Strengths and weaknesses of pneumococcal conjugate vaccines

Streptococcus pneumoniae serotype distribution in low- and middle-income countries of South Asia: Do we need to revisit the pneumococcal vaccine strategy?

S. pneumoniae serotypes responsible for pneumococcal disease differ with respect to disease severity, invasiveness, antimicrobial susceptibility, geographies, immunization history, age groups, and with time. Although PCVs have blunted the pneumococcal disease burden, they are plagued with numerous challenges, especially the emergence of NVTs. In this review, we show that there are diverse serotypes, especially NVTs, responsible for causing pneumococcal diseases in LMICs of South Asia across different studies conducted between 2012 and 2024. We propose that pharmaceutical/biotech companies should tailor/customize the PCVs as per the region-specific serotype prevalence based on surveillance data. Furthermore, protein-based vaccines, or WCVs, have been explored and can serve as viable alternatives to address the limitations associated with PCVs. However, robust studies are warranted in different geographies to demonstrate its efficacy and safety in clinical trials as well as the real-world effectiveness of these promising candidates.

Refinement of a novel staphylococcal superantigen-like poly protein vaccine

Staphylococcus aureus is a community- and hospital-associated pathogen of global significance. Despite several decades of investment there is no licenced vaccine and antimicrobial resistance is increasing, complicating effective treatment of infection. We have developed a novel fusion vaccine (PolySSL) containing mutated forms of three immune evasion factors, Staphylococcal Superantigen-Like (SSL) proteins 3, 7 and 11, that are common to all S. aureus isolates. Mice given the PolySSL vaccine have a robust specific serum IgG response, attenuated signs of infection, and a significantly reduced S. aureus tissue burden after an intra-peritoneal challenge with S. aureus. A comparison of six different versions of the vaccine (PolySSL 3711, 7113, 7311 and DualSSL 73, 311, 711) suggests inclusion of all three SSLs is required, the 7113 order produces the most significant reduction in bacterial liver and kidney burden, and that SSL7 is the most important component. The likely requirement for a multi-valent vaccine was examined by immunising groups of mice with six PolySSL7113 variants (adjuvanted with AdjuPhos) encompassing most S. aureus strains of clinical significance. SSL7 was confirmed to be the dominant antigen eliciting endpoint titres ≥105 irrespective of the variant used, whereas IgG responses to SSL3 and SSL11 were lower (∼103) and more variable. The highest inhibition of the interaction between the six wildtype variants of SSL7 and either IgA or complement C5 was typically obtained with variant-matched anti-sera. Conversely, anti-sera from these mice showed failed to stop SSL3 from blocking TLR2 signalling. An improved version of the PolySSL vaccine has been generated by altering the protein order, but these data suggest a multi-valent vaccine will be required to elicit robust inhibitory cross-variant antibody responses. A path to further improvement may be through use of a different adjuvant to broaden and enhance immunity to SSLs 3, 7 and 11.

Evaluation of Fourier-Transform Infrared Spectroscopy with IR Biotyper® system for Streptococcus pneumoniae serotyping

PURPOSE

Streptococcus pneumoniae is an important human pathogen and its virulence is centered on the expression of a polysaccharide capsule. Serotyping pneumococci has clinical and epidemiological relevance. As the gold standard (Quellung reaction) is expensive and somehow laborious, alternative methodologies for timely serotyping are desirable. We aimed to evaluate IR Biotyper® (Bruker), which is based on FT-IRS, as a tool for serotyping S. pneumoniae by customizing a classifier focusing on PCV15 serotypes.

METHODS

Initially, we evaluated the Pneumococci serogrouper (Bruker) included in the IR Biotyper® software (v.4.0) using 188 retrospective isolates of S. pneumoniae previously serotyped by the gold standard. Lately, these isolates were used to construct (n = 83) and validate (n = 105) the PCV15-Classifier. Overall, 1246 spectra were obtained to create a classification model using artificial neural network (ANN) machine learning in 400 cycles. Finally, prospective S. pneumoniae (n = 61), recovered from patients attended at hospitals in South Brazil, were used for a "real-life" evaluation of both classifiers.

RESULTS

Agreement was higher when using PCV15-Classifier instead of Pneumococci serogrouper (Bruker) among both, retrospective (86.7% versus 68.1%; p = 0.0004) and prospective isolates (75.4% versus 70.5%; p = 0.54), highlighting (i) its better performance for epidemiologically relevant serotypes, such as 3, and (ii) its capacity to discriminate between serotypes of serogroup 19 (19F and 19A).

CONCLUSION

Altogether, our results reiterate the usefulness of IR Biotyper® for serotyping S. pneumoniae applying a customized classifier, which can be re-trained whenever needed, following the evolution of serotype distribution.

Serotype dynamics of Streptococcus pneumoniae in some countries in Eastern Europe and Central Asia

The burden of pneumococcal disease remains a global challenge. The purpose of this work was to assess the serotype composition of S. pneumoniae circulating among children under 5 years of age in Eastern European (the Russian Federation and the Republic of Belarus) and Central Asian (the Republic of Kazakhstan) countries which are characterized by close cultural and economic ties. The most pronounced changes were noted in the Russian Federation. In the pre-vaccination period (before 2015) PCV13 covered 66 % - 90 % of prevalent serotypes. In 2016-2018 coverage decreased to 59.2 %. During this study period (2020-2023) PCV 13 related serotypes in healthy children and those with respiratory infections dropped further to 23.2 % and 35.7 %, respectively. In Kazakhstan, vaccine-related serotypes among healthy children and children with RTI were more prevalent than in Russia (51.5-58.6 % vs 23.2-35.7 %) despite both countries having introduced pneumococcal vaccination at the same time, and both countries reporting vaccination rates above 90 % in children under 5 years of age. In the Republic of Belarus, in the absence of a universal vaccination program, PCV13 covers 86.4 % of serotypes. Serotypes 19F (31 %), 3 (16.2 %), 19 A (10.3 %), and 14 (10 %) predominate among S. pneumoniae causing acute otitis media in children. Expanding the serotype/serogroup composition of new vaccines may provide protection against potentially invasive non-vaccine strains in the future.

