial conjugate vaccines

Bacterial conjugate vaccines are based on the principle of coupling immunogenic bacterial capsular polysaccharides to a carrier protein to facilitate the induction of memory T-cell responses. Following the success of Haemophilus influenzae type b conjugate vaccines in the 1980s, conjugate vaccines for Streptococcus pneumoniae and Neisseria meningitidis infections were developed and proven to be effective in protecting children against invasive disease. In this review, the use of conjugate vaccines in human newborns is discussed. Neonatal Haemophilus influenzae type b and pneumococcal conjugate vaccination schedules have been trialed and proven to be safe, with the majority of studies demonstrating no evidence for the induction of immune tolerance. Whether their neonatal administration also results in an earlier induction of clinical protection in the first 2-3 critical months of life is still to be demonstrated.

Pneumococcal polysaccharide vaccine at 12 months of age produces functional immune responses

BACKGROUND

Infections with Streptococcus pneumoniae (pneumococcus) are a cause of significant child mortality. Pneumococcal glycoconjugate vaccines are expensive and provide limited serotype coverage. The 23-valent pneumococcal polysaccharide vaccine (Pneumovax) might provide wider serotype coverage but is reported to be weakly immunogenic in children less than 2 years of age. We have previously reported that Pneumovax administered to healthy 12-month-old Fijian infants elicits significant serotype-specific IgG responses. However, the functional capacity of these responses in 12-month-old infants is not known.

OBJECTIVE

We sought to assess the functional, serotype-specific immune response of 12-month-old infants after immunization with Pneumovax.

METHODS

Functional responses of 12-month-old infants were assessed by using the opsonophagocytic and antibody avidity assay against 8 serotypes and 23 serotypes, respectively.

RESULTS

Seventy-one percent of infants produced strong opsonophagocytic activity against 4 of 8 serotypes, and 30% produced high-avidity serotype-specific IgG antibodies to 10 of 23 serotypes at 2 weeks after Pneumovax. Responses were protective for most serotypes that cause disease in Western countries, whereas responses to most of the epidemiologically relevant serotypes for developing countries were low.

CONCLUSION

This is the first comprehensive study evaluating the functional antibody response to Pneumovax in 12-month-old infants. Pneumovax induced functional antibody responses to several serotypes causing disease in Western countries but induced poorer responses to serotypes that are responsible for the majority of disease in developing countries. Pneumovax might be of benefit in some populations, but further studies are required before this can be recommended in developing countries.