Meningococcal polysaccharide A O-acetylation levels do not impact the immunogenicity of the quadrivalent meningococcal tetanus toxoid conjugate vaccine: results from a randomized, controlled phase III study of healthy adults aged 18 to 25 years

A new fully liquid presentation of MenACWY-CRM conjugate vaccine: Results from a multicentre, randomised, controlled, observer-blind study

BACKGROUND

The currently licensed quadrivalent MenACWY-CRM conjugate vaccine presentation consists of two vials (lyophilised MenA and liquid MenCWY) to be reconstituted before injection. A new fully liquid formulation in a single vial has been developed to further improve the vaccine presentation. Since the MenA structure is subject to hydrolytic degradation, this study was conducted to compare the immunogenicity and safety of the investigational MenACWY-CRM liquid vaccine with the licensed vaccine.

METHODS

In this multicentre, randomised, controlled, observer-blind, phase 2b study, 979 healthy adults were administered a single dose of MenACWY-CRM liquid presentation or the currently licensed MenACWY-CRM vaccine. MenA free saccharide generation was accelerated to approximately 30% in the liquid presentation and MenA polysaccharide O-acetylation was reduced to approximately 40%, according to a controlled procedure. Immunological non-inferiority of the MenACWY-CRM liquid to the licensed vaccine, as measured by human serum bactericidal assay (hSBA) geometric mean titres (GMTs) against MenA 1 month post-vaccination, was the primary study objective. Safety assessment was among the secondary objectives.

RESULTS

Immune responses against each serogroup were similar between the two vaccine groups and was non-inferior for MenA. Adjusted hSBA GMTs for MenA were 185.16 and 211.33 for the MenACWY-CRM liquid presentation and currently licensed vaccine presentation, respectively. The between-group ratio of hSBA GMTs for MenA was 0.88, with a two-sided 95% confidence interval lower limit of 0.64, greater than the prespecified non-inferiority margin of 0.5, thus meeting the primary study objective. Both vaccines were well tolerated. No serious adverse events were considered related to vaccination.

CONCLUSIONS

The levels of MenA free saccharide and polysaccharide O-acetylation did not affect the immunogenicity of the fully liquid presentation, which was demonstrated to be non-inferior to the immunogenicity of the currently licensed MenACWY-CRM vaccine against MenA. The immunogenicity, reactogenicity and safety profiles of the two vaccine presentations were similar.

Immunological non-inferiority of a new fully liquid presentation of the MenACWY-CRM vaccine to the licensed vaccine: results from a randomized, controlled, observer-blind study in adolescents and young adults

A fully liquid MenACWY-CRM vaccine presentation has been developed, modifying the meningococcal serogroup A (MenA) component from lyophilized to liquid. The safety and immunogenicity of the liquid presentation at the end of the intended shelf-life (aged for 24 or 30 months) were compared to the licensed lyophilized/liquid presentation. This multicenter, randomized (1:1), observer-blind, phase 2b study (NCT03433482) enrolled adolescents and young adults (age 10-40 years). In part 1, 844 participants received one dose of liquid presentation stored for approximately 24 months or licensed presentation. In part 2, 846 participants received one dose of liquid presentation stored for approximately 30 months or licensed presentation. After storage, the MenA free saccharide (FS) level was approximately 25% and O-acetylation was approximately 45%. The primary objective was to demonstrate non-inferiority of the liquid presentation to licensed presentation, as measured by human serum bactericidal assay (hSBA) geometric mean titers (GMTs) against MenA, 1-month post-vaccination. Immune responses against each vaccine serogroup were similar between groups. Between-group ratios of hSBA GMTs for MenA were 1.21 (part 1) and 1.11 (part 2), with two-sided 95% confidence interval lower limits (0.94 and 0.87, respectively) greater than the prespecified non-inferiority margin (0.5), thus meeting the primary study objective. No safety concerns were identified. Despite reduced O-acetylation of MenA and increased FS content, serogroup-specific immune responses induced by the fully liquid presentation were similar to those induced by the licensed MenACWY-CRM vaccine, with non-inferior anti-MenA responses. The safety profiles of the vaccine presentations were similar.

