Serogroup C meningococcal glycoconjugate vaccine in adolescents: persistence of bactericidal antibodies and kinetics of the immune response to a booster vaccine more than 3 years after immunization

Polysaccharide Vaccines: A Perspective on Non-Typhoidal Salmonella

Polysaccharides are often the most abundant antigens found on the extracellular surfaces of bacterial cells. These polysaccharides play key roles in interactions with the outside world, and for many bacterial pathogens, they represent what is presented to the human immune system. As a result, many vaccines have been or currently are being developed against carbohydrate antigens. In this review, we explore the diversity of capsular polysaccharides (CPS) in Salmonella and other selected bacterial species and explain the classification and function of CPS as vaccine antigens. Despite many vaccines being developed using carbohydrate antigens, the low immunogenicity and the diversity of infecting strains and serovars present an antigen formulation challenge to manufacturers. Vaccines tend to focus on common serovars or have changing formulations over time, reflecting the trends in human infection, which can be costly and time-consuming. We summarize the approaches to generate carbohydrate-based vaccines for Salmonella, describe vaccines that are in development and emphasize the need for an effective vaccine against non-typhoidal Salmonella strains.

RNA-dependent RNA polymerase (RdRp) inhibitors: The current landscape and repurposing for the COVID-19 pandemic

The widespread nature of several viruses is greatly credited to their rapidly altering RNA genomes that enable the infection to persist despite challenges presented by host cells. Within the RNA genome of infections is RNA-dependent RNA polymerase (RdRp), which is an essential enzyme that helps in RNA synthesis by catalysing the RNA template-dependent development of phosphodiester bonds. Therefore, RdRp is an important therapeutic target in RNA virus-caused diseases, including SARS-CoV-2. In this review, we describe the promising RdRp inhibitors that have been launched or are currently in clinical studies for the treatment of RNA virus infections. Structurally, nucleoside inhibitors (NIs) bind to the RdRp protein at the enzyme active site, and nonnucleoside inhibitors (NNIs) bind to the RdRp protein at allosteric sites. By reviewing these inhibitors, more precise guidelines for the development of more promising anti-RNA virus drugs should be set, and due to the current health emergency, they will eventually be used for COVID-19 treatment.

Antibody persistence following meningococcal ACWY conjugate vaccine licensed in the European Union by age group and vaccine

INTRODUCTION

Meningococcal disease caused by Neisseria meningitidis is a major cause of meningitis and septicemia with high rates of morbidity and mortality worldwide. MenACWY-TT and MenACWY-CRM₁₉₇ are meningococcal conjugate vaccines approved for use in children and adults in the UK. The aim of this review was to evaluate and compare antibody responses and persistence in different age groups after MenACWY-TT and MenACWY-CRM₁₉₇.

AREAS COVERED

Randomized trials showed that MenACWY-TT is immunogenic at all ages. MenACWY-CRM₁₉₇ is immunogenic for infants and adults, but there is a lack of data for children aged 1 to 2 years. Studies on MenACWY-TT indicated that serum bactericidal antibody (SBA) utilizing baby rabbit complement (rSBA) titers were significantly higher and more stable than SBA using human complement (hSBA) titers, compared with hSBA titers, which were lower and declined more rapidly by 1 year following post-primary MenACWY-TT and MenACWY-CRM₁₉₇ vaccination, especially for MenA.

EXPERT OPINION

MenACWY-TT and MenACWY-CRM₁₉₇ are both well tolerated and induce similar antibody persistence and immunogenicity against all four serogroups for individuals more than one year old. rSBA assay is a more robust assay than the hSBA assay when vaccinating with MenACWY-TT, while rSBA and hSBA assays had similar antibody persistence when vaccinating with MenACWY-CRM₁₉₇.

Common Genetic Variations Associated with the Persistence of Immunity following Childhood Immunization

Vaccines have revolutionized public health, preventing millions of deaths each year, particularly in childhood. Yet, there is considerable variability in the magnitude and persistence of vaccine-induced immunity. Maintenance of specific antibody is essential for continuity of vaccine-induced serological protection. We conducted a genome-wide association study into the persistence of immunity to three childhood vaccines: capsular group C meningococcal (MenC), Haemophilus influenzae type b, and tetanus toxoid (TT) vaccines. We detail associations between variants in a locus containing a family of signal-regulatory proteins and the persistence MenC immunity. We postulate a regulatory role for the lead SNP, with supporting epigenetic and expression quantitative trait loci data. Furthermore, we define associations between SNPs in the human leukocyte antigen (HLA) locus and the persistence of TT-specific immunity. Moreover, we describe four classical HLA alleles, HLA DRB1^∗0301, HLA DQB1^∗0201, HLA DQB1^∗0602, and HLA DRB1^∗1501, associated with TT-specific immunity, independent of the lead SNP association.

Polysaccharide structure dictates mechanism of adaptive immune response to glycoconjugate vaccines

Glycoconjugate vaccines are among the most effective interventions for preventing several serious infectious diseases. Covalent linkage of the bacterial capsular polysaccharide to a carrier protein provides CD4⁺ T cells with epitopes that facilitate a memory response to the polysaccharide. Classically, the mechanism responsible for antigen processing was thought to be similar to what was known for hapten-carrier conjugates: protease digestion of the carrier protein in the endosome and presentation of a resulting peptide to the T cell receptor on classical peptide-recognizing CD4⁺ T cells. Recently, an alternative mechanism has been shown to be responsible for the memory response to some glycoconjugates. Processing of both the protein and the polysaccharide creates glycopeptides in the endosome of antigen-presenting cells. For presentation, the peptide portion of the glycopeptide is bound to MHCII, allowing the covalently linked glycan to activate carbohydrate-specific helper CD4⁺ T cells (Tcarbs). Herein, we assessed whether this same mechanism applies to conjugates prepared from other capsular polysaccharides. All of the glycoconjugates tested induced Tcarb-dependent responses except that made with group C Neisseria meningitidis; in the latter case, only peptides generated from the carrier protein were critical for helper T cell recognition. Digestion of this acid-sensitive polysaccharide, a linear homopolymer of α(2 → 9)-linked sialic acid, to the size of the monomeric unit resulted in a dominant CD4⁺ T cell response to peptides in the context of MHCII. Our results show that different mechanisms of presentation, based on the structure of the carbohydrate, are operative in response to different glycoconjugate vaccines.

Protection Against Invasive Infections in Children Caused by Encapsulated Bacteria

The encapsulated bacteria Streptococcus pneumoniae, Neisseria meningitis, Haemophilus influenzae, and Streptococcus agalactiae (Group B Streptococcus) have been responsible for the majority of severe infections in children for decades, specifically bacteremia and meningitis. Isolates which cause invasive disease are usually surrounded by a polysaccharide capsule, which is a major virulence factor and the key antigen in protective protein-polysaccharide conjugate vaccines. Protection against these bacteria is largely mediated via polysaccharide-specific antibody and complement, although the contribution of these and other components, and the precise mechanisms, vary between species and include opsonophagocytosis and complement-dependent bacteriolysis. Further studies are required to more precisely elucidate mechanisms of protection against non-type b H. influenzae and Group B Streptococcus.