A phase 3 study of 20-valent pneumococcal conjugate vaccine in healthy toddlers previously vaccinated in infancy with 13-valent pneumococcal conjugate vaccine

This phase 3, randomized, partially double-blind study investigated the safety, tolerability, and immunogenicity of 20-valent pneumococcal conjugate vaccine (PCV20) in healthy toddlers ≥12-<24 months of age who had previously received 2 infant doses of 13-valent PCV (PCV13). Participants were randomized to receive 1 or 2 doses of PCV20 (the second dose was administered 56-70 days after the first dose), or 1 dose of PCV13. The primary pneumococcal immunogenicity endpoint was the percentages of participants with predefined serotype-specific immunoglobulin G (IgG) concentrations (≥0.35 μg/mL) for the 7 additional serotypes 1 month after the last vaccination. Percentages of participants with predefined IgG concentrations for the 13 matched serotypes, IgG geometric mean concentrations, and opsonophagocytic activity (OPA) geometric mean titers were also evaluated for all 20 vaccine serotypes. Safety endpoints included local reactions, systemic events, adverse events, and serious adverse events. Overall, 356 participants were randomized (2-dose PCV20, n = 121; 1-dose PCV20, n = 118; PCV13, n = 117). One month after 1 PCV20 dose, ≥75.9 % of participants had IgG concentrations ≥0.35 μg/mL for all 7 additional serotypes, except serotype 12F (54.6 %). After 2 PCV20 doses, the percentage of participants with IgG concentrations ≥0.35 μg/mL for the 7 additional serotypes was ≥91.2 %. PCV20 elicited IgG and OPA responses for all 20 serotypes including serotype 12F. IgG distributions were well differentiated and substantially higher in PCV20 groups than the PCV13 group for the 7 additional serotypes, and generally similar between all groups for the 13 matched serotypes. In conclusion, a single toddler dose of PCV20 after 2 infant PCV13 doses elicited immune responses expected to help provide protection against the 7 additional serotypes and to provide similar protection against the 13 matched serotypes as PCV13. These data support a transition from PCV13 to PCV20 at the toddler dose. The safety and tolerability profile of PCV20 was similar to PCV13. Trial registration:Clinicaltrials.gov, NCT05408429.

Cost-Effectiveness and Public Health Impact of 24-Valent Pneumococcal Conjugate Vaccine Compared With the Recommended Pneumococcal Vaccines in Older Adults

INTRODUCTION

The potential impact of an in-development 24-valent pneumococcal conjugate vaccine compared with that of currently recommended vaccines in older adults is unclear. Similar to most currently available pneumococcal conjugate vaccines, 24-valent pneumococcal conjugate vaccine's formulation is based on childhood pneumococcal disease epidemiology. Decision analysis techniques were used to estimate 24-valent pneumococcal conjugate vaccine cost-effectiveness and public health effects in U.S. older adults.

METHODS

A Markov model compared 24-valent pneumococcal conjugate vaccine with currently recommended U.S. pneumococcal vaccination strategies in older adults (aged ≥65 years) and with no vaccination. Age-, race-, and chronic medical condition-specific pneumococcal illness risks and serotype-specific disease risks were obtained from Centers for Disease Control and Prevention data. Vaccine effectiveness was estimated using Delphi panel and clinical trial data. Vaccination and pneumococcal illness costs were from U.S.

DATABASES

Scenario analyses examined indirect effects of childhood pneumococcal vaccination on adult disease. Data were collected and analyses were performed in 2024.

RESULTS

The 24-valent pneumococcal conjugate vaccine prevented fewer pneumococcal disease cases and deaths than the recently recommended 21-valent pneumococcal conjugate vaccine, which is formulated on the basis of adult pneumococcal disease serotypes. In cost-effectiveness analyses, 21-valent pneumococcal conjugate vaccine was economically favorable compared with 24-valent pneumococcal conjugate vaccine and all other vaccination strategies, both without and with consideration of potential childhood vaccination indirect effects. These findings were robust and consistent with those in deterministic and probabilistic sensitivity analyses.

CONCLUSIONS

In older adults, 24-valent pneumococcal conjugate vaccine was clinically and economically unfavorable compared with 21-valent pneumococcal conjugate vaccine, which covers more adult disease-causing pneumococcal serotypes and is less susceptible to childhood vaccination indirect effects.

Incidence Rates for Invasive Streptococcus pneumoniae and Haemophilus influenzae Infections in US Military Pediatric Dependents Before and During COVID-19

Background/Objectives: Invasive Streptococcus pneumoniae disease (IPD) and invasive Haemophilus influenzae (IHI) infections cause disease in pediatric patients. The COVID-19 pandemic brought about a change in the rates of common viral illnesses that can lead to superimposed bacterial infections. Methods: A repeated monthly cross-sectional study was performed using inpatient data from the Military Health System Data Repository (MDR) to observe differences in IPD and IHI hospitalization rates before and during the COVID-19 pandemic starting in March 2018 and continuing to February 2023. Our study included a cohort of 1.27 million children under the age of 5 years old. Results: A total of 200 unique cases of IPD and 171 unique cases of IHI were identified. In Year 1 of the pandemic, the hospitalization rates for IHI and IPD decreased. In Year 2, IPD returned to the pre-pandemic baseline, and IHI remained below the baseline. In Year 3, IPD increased above the baseline, and IHI returned to the baseline. Conclusions: These data support the notion that the interventions implemented to reduce the spread of COVID-19, such as hand hygiene and social distancing, likely led to a reduction in the incidence of invasive disease. The subsequent relaxation of these mitigation strategies likely led to a resurgence of IHI and an increase in IPD in our population.