Structural and mechanistic basis of capsule O-acetylation in Neisseria meningitidis serogroup A

O-Acetylation of the capsular polysaccharide (CPS) of Neisseria meningitidis serogroup A (NmA) is critical for the induction of functional immune responses, making this modification mandatory for CPS-based anti-NmA vaccines. Using comprehensive NMR studies, we demonstrate that O-acetylation stabilizes the labile anomeric phosphodiester-linkages of the NmA-CPS and occurs in position C3 and C4 of the N-acetylmannosamine units due to enzymatic transfer and non-enzymatic ester migration, respectively. To shed light on the enzymatic transfer mechanism, we solved the crystal structure of the capsule O-acetyltransferase CsaC in its apo and acceptor-bound form and of the CsaC-H228A mutant as trapped acetyl-enzyme adduct in complex with CoA. Together with the results of a comprehensive mutagenesis study, the reported structures explain the strict regioselectivity of CsaC and provide insight into the catalytic mechanism, which relies on an unexpected Gln-extension of a classical Ser-His-Asp triad, embedded in an α/β-hydrolase fold.

Cost-effectiveness of meningococcal polysaccharide serogroups A, C, W-135 and Y conjugate vaccine in Australian adolescents

OBJECTIVES

The incidence of invasive meningitis disease (IMD) is increasing in Australia. A conjugate vaccine of meningococcal polysaccharide serogroups A, C, W and Y (MenACWY) is currently indicated for infants aged 12 months on the Australian National Immunisation Program. This study sought to determine the cost-effectiveness of a broader MenACWY vaccination program for Australians aged 15 to 19 years.

METHODS

A Markov model was constructed to simulate the incidence and consequences of IMD in Australians aged 0-84 years, with follow up until age 85 years. The model comprised four health states: 'Alive with no previous IMD', 'Alive, post IMD without long-term complications', 'Alive, post IMD with long-term complications' and 'Dead'. Decision analysis compared the clinical consequences and costs of a vaccination program versus no vaccination from the perspective of the Australian health care system. Age-specific incidence of IMD and fatality rates were derived from Australian surveillance data. Vaccine coverage, vaccine efficacy and herd immunity were based on published data. The total cost for MenACWY vaccination was AU$56 per dose. Costs and health outcomes were discounted by 5% per annum (in the base-case analysis).

RESULTS

Compared to no vaccination, a MenACWY vaccination program targeted at Australians aged 15-19 years was expected to prevent 1664 IMD cases in the Australian population aged 0-84 years followed up until age 85 years. The program would lead to 1131 life years (LYs) and 2058 quality adjusted life years (QALYs) gained at a total cost of AU$115 million (all discounted values). These equated to incremental cost-effectiveness ratios of AU$101,649 per LY gained and AU$55,857 per QALY gained. A probabilistic sensitivity analysis demonstrated a likelihood of cost-effectiveness of 34.6%, assuming a willingness to pay threshold of AU$50,000 per QALY gained.

CONCLUSION

The likelihood of this program being cost-effective under a willingness to pay threshold AU$50,000 per QALY gained is 35%.

NMR Assays for Estimating the O-Acetyl Content of Meningococcal Polysaccharide Serogroup A in Quadrivalent Conjugate Vaccine Formulation

The use of multivalent glycoconjugate vaccines has dramatically contributed to reduce the incidence of meningococcal infectious disease. The advanced structural characterization of polysaccharide conjugates leads to enhancements in the quality and control of the products. Here, we report a novel nuclear magnetic resonance (NMR) method to confirm the identity and structural conformity (e.g., O-acetyl content) of saccharide antigens that comprise a licensed tetravalent meningococcal serogroups A, C, W, and Y vaccine. For the first time, the NMR methodology is applied on a formulation (licensed vaccine) containing a large excess of excipient (i.e., sucrose) without analytical sample pretreatment. This work confirms the applicability of a rapid and easy NMR assay on a multivalent conjugate vaccine, which might be extended to other combination vaccines that are already licensed or in clinical development.