Waning Immunity and Microbial Vaccines-Workshop of the National Institute of Allergy and Infectious Diseases

Since the middle of the 20th century, vaccines have made a significant public health impact by controlling infectious diseases globally. Although long-term protection has been achieved with some vaccines, immunity wanes over time with others, resulting in outbreaks or epidemics of infectious diseases. Long-term protection against infectious agents that have a complex life cycle and antigenic variation remains a key challenge. Novel strategies to characterize the short- and long-term immune responses to vaccines and to induce immune responses that mimic natural infection have recently emerged. New technologies and approaches in vaccinology, such as adjuvants, delivery systems, and antigen formulations, have the potential to elicit more durable protection and fewer adverse reactions; together with in vitro systems, these technologies have the capacity to model and accelerate vaccine development. The National Institute of Allergy and Infectious Diseases (NIAID) held a workshop on 19 September 2016 that focused on waning immunity to selected vaccines (for Bordetella pertussis, Salmonella enterica serovar Typhi, Neisseria meningitidis, influenza, mumps, and malaria), with an emphasis on identifying knowledge gaps, future research needs, and how this information can inform development of more effective vaccines for infectious diseases.

Antibody persistence up to 5 y after vaccination with a quadrivalent meningococcal ACWY-tetanus toxoid conjugate vaccine in adolescents

Long-term protection against meningococcal disease relies on antibody persistence after vaccination. We report antibody persistence up to 5 y after vaccination in adolescents who received a single dose of either meningococcal serogroups A, C, W, Y tetanus toxoid conjugate vaccine (MenACWY-TT, Pfizer) or MenACWY polysaccharide vaccine (MenPS, GSK Vaccines) at the age of 11-17 y in the randomized controlled primary study NCT00464815. In this phase III, open, controlled, multi-center persistence follow-up study conducted in India and the Philippines (NCT00974363), antibody persistence was evaluated by a serum bactericidal antibody assay using rabbit complement (rSBA) yearly, up to year 5 after vaccination. Serious adverse events (SAEs) related to study participation were recorded. Five years after a single dose of MenACWY-TT, the percentage of participants (N = 236) with rSBA titers ≥1:8 was 97.5% for serogroup A, 88.6% for serogroup C, 86.0% for serogroup W and 96.6% for serogroup Y. The percentages in the MenPS group (N = 86) were 93.0%, 87.1%, 34.9% and 66.3%, respectively. Exploratory analysis indicated a higher percentage of subjects with rSBA titers ≥1:8 for serogroups W and Y, and higher rSBA geometric mean antibody titers for serogroups A, W and Y in the MenACWY-TT group than the MenPS group at each time point (years 3, 4 and 5). No differences between groups were observed for serogroup C. No SAEs related to study participation were reported. In conclusion, the results of this follow-up study indicate that antibodies persisted up to 5 y after a single dose of MenACWY-TT in adolescents.

Use of a booster dose of capsular group C meningococcal glycoconjugate vaccine to demonstrate immunologic memory in children primed with one or two vaccine doses in infancy

BACKGROUND

Use of a polysaccharide vaccine challenge to demonstrate immunologic memory after priming with capsular group C meningococcal conjugate vaccines (MenCC) risks induction of immunologic hyporesponsiveness. For this reason, MenCC vaccines are now used as probes of immunologic memory, however, no studies have demonstrated their ability to distinguish primed from unprimed children.

METHODS

This study was part of a randomised controlled trial investigating the immunogenicity of a booster dose of the combined Haemophilus influenzae type b and MenC-tetanus toxoid vaccine (Hib-MenC-TT) in infants receiving reduced dose MenCC vaccine priming schedules (one MenC-CRM/MenC-TT or two MenC-CRM vaccine doses) compared with an unprimed group. Antibody kinetics were studied in a subset of 269 children by measuring changes in the MenC serum bactericidal antibody, using rabbit complement, (MenC rSBA) titres and MenC specific IgG memory B-cells before and at 6 and 28days following the 12month booster vaccination.

RESULTS

At 6days after the 12monthMenCC vaccine, the rise in MenC rSBA titres and MenC specific IgG memory B-cells of the primed groups were significantly higher than the infant MenCC naïve group. Participants primed with one MenC-TT dose had the highest increase in MenC rSBA titres compared with all other groups. The MenC rSBA titres at the 28th compared with the 6th day after boosting was significantly higher in those primed with a single MenC-TT/MenC-CRM vaccine in infancy compared with those who were not primed or who were primed with two doses of the MenC-CRM vaccine.

CONCLUSION

Immunologic memory can be demonstrated by a MenCC booster vaccination but is affected by the type and number of MenCC doses used for infant priming. The MenC rSBA responses can be used to demonstrate successful immunologic priming.

Antibody persistence after serogroup C meningococcal conjugate vaccine in children with sickle cell disease

BACKGROUND

A decline of protective antibody titers after MCC vaccine has been demonstrated in healthy children, this may be an issue of concern for risk groups. The aim of this study was to evaluate the persistence of bactericidal antibodies after MCC vaccine in sickle cell disease (SCD) patients. The type of vaccine used and booster response were also analyzed.

METHODS

SCD patients (n=141) previously immunized with MCC vaccines had blood drawn 2-8 years after the last priming dose. They were distributed according to age at primary immunization into groups: <2 years and 2-13 years and evaluated by years since vaccination (2-3, 4-5 and 6-8). Serum bactericidal antibodies with baby rabbit complement (rSBA) and serogroup C-specific IgG concentrations were measured. The correlate of protection was rSBA titer ⩾8. Subjects with rSBA <8 received a booster dose and antibody levels re-evaluated after 4-6 weeks.

RESULTS

For children primed under 2years of age rSBA titer ⩾8 was demonstrated in 53.3%, 21.7% and 35.0%, 2-3, 4-5, 6-8years, respectively, after vaccination, compared with 70.0%, 45.0% and 53.5%, respectively, for individuals primed at ages 2-13years. rSBA median titers and IgG median levels were higher in the older group. Six to eight years after vaccination the percentage of patients with rSBA titers ⩾8 was significantly higher in the group primed with MCC-TT (78.5%) compared with those primed with MCC-CRM197 [Menjugate® (33.3%) or Meningitec® (35.7%)] (p=0.033). After a booster, 98% achieved rSBA titer ⩾8.

CONCLUSION

Immunity to meningococcal serogroup C in SCD children declines rapidly after vaccination and is dependent on the age at priming. Booster doses are needed to maintain protection in SCD patients. Persistence of antibodies seems to be longer in individuals primed with MCC-TT vaccine comparing to those immunized with MCC-CRM197.

Persistence of the immune response after MenACWY-CRM vaccination and response to a booster dose, in adolescents, children and infants

Persistence of bactericidal antibodies following vaccination is extremely important for protection against invasive meningococcal disease, given the epidemiology and rapid progression of meningococcal infection. We present an analysis of antibody persistence and booster response to MenACWY-CRM, in adolescents, children and infants, from 7 clinical studies. Immunogenicity was assessed using the serum bactericidal assay with both human and rabbit complement. Post-vaccination hSBA titers were high, with an age- and serogroup-specific decline in titers up to 1 y and stable levels up to 5 y The waning of hSBA titers over time was more pronounced among infants and toddlers and the greatest for serogroup A. However, rSBA titers against serogroup A were consistently higher and showed little decline over time, suggesting that protection against this serogroup may be sustained. A single booster dose of MenACWY-CRM administered at 3 to 5 y induced a robust immune response in all age groups.

Different Dynamics for IgG and IgA Memory B Cells in Adolescents following a Meningococcal Serogroup C Tetanus Toxoid Conjugate Booster Vaccination Nine Years after Priming: A Role for Priming Age?

Background

Antibody levels wane rapidly after Meningococcal serogroup C conjugate (MenCC) vaccination in young children, rendering the need for an adolescent booster dose. It is not clear whether circulating memory B cells are associated with persistence of MenC-specific antibody levels.

Methods

Measurement of MenC-specific IgG and IgA memory B cells and levels of serum and salivary MenC-specific IgG and IgA in healthy 10-, 12- and 15-year-olds prior to and one month and one year after a MenCC booster vaccination. All participants had received a primary MenCC vaccination nine years earlier.

