Infection from Streptococcus pneumoniae can lead to serious complications, such as meningitis and pneumonia, in children under 2 years of age, older adults, and immunocompromised populations. Conjugate vaccines against the pathogen have been licensed for the prevention of invasive pneumococcal disease. Conjugate vaccine development is an involved process demanding extensive characterization of both the polysaccharide (PS) and protein (Pr) moieties in complex structures. One powerful tool in our analytical tool kit that can shed light on various analytical attributes of conjugate vaccines, such as molecular weight and composition and conjugation efficiency, is the size-exclusion chromatography-multi-angle light scattering detector (SEC-MALS) technique. Herein, we demonstrate the applicability of the SEC-MALS approach for pneumococcal conjugate vaccine product characterization. Capsular polysaccharides for serotypes (STs) 1, 3, 5, 10 A, 18 C, 24 F, and 33 F conjugated to rCRM197 carrier protein were chosen for this study. The technique was very straightforward, with a high degree of accuracy (>90% based on standards) and repeatability (<2% RSD) for conjugate molar mass measurements. In addition, leveraging the capability of SEC-MALS for compositional analysis, we were able to get detailed information on the molecular assembly and conformation of the conjugates and further tweak the conjugation process to yield conjugates of a desired molar mass. Thus, this study highlights the usefulness of the SEC-MALS technique for in-depth conjugate vaccine biophysical characterization, which is critical for achieving optimal product attributes, driving manufacturing consistency and vaccine potency.

Lyme disease is a growing public health concern that is geographically focused in regions where ticks that carry the causative bacteria, Borrelia burgdorferi sensu lato (s.l.), are endemic. Outer surface protein A (OspA) is expressed by B. burgdorferi s.l. spirochetes during the tick phase and OspA antibodies introduced during tick feeding can block transmission and prevent B. burgdorferi infection. Candidate Lyme disease vaccine VLA15 is comprised of the C-terminal domains of the six B. burgdorferi s.l. OspA serotypes (ST) prevalent in North America and Europe. We report herein that non-human primates immunized with VLA15 were protected against challenge with Ixodes scapularis ticks bearing B. burgdorferi sensu stricto (s.s.) (OspA ST1). Levels of residual B. burgdorferi s.s. tick colonization were reduced in ticks that fed on VLA15-immunized primates compared to those immunized with full length-OspA ST1 (FL-OspA) at a point when OspA-binding IgG levels were similar. Furthermore, monoclonal antibodies targeting the C-terminal half of OspA, elicited by FL-OspA immunization in primates, were more effective at complement-mediated bactericidal killing in vitro and clearance of spirochetes in ticks versus those directed against other parts of the protein.

Legionella species are ubiquitous bacteria found worldwide in water, moist environments, soils, and compost. Infection occurs through the inhalation of aerosols, leading to either Pontiac fever or Legionnaires’ disease (LD). Current routine diagnostics typically combine culture-based isolation with Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) for species identification and the Latex Agglutination Test (LAT) for serotyping. However, this workflow is fragmented: MALDI-TOF MS lacks serogroup-specific resolution, while LAT relies on subjective visual interpretation. Therefore, this study evaluated Fourier-transform infrared spectroscopy (FT-IR) as a rapid, high-resolution typing method for Legionella isolates to assess its potential as a single-step diagnostic tool. A total of 200 clinical and environmental Legionella isolates were analyzed using FT-IR, including L. pneumophila serogroups (SG) 1–15 and various non-pneumophila species. Spectral data were analyzed using Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA). While MALDI-TOF MS provided accurate species identification, FT-IR spectroscopy demonstrated superior typing capabilities by successfully distinguishing L. pneumophila SG 1 distinct from the SG 2–15 complex and allowing for clear discrimination of most non-pneumophila species. Additionally, FT-IR resolved isolates that showed ambiguous or non-reactive results in LAT. These findings demonstrate that FT-IR overcomes the serotyping limitations of MALDI-TOF MS and offers a more objective, cost-efficient extension to the current multi-step routine, potentially closing the diagnostic gap between simple species identification and deep strain characterization.