Immunogenicity and safety of meningococcal group A, C, W and Y tetanus toxoid conjugate vaccine: review of clinical and real-world evidence

Protection by meningococcal group A, C, W and Y (MenACWY) vaccines against four meningococcal disease-causing serogroups is increasingly important because of changing epidemiologic patterns of meningococcal disease, including recent meningococcal serogroup W outbreaks/disease clusters. The MenACWY vaccine conjugated to tetanus toxoid (MenACWY-TT) has been extensively evaluated across the age spectrum (age ≥6 weeks) in randomized Phase II and III and in postmarketing studies. Results support the robust immunogenicity of MenACWY-TT across ages and coadministration with other vaccines. The safety profile is similar regardless of age, primary versus booster vaccination, or concomitant administration; local (swelling, pain, redness) and systemic (fever, fatigue, headache, drowsiness, loss of appetite, irritability) reactogenicity events are most common. These data support use of MenACWY-TT to protect against MenACWY disease.

Meningococcal Group A, C, W, and Y Tetanus Toxoid Conjugate Vaccine: A Review of Clinical Data in Adolescents

MenACWY-TT (Nimenrix) is a quadrivalent meningococcal vaccine containing polysaccharides from serogroups A, C, W, and Y conjugated to a tetanus toxoid carrier protein. MenACWY-TT is licensed in some countries as a three-dose primary series in individuals as young as 6 weeks of age and as a single dose in individuals ≥12 months of age. MenACWY-TT use is supported by long-term immunogenicity and safety across age groups, including data from several phase 2, 3, and 4 clinical studies in adolescents and young adults. Adolescents are an important population in the epidemiology, transmission, and prevention of invasive meningococcal disease, with this age-based population having the highest risk for carriage and transmission as well as one of the highest risks of disease. This age group is emerging as a target population in meningococcal vaccination programs globally, as vaccinating adolescents and young adults could potentially not only decrease disease rates directly for those vaccinated but also indirectly for unvaccinated individuals by decreasing carriage and eliciting herd protection. This review will consider available data for MenACWY-TT in adolescents, including safety and immunogenicity, booster and memory responses, persistence, and coadministration with other vaccines, with an emphasis on the rationale for use of MenACWY-TT and other quadrivalent meningococcal vaccines in adolescents to address the changing epidemiology of meningococcal disease.

Role of O-Acetylation in the Immunogenicity of Bacterial Polysaccharide Vaccines

The incidence of infectious diseases caused by several bacterial pathogens such as Haemophilus influenzae type b, Streptococcus pneumoniae, and Neisseria meningitidis, has been dramatically reduced over the last 25 years through the use of glycoconjugate vaccines. The structures of the bacterial capsular polysaccharide (CPS) antigens, extracted and purified from microbial cultures and obtained with very high purity, show that many of them are decorated by O-acetyl groups. While these groups are often considered important for the structural identity of the polysaccharides, they play a major role in the functional immune response to some vaccines such as meningococcal serogroup A and Salmonella typhi Vi, but do not seem to be important for many others, such as meningococcal serogroups C, W, Y, and type III Group B Streptococcus. This review discusses the O-acetylation status of CPSs and its role in the immunological responses of these antigens.

Routinely vaccinating adolescents against meningococcus: targeting transmission & disease

Adolescents have the highest rates of meningococcal carriage and transmission. Interrupting the adolescent habitat in order to reduce carriage and transmission within adolescents and to other age groups could help to control meningococcal disease at a population level. Compared to immunization strategies restricted to young children, a strategy focused on adolescents may have more profound and long-lasting indirect impacts, and may be more cost effective. Despite challenges in reaching this age-group, experience with other vaccines show that high vaccine coverage of adolescents is attainable.

Factors contributing to the immunogenicity of meningococcal conjugate vaccines

Various glycoprotein conjugate vaccines have been developed for the prevention of invasive meningococcal disease, having significant advantages over pure polysaccharide vaccines. One of the most important features of the conjugate vaccines is the induction of a T-cell dependent immune response, which enables both the induction of immune memory and a booster response after repeated immunization. The nature of the carrier protein to which the polysaccharides are chemically linked, is often regarded as the main component of the vaccine in determining its immunogenicity. However, other factors can have a significant impact on the vaccine's profile. In this review, we explore the physico-chemical properties of meningococcal conjugate vaccines, which can significantly contribute to the vaccine's immunogenicity. We demonstrate that the carrier is not the sole determining factor of the vaccine's profile, but, moreover, that the conjugate vaccine's immunogenicity is the result of multiple physico-chemical structures and characteristics.