Results

The number of circulating MenC-specific IgG memory B cells prior to booster was low and not predictive for MenC-specific IgG responses in serum or saliva post-booster, whereas the number of MenC-specific IgA memory B cells pre-booster positively correlated with MenC-specific IgA levels in saliva post-booster (R = 0.5, P<0.05). The booster induced a clear increase in the number of MenC-specific IgG and IgA memory B cells. The number of MenC-PS-specific IgG memory B cells at 1 month post-booster was highest in the 12-year-olds. The number of MenC-specific memory B cells at one month post-booster showed no correlation with the rate of MenC-specific antibody decay throughout the first year post-booster.

Conclusions

Circulating MenC-specific IgA memory B cells correlate with IgA responses in saliva, whereas circulating MenC-specific IgG memory B cells are not predictive for MenC-specific IgG responses in serum or saliva. Our results are suggestive for age-dependent differences in pre-existing memory against MenC.

Randomized Trial to Compare the Immunogenicity and Safety of a CRM or TT Conjugated Quadrivalent Meningococcal Vaccine in Teenagers who Received a CRM or TT Conjugated Serogroup C Vaccine at Preschool Age

BACKGROUND

Protection after meningococcal C (MenC) conjugate (MCC) vaccination in early childhood is short-lived. Boosting with a quadrivalent vaccine in teenage years, a high-risk period for MenC disease, should protect against additional serogroups but might compromise MenC response. The carrier protein in the primary MCC vaccine determines the response to MCC booster in toddlers, but the relationship between primary vaccine and booster given later is unclear. This study compared responses to a CRM-conjugated or tetanus toxoid (TT)-conjugated MenACWY vaccine in teenagers primed with different MCC vaccines at preschool age.

METHODS

Ninety-three teenagers (16-19 years), who were previously randomized at age 3-6 years to receive single-dose MCC-CRM or MCC-TT, were randomized to receive either MenACWY-CRM or MenACWY-TT booster. Serum bactericidal antibodies (SBA, protective titer ≥ 8) were measured before, 1 month and 6 or 9 months after boosting.

RESULTS

Preboosting, MCC-TT-primed teenagers had significantly higher MenC SBA titers than those MCC-CRM-primed (P = 0.02). Postboosting, both MenACWY vaccines induced protective SBA titers to all 4 serogroups in most participants (≥ 98% at 1 month and ≥ 90% by 9 months postboost). The highest MenC SBA titers were seen in those MCC-TT-primed and MenACWY-TT-boosted [geometric mean titer (GMT) ~ 22,000] followed by those boosted with MenACWY-CRM irrespective of priming (GMT ~ 12,000) and then those MCC-CRM-primed and MenACWY-TT-boosted (GMT ~ 5500). The estimated postbooster MenC SBA decline beyond 1 month was ~40% as time since booster doubles. Both vaccines were well tolerated with no attributable serious adverse events.

CONCLUSION

Both MenACWY vaccines safely induced protective sustained antibody responses against all targeted serogroups in MCC-primed teenagers.

Natural antibody repertoires: development and functional role in inhibiting allergic airway disease

In this review we discuss the effects of microbial exposure on the B cell repertoire. Neonatal exposure to conserved bacterial carbohydrates and phospholipids permanently reprograms the natural antibody repertoire directed toward these antigens by clonal expansion, alterations in clonal dominance, and increased serum antibody levels. These epitopes are present not only in bacterial cell walls, but also in common environmental allergens. Neonatal immunization with bacterial polysaccharide vaccines results in attenuated allergic airway responses to fungi-, house dust mite-, and cockroach-associated allergens in mouse models. The similarities between mouse and human natural antibody repertoires suggest that reduced microbial exposure in children may have the opposite effect, providing a potential mechanistic explanation for the hygiene hypothesis. We propose that understanding the effects of childhood infections on the natural antibody repertoire and the mechanisms of antibody-mediated immunoregulation observed in allergy models will lead to the development of prevention/interventional strategies for treatment of allergic asthma.

Glycoconjugate vaccines: an update

INTRODUCTION

Globally, the three main pathogens causing serious infections are Haemophilus influenzae type b, Streptococcus pneumoniae and Neisseria meningitidis. Over the last 5 years, new vaccines protecting against these bacteria have been developed and introduced in various countries.

AREAS COVERED

This review describes the recently licensed glycoconjugates being used to protect against these encapsulated bacteria. Immunogenicity and safety data that led to licensure or licensure expansion of these glycoconjugates are discussed in addition to the resultant impact on the disease burden.

EXPERT OPINION

The maintenance of robust immunisation programmes with high uptake rates is important in maintaining low rates of disease. Epidemiological surveillance systems are essential in monitoring any changes in infectious disease trends and in identifying emerging infections such as from non-typeable H. influenzae, pneumococcal serotype replacement disease and changes in the epidemiology of meningococcal serogroups. This is important to guide future vaccine development. Accessibility of these glycoconjugate vaccines in resource poor regions, which bear the highest disease burden from these pathogens, remains challenging largely due to high vaccine pricing. Recent aids from public and private funding, tiered vaccine pricing and the transfer of vaccine technology have helped in introducing these vaccines where they are most needed.

Antibody persistence after primary and booster doses of a quadrivalent meningococcal conjugate vaccine in adolescents

BACKGROUND

The aim of this study was to evaluate antibody persistence 5 years after primary vaccination with the quadrivalent meningococcal conjugate vaccines MenACWY-CRM or MenACWY-D and 2 years after a booster dose of MenACWY-CRM, in the context of a phase 3 study.

METHODS

Subjects (aged 19.2 ± 2.3 years) were assigned to 5 groups according to whether they had previously received primary vaccination (at 14.2 ± 2.2 years) with MenACWY-CRM (N = 131) or MenACWY-D (N = 76), a booster dose of MenACWY-CRM 3 years after primary vaccination with MenACWY-CRM (N = 44) or MenACWY-D (N = 31) or no vaccination (N = 107). The immunogenicity measures were percentages of subjects with serum bactericidal activity (hSBA) ≥ 1:8 for serogroups A, C, W and Y and hSBA geometric mean titers. Comparisons with age-matched, vaccine-naive subjects were performed.

RESULTS

A majority of subjects vaccinated 5 years previously maintained hSBA ≥ 1:8 against serogroups C, W and Y in the MenACWY-CRM (59%-82%) and MenACWY-D groups (54%-73%); this was lower for serogroup A in both groups. There was a decline in antibody titers after primary vaccination, especially in the first 2 years postprimary vaccination, with steady concentrations during the next 3 years. Two years after MenACWY-CRM booster vaccination the percentages of subjects with hSBA ≥ 1:8 ranged from 77% to 100% across serogroups and geometric mean titers were 2.5- to 8-fold higher than prebooster values across serogroups.

CONCLUSIONS

Booster vaccination with MenACWY-CRM elicited a robust immune response during the 2-year follow-up period, irrespective of previous vaccination.

Timing of an adolescent booster after single primary meningococcal serogroup C conjugate immunization at young age; an intervention study among Dutch teenagers

BACKGROUND

Meningococcal serogroup C (MenC) specific antibody levels decline rapidly after a single primary MenC conjugate (MenCC) vaccination in preschool children. A second MenCC vaccination during (pre)adolescence might attain longer lasting individual and herd protection. We aimed to establish an appropriate age for a (pre)adolescent MenCC booster vaccination.

METHODS

A phase-IV trial with healthy 10-year-olds (n = 91), 12-year-olds (n = 91) and 15-year-olds (n = 86) who were primed with a MenCC vaccine nine years earlier. All participants received a booster vaccination with the same vaccine. Serum bactericidal antibody assay titers (SBA, using baby rabbit complement), MenC-polysaccharide (MenC-PS) specific IgG, IgG subclass and avidity and tetanus-specific IgG levels were measured prior to (T0) and 1 month (T1) and 1 year (T2) after the booster. An SBA titer ≥8 was the correlate of protection.