Pneumococcal conjugate vaccines (PCVs) were implemented in the childhood vaccination program of the Community of Madrid (CM) in 2007, but despite very high vaccination coverage since then, increasing trends in invasive pneumococcal disease (IPD) have been observed in recent years. Epidemiological, clinical, and microbiological data from the Notifiable Disease Surveillance System on IPD cases in children aged 0-17 years in the CM during the period 2007-2024 were analysed. A descriptive analysis was conducted by sex, age-group, clinical presentation, laboratory results, prior vaccination, and antibiotic resistance. Incidence rates (IRs) and IR ratios (IRRs) were calculated overall and by serotypes (STs) covered by each vaccine and the most relevant STs using 2015-2019 as reference period. Between 2007 and 2024, 1,856 cases of IPD were notified: 1,052 (56.7%) in boys and 804 (43.3%) in girls. By age-group, there were 431 cases (23.2%) in < 1 year, 994 (53.6%) in those aged 1-4 years, and 431 (23.2%) in those aged 5-17 years. PCV7, PCV13, PCV15, and PCV20 vaccine included STs IRs increased 7.0, 2.9, 2.3, and 1.5 times, respectively (all P < 0.05), in 2024. STs 24A, 14, 15A, 10A, and 3 IRs also increased (IRRs: 30.5, 17.8, 2.8, 2.7, and 2.6, respectively; all P < 0.05). No strains of the STs 1, 5, or 7F were detected in 2024, and STs 19A decreased to 2.2%. IRs for children and adolescents increased between 2022 and 2024 in the CM, associated to the rise of some PCVs STs, as ST14, while the still persistent ST3 started to decline after 2022.

BackgroundAntimicrobial resistance (AMR) is a global public threat. Pneumococcal conjugate vaccines (PCVs) contribute both directly and indirectly to combating AMR. The US Advisory Committee on Immunization Practices (ACIP) recommends PCV21 for adults ≥50 years (yrs). PCV21 provides serotype (ST) coverage for 83% of invasive pneumococcal disease (IPD) with 30% of cases caused by eight STs not included in other licensed vaccines. It is important to monitor S. pneumoniae epidemiology and AMR trends to understand the impact of new PCVs. We evaluated ST distribution and antimicrobial susceptibility of S. pneumoniae obtained from adult patients (≥18 yrs) with invasive pneumococcal disease (IPD) and non-IPD during 2022-2023.Methods: S. pneumoniae isolates causing IPD and non-IPD were collected from 30 sites in 19 states between 2022 and 2023. Whole genome sequencing of the S. pneumoniae isolates was performed using Illumina NextSeq sequencers (Illumina, San Diego, CA, USA). Capsular locus sequences were extracted and analyzed using the PneumoCaT database for serotype determination. Antimicrobial susceptibility tests were performed using the broth microdilution method.ResultsAmong the 675 S. pneumoniae isolates, ST3 was the most common (12.3%), followed by 35B (9.8%), 9N (6.8%), 22F (6.4%), 11A (6.1%), 19F (6.1%), 23A (5.6%), and 15A (5.2%), with PCV21 covering 83% of isolates compared to 50% for PCV20. PCV20 STs demonstrated susceptibility to penicillin (80.7%), ceftriaxone (99.4%), and azithromycin (63.5%). In contrast, PCV21 STs demonstrated lower susceptibility to penicillin (65.3%), ceftriaxone (98.8%), and azithromycin (53.7%). PCV21 unique STs demonstrated the lowest susceptibility to penicillin (52%), azithromycin (49.5%), and doxycycline (77.8%) compared to other vaccine types. Serotypes, 35B (3%), 23A (52.6%), and 23B (52.6%) demonstrated the lowest penicillin susceptibility.ConclusionNewly introduced PCVs include several serotypes associated with high rates of AMR, particularly PCV21 whose unique serotypes had the lowest penicillin susceptibility. Thus, new PCVs have the potential to help reduce AMR. However, continued surveillance is needed to evaluate trends in the impact of PCVs on ST epidemiology and AMR over time.DisclosuresMekki Bensaci, PhD, Merck: Employee Karri A. A. Bauer, PharmD, Merck: Employee Kenneth Klinker, PharmD, Merck: Employee Jason Cota, PharmD, Merck: Employee Pavel Prusakov, PharmD, Merck: Employee Rodrigo E. Mendes, PhD, GSK: Grant/Research Support|Shionogi & Co., Ltd.: Grant/Research Support|United States Food and Drug Administration: FDA Contract Number: 75F40123C00140 Kristen Feemster, MD, Merck: Employee