Meningococcal quadrivalent tetanus toxoid conjugate vaccine (MenACWY-TT, Nimenrix™): A review of its immunogenicity, safety, co-administration, and antibody persistence

INTRODUCTION

Meningococcal disease is a major cause of morbidity and mortality worldwide with reported epidemics and outbreaks in different parts of the world. Despite the availability of antimicrobial therapy, challenges remain in early recognition and prevention of disease. Several vaccines have been developed to date aiming at preventing disease spread.

DISCUSSION

MenACWY-TT (Nimenrix™) has been extensively studied for use in different age groups. Phase II and III randomized trials have demonstrated its immunogenicity when administered in children aged 1 year and older, adolescents and adults. It has an acceptable safety profile with minor adverse events comparable to other vaccines. Follow up studies have shown persistence of protective antibodies up to three years. MenACWY-TT was safely and effectively co-administered with different recommended vaccines.

CONCLUSION

MenACWY-TT is a safe and immunogenic vaccine that can be used to protect against these four serogroups in individuals older than 1 year of age.

Immunogenicity of meningococcal quadrivalent (serogroup A, C, W135 and Y) tetanus toxoid conjugate vaccine: systematic review and meta-analysis

Meningococcal meningitis represents one of the leading cause of bacterial meningitis in developed countries. Among the thirteen described serogroups, only five are usually responsible of invasive infections making immunisation against multiple serogroups the best strategy to protect individuals from this disease. Herein we carried out a systematic review and meta-analysis, in accordance with the PRISMA statement, of the recently EU-licensed meningococcal ACWY-tetanus toxoid conjugate vaccine (MenACWY-TT). We included 15 randomised clinical trials, comparing MenACWY-TT and Men-PS (ten studies), MenACWY-TT and MenC-CRM197 (four studies) and MenACWY-TT and MenACWY-DT (one study). All studies included in the meta-analysis showed high immunogenicity for MenACWY-TT vaccines in all tested serogroups. Our results suggest that the MenACWY-TT vaccine is as immunogenic as the other commercial available meningococcal vaccines.

Meningococcal serogroups A, C, W-135, and Y tetanus toxoid conjugate vaccine: a new conjugate vaccine against invasive meningococcal disease

Invasive meningococcal disease is a serious infection that occurs worldwide. It is caused by Neisseria meningitidis, of which six serogroups (A, B, C, W-135, X, and Y) are responsible for most infections. The case fatality rate of meningococcal disease remains high and can lead to significant sequelae. Vaccination remains the best strategy to prevent meningococcal disease. Polysaccharide vaccines were initially introduced in the late 1960s but their limitations (poor immunogenicity in infants and toddlers and hyporesponsiveness after repeated doses) have led to the development and use of meningococcal conjugate vaccines, which overcome these limitations. Two quadrivalent conjugated meningococcal vaccines – MenACWY-DT (Menactra^®) and MenACWY-CRM₁₉₇ (Menveo^®) – using diphtheria toxoid or a mutant protein, respectively, as carrier proteins have already been licensed in the US. Recently, a quadrivalent meningococcal vaccine conjugated to tetanus toxoid (MenACWY-TT; Nimenrix^®) was approved for use in Europe in 2012. The immunogenicity of MenACWY-TT, its reactogenicity and safety profile, as well as its coadministration with other vaccines are discussed in this review. Clinical trials showed that MenACWY-TT was immunogenic in children above the age of 12 months, adolescents, and adults, and has an acceptable reactogenicity and safety profile. Its coadministration with several other vaccines that are commonly used in children, adolescents, and adults did not affect the immunogenicity of MenACWY-TT or the coadministered vaccine, nor did it affect its reactogenicity and safety. Other studies are now ongoing in order to determine the immunogenicity, reactogenicity, and safety of MenACWY-TT in infants from the age of 6 weeks.