Adults with low opsonic natural antibody levels against Streptococcus pneumoniae show enhanced response to PPSV23 vaccination

BACKGROUND

Pneumococcal diseases pose a significant public health concern globally, particularly among young children and the elderly. Vaccination plays a crucial role in their prevention. This study evaluated the functional immune responses to Pneumococcal polysaccharide vaccine serotypes in healthy Indian adults before and after administering a single dose of PPSV23 immunization.

METHODS

A total of 125 healthy participants aged 18-65 received the PPSV23 vaccine, and their pre- and post-immunization sera were analyzed by MOPA. Opsonic Index, Geometric mean OPA titers and fold increase for each serotype was calculated.

RESULTS

The highest baseline OPA GMTs were observed for serotypes 33F,17F,9N,20, and 6B. The lowest OPA GMTs were noted against types 1 and 12F. OPA GMTs post-vaccination increased significantly for all serotypes, with geometric mean fold rise (GMFR) ranging from 4.3 to 267.5. Participants with low pre-immunization OPA titers (<8 & <64) showed significant increases in OI fold raise across all tested serotypes post-vaccination. This robust immune response was consistent across serotypes, indicating highly effective seroconversion in individuals with low baseline antibody levels.

CONCLUSION

The PPSV23 vaccine elicits a strong immunogenic response in individuals with low pre-immunization OPA titers, achieving substantial increases in opsonic index fold raise across various serotypes.

Effect of O-Acetylation on the Antigenicity and Glycoconjugate Immunogenicity of the Streptococcus Pneumoniae Serotype 7F Capsular Polysaccharide

Streptococcus pneumoniae is a bacterial pathogen causing diseases as severe as pneumonia, sepsis and meningitis. Most commercial pneumococcal conjugate vaccines contain the 7F serotype, which is epidemiologically relevant and highly invasive. This serotype contains an O-acetyl group at the internal L-rhamnose of its polysaccharide repeating unit. Herein we report on the role of the O-acetyl moiety of 7F polysaccharide in both antigen recognition and the induction of a protective antibody response against 7F. Fully and partially de-O-acetylated 7F polysaccharides were chemically prepared and compared with the O-acetylated counterpart in their antigenicity and immunogenicity of their tetanus toxoid glycoconjugates. These comparative studies showed a slight but consistent decrease in the antigenicity for the fully de-O-acetylated polysaccharide, but not for the partly de-O-acetylated variant. The glycoconjugates derived from the O-acetylated and the fully de-O-acetylated polysaccharides had similar sizes and polysaccharide-to-protein ratio, and all proved both to be immunogenic and induce opsonophagocytic responses in mice. Nevertheless, the immune response elicited by the O-acetylated glycoconjugate was better in both quantity and quality, proving that the O-acetyl group is not strictly necessary but also not irrelevant for the antigenicity and immunogenicity of the 7F serotype polysaccharide and its glycoconjugates.

Immunogenicity and safety of the 15-valent pneumococcal conjugate vaccine, a systematic review and meta-analysis

Pneumococcal infections are a serious health issue associated with increased morbidity and mortality. This systematic review evaluated the efficacy, effectiveness, immunogenicity, and safety of the pneumococcal conjugate vaccine (PCV)15 compared to other pneumococcal vaccines or no vaccination in children and adults. We identified 20 randomized controlled trials (RCTs). A meta-analysis of six RCTs in infants showed that PCV15 was non-inferior compared with PCV13 for 12 shared serotypes. Based on a meta-analysis of seven RCTs in adults, PCV15 was non-inferior to PCV13 for 13 shared serotypes. For the unique PCV15 serotypes, 22F and 33F, immune responses were higher in infants and adults vaccinated with PCV15 compared to those receiving PCV13. Regarding safety, meta-analyses indicated comparable risks of adverse events between PCV15 and PCV13 in infants. Adults receiving PCV15 had a slightly higher risk of adverse events, though serious events were similar between groups.

Quantitation and characterization of serotype 6A activation for pneumococcal conjugate vaccine by cryo-EM and SEC methods

Pneumococcal conjugate vaccines (PCV) typically consist of capsular polysaccharides from different S. pneumoniae serotypes which are covalently attached to carrier protein. A well-established process to manufacture PCV is through activating polysaccharide by oxidation of vicinal diols to aldehydes, followed by protein conjugation via reductive amination. Polysaccharide activation is a crucial step that affects vaccine product critical attributes including conjugate size and structure. Therefore, it is highly desired to have robust analytical methods to well characterize this activation process. In this study, using pneumococcal serotype 6A as the model, we present two complimentary analytical methods for characterization of activated polysaccharide. First, a size exclusion chromatography (SEC) method was developed for quantitative measurement of polysaccharide activation levels. This SEC method demonstrated good assay characteristics on accuracy, precision and linearity. Second, a gold nanoparticle labeled cryo-electron microscopy (Cryo-EM) technique was developed to visualize activation site distribution along polysaccharide chain and provide information on activation heterogeneity. These two complimentary methods can be utilized to control polysaccharide activation process and ensure consistent delivery of conjugate vaccine products.

Clinical features and immune memory of breakthrough infection in children after age-appropriate 13-valent pneumococcal conjugate vaccination in Taiwan

PURPOSE

As certain vaccine serotypes are still circulating within the community during the PCV13 era, we aimed to delineate the clinical features and assess the immunity following breakthrough infections in children.

METHODS

101 PCVs-vaccinated children < 18 years with culture confirmed PCV13 serotype breakthrough infection (25/101, invasive pneumococcal disease [IPD]) was identified in Taiwan in 2015-2019. Immunoglobulin G (IgG) antibody levels, IgM+ memory B cells (MBCs), and isotype-switched immunoglobulin (sIg+) MBC specific to serotypes 3, 14, 19 A were assessed prior to and one month after an additional PCV13 booster in 9 patients. A cohort of 89 previously vaccinated, healthy children were enrolled as controls.