RESULTS

258 (96.3%) participants completed all three study visits. At T0, 19% of the 10-year-olds still had an SBA titer ≥8, compared to 34% of the 12-year-olds (P = 0.057) and 45% of the 15-year-olds (P<0.001). All participants developed high SBA titers (GMTs>30,000 in all age groups) and MenC-PS specific IgG levels at T1. IgG levels mainly consisted of IgG1, but the contribution of IgG2 increased with age. At T2, 100% of participants still had an SBA titer ≥8, but the 15-year-olds showed the highest protective antibody levels and the lowest decay.

CONCLUSION

Nine years after primary MenCC vaccination adolescents develop high protective antibody levels in response to a booster and are still sufficiently protected one year later. Our results suggest that persistence of individual--and herd--protection increases with the age at which an adolescent booster is administered.

TRIAL REGISTRATION

EU Clinical Trials Database 2011-000375-13 Dutch Trial Register NTR3521.

Randomized clinical trial to evaluate the immunogenicity of quadrivalent meningococcal conjugate and polysaccharide vaccines in adults in the United kingdom

Meningococcal conjugate vaccines are today successfully deployed in universal programs for children and adolescents in different geographic regions to control meningitis and septicemia. However, in adults, the advantages of these conjugates over the older polysaccharide vaccines are less clear. In this randomized clinical trial, we demonstrated that both conjugate and polysaccharide quadrivalent meningococcal vaccines elicit protective antibody responses in adults aged 18 to 70. (This study has been registered at www.clinicaltrials.gov under registration no. NCT00901940.).

Persistence of serogroup C antibody responses following quadrivalent meningococcal conjugate vaccination in United States military personnel

Serogroup C meningococcal (MenC) disease accounts for one-third of all meningococcal cases and causes meningococcal outbreaks in the U.S. Quadrivalent meningococcal vaccine conjugated to diphtheria toxoid (MenACYW_D) was recommended in 2005 for adolescents and high risk groups such as military recruits. We evaluated anti-MenC antibody persistence in U.S. military personnel vaccinated with either MenACYW_D or meningococcal polysaccharide vaccine (MPSV4). Twelve hundred subjects vaccinated with MenACYW_D from 2006 to 2008 or MPSV4 from 2002 to 2004 were randomly selected from the Defense Medical Surveillance System. Baseline serologic responses to MenC were assessed in all subjects; 100 subjects per vaccine group were tested during one of the following six post-vaccination time-points: 5–7, 11–13, 17–19, 23–25, 29–31, or 35–37 months. Anti-MenC geometric mean titers (GMT) were measured by rabbit complement serum bactericidal assay (rSBA) and geometric mean concentrations (GMC) by enzyme-linked immunosorbent assay (ELISA). Continuous variables were compared using the Wilcoxon rank sum test and the proportion of subjects with an rSBA titer ≥8 by chi-square. Pre-vaccination rSBA GMT was <8 for the MenACWY_D group. rSBA GMT increased to 703 at 5–7 months post-vaccination and decreased by 94% to 43 at 3 years post-vaccination. GMT was significantly lower in the MenACWY_D group at 5–7 months post-vaccination compared to the MPSV4 group. The percentage of MenACWY_D recipients achieving an rSBA titer of ≥8 decreased from 87% at 5–7 months to 54% at 3 years. There were no significant differences between vaccine groups in the proportion of subjects with a titer of ≥8 at any time-point. GMC for the MenACWY_D group was 0.14 µg/mL at baseline, 1.07 µg/mL at 5–7 months, and 0.66 µg/mL at 3 years, and significantly lower than the MPSV4 group at all time-points. Anti-MenC responses wane following vaccination with MenACYW_D; a booster dose is needed to maintain protective levels of circulating antibody.

Long-term seroprotection after an adolescent booster meningococcal serogroup C vaccination

OBJECTIVES

To determine long-term seroprotection after serogroup C meningococcal (MenC) vaccination at the age of 9-12 years, with or without booster vaccination at the age of 13-15 years.

DESIGN

Observational cohort study; follow-on from randomised study.

SETTING

Participants were recruited from English secondary schools (in Oxfordshire and Buckinghamshire).

PARTICIPANTS AND INTERVENTIONS

Participants were primed with MenC CRM-glycoconjugate vaccine at the age of 9-12 years in the UK routine immunisation campaign. In previous studies they were randomised at 13 to 15 years of age to receive a booster dose of MenC-CRM glycoconjugate vaccine (CRM-group) or bivalent meningococcal serogroup A/C polysaccharide vaccine (PS-group), or they received no additional doses of MenC vaccine (control group). In this follow-on study, a blood sample was obtained 11 years after primary immunisation. Of 531 individuals eligible to participate, 134 were enrolled, and 124 were included in the analysis.

MAIN OUTCOME MEASURES

MenC serum bactericidal antibody (SBA) geometric mean titre; proportion of participants with SBA titre ≥8 (putative protective threshold).

RESULTS

Median ages at priming, boosting and blood sampling were 10.61, 14.42 and 22.11 years, respectively. Geometric mean titres for MenC SBA were: CRM group 1373 (95% CI 954 to 1977); PS group 1024 (687 to 1526); and controls 284 (167 to 483). SBA titres ≥8 were present in 50/54 (92.6%) controls and 70/70 (100%) boosted individuals.

CONCLUSIONS

The planned introduction in the UK of an adolescent booster of MenC conjugate vaccine in 2013 is likely to provide sustained protection against MenC disease.

TRIAL REGISTRATION

Registered on ClinicalTrials.gov (NCT01459432).

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.

Meningococcal vaccines: current issues and future strategies

Since the introduction of the first meningococcal conjugate vaccines in 1999, remarkable progress has been made in reducing the morbidity and mortality caused by meningococcal disease. Currently, varying meningococcal conjugate vaccines provide protection against serogroups A, C, Y, and W meningococcal disease. A large impact has been seen after vaccine introduction, particularly in the UK after vaccinating all 1-17 year olds. The introduction of serogroup A conjugate vaccine in the meningitis belt has the potential to control epidemics of disease that disproportionately affect this area of the world. Issues remain that require continued vigilance with disease surveillance and frequent reassessment of vaccine strategies. These issues include duration of protection, potential increases in non-vaccine serogroups, and vaccine safety and potential interference with other routine vaccines. Serogroup B meningococcal vaccines are protein-based vaccines, with the first approved in early 2013. Understanding the potential impact of serogroup B vaccines is critical to developing future meningococcal vaccination strategies.

Phase II study of a three-dose primary vaccination course of DTPa-IPV/Hib-MenC-TT followed by a 12-month Hib-MenC-TT booster in healthy infants

AIM

To test for immunologic noninferiority of antibody responses to Hib and MenC using a 6-in-1 combination vaccine (DTPa-IPV/Hib-MenC-TT) compared with DTPa-IPV-Hib plus MenC-CRM197, before and after a 12-month Hib-MenC-TT booster.

METHODS

Pragmatic open-label, randomized, multicenter, UK study. "6-in-1" group received DTPa-IPV/Hib-MenC-TT at 2, 3 and 4 months; control group received DTPa-IPV-Hib at 2, 3 and 4 months and MenC-CRM197 at 3 and 4 months. Both groups received Hib-MenC-TT at 12 months. Concomitant vaccines: pneumococcal conjugate vaccine at 2, 4 and 13 months, and measles, mumps and rubella vaccine at 13 months.