Streptococcus pneumoniae (Sp) is an opportunistic pathogen that colonizes the mucosal surfaces of the human upper respiratory tract. While transcriptomic studies of Sp have become more common, most have focused on laboratory-adapted strains such as D39 or TIGR4. These strains, though widely used in research, may not fully capture the biology of clinical isolates, particularly the hypervirulent serotype 1 (S1). S1 is clinically significant due to its association with invasive disease, epidemic outbreaks and a distinct global distribution, particularly in regions with a high pneumococcal disease burden. Unlike many other serotypes, S1 is frequently linked to hypervirulence and a propensity for rapid spread, making it a high-priority target for understanding the molecular mechanisms underpinning pneumococcal pathogenesis. In this study, we conducted a comprehensive in vitro transcriptomic analyses of Sp S1 strains, positioning this work as a valuable resource for the pneumococcal research community. Using a straightforward approach, we cultured three distinct S1 strains - ST306, ST217 and ST615, representing European, African and South American S1 lineages, respectively - in Brain Heart Infusion medium and compared transcriptomic profiles during exponential growth to those of the well-characterized laboratory-adapted D39 strain. Our analysis revealed significant differential expression of 292 genes in all three S1 isolates compared to D39. Among these, 151 genes had higher expression, including those involved in competence pathways and purine metabolism, while 141 genes exhibited lower expression, particularly those linked to lactose metabolism and iron/amino acid transport. These findings underscore the distinct molecular features of S1 strains, which likely contribute to the unique pathogenic properties of this serotype. The identification of the distinct transcriptional signatures of hypervirulent S1 strains paves the way for future efforts to design targeted therapeutics against pneumococcal S1 infections.

Introduction: Streptococcus suis is a zoonotic pathogen of great relevance to the swine industry, characterized by high genetic diversity and multiple serovars (SVs) with varying clinical prevalence. Biofilm formation represents a key factor in its virulence, antimicrobial resistance and infection persistence. Methods: We integrated gene expression profiling of biofilm-associated genes by RT-qPCR and antimicrobial susceptibility in planktonic and mature biofilm against five antibiotics in S. suis field isolates belonging to SV1, SV2, SV7 and SV9. Results: Expression of quorum sensing and adhesion genes (luxS, fbps, sadP and srtA) was significantly higher in SV2, the poorest biofilm formers, and inversely correlated with biofilm biomass, suggesting these factors act during early biofilm establishment. Correlation analysis indicated coordinated regulation among genes involved in quorum sensing, adhesion and capsule synthesis. Antimicrobial susceptibility testing revealed a high frequency of non-wild type phenotypes in planktonic cells for tetracycline, erythromycin and clindamycin (>80%), while ampicillin and ciprofloxacin were less frequent. Mature biofilms exhibited a significant increase in antimicrobial tolerance for all antibiotics tested, with SV2 showing the greatest susceptibility. Conclusions: These data highlight serovar-specific biofilm regulation patterns and enhanced drug tolerance in established S. suis biofilms.

Hypervirulent serotype 1 pneumococci display high levels of nasal shedding and rapid onward transmission.

Background/Objectives: Group B Streptococcus (GBS) is a significant cause of perinatal infection in neonates and infants. Complications could include neonatal sepsis and meningitis, preterm birth, stillbirth, or death. Though no GBS vaccine is currently licensed, maternal immunization is expected to be a highly effective strategy to address invasive GBS disease—particularly in low- and middle-income countries (LMICs), where the disease burden is the greatest and access to existing interventions is limited. In this study, we present a novel hexavalent GBS vaccine candidate with a unique combination of serotypes (ST)—Ia, Ib, II, III, V, and VII—that could be an efficacious and cost-effective intervention, with the broadest coverage of 99% against circulating serotypes globally. Methods: The 6-valent conjugate vaccine candidate, GBS-06, is developed using a novel approach by linking the six polysaccharides (PS) to recombinant cross-reactive material 197 (rCRM197) carrier protein derivatized with a hydrazide-polyethylene glycol-hydrazide (HZ-PEG-HZ) linker. A repeat-dose GLP toxicology study with GBS-06 was conducted at the highest clinical dose of 20 µg in rabbits with saline as the placebo control. Results: The results reveal induction of robust anti-capsular polysaccharide-specific IgG responses against each of the six serotypes after each dose with the highest antibody GMCs at Day 49 following the third dose. Conclusions: Hence, this work is the first demonstration of strong immunogenicity achieved using a linker (HZ-PEG-HZ) for GBS glycoconjugate vaccine development. The positive data from the study have strong implications in the advancement of the candidate for evaluation in clinical trials and provide a licensure pathway for maternal immunization.