RESULTS

The majority (88%) of the breakthrough infection occurred in children under 7 years old. Infection by serotypes 3 and 19 A increased in children aged 5-17 years in 2018-2019. The pre-booster serotype 3- and 19 A-specific IgG in both children with breakthrough infection and controls were lower than the IPD protective thresholds (2.83 µg/mL for 3; 1.00 µg/mL for 19 A). Breakthrough infected children showed higher geometric mean ratio in serotype-specific IgG, IgM+ MBCs and sIg+ MBC after an additional PCV13 booster, compared to the controls.

CONCLUSIONS

Most breakthrough infections occurred in previously healthy preschool-aged children, but such infections may still occur in school-aged children due to waning immunity. Breakthrough infections may also enhance the anamnestic response elicited by PCV13.

Evaluation of GC-MS for identification and characterization of pneumococcal serotype 24A, 24B, and 24F capsular polysaccharide

Analysis of pneumococcal polysaccharides (PnPs) has been an arduous task, especially in similar serotypes. Pneumococci invades the host immune response by modulating capsule structure with small genetic changes making them indistinguishable from similar serotypes by conventional modes of analysis. The new serotype 24F causing invasive pneumococcal-resistant infection is an analytical challenge for its analysis as related serotypes 24A and 24B Ps share a common backbone. The difference in the branched chain which contains arabinitol and ribitol in 24F and 24B respectively are stereoisomers making their identification even more challenging. The composition analysis by GC-MS revealed distinct peaks for arabinitol in 24F and 24A Ps and ribitol in Pn 24B serotype polysaccharide. The mass spectral analysis confirmed their identification along with a heterologous cross-reactivity which confirmed anti-Pn-24F mAb reactive to Pn 24B than Pn 24A. The quantitative analysis of pneumococcal 24A, 24B and 24F using GC-MS showed sensitive analysis over the concentration range 3.125-200 μg/mL with regression coefficient >0.99 making ideal modality for the characterization, identification, and quantitation of pneumococcal 24A, 24B and 24F similar serotypes.

Cost-Effectiveness Analysis of Pneumococcal Vaccines in the Pediatric Population: A Systematic Review

Objectives: Pneumococcal disease, caused by Streptococcus pneumoniae, is the leading cause of mortality in children worldwide. The tremendous direct cost of hospital admissions and significant indirect costs from productivity loss contribute considerably to its economic burden, with vaccination being the only efficient protection against the illness. Our study aims to summarize the cost-effectiveness of the pneumococcal conjugate vaccine (PCV) implemented in the pediatric population. Methods: Employing the online databases PubMed, Embase, and Medline, we looked for economic evaluations from 2018 until March 2024. The Incremental Cost-Effectiveness Ratios (ICER) and Quality-Adjusted Life Years (QALY) were the primary outcomes for measuring the cost-effectiveness of PCVs. A 28-item CHEERS 2022 checklist was applied to assess the quality of the collected studies. Results: Of the 16 papers found, 9/16 discussed the lower-valent vaccines (PCV13, PCV10) and 7/16 examined the higher-valent vaccines (PCV20, PCV15). PCV13 and PCV10 involved greater costs and generated more QALY compared to no vaccination. Both PCV15 and PCV20 averted substantial healthcare costs and yielded greater quality of life than PCV13. Additionally, PCV20 was a dominant strategy compared to PCV15. Conclusions: Utilizing PCV13 is a very cost-effective option compared to not getting vaccinated. Transitioning from PCV13 to PCV20 would result in higher QALY gain and more cost-saving than switching to PCV15.

Nasal microbionts differentially colonize and elicit cytokines in human nasal epithelial organoids

Nasal colonization by Staphylococcus aureus or Streptococcus pneumoniae is associated with an increased risk of infection by these pathobionts, whereas nasal colonization by Dolosigranulum species is associated with health. Human nasal epithelial organoids (HNOs) physiologically recapitulate human nasal respiratory epithelium with a robust mucociliary blanket. We reproducibly monocolonized HNOs with these three bacteria for up to 48 hours with varying kinetics across species. HNOs tolerated bacterial monocolonization with localization of bacteria to the mucus layer and minimal cytotoxicity compared to uncolonized HNOs. Human nasal epithelium exhibited both species-specific and general cytokine responses, without induction of type I interferons, consistent with colonization rather than infection. Only live S. aureus colonization induced IL-1 family cytokines, suggestive of inflammasome signaling. D. pigrum and live S. aureus decreased CXCL10, whereas S. pneumoniae increased CXCL11, chemokines involved in antimicrobial responses. HNOs are a compelling model system to reveal host-microbe dynamics at the human nasal mucosa.

Vaccine-induced strain replacement: theory and real-life implications

The value of preventive medicine is superior to treatment with vaccinations occupying high priority. Nevertheless, heavy pressure has started to form in regard to strains not included in vaccines contributing to the changing epidemiology of pathogen subtypes leading to 'vaccine-induced strain replacement'. Among other mechanisms, increasing fitness of nonvaccine strains and metabolic shifts in the subtypes have been described. Classical examples include pneumococcal infections and viral diseases, such as the human papilloma virus. Recently, it has been described in SARS-CoV-2, leading to the emergence of new subtypes, such as Omicron and Delta variants. The phenomenon has also been reported in Mycobacterium tuberculosis, Neisseria meningitidis and rotavirus. This study addresses the concepts, examples and implications of this phenomenon.

Modeling 1-Cyano-4-Dimethylaminopyridine Tetrafluoroborate (CDAP) Chemistry to Design Glycoconjugate Vaccines with Desired Structural and Immunological Characteristics

Glycoconjugation is a well-established technology for vaccine development: linkage of the polysaccharide (PS) antigen to an appropriate carrier protein overcomes the limitations of PS T-independent antigens, making them effective in infants and providing immunological memory. Glycoconjugate vaccines have been successful in reducing the burden of different diseases globally. However, many pathogens still require a vaccine, and many of them display a variety of glycans on their surface that have been proposed as key antigens for the development of high-valency glycoconjugate vaccines. CDAP chemistry represents a generic conjugation strategy that is easily applied to PS with different structures. This chemistry utilizes common groups to a large range of PS and proteins, e.g., hydroxyl groups on the PS and amino groups on the protein. Here, new fast analytical tools to study CDAP reaction have been developed, and reaction conditions for PS activation and conjugation have been extensively investigated. Mathematical models have been built to identify reaction conditions to generate conjugates with wanted characteristics and successfully applied to a large number of bacterial PSs from different pathogens, e.g., Klebsiella pneumoniae, Salmonella Paratyphi A, Salmonella Enteritidis, Salmonella Typhimurium, Shighella sonnei and Shigella flexneri. Furthermore, using Salmonella Paratyphi A O-antigen and CRM197 as models, a design of experiment approach has been used to study the impact of conjugation conditions and conjugate features on immunogenicity in rabbits. The approach used can be rapidly extended to other PSs and accelerate the development of high-valency glycoconjugate vaccines.