RESULTS

One hundred forty-two children were randomized to each group. One hundred children in the "6-in-1" group and 112 control group children completed the study according-to-protocol. One month postprimary immunizations: 100% of "6-in-1" group and 93.3% of control children had anti-polyribosylribitol phosphate (PRP) IgG ≥0.15 µg/mL; 96.2% and 100%, respectively, had rSBA-MenC titers ≥1:8. One month after booster all children met these thresholds, with anti-PRP geometric mean concentrations of 66.7 (53.3; 83.5) in "6-in-1" recipients and 26.9 (20.9; 34.6) in control children (4.4 [3.5; 5.4] and 3.0 [2.2-4.2] postprimary immunizations, respectively,). rSBA-MenC geometric mean titers were 3062.9 (2421.2; 3874.6) and 954.0 (761.3; 1195.5), respectively, postbooster and 393.2 (292.5; 528.7) and 3110.5 (2612; 3704.2) postprimary.

CONCLUSION

Noninferiority of DTPa-IPV/Hib-MenC-TT compared with DTPa-IPV/Hib plus MenC-CRM197 was demonstrated. In the "6-in-1" group, lower postprimary and greater postbooster rSBA-MenC geometric mean titers suggest memory B-cell priming may be favored by this vaccine over plasma cell induction. Furthermore, greater immunogenicity of TT conjugates used in both primary and booster vaccines in this group may be important.

MenACWY-TT vaccine for active immunization against invasive meningococcal disease

Meningococcal disease remains a significant global cause of morbidity and mortality despite the availability of polysaccharide and conjugate vaccines. The implementation of monovalent meningococcal serogroup C vaccine in developed countries has significantly decreased the incidence of meningococcal disease, while the recent introduction of monovalent serogroup A conjugate vaccine in the African meningitis belt aims to reduce the incidence of high endemic disease in this area. Three quadrivalent meningococcal vaccines have already been licensed; a polysaccharide (MenACWY-PS) and two conjugated (MenACWY-DT and MenACWY-CRM) vaccines. An investigational MenACWY-TT vaccine is described in this article. Clinical trials in infants older than 9 months of age, toddlers, children, adolescents and adults have indicated that this vaccine is well tolerated and immunogenic. The inclusion of a spacer molecule coupled with the polysaccharide (for serogroups A and C) and tetanus toxoid as the carrier protein aims to elicit robust immune responses. The tolerability of this vaccine is comparable to that of polysaccharide quadrivalent vaccines and monovalent meningococcal serogroup C vaccines. More importantly, the immunogenicity, antibody persistence and induction of immune memory aim to provide protection to a wide range of susceptible subjects.

Importance of circulating antibodies in protection against meningococcal disease

Neisseria meningitidis infection results in life-threatening illnesses, including bacteremia, sepsis and meningitis. Early diagnosis and treatment are a challenge due to rapid disease progression, resulting in high mortality and morbidity in survivors. Disease can occur in healthy individuals, however, risk of infection is higher in patients with certain risk factors. N meningitidis carriage and case-fatality rates are high in adolescents and young adults. The absolute incidence of meningococcal disease has decreased partially due to increasing meningococcal vaccination rates. Maintaining protective levels of circulating antibodies by vaccination is necessary for clinical protection against disease. The Centers for Disease Control and Prevention Advisory Committee on Immunization Practices guidelines recommend vaccination for all individuals aged 11 through 12 years, followed by a booster dose at age 16 years for maintenance of protective antibody levels throughout the high-risk years. Despite these guidelines, many adolescents remain unvaccinated and susceptible to infection and disease. 

B cell memory to a serogroup C meningococcal conjugate vaccine in childhood and response to booster: little association with serum IgG antibody

The maintenance of adequate serum Ab levels following immunization has been identified as the most important mechanism for individual long-term protection against rapidly invading encapsulated bacteria. The mechanisms for maintaining adequate serum Ab levels and the relationship between Ag-specific memory B cells and Ab at steady state are poorly understood. We measured the frequency of circulating serogroup C meningococcal (MenC)-specific memory B cells in 250 healthy 6- to 12-y-old children 6 y following MenC conjugate vaccine priming, before a booster of a combined Haemophilus influenzae type b-MenC conjugate vaccine and then 1 wk, 1 mo, and 1 y after the booster. We investigated the relationship between circulating MenC-specific memory B cell frequencies and Ab at baseline and following the booster vaccine. We found very low frequencies of circulating MenC-specific memory B cells at steady state in primary school-aged children and little association with MenC IgG Ab levels. Following vaccination, there were robust memory B cell booster responses that, unlike Ab levels, were not dependent on age at priming with MenC. Measurement of B cell memory in peripheral blood does not predict steady state Ab levels nor the capacity to respond to a booster dose of MenC Ag.

Persistence of the immune response at 5 years of age following infant immunisation with investigational quadrivalent MenACWY conjugate vaccine formulations

BACKGROUND AND AIMS

Serogroup A, C, W-135 and Y meningococcal (MenACWY) conjugate vaccines are recommended for routine adolescent immunisation in the United States and Canada. We evaluated the persistence of bactericidal antibodies through early childhood, following infant immunisation with varying schedules of MenACWY-CRM(197) vaccine.

METHODS

UK and Canadian infants were immunised with 2-3 doses of MenACWY-CRM(197) or 2 doses of serogroup C meningococcal (MenC) conjugate vaccine, and either MenACWY-CRM(197), 1/5 dose of MenACWY polysaccharide vaccine or no booster at 12 months. Control groups recruited at 60 months had received country-specific infant doses of MenC conjugate vaccine. hSBA titres were measured in participants at 40 and 60 months of age.

RESULTS

382 children were enrolled in 12 groups (22-40 per group). By age 60 months, 3-11% of children primed and boosted with MenACWY-CRM(197) had hSBA titres≥1:8 against serogroup A, 14-45% against serogroup C, 57-85% against serogroup W-135 and 42-71% against serogroup Y. Children primed with MenC and boosted with MenACWY-CRM(197) had similar results, except for serogroup C (59%). In age-matched controls administered MenC vaccine at 2, 3, and 4 months (UK), 2 and 12 months or 12 months only (Canada), percentages with hSBA titres≥1:8 were 0-3%, 29-53%, 34-36% and 10-29% against serogroups A, C, W-135 and Y respectively.

CONCLUSIONS

Serogroup-specific bactericidal antibody wane following infant immunisation with MenACWY-CRM(197), most markedly against serogroup A. Best persistence against serogroup C is observed with MenC conjugate vaccine priming and MenACWY-CRM(197) at 12 months, compared to schedules using only MenACWY-CRM(197), with the potential for providing broader protection compared to monovalent MenC vaccines alone.

Reducing inequalities with vaccines: New Zealand's MeNZB vaccine initiative to control an epidemic

Disadvantaged children of Māori and Pacific origin in New Zealand carry an inequitable burden of infectious diseases, many of which are preventable, some by vaccine. Immunisation is recognised in the developing world as a cheap, effective and efficient means of reducing inequalities. The MeNZB immunisation programme delivered in 2004-2006 towards the expected natural end of a projected 15-year epidemic appears to have had an effect (difficult to prove conclusively) on reducing the disproportionate burden of meningococcal disease carried by this group of children. It was delayed by the late engagement of the New Zealand Ministry of Health, fully briefed from 1996, leading to unnecessary and potentially avoidable deaths and sequelae, many lifelong. Further, failure to adequately assess vaccine effectiveness means that the contribution of MeNZB to the observed reduction in disease, particularly in those aged less than five years, will never be reliably known. However, the MeNZB campaign has at least left a legacy: the National Immunisation Register, which should enable New Zealand to minimise the 'vaccine inverse care law' and contribute to reducing ethnic inequity in the burden of vaccine preventable diseases.