BackgroundIn 2021–2022, Queensland, Australia observed an increase in Legionnaire's disease cases, predominantly due to Legionella longbeachae. This study assessed seroprevalence at time points 2016 and 2023, representing before and after the higher incidence and explored if demographic, environmental and geographical factors associated with legionellosis seroprevalence.MethodsA total of 1001 human plasma samples (496 from 2016/505 from 2023) were analysed for the presence of Legionella antibodies (IgG) using indirect immunofluorescence assays. Primary screens detected IgG to L. pneumophila serogroups (SG) 1–6, SG 7–14, or “other” Legionella spp. Samples positive for “other” underwent secondary screening for L. longbeachae SG 1 and 2. A chi-square test assessed associations between seroprevalence and demographics, while a generalized linear model evaluated rainfall, temperature, and land cover associations.ResultsWhile total Legionella seroprevalence remained stable (32.46% vs 32.28%) between 2016 and 2023, we observed a decrease in L. pneumophila (SG 1–6: 19%–13% [P = .0182] and SG 7–14: 24%–18% [P = .0257]) and an increase in L. longbeachae (1%–3% [P = .0355]) seropositivity. L. pneumophila seroprevalence positively associated with higher rainfall and land cover, with croplands and urban areas showing increased prevalence.ConclusionsBetween 2016 and 2023, total Legionella seroprevalence remained unchanged. However, rainfall and specific land cover types were positively associated with seropositivity for certain Legionella spp. This study highlights the importance of assessing Legionella exposure risks in high-risk areas, particularly for vulnerable individuals such as the elderly, immunosuppressed, or those with co-morbidities.

Identification of novel Listeria monocytogenes serotype 4h with specific antisera against wall teichoic acid.

Immunogenicity and safety of different immunisation schedules of the VLA15 Lyme borreliosis vaccine candidate in adults, adolescents, and children: a randomised, observer-blind, placebo-controlled, phase 2 trial.

Abstract Background In France, effective pneumococcal conjugate vaccines (PCVs) and the high vaccine coverage rate (VCR) of 95% have led to a substantial decline in pediatric invasive pneumococcal disease (IPD) incidence. PCV13 is currently used in a 2+1 dosing regimen; PCV15 and PCV20 are expected to be introduced soon. Breakthrough IPD (bIPD), defined as fully vaccinated individuals who develop vaccine type IPD, persists for some PCV13 serotypes (STs). As ST-specific immune responses decrease with increased PCV valency, understanding the potential impact of PCV15 and PCV20 on PCV13 STs bIPD is important. IPD Breakthrough disease incidence per 100,000 children under two years of age. Methods We evaluated the expected impact of PCV15 in a 2+1 regimen, or PCV20 in either a 2+1 or 3+1 regimen on PCV13 ST bIPD incidence in children &amp;lt; 2 years of age over 5 and 10 years using a compartmental dynamic transmission model. The model incorporated historical PCV introductions and calibrated age- and ST-specific IPD data spanning 2000-2019. Predicted ST-specific vaccine effectiveness (VE) for PCV15 and PCV20 were used1,2. Incidence of bIPD was evaluated across 3 ST groupings: PCV7 STs, PCV13-non-ST3 STs, and ST3. VCRs were maintained at 95% in the model. Results were compared to 2019 IPD incidence. Results Using previously published ST-specific VE predictions, routine use of PCV15 in children led to fewer PCV13 ST bIPD cases than use of PCV20. PCV15 reduced bIPD incidence in all 3 ST groups (-30% to -87%, Table 1). The introduction of PCV20 in a 2+1 or 3+1 regimen resulted in more bIPD cases from PCV7 and PCV13-non-ST3 STs. ST3 bIPD was maintained at current levels in a 2+1 regimen but decreased with PCV20 in a 3+1 regimen. Conclusion Using published predicted VEs, implementation of PCV20 in a 2+1 or 3+1 regimen led to a substantial increase in bIPD incidence of PCV7 and PCV13 non-ST3 STs relative to currently used PCV13 2+1 regimen. PCV15 in a 2+1 regimen reduced bIPD incidence across all ST groups, with the largest impact on ST3. As higher-valent PCVs are introduced, the impact of their reduced ST-specific immune responses, and therefore lower predicted VE on pediatric PCV13 STs, should be weighed against the benefits of additional ST coverage. 1Ryman J, et al. Expert Rev Vaccines. 2024;23(1):60-68. 2Ryman J, et al. Expert Rev Vaccines. 2024;23(1):467-473. Disclosures Kevin Bakker, PhD, Merck &amp; Co., Inc.: Grant/Research Support|Merck &amp; Co., Inc.: Stocks/Bonds (Public Company) Rachel Oidtman, PhD, Merck &amp; Co., Inc.: Full time employee|Merck &amp; Co., Inc.: Stocks/Bonds (Public Company) Giulio Meleleo, PhD, Merck &amp; Co., Inc.: Vendor Priscilla Velentgas, PhD, Merck &amp; Co., Inc., Rahway, NJ, USA: Grant/Research Support|Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Public Company) Kenneth Klinker, PharmD, Merck &amp; Co., Inc., Rahway, NJ, USA: Grant/Research Support|Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Public Company) Natalie Banniettis, MD, Merck &amp; Co., Inc., Rahway, NJ, USA: Grant/Research Support|Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Public Company) Kristen A. Feemster, MD, MPH, MSHPR, FAAP, Merck &amp; Co., Inc., Rahway, NJ, USA: Grant/Research Support|Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Public Company) Jessica Weaver, PhD, MPH, Merck &amp; Co. Inc.: Employment|Merck &amp; Co. Inc.: Stocks/Bonds (Public Company)