Therapeutic potential activity of quercetin complexes against Streptococcus pneumoniae

This study investigates quercetin complexes as potential synergistic agents against the important respiratory pathogen Streptococcus pneumoniae. Six quercetin complexes (QCX1-6) were synthesized by reacting quercetin with various metal salts and boronic acids and characterized using FTIR spectroscopy. Their antibacterial activity alone and in synergism with antibiotics was evaluated against S. pneumoniae ATCC 49619 using disc diffusion screening, broth microdilution MIC determination, and checkerboard assays. Complexes QCX-3 and QCX-4 demonstrated synergy when combined with levofloxacin via fractional inhibitory concentration indices ≤ 0.5 as confirmed by time-kill kinetics. Molecular docking elucidated interactions of these combinations with virulence enzymes sortase A and sialidase. A biofilm inhibition assay found the synergistic combinations more potently reduced biofilm formation versus monotherapy. Additionally, gene-gene interaction networks, biological activity predictions and in-silico toxicity profiling provided insights into potential mechanisms of action and safety.

Analysis of Immunobiological Properties of Recombinant Streptococcus pneumoniae Pneumolysin

We compared the immunogenicity of recombinant S. pneumoniae pneumolysin (rPly) when administered with and without Al(OH)3 adjuvant, and evaluated the protective properties of recombinant protein in the active defense experiment. It was shown that double immunization with rPly+Al(OH)3 increases the levels of IgG antibodies in comparison with the control (p<0.01), while triple immunization results in a more significant increase in IgG antibody levels (p<0.001). Double immunization with rPly without Al(OH)3 does not induce a significant increase in antibody levels in comparison with the control, while triple immunization results in a slight but significant increase in antibody levels (p<0.05). The active defense test proved the protective activity of rPly against S. pneumoniae serotype 3 at intranasal infection.

Pneumococcal Vaccination Strategies in 50-Year-Olds to Decrease Racial Disparities: A US Societal Perspective Cost-Effectiveness Analysis

OBJECTIVES

This study assesses the impact of expanding pneumococcal vaccination to all 50-year-olds to decrease racial disparities by estimating from the societal perspective, the cost-effectiveness of 20-valent pneumococcal conjugate vaccine (PCV20) and 15-valent conjugate vaccine followed by 23-valent polysaccharide vaccine (PCV15/PPSV23) for 50-year-olds.

METHODS

A Markov model compared the cost-effectiveness of PCV20 or PCV15/PPSV23 in all general population 50- and 65-years-olds compared with current US recommendations and with no vaccination in US Black and non-Black cohorts. US data informed model parameters. Pneumococcal disease societal costs were estimated using direct and indirect costs of acute illness and of pneumococcal-related long-term disability and mortality. Hypothetical 50-year-old cohorts were followed over their lifetimes with costs and effectiveness discounted 3% per year. Deterministic and probabilistic sensitivity analyses assessed model uncertainty.

RESULTS

In Black cohorts, PCV20 for all at ages 50 and 65 was the least costly strategy and had greater effectiveness than no vaccination and current recommendation strategies, whereas PCV15/PPSV23 at 50 and 65 cost more than $1 million per quality-adjusted life year (QALY) gained compared with PCV20 at 50 and 65. In non-Black cohorts, PCV20 at 50 and 65 cost $62 083/QALY and PCV15/PPSV23 at 50 and 65 cost more than $1 million/QALY with current recommendations, again being more costly and less effective. In probabilistic sensitivity analyses, PCV20 at 50 and 65 was favored in 85.7% (Black) and 61.8% (non-Black) of model iterations at a $100 000/QALY gained willingness-to-pay threshold.

CONCLUSIONS

When considering the societal costs of pneumococcal disease, PCV20 at ages 50 and 65 years in the general US population is a potentially economically viable strategy, particularly in Black cohorts.

Vaccines for the Elderly and Vaccination Programs in Europe and the United States

The share of the elderly population is growing worldwide as life expectancy increases. Immunosenescence and comorbidities increase infectious diseases' morbidity and mortality in older adults. Here, we aimed to summarize the latest findings on vaccines for the elderly against herpes zoster, influenza, respiratory syncytial virus (RSV), COVID-19, and pneumococcal disease and to examine vaccine recommendation differences for this age group in Europe and the United States. PubMed was searched using the keywords "elders" and "vaccine" alongside the disease/pathogen in question and paraphrased or synonymous terms. Vaccine recommendations were also sought in the European and US Centers for Disease Control and Prevention databases. Improved vaccines, tailored for the elderly, mainly by using novel adjuvants or by increasing antigen concentration, are now available. Significant differences exist between immunization policies, especially between European countries, in terms of the recipient's age, number of doses, vaccination schedule, and implementation (mandatory or recommended). Understanding the factors that influence the immune response to vaccination in the elderly may help to design vaccines that offer long-term protection for this vulnerable age group. A consensus-based strategy in Europe could help to fill the gaps in immunization policy in the elderly, particularly regarding vaccination against RSV and pneumococcus.