Is a single dose of meningococcal serogroup C conjugate vaccine sufficient for protection? experience from the Netherlands

BACKGROUND

The first meningococcal serogroup C (MenC) conjugate vaccine was licensed in 1999 and introduced in the United Kingdom. Countries that have implemented the MenC vaccine since then in their national immunisation programmes use different schedules. Nevertheless, all involved countries seem to experience substantial declines in the incidence of MenC disease.

DISCUSSION

Since 2001, the MenC conjugate vaccine has been implemented in the Netherlands by offering a single dose to all children aged 14 months. Prior to the introduction of the vaccine into the national immunisation programme, a catch-up vaccination campaign was initiated in which a single dose of the MenC conjugate vaccine was offered to all children aged from 14 months up to and including 18 years. Since then, there has been no report of any case of MenC disease among immunocompetent vaccinees. Administration of a single dose of MenC conjugate vaccine after infancy could be beneficial considering the already complex immunisation schedules with large numbers of vaccinations in the first year of life. The present paper deals with the advantages and critical aspects of a single dose of the MenC conjugate vaccine.

SUMMARY

A single dose of MenC conjugate vaccine at the age of 14 months in combination with a catch up vaccine campaign appeared to be a successful strategy to prevent MenC disease in the Netherlands, thereby confirming that a single dose of the vaccine could sufficiently protect against disease. Nevertheless, this approach can only be justified in countries with a relatively low incidence of serogroup C meningococcal disease in the first year of life. Furthermore, a good surveillance programme is recommended for timely detection of vaccine breakthroughs and outbreaks among non-vaccinees, since long-term protection after a single dose in the second year of life cannot currently be guaranteed.

Vaccine development against Neisseria meningitidis

Meningococcal disease is communicable by close contact or droplet aerosols. Striking features are high case fatality rates and peak incidences of invasive disease in infants, toddlers and adolescents. Vaccine development is hampered by bacterial immune evasion strategies including molecular mimicry.As for Haemophilus influenzae and Streptococcus pneumoniae, no vaccine has therefore been developed that targets all serogroups of Neisseria meningitidis. Polysaccharide vaccines available both in protein conjugated and non-conjugated form, have been introduced against capsular serogroups A, C,W-135 and Y, but are ineffective against serogroup B meningococci, which cause a significant burden of disease in many parts of the world. Detoxified outer membrane vesicles are used since decades to elicit protection against epidemic serogroup B disease. Genome mining and biochemical approaches have provided astounding progress recently in the identification of immunogenic, yet reasonably conserved outer membrane proteins. As subcapsular proteins nevertheless are unlikely to immunize against all serogroup B variants, thorough investigation by surrogate assays and molecular epidemiology approaches are needed prior to introduction and post-licensure of protein vaccines. Research currently addresses the analysis of life vaccines, meningococcus B polysaccharide modifications and mimotopes, as well as the use of N. lactamica outer membrane vesicles.

Two decades of experience with the Haemophilus influenzae serotype b conjugate vaccine in the United Kingdom

BACKGROUND

The Haemophilus influenzae serotype b (Hib) conjugate vaccine was introduced into the UK national childhood immunization program in 1992 after clinical trials reported the vaccine to be highly immunogenic in infants as young as two months of age.

OBJECTIVE

The goal of this study was to describe and comment on the impact of routine Hib immunization on the epidemiology of invasive Hib disease in the United Kingdom. In addition, the development of Hib polysaccharide and conjugate vaccines was reviewed.

METHODS

A literature search was conducted of PubMed for invasive Hib disease epidemiology in the United Kingdom. The UK Health Protection Agency Web site was also searched for relevant publications.

RESULTS

The incidence of invasive Hib incidence in children aged <5 years fell from 21/100,000 to 44/100,000 in the prevaccine era to 0.63/100,000 in 1998, with an estimated vaccine failure rate of 2.2/100,000 vaccinees. After 1999, however, invasive Hib disease increased, particularly in toddlers, and peaked in 2003. Potential reasons for the resurgence included a greater-than-expected decline in Hib antibodies after primary immunization, waning of herd immunity offered by the initial catch-up campaign, and use of a less immunogenic Hib combination vaccine containing acellular pertussis in 2000-2001. In response to the resurgence, a Hib combination vaccine containing whole-cell pertussis was reintroduced in 2002, followed by a childhood Hib booster campaign in 2003. In 2004, the recommended infant vaccine was changed to a different Hib/acellular pertussis combination vaccine containing inactivated polio, which had a satisfactory Hib response, was less reactogenic, and eliminated the risk of vaccine-associated paralytic poliomyelitis. This action was followed by introduction of a routine 12-month Hib booster in 2006. Together, these measures led to a decline in invasive Hib disease across all age groups. In 2010, there were only 30 invasive Hib cases, with 6 reported in children aged <5 years and no deaths in this age group since 2007.

CONCLUSIONS

Control of Hib disease is currently the best that has been achieved since the introduction of the routine Hib vaccination almost 20 years ago.

Meningococcal conjugate vaccines policy update: booster dose recommendations

The Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention and the American Academy of Pediatrics approved updated recommendations for the use of quadravalent (serogroups A, C, W-135, and Y) meningococcal conjugate vaccines (Menactra [Sanofi Pasteur, Swiftwater, PA] and Menveo [Novartis, Basel, Switzerland]) in adolescents and in people at persistent high risk of meningococcal disease. The recommendations supplement previous Advisory Committee on Immunization Practices and American Academy of Pediatrics recommendations for meningococcal vaccinations. Data were reviewed pertaining to immunogenicity in high-risk groups, bactericidal antibody persistence after immunization, current epidemiology of meningococcal disease, meningococcal conjugate vaccine effectiveness, and cost-effectiveness of different strategies for vaccination of adolescents. This review prompted the following recommendations: (1) adolescents should be routinely immunized at 11 through 12 years of age and given a booster dose at 16 years of age; (2) adolescents who received their first dose at age 13 through 15 years should receive a booster at age 16 through 18 years or up to 5 years after their first dose; (3) adolescents who receive their first dose of meningococcal conjugate vaccine at or after 16 years of age do not need a booster dose; (4) a 2-dose primary series should be administered 2 months apart for those who are at increased risk of invasive meningococcal disease because of persistent complement component (eg, C5-C9, properdin, factor H, or factor D) deficiency (9 months through 54 years of age) or functional or anatomic asplenia (2-54 years of age) and for adolescents with HIV infection; and (5) a booster dose should be given 3 years after the primary series if the primary 2-dose series was given from 2 through 6 years of age and every 5 years for persons whose 2-dose primary series or booster dose was given at 7 years of age or older who are at risk of invasive meningococcal disease because of persistent component (eg, C5-C9, properdin, factor H, or factor D) deficiency or functional or anatomic asplenia.

Timing of adolescent meningococcal conjugate vaccination attitudes and practices of pediatricians and family medicine physicians

BACKGROUND

The meningococcal conjugate vaccine (MCV4) was recommended for those aged 11-18 years in 2005. Initial supply issues led to an emphasis on immunizing older adolescents. When supply improved in 2007, routine immunization was recommended for those aged 11-12 years.

PURPOSE

Among a U.S. sample of pediatricians and family medicine physicians, describe (1) recommendation and administration practices for MCV4; (2) preferences regarding MCV4 administration; and (3) attitudes and characteristics associated with recommendation for those aged >12 years.

METHODS

A mail and Internet survey in a nationally representative sample of physicians was conducted between December 2009 and March 2010. Analysis was conducted between March 2010 and October 2010, including a multivariable analysis to examine factors associated with deferring MCV4 to ages >12 years.