Abstract Background Preventing vaccine-derived polio is crucial, yet polio evolution and transmission mechanisms remain unclear. Our previous study in Mayan infants found that preexisting OPV-induced polio antibodies did not affect S3 immunogenicity. We now explore if viral mutations differ in those with and without preexisting antibodies. Using NGS, we identify and characterize vaccine poliovirus’ mutation patterns from stool sample isolates post one and two OPV doses. We hypothesize that OPV-induced intestinal immunity will correlate with increased mutations after the 2nd dose compared to the 1st. S1 Canonical Mutations vs. Mutation Rates Post 1st and 2nd Dose of 116 OPV Isolates Methods 179 OPV samples from a previous study were used. Participants received an OPV dose at study weeks 1 and 9 with stool samples collected at weeks 0, 1, 2, 4, 6, 8, 9, 10, 14, 16, and 17. A multiplex qPCR was used to determine serotype positivity. PCR amplicons created from stool viral RNA were purified and sequenced. Sequences were analyzed using the Illumina workflow nf-core/viralrecon (ver 2.5) and R (ver. 4.2.2). S2 Canonical Mutations vs. Mutation Rates Post 1st and 2nd Dose of 82 OPV Isolates Results 303 isolates were sequenced: 127 serotype 1 (S1), 91 serotype 2 (S2) and 85 serotype 3 (S3); 35 from week 0, 187 from weeks 1-8 (post dose 1: D1) and 81 from weeks 9-17 (post dose 2: D2). S1 and S2 in D2 showed significantly higher mutation rates (% of samples with mutation(s) at a given genome location) at all positions (S1 p = 0.0014, S2 p &amp;lt; 2.2e-16), while S3 showed no difference (p = 0.9899). For canonical mutations, S1 D2 had higher mutations at G480A (D1 65.3% vs. D2 68.6%) and A2795G (D1 8.5% vs. D2 10.5%), but 0% at A2438T while D1 had 6%; no mutations were seen at T525C and T2879C. For S2, D2 had higher mutations at A481G (D1 11.4% vs. D2 16.7%), with no mutations at T2909C in either set. In S3, D2 showed higher mutations at T472C (D1 36.6% vs. D2 46.4%), but lower mutations at C2493T (D1 26.9% vs. D2 16.7%) and T2034C (D1 3.8% vs. D2 0%). S3 Canonical Mutations vs. Mutation Rates Post 1st and 2nd Dose of 70 OPV Isolates Conclusion Overall, isolates post the 2nd OPV dose showed significantly higher mutation rates for S1 and S2, but not for S3. Preexisting antibodies may be associated with higher mutation rates and long-term likelihood of neurovirulent reversion. Serotype differences may be related to shedding patterns and other serotype specific characteristics. Further studies are planned to understand the impact of pre-existing intestinal immunity on polio viral mutation and evolution. Disclosures Yvonne A. Maldonado, MD, Pfizer: Grant/Research Support|Pfizer: Member, DSMB