Vaccines and Monoclonal Antibodies as Alternative Strategies to Antibiotics to Fight Antimicrobial Resistance

Antimicrobial resistance (AMR) is one of the most critical threats to global public health in the 21st century, causing a large number of deaths every year in both high-income and low- and middle-income countries. Vaccines and monoclonal antibodies can be exploited to prevent and treat diseases caused by AMR pathogens, thereby reducing antibiotic use and decreasing selective pressure that favors the emergence of resistant strains. Here, differences in the mechanism of action and resistance of vaccines and monoclonal antibodies compared to antibiotics are discussed. The state of the art for vaccine technologies and monoclonal antibodies are reviewed, with a particular focus on approaches validated in clinical studies. By underscoring the scope and limitations of the different emerging technologies, this review points out the complementary of vaccines and monoclonal antibodies in fighting AMR. Gaps in antigen discovery for some pathogens, as well as challenges associated with the clinical development of these therapies against AMR pathogens, are highlighted.

Analysis of Toxicity of Recombinant Pneumolysin from Streptococcus pneumoniae

We studied toxicity of recombinant Streptococcus pneumoniae pneumolysin protein in experiments on mice and its cytopathogenic effect on cultures of Vero green monkey kidney cells and human lung carcinoma A549 cells in vitro. In vivo and in vitro experiments proved the absence of compromised toxicity and direct cytopathogenic action of the recombinant protein.

Immunogenicity of Current and Next-Generation Pneumococcal Conjugate Vaccines in Children: Current Challenges and Upcoming Opportunities

Global use of pneumococcal conjugate vaccines (PCVs) with increasingly broader serotype coverage has helped to reduce the burden of pneumococcal disease in children and adults. In clinical studies comparing PCVs, higher-valency PCVs have met noninferiority criteria (based on immunoglobulin G geometric mean concentrations and response rates) for most shared serotypes. A numeric trend of declining immunogenicity against shared serotypes with higher-valency PCVs has also been observed; however, the clinical relevance is uncertain, warranting additional research to evaluate the effectiveness of new vaccines. Novel conjugation processes, carriers, adjuvants, and vaccine platforms are approaches that could help maintain or improve immunogenicity and subsequent vaccine effectiveness while achieving broader protection with increasing valency in pneumococcal vaccines.

Identification and Quantification of a Pneumococcal Cell Wall Polysaccharide by Antibody-Enhanced Chromatography Assay

Multivalent pneumococcal vaccines have been developed successfully to combat invasive pneumococcal diseases (IPD) and reduce the associated healthcare burden. These vaccines employ pneumococcal capsular polysaccharides (PnPs), either conjugated or unconjugated, as antigens to provide serotype-specific protection. Pneumococcal capsular polysaccharides used for vaccine often contain residual levels of cell wall polysaccharides (C-Ps), which can generate a non-serotype specific immune response and complicate the desired serotype-specific immunity. Therefore, the C-P level in a pneumococcal vaccine needs to be controlled in the vaccine process and the anti C-P responses need to be dialed out in clinical assays. Currently, two types of cell-wall polysaccharide structures have been identified: a mono-phosphocholine substituted cell-wall polysaccharide C-Ps1 and a di-phosphocholine substituted C-Ps2 structure. In our effort to develop a next-generation novel pneumococcal conjugate vaccine (PCV), we have generated a monoclonal antibody (mAb) specific to cell-wall polysaccharide C-Ps2 structure. An antibody-enhanced HPLC assay (AE-HPLC) has been established for serotype-specific quantification of pneumococcal polysaccharides in our lab. With the new anti C-Ps2 mAb, we herein extend the AE-HPLC assay to the quantification and identification of C-Ps2 species in pneumococcal polysaccharides used for vaccines.

Safety, tolerability and immunogenicity of a novel 24-valent pneumococcal vaccine in toddlers: A phase 1 randomized controlled trial

BACKGROUND

Pneumococcal conjugate vaccines (PCVs) significantly reduced pneumococcal disease burden. Nevertheless, alternative approaches for controlling more serotypes are needed. Here, the safety, tolerability, and immunogenicity of a 24-valent (1/2/3/4/5/6A/6B/7F/8/9N/9V/10A/11A/12F/14/15B/17F/18C/19A/19F/20B/22F/23F/33F) pneumococcal vaccine based on Multiple Antigen-Presenting System (MAPS) technology (Pn-MAPS24v) was assessed in toddlers.

METHODS

In this phase 1, blinded, dose-escalation, active-controlled multicenter study conducted in the United States (September/2020-April/2022), 12-15-month-old toddlers primed with three doses of 13-valent PCV (PCV13) were randomized 3:2 to receive a single dose of one of three Pn-MAPS24v dose levels (1 μg/2 μg/5 μg per polysaccharide) or PCV13 intramuscularly. Reactogenicity (within 7 days), treatment-emergent adverse events (TEAEs, within 180 days), serious/medically attended adverse events (SAEs/MAAEs, within 180 days), and immunogenicity (serotype-specific anti-capsular polysaccharide immunoglobulin G [IgG] and opsonophagocytic activity [OPA] responses at 30 days post-vaccination) were assessed.

RESULTS

Of 75 toddlers enrolled, 74 completed the study (Pn-MAPS24v 1 μg/2 μg/5 μg: 15/14/16, PCV13: 29). Frequencies of local (60 %/67 %/31 %) and systemic events (67 %/67 %/75 %) in the Pn-MAPS24v 1 μg/2 μg/5 μg and the PCV13 (55 %, 79 %) groups were in similar ranges. TEAEs were reported by 47 %/40 %/63 % of Pn-MAPS24v 1 μg/2 μg/5 μg recipients and 52 % of PCV13 recipients. No vaccine-related SAE was reported. At 30 days post-vaccination, for each of the 13 common serotypes, ≥93 % of participants in each group had IgG concentrations ≥0.35 μg/mL; >92 % had OPA titers ≥lower limit of quantitation (LLOQ), except for serotype 1 (79 %). For 7/11 unique serotypes (2/8/9N/11A/17F/22F/33F), at all dose levels, ≥78 % of Pn-MAPS24v recipients in each group had IgG concentrations ≥0.35 μg/mL and 80 %-100 % had OPA titers ≥LLOQ.

CONCLUSIONS

In 12-15-month-old toddlers, a single dose of Pn-MAPS24v showed an acceptable safety profile, regardless of dose level; AEs were reported at similar frequencies by Pn-MAPS24v and PCV13 recipients. Pn-MAPS24v elicited IgG and OPA responses to all common and most unique serotypes. These results support further clinical evaluation in infants.

Time-resolved RNA-seq analysis to unravel the in vivo competence induction by Streptococcus pneumoniae during pneumonia-derived sepsis

Competence development in Streptococcus pneumoniae (pneumococcus) is tightly intertwined with virulence. In addition to genes encoding genetic transformation machinery, the competence regulon also regulates the expression of allolytic factors, bacteriocins, and cytotoxins. Pneumococcal competence system has been extensively interrogated in vitro where the short transient competent state upregulates the expression of three distinct phases of "early," "late," and "delayed" genes. Recently, we have demonstrated that the pneumococcal competent state develops naturally in mouse models of pneumonia-derived sepsis. To unravel the underlying adaptive mechanisms driving the development of the competent state, we conducted a time-resolved transcriptomic analysis guided by the spatiotemporal live in vivo imaging system of competence induction during pneumonia-derived sepsis. Mouse lungs infected by the serotype 2 strain D39 expressing a competent state-specific reporter gene (D39-ssbB-luc) were subjected to RNA sequencing guided by monitoring the competence development at 0, 12, 24, and, at the moribund state, >40 hours post-infection (hpi). Transcriptomic analysis revealed that the competence-specific gene expression patterns in vivo were distinct from those under in vitro conditions. There was significant upregulation of early, late, and some delayed phase competence-specific genes as early as 12 hpi, suggesting that the pneumococcal competence regulon is important for adaptation to the lung environment. Additionally, members of the histidine triad (pht) gene family were sharply upregulated at 12 hpi followed by a steep decline throughout the rest of the infection cycle, suggesting that Pht proteins participate in the early adaptation to the lung environment. Further analysis revealed that Pht proteins execute a metal ion-dependent regulatory role in competence induction.IMPORTANCEThe induction of pneumococcal competence for genetic transformation has been extensively studied in vitro but poorly understood during lung infection. We utilized a combination of live imaging and RNA sequencing to monitor the development of a competent state during acute pneumonia. Upregulation of competence-specific genes was observed as early as 12 hour post-infection, suggesting that the pneumococcal competence regulon plays an important role in adapting pneumococcus to the stressful lung environment. Among others, we report novel finding that the pneumococcal histidine triad (pht) family of genes participates in the adaptation to the lung environment and regulates pneumococcal competence induction.

PCV15, a pneumococcal conjugate vaccine, for the prevention of invasive pneumococcal disease in infants and children

INTRODUCTION

Streptococcus pneumoniae is a causative agent of pneumonia and acute otitis media (AOM), as well as invasive diseases such as meningitis and bacteremia. PCV15 (V114) is a new 15-valent pneumococcal conjugate vaccine (PCV) approved for use in individuals ≥6 weeks of age for the prevention of pneumonia, AOM, and invasive pneumococcal disease.

AREAS COVERED

This review summarizes the V114 Phase 3 development program leading to approval in infants and children, including pivotal studies, interchangeability and catch-up vaccination studies, and studies in at-risk populations. An integrated safety summary is presented in addition to immunogenicity and concomitant use of V114 with other routine pediatric vaccines.

EXPERT OPINION

Across the development program, V114 demonstrated a safety profile that is comparable to PCV13 in infants and children. Immunogenicity of V114 is comparable to PCV13 for all shared serotypes except serotype 3, where V114 demonstrated superior immunogenicity. Higher immune responses were demonstrated for V114 serotypes 22F and 33F. Results of the ongoing study to evaluate V114 efficacy against vaccine-type pneumococcal AOM and anticipated real-world evidence studies will support assessment of vaccine effectiveness and impact, with an additional question of whether higher serotype 3 immunogenicity translates to better protection against serotype 3 pneumococcal disease.

Complete genome analysis of Lactiplantibacillus plantarum VHProbi P06, a novel probiotic that resists Streptococcus pneumoniae in the upper respiratory tract

The purpose of this study was to screen lactic acid bacteria active against Streptococcus pneumoniae and to analyze the genetic basis of their probiotic functions from the genome. We isolated a novel Lactiplantibacillus plantarum VHProbi P06 from pickles, which showed strong antibacterial activity against S. pneumoniae, adhesion to 5-8F cells, and inhibition of S. pneumoniae colonization in the respiratory tract. Genome of VHProbi P06 was analyzed, we found one class II bacteriocin synthesis gene cluster. Genome of the strain contained 42 adhesion-related protein-coding genes, and implicated three exopolysaccharide biosynthesis gene clusters with low homologous to L. plantarum WCFS1. Moreover, VHProbi P06 possessed 3 intact phage regions and 117 Carbohydrate Active Enzyme genes. By comparing the genomes of five L. plantarum, 275 unique genes were found in VHProbi P06. Finally, the gene prediction was verified, the bacteriocin PlnJK produced by P06 was identified by LC-MS/MS, and the laminar exopolysaccharide with a weight-averaged molecular of 125.37 KDa was also found. This study provides a theoretical basis for the application of VHProbi P06 to the upper respiratory tract to resist pathogenic bacteria.

Recent progress in pneumococcal protein vaccines

Pneumococcal infections continue to pose a significant global health concern, necessitating the development of effective vaccines. Despite the progress shown by pneumococcal polysaccharide and conjugate vaccines, their limited coverage and the emergence of non-vaccine serotypes have highlighted the need for alternative approaches. Protein-based pneumococcal vaccines, targeting conserved surface proteins of Streptococcus pneumoniae, have emerged as a promising strategy. In this review, we provide an overview of the advancements made in the development of pneumococcal protein vaccines. We discuss the key protein vaccine candidates, highlight their vaccination results in animal studies, and explore the challenges and future directions in protein-based pneumococcal vaccine.

Serotype replacement and an increase in non-encapsulated isolates among community-acquired infections of Streptococcus pneumoniae during post-vaccine era in Japan

OBJECTIVES

It is feared that the serotype replacement of Streptococcus pneumoniae occurred by the introduction of pneumococcal vaccines as periodical inoculation leads to reduced efficacy of the approved vaccines and altered antimicrobial susceptibility.

METHODS

We determined serotypes of 351 S. pneumoniae isolates collected at a commercial clinical laboratory in Hokkaido prefecture, Japan, from December 2018 to February 2019 by using the polymerase chain reaction procedure of the US Centers for Disease Control and Prevention. Antimicrobial susceptibility and resistance gene profiles were also examined.

RESULTS

Vaccine coverage rates were 7.9% for 13-valent conjugate vaccine, and 32.5% for 23-valent polysaccharide vaccine, respectively. Non-typable strains were 19.7%. cpsA-positive isolates (group I), and null capsule clade (NCC)1, NCC2 and NCC3 (group II) comprised 31.3%, 28.4%, 32.8%, and 7.5% of the 69 non-typable strains, respectively. No penicillin-resistant/intermediate isolates were found; however, serotypes 35B and 15A/F showed low susceptibility to β-lactams. Only five strains (1.4%) were levofloxacin-resistant, and all were from the older persons, and three strains were serotype 35B.

CONCLUSION

The progression of serotype replacement in non-invasive pneumococcal infections has occurred during the post-vaccine era in Japan, and non-encapsulated isolates, such as NCC, have increased. Antimicrobial susceptibility is not worsened.

Emerging vaccine strategies against the incessant pneumococcal disease

The incidence of invasive pneumococcal disease (IPD) caused by infection with the pathogen Streptococcus pneumoniae (Spn) has been on a downward trend for decades due to worldwide vaccination programs. Despite the clinical successes observed, the Center for Disease Control (CDC) reports that the continued global burden of S. pneumoniae will be in the millions each year, with a case-fatality rate hovering around 5%. Thus, it is a top priority to continue developing new Spn vaccination strategies to harness immunological insight and increase the magnitude of protection provided. As emphasized by the World Health Organization (WHO), it is also crucial to broaden the implementation of vaccines that are already obtainable in the clinical setting. This review focuses on the immune mechanisms triggered by existing pneumococcal vaccines and provides an overview of the current and upcoming clinical strategies being employed. We highlight the associated challenges of serotype selectivity and using pneumococcal-derived proteins as alternative vaccine antigens.

Exploring the variables influencing the immune response of traditional and innovative glycoconjugate vaccines

Vaccines are cost-effective tools for reducing morbidity and mortality caused by infectious diseases. The rapid evolution of pneumococcal conjugate vaccines, the introduction of tetravalent meningococcal conjugate vaccines, mass vaccination campaigns in Africa with a meningococcal A conjugate vaccine, and the recent licensure and introduction of glycoconjugates against S. Typhi underlie the continued importance of research on glycoconjugate vaccines. More innovative ways to produce carbohydrate-based vaccines have been developed over the years, including bioconjugation, Outer Membrane Vesicles (OMV) and the Multiple antigen-presenting system (MAPS). Several variables in the design of these vaccines can affect the induced immune responses. We review immunogenicity studies comparing conjugate vaccines that differ in design variables, such as saccharide chain length and conjugation chemistry, as well as carrier protein and saccharide to protein ratio. We evaluate how a better understanding of the effects of these different parameters is key to designing improved glycoconjugate vaccines.

Glycoconjugate vaccines against antimicrobial resistant pathogens

INTRODUCTION

Antimicrobial resistance (AMR) is responsible for the death of millions worldwide and stands as a major threat to our healthcare systems, which are heavily reliant on antibiotics to fight bacterial infections. The development of vaccines against the main pathogens involved is urgently required as prevention remains essential against the rise of AMR.

AREAS COVERED

A systematic research review was conducted on MEDLINE database focusing on the six AMR pathogens defined as ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Escherichia coli), which are considered critical or high priority pathogens by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC). The analysis was intersecated with the terms carbohydrate, glycoconjugate, bioconjugate, glyconanoparticle, and multiple presenting antigen system vaccines.

EXPERT OPINION

Glycoconjugate vaccines have been successful in preventing meningitis and pneumoniae, and there are high expectations that they will play a key role in fighting AMR. We herein discuss the recent technological, preclinical, and clinical advances, as well as the challenges associated with the development of carbohydrate-based vaccines against leading AMR bacteria, with focus on the ESKAPE pathogens. The need of innovative clinical and regulatory approaches to tackle these targets is also highlighted.

A review of evidence for pneumococcal vaccination in adults at increased risk of pneumococcal disease: risk group definitions and optimization of vaccination coverage in the United Kingdom

INTRODUCTION

Pneumococcal disease (PD) significantly contributes to morbidity and mortality, carrying substantial economic and public health burden. This article is a targeted review of evidence for pneumococcal vaccination in the UK, the definitions of groups at particular risk of PD and vaccine effectiveness.

AREAS COVERED

Relevant evidence focusing on UK data from surveillance systems, randomized controlled trials, observational studies and publicly available government documents is collated and reviewed. Selected global data are included where appropriate.

EXPERT OPINION

National vaccination programs have reduced the incidence of vaccine-type PD, despite the rising prominence of non-vaccine serotypes in the UK. The introduction of higher-valency conjugate vaccines provides an opportunity to improve protection against PD for adults in risk groups. Several incentives are in place to encourage general practitioners to vaccinate risk groups, but uptake is low-suboptimal particularly among at-risk individuals. Wider awareness and understanding among the public and healthcare professionals may increase vaccination uptake and coverage. National strategies targeting organizational factors are urgently needed to achieve optimal access to vaccines. Finally, identifying new risk factors and approaches to risk assessment for PD are crucial to ensure those at risk of PD can benefit from pneumococcal vaccination.