RESULTS

Response rates were 88% (pediatricians 367/419) and 63% (family medicine physicians 268/423). In all, 95% of pediatricians and 73% of family medicine physicians reported administering MCV4 routinely to those aged 11-18 years (p<0.0001); 83% (pediatricians) and 45% (family medicine physicians) reported strongly recommending MCV4 for those aged 11-12 years (p<0.0001); 27% (pediatricians) and 40% (family medicine physicians) preferred to administer MCV4 to those aged >12 years (p<0.0001). Compared with those who strongly recommend for those aged 11-12 years, physicians who do not regularly stock MCV4, family medicine physicians, and physicians concerned about waning immunity were more likely to defer their recommendation, whereas physicians practicing in the Northeast and those with more Latino patients were less likely to defer.

CONCLUSIONS

Most pediatricians and family medicine physicians administer MCV4, but many, especially family medicine physicians and those concerned about waning immunity, defer their recommendation for MCV4 to patients aged >12 years.

Persistence of serum bactericidal antibody one year after a booster dose of either a glycoconjugate or a plain polysaccharide vaccine against serogroup C Neisseria meningitidis given to adolescents previously immunized with a glycoconjugate vaccine

BACKGROUND

Bactericidal antibody induced by immunization of infants with serogroup C Neisseria meningitidis (MenC) vaccines wanes rapidly during childhood. Adolescents are at particular risk from meningococcal disease, therefore they might benefit from a booster dose of vaccine. The duration of serologic response to such a booster in adolescents is unknown.

METHODS

In a previous study, English schoolchildren, aged 9 to 12 years, who had received a monovalent MenC glycoconjugate vaccine in 1999-2000, were given either a plain polysaccharide vaccine (MenC-PS group, n = 150) or a glycoconjugate vaccine (MenC-CRM group, n = 95) at 13 to 15 years of age. In this follow-up study, serum bactericidal antibody titers and specific immunoglobulin G concentrations were assessed 1 year later. Results were compared with unboosted controls of similar age (control group, n = 298).

RESULTS

Compliance with study protocol was achieved for 146 of the MenC-PS group, 92 of the MenC-CRM group, and 293 of the control group. Compared with the control group, both the MenC-PS and MenC-CRM groups had a significantly higher (P < 0.0001) geometric mean serum bactericidal antibody titers 1 year after the booster dose (geometric mean titers for MenC-PS group 3388 [95% confidence interval {CI}: 2460-4665]; MenC-CRM group 4417 [95% CI: 2951-6609]; control group 316 [95% CI: 252-396]). Specific immunoglobulin G concentration also rose and remained elevated 1 year after the booster.

CONCLUSIONS

A booster dose of MenC vaccine given to adolescents produced a marked rise in bactericidal antibody, which remained elevated 1 year later. Introduction of an adolescent booster of MenC vaccine might provide enhanced long-term population control of the disease.

Maintenance of immune response throughout childhood following serogroup C meningococcal conjugate vaccination in early childhood

The objectives of this study were to evaluate the kinetics of antibody decline through childhood in a longitudinal study of a single cohort following serogroup C meningococcal (MenC) vaccine immunization in early childhood and to calculate the proportion of 11 to 13 year olds with protective levels of bactericidal antibody 10 years after immunization. United Kingdom children aged 11 to 13 years in 2010 who had previously taken part in a longitudinal study at the Oxford Vaccine Group had blood samples drawn between 2001 and 2010. Sera from each time point were analyzed for the MenC serum bactericidal antibody titer using a baby rabbit complement (rSBA) assay. The median age at MenC immunization was 21 months (range, 1 year 3 months to 3 years 9 months). The MenC rSBA geometric mean titer (GMT) at age 3.5 to 5 years was 8.0 (95% confidence interval, 6.5 to 9.9; n = 287). By age 11.5 to 13.5 years, the rSBA GMT had declined to 3.3 (2.5 to 4.4; n = 98). The percentage of children with rSBA titers of ≥1:8 (the threshold for protection) also declined from 38% (35% to 41%) to 15% (12% to 19%). We concluded that MenC rSBA titers wane rapidly following vaccination in early childhood and continue to decline into the second decade of life. Since nasopharyngeal colonization in adolescents probably provides the major reservoir for MenC in the population, declining immunity in this cohort is of concern. Sustaining high levels of antibody through booster vaccination in this cohort is likely necessary to avoid a resurgence of disease in the decade ahead.

Meningococcal conjugate vaccines: optimizing global impact

Meningococcal conjugate vaccines have several advantages over polysaccharide vaccines, including the ability to induce greater antibody persistence, avidity, immunologic memory, and herd immunity. Since 1999, meningococcal conjugate vaccine programs have been established across the globe. Many of these vaccination programs have resulted in significant decline in meningococcal disease in several countries. Recent introduction of serogroup A conjugate vaccine in Africa offers the potential to eliminate meningococcal disease as a public health problem in Africa. However, the duration of immune response and the development of widespread herd immunity in the population remain important questions for meningococcal vaccine programs. Because of the unique epidemiology of meningococcal disease around the world, the optimal vaccination strategy for long-term disease prevention will vary by country.

Kinetics of immune responses to nasal challenge with meningococcal polysaccharide one year after serogroup-C glycoconjugate vaccination

BACKGROUND

Recipients of serogroup-C glycoconjugate meningococcal vaccine (MCC) exhibit waning of serum bactericidal antibody (SBA) titers, but the rate of decline and the speed of their immunological memory in response to new meningococcal nasopharyngeal colonization are unknown.

METHODS

In a prospective challenge study, we measured persistence of SBA and anti-Neisseria meningitidis serogroup-C (MenC) immunoglobulin (Ig) G and IgA in adults aged 18-39, 28 days and 12 months after receiving MCC. Volunteers were then challenged intranasally with 50 μg MenC polysaccharide to mimic meningococcal colonization, and systemic and mucosal antibody responses were measured.

RESULTS

All subjects had protective SBA titers (≥8) 28 days after MCC vaccination, but 12.3% and 20.2% had unprotective (<8) or low (<128) levels, respectively, after 12 months. Following rechallenge (12 months postvaccination) and measurement of antibody responses after 4, 7, and 10 days, rises in SBA titers were only observed in subjects with low (<128) or nonprotective (<8) prerechallenge SBA titers. In subjects with pre rechallenge SBA titers <8, the majority did not reach a protective SBA titer until 7 days post-rechallenge. MenC-specific IgG levels rose in both serum and saliva in correlation with SBA titers. No detectable rise in salivary IgA was observed.

CONCLUSIONS

In those individuals who fail to retain protective SBA 12 months after MCC, immunological memory fails to generate protective systemic and mucosal antibodies until 7 days post intranasal challenge with cognate meningococcal polysaccharide. This is likely too slow to protect from natural meningococcal infection. MCC vaccinees rely on persistence of antibody levels rather than immunological memory for sustained protection.

Long-term protection after immunization with protein-polysaccharide conjugate vaccines in infancy

The polysaccharide-encapsulated bacteria, Haemophilus influenzae type b, Neisseria meningitidis and Streptococcus pneumoniae are important causes of invasive bacterial infection in childhood, accounting for most of the cases of bacterial pneumonia and meningitis worldwide. Protein-polysaccharide conjugate vaccines have been developed over the last 20 years and have proven very effective in controlling these infections. Although studies have consistently shown that herd immunity is critical for population protection, long-term individual protection against polysaccharide-encapsulated bacteria appears to depend on persisting antibody and, perhaps to a lesser extent, immunological memory. However, some studies have reported that the concentration of serum antibody and vaccine effectiveness are not sustained after infant immunization, despite persistence of immunological memory. In this article, we detail the mechanisms of protection against invasion by encapsulated bacteria, describe the age-dependent B-cell and antibody responses to protein-polysaccharide conjugate vaccines and propose strategies to guarantee protection during periods of increased disease burden.

Age-related immunity to meningococcal serogroup C vaccination: an increase in the persistence of IgG2 correlates with a decrease in the avidity of IgG

BACKGROUND

All children and adolescents between 1 and 19 years of age in The Netherlands received a single meningococcal serogroup C conjugate (MenCC) vaccine in 2002. During follow-up 4-5 years later, the persistence of MenC polysaccharide-specific IgG was found to be dependent on age of vaccination with higher IgG levels in the oldest immunized age categories.

METHODS AND FINDINGS

Two cross-sectional population-based serum banks, collected in 1995/1996 and in 2006/2007, were used for this study. We measured MenC polysaccharide-specific IgM, the IgG1 and IgG2 subclasses and determined the avidity of the IgG antibodies. We report that the age-related persistence of IgG after immunization with the MenCC vaccine seemed to result from an increase of IgG2 levels with age, while IgG1 levels remained stable throughout the different age-cohorts. Furthermore, an age-related increase in IgM levels was observed, correlating with the persistence of IgG antibodies with age. It is noteworthy that the increase in IgG2 correlated with a reduced IgG-avidity with age.

CONCLUSION

These date indicate that the classical characteristics of a T-cell-dependent antibody response as elicited by protein based vaccines might not be completely applicable when conjugate vaccines are administered to older children and adolescents up to 18 years of age. The response elicited by the MenCC vaccine seemed to be more a mixture of both T cell dependent and T cell independent responses in terms of humoral immunological characteristics.

Epidemiology, molecular characterization and antibiotic resistance of Neisseria meningitidis from patients ≤15 years in Manhiça, rural Mozambique

Background

The epidemiology of meningococcal disease in Mozambique and other African countries located outside the “meningitis belt” remains widely unknown. With the event of upcoming vaccines microbiological and epidemiological information is urgently needed.

Methods

Prospective surveillance for invasive bacterial infections was conducted at the Manhiça District hospital (rural Mozambique) among hospitalized children below 15 years of age. Available Neisseria meningitidis isolates were serogrouped and characterized by Multilocus Sequence Typing (MLST). Antibiotic resistance was also determined.

Results

Between 1998 and 2008, sixty-three cases of confirmed meningococcal disease (36 meningitis, 26 sepsis and 1 conjunctivitis) were identified among hospitalized children. The average incidence rate of meningococcal disease was 11.6/100,000 (8/100,000 for meningitis and 3.7/100,000 for meningococcemia, respectively). There was a significant rise on the number of meningococcal disease cases in 2005–2006 that was sustained till the end of the surveillance period. Serogroup was determined for 43 of the 63 meningococcal disease cases: 38 serogroup W-135, 3 serogroup A and 2 serogroup Y. ST-11 was the most predominant sequence type and strongly associated with serogroup W-135. Two of the three serogroup A isolates were ST-1, and both serogroup Y isolates were ST-175. N. meningitidis remained highly susceptible to all antibiotics used for treatment in the country, although the presence of isolates presenting intermediate resistance to penicillin advocates for continued surveillance.

Conclusions

Our data show a high rate of meningococcal disease in Manhiça, Mozambique, mainly caused by serogroup W-135 ST-11 strains, and advocates for the implementation of a vaccination strategy covering serogroup W-135 meningococci in the country.

Persistence of immunity following a booster dose of Haemophilus influenzae type B-Meningococcal serogroup C glycoconjugate vaccine: follow-up of a randomized controlled trial

BACKGROUND

Antibodies against Haemophilus influenzae type b (Hib) and serogroup C Neisseria meningitidis (MenC) wane after early infant immunization.

METHODS

Children previously immunized in a randomized controlled trial at ages 2, 3, and 4 months with DTPa-IPV-Hib and MenC-CRM197 (MenC-CRM group) or DTPa-IPV and Hib-MenC-TT (Hib-MenC-TT group) had blood samples drawn at 1 and 2 years following a booster dose of Hib-MenC-TT at 12 to 15 months of age. A blood sample was also drawn at the year 2 follow-up from a separately recruited age-matched control group who had not received a booster.

RESULTS

In 271 children at year 1, mean 14.6 months (range: 12-18 months) following the Hib-MenC-TT booster, MenC bactericidal titers above the protective threshold (rSBA ≥ 1:8) was demonstrated in 89.0% of the Hib-MenC-TT group and 69.5% of MenC-CRM participants. Antipolyribosylribitol phosphate Ig ≥ 1.0 μg/mL (Hib correlate for long-term protection) was seen in 94.9% and 82.5%, respectively.In 379 participants (including 72 control children) at year 2 (age: 39-43 months, 25-31 months post Hib-MenC-TT) persistence of MenC antibodies was demonstrated in 67.1% of the Hib-MenC-TT group and 40.5% of the MenC-CRM group, compared with 44.1% of control group participants. Antipolyribosylribitol phosphate Ig ≥ 1.0 μg/mL was seen in 89.0%, 74.7%, and 38.9%, respectively.

CONCLUSIONS

A toddler Hib-MenC-TT booster helps sustain immunity against Hib to 3½ years of age. Persistence of MenC antibody is similar in children primed with MenC-CRM197 in infancy who receive a booster Hib-MenC-TT, to those who receive no booster. Persistence of MenC antibody is better when primed and boosted with Hib-MenC-TT.

Serum antibody kinetics following nasal or parenteral challenge with meningococcal polysaccharide in healthy adults

Limited data are available on the kinetics of meningococcal serogroup C (MenC)-specific antibody responses following parenteral or nasal challenge in those who have received prior MenC vaccination (polysaccharide or conjugate). Young adults who had previously received either meningococcal A/C polysaccharide (MACP) or MenC conjugate (MCC) vaccine or naïve subjects were challenged with MACP via one of two routes, nasal or parenteral. Blood samples were taken prevaccination and on days 1 to 4 and day 10 postvaccination. MenC serum bactericidal antibody (SBA) and MenC-specific IgG were measured. Following parenteral challenge, MenC SBA and IgG responses were seen to occur between 4 and 7 days postchallenge. A lower proportion of subjects responded following nasal challenge, with naïve subjects showing little change in SBA geometric mean titer (GMT) and IgG geometric mean concentration (GMC) over the 10 days following challenge. Increases in SBA GMTs were seen between 4 and 7 days after nasal challenge in those who had received prior MCC and between 7 and 10 days in those who had received prior MACP, and the responses in the prior-MACP group were of lower magnitude than the responses of the prior-MCC group. The data presented here indicate that, following MCC vaccination, memory has been induced at the mucosal level, and these subjects were able to respond with increases in SBA levels. These results demonstrate that the speed of response (primary or secondary) to challenge with MenC polysaccharide via the nasal or parenteral route does not differ and support concerns that immunological memory alone is too slow to provide protection.

Challenges in immunisation against bacterial infection in children

Polysaccharide-encapsulated organisms such as S. pneumoniae, H. influenzae type b and N. meningitidis are the leading causes of serious invasive bacterial diseases and pneumonia in children. The use of conjugate vaccines in developed countries has markedly decreased the burden of disease and mortality from these organisms through direct protection of the immunised and through herd immunity. Although conjugate vaccines are highly immunogenic, antibody levels after immunisation in early infancy wane, leading to the need for programmes which include booster doses. Understanding the generation of long-term immunity could lead to improvements in vaccine formulation and scheduling with the ultimate goal of providing more sustained protection. Prematurity is a risk factor for disease caused by polysaccharide-encapsulated bacteria and the available data indicate that preterm infants should be immunised according to their chronological age to provide early protection.