Abstract Background Adults with certain underlying chronic medical conditions are at increased risk of pneumococcal disease (PD). V116 is an investigational, 21-valent, adult-specific pneumococcal conjugate vaccine (PCV) containing the most prevalent serotypes (STs) associated with PD in adults from regions with established pediatric vaccination programs. The Phase 3 STRIDE-8 study (NCT05696080) evaluated the safety and tolerability of V116 in adults 18–64 years of age at increased risk of PD. Immunogenicity of V116 was compared with sequential administration of 15-valent PCV (PCV15) followed by 23-valent pneumococcal polysaccharide vaccine (PPSV23). Methods Pneumococcal vaccine-naïve participants with ≥1 underlying chronic medical conditions (including diabetes mellitus, heart disease, kidney disease, liver disease, and lung disease) at increased risk of PD were randomized 3:1 to receive one dose of V116 on Day 1 followed by placebo at Week 8 or one dose of PCV15 on Day 1 followed by one dose of PPSV23 at Week 8. Safety was evaluated as the proportion of participants with adverse events (AEs). Immunogenicity was assessed by serotype-specific opsonophagocytic activity (OPA) geometric mean titers (GMTs) and immunoglobulin G (IgG) geometric mean concentrations (GMCs) for STs in V116 at baseline (Day 1) and 30 days post-vaccination (Day 30 for V116 + placebo and Week 12 for PCV15 + PPSV23). Results Of 518 participants randomized, 516 were vaccinated and received either V116 (n=386) or PCV15 (n=130) on Day 1; 96.7% of participants completed the trial. One or more AEs occurred in 265 (68.7%) and 118 (90.8%) participants vaccinated with V116 + placebo or PCV15 + PPSV23, respectively (Table 1). V116 was immunogenic for all 21 STs based on OPA GMTs, with comparable responses to PCV15 + PPSV23 for the 13 STs common to V116 and PCV15 + PPSV23, and higher responses for the eight STs unique to V116 (Figure 1). IgG GMCs were consistent with OPA GMTs (Figure 2). Conclusion V116 is well tolerated and immunogenic in adults 18–64 years of age at increased risk of PD, with comparable immune responses to PCV15 + PPSV23 for common STs and higher immune responses for unique STs. These findings support V116 as a novel population-specific vaccine for the prevention of PD in adults with chronic medical conditions at increased risk of PD. Disclosures Paul Scott, MD, Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Jayani Pathirana, MBBS, Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Michael Nissen, MD, CSL Seqirus: Education|GSK: Education|Pfizer: Education Amy Falk Russell, MS, Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Doreen Fernsler, BS, Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Muhammad Waleed, PhD, Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Jianing Li, PhD, Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Ulrike K. Buchwald, MD, Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Heather L. Platt, MD, Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company)

Abstract Background Despite the success of pediatric pneumococcal conjugate vaccine (PCV) programs in the US, acute respiratory illness, including acute otitis media (AOM) due to Streptococcus pneumoniae (SPN) persists. PCV13 has been recommended for pediatric routine use since 2010. With recent adoption of higher-valency PCVs, there is a continued need to survey pathogens causing AOM in children.Table 1:Bacterial Results of Nasal Specimens in Children 6-35 Months Diagnosed with Acute Otitis Media (Cohorts 1&amp;2) or Upper Respiratory Infection (Cohort 3) Methods Children aged 6 to 35 months diagnosed with AOM (Cohort 1 &amp; 2) and upper respiratory infection (URI, Cohort 3) were enrolled from primary care and ENT practices in Pittsburgh, PA. Nasal specimens (nasopharyngeal or mid-turbinate) were collected for all children. Middle ear fluid (MEF) specimens were collected by tympanocentesis for children enrolled in Cohort 1. MEF and nasal specimens were cultured for SPN, Hemophilus influenzae (Hflu), and Moraxella catarrhalis (Mcat). Serotypes (ST) and susceptibility testing were determined for SPN isolates.Table 2:Correlation of Bacterial Cultures of Nasal and Middle Ear Fluid (MEF) Specimens (n=72 pairs) in Children 6-35 Months Diagnosed with Acute Otitis Media (Cohort 1) Results From October 2019 to January 2024, 545 children were enrolled (Cohort 1: n=72; Cohort 2: n=322; Cohort 3: n=151). Among nasal specimens from children with AOM (n=394), SPN, Hflu and Mcat were detected in 47%, 44% and 70%, respectively. In MEF specimens from children with AOM (n=72), SPN, Hflu and Mcat were detected in 15%, 54% and 17% respectively. Nasal-MEF pairs were concordant for 79% (57/72). Children with Hflu had higher rates of nasal-MEF concordance than children with SPN or Mcat. In nasal specimens from children with URI (n=151), SPN, Hflu and Mcat were detected in 36%, 18% and 54%, respectively. In nasal specimens, co-detection of bacterial pathogens occurred more often in those with AOM (220/394, 56%) than URI (49/151, 32%). Of the SPN ST results available (nasal: n=174; MEF: n=8), 35B, 15B, 3, and 15C were most frequent; 8% of nasal and 50% of MEF were PCV13 STs. SPN was found simultaneously in the nasal-MEF pairs of 10/72 children, of which STs are available for 7 pairs; 6/7 pairs agreed, 1 disagreed (nasal:35B and MEF:3). SPN nonsusceptible to penicillin were uncommon (2% of nasal and 9% of MEF isolates).Figure 1:Distribution of S. pneumoniae Serotypes by Isolate Source Conclusion STs 3 and 19A, included in PCV13, were responsible for half of SPN isolates found in MEF of children with AOM. Continued surveillance is still warranted to guide vaccine development and therapeutic decision-making for children. Disclosures Judith M. Martin, MD, Centers for Disease Control and Prevention: funding to the institution to support this work|Centers for Disease Control and Prevention: funding to the institution for unrelated work|Merck, Sharp and Dhome: funding to the institution to support this work|Moderna: funding to the institution for unrelated work|NIH: funding to the institution for unrelated work Matthew C. Lee, BA, Centers for Disease Control and Prevention (CDC): Grant paid to the institution|Merck Sharpe &amp; Dohme: Grant paid to the institution Jessica Weaver, PhD, MPH, Merck &amp; Co. Inc.: Employment|Merck &amp; Co. Inc.: Stocks/Bonds (Public Company) Meghan White, PharmD, Merck Sharp &amp; Dohme, LLC: Employee|Merck Sharp &amp; Dohme, LLC: Stocks/Bonds (Public Company) Alejandro Hoberman, MD, Kaizen Biosciences: Advisor/Consultant|Kaizen Biosciences: Pediatric oral suspension formulation of amoxicillin-clavulanate potassium and the method for use.|Kaizen Biosciences: Ownership Interest|Not licensed: Method and apparatus for aiding diagnosis of otitis media by classifying tympanic membrane images.

BackgroundSubstantial reductions in invasive pneumococcal disease (IPD) occurred during the COVID-19 pandemic. Disease incidence then increased in 2022. We assessed whether the epidemiology of IPD had changed in 2022/3 when compared to that prior to the pandemic.Figure 1:Incidence of IPD in adults by age group, Toronto and Peel region, Canada, 2015-2023MethodsTIBDN performs population-based surveillance for IPD in Toronto/Peel region (pop 4.5M). Microbiology laboratories serving area residents report sterile site isolates of S. pneumoniae; annual audits ensure completeness. Isolates are serotyped at Canada's National Microbiology Laboratory. Population data estimates are from Statistics Canada. We compared IPD in adults occurring in 2017-2019 to that in 2022-23.Figure 2:Proportion of infecting strains of serotypes included in PCV20 or PCV21/V116, by age group, 2016-2023, TIBDNEach panel shows, for a different age group, the change over time of the proportion of IPD caused by isolates of serotypes included in PCV20 (orange dashed line), and PCV21(V116) (the solid blue line).ResultsOverall, 1047 IPD cases occurred in 2017-19 and 613 in 2022-23. Serotype is available for 970 (93%) and 562 (92%) of cases, and clinical information for 993 (95%) and 537 (88%) cases, respectively. Annual IPD incidence in all age groups declined during the pandemic, but has returned to 2019 rates (Figure 1). In 2022-23 compared to 2017-19, the median age of IPD patients did not differ [64y (IQR 51-75) vs 65y (52-76), P=.39] but males were more commonly affected (62% v 56%, P=.03) as were patients with cardiac (22% v 17%, P=.01) and renal (12% v 7.3% P=.007) disease (Table). Long term care (LTC) residents were less likely to have IPD in 2022-23 (1.3% v 4.5%, P< .0001). Outcomes (hospital admission, ICU admission, 30 day mortality) did not differ (Table). Between 2017-2019 and 2022-23, the proportion of IPD isolates of serotypes (STs) in PCV7 increased from 10.8% (163/970) to 18% (103/562), P< .001, while proportion of STs in PCV13 declined from 21% (207) to 16% (90), P=.01, resulting in no change in the proportion of STs in PCV20 (67% to 69%, P=.31), but a decline in the proportion in PCV21(V116) (79% to 71%, P< .001). The decline in PCV21(V116) ST proportions was more prominent in younger adults (Figure 2).Table.Characteristics of adults with IPD pre- (2017-2019) and post- (2022-2023) pandemic, Toronto and Peel Region, CanadaConclusionThe incidence of IPD in adults has returned to pre-pandemic levels, but differences in epidemiology persist: some (reduced disease in women and LTC residents) may be due to residual changes associated with the pandemic. Currently, PCV20 and PCV21(V116) have similar coverage in adults < 75 yrs of age in our population. Whether these changes will persist is uncertain.DisclosuresAllison McGeer, MD, AstraZeneca: Honoraria|GSK: Honoraria|Merck: Honoraria|Moderna: Honoraria|Novavax: Honoraria|Pfizer: Grant/Research Support|Pfizer: Honoraria|Roche: Honoraria|Seqirus: Grant/Research Support|Seqirus: Honoraria

Abstract Background Pneumococcal conjugate vaccines (PCVs) were first introduced in the pediatric United Kingdom (UK) immunization program in 2006 and subsequently led to a significant decline in invasive pneumococcal disease (IPD) for vaccine type serotypes (STs). Although pediatric PCVs provide some indirect protection to adults, a significant IPD burden remains in older adults. Here, we compared three adult vaccines in the 65+ year-old population: the current recommendation of PPV23, the recently licensed-in-adults PCV20, and a new adult-focused 21-valent PCV, V116. All scenarios assumed continued PCV13 vaccination in pediatrics. Methods A population-level compartmental dynamic transmission model was adapted to the UK setting. The model described Streptococcus pneumoniae (SP) carriage transmission dynamics and disease progression in the presence of age- and ST-specific pneumococcal vaccines. We calibrated the model to age- and ST-specific IPD data in the UK. We used the calibrated model to make epidemiological projections under the three different vaccination scenarios. Results After 10 years, preliminary results show the routine use of V116 or PCV20 in 65+ year-olds resulted in 17.7% and 13.9% reductions in IPD incidence from current values, respectively. The continued use of PPV23 resulted in a 0.6% increase in IPD incidence. Under the V116 vaccination scenario, we projected a 15.5% reduction in IPD incidence in STs included in V116 but not PCV20 (9N, 15A, 15C [generated from deOAc-15B], 16F, 17F, 20A, 23A, 23B, 24F, 31, and 35B) in 65+ year-olds, compared to 14.5% and 10.7% increases in incidence with PCV20 or PPV23 vaccination, respectively. For STs included in PCV20 but not V116 (1, 4, 5, 6B, 9V, 14, 15B 18C, 19F, and 23F), 10-year projections revealed decreases of 27.4%, 49.2%, and 32% in IPD incidence from the current incidence values with V116, PCV20, or PPV23 vaccination in the 65+ year-old population. Conclusion Routine vaccination with V116 in older adults led to greater reductions in IPD among the 65+ year-old population compared to PCV20 and PPV23 vaccination. The model projected that with V116 vaccination in older adults, there would be no resurgence of the STs included in PCV20 but not V116 due to indirect protection offered by the pediatric vaccination program. Disclosures Rachel Oidtman, PhD, Merck &amp; Co., Inc.: Full time employee|Merck &amp; Co., Inc.: Stocks/Bonds (Public Company) Giulio Meleleo, PhD, Merck &amp; Co., Inc.: Vendor Ian Matthews, PhD, MSD (UK) Ltd., Value, Access, and Devolved Nations (VAD): Full time employee|MSD (UK) Ltd., Value, Access, and Devolved Nations (VAD): Stocks/Bonds (Public Company) Dionysios Ntais, n/a, MSD (UK) Ltd., Value, Access, and Devolved Nations (VAD): Full time employee|MSD (UK) Ltd., Value, Access, and Devolved Nations (VAD): Stocks/Bonds (Public Company) Robert Nachbar, PhD, Merck &amp; Co., Inc.: US 7,219,020, US 5,292,741|Merck &amp; Co., Inc.: Vendor|Merck &amp; Co., Inc.: Stocks/Bonds (Public Company) Oluwaseun Sharomi, MSc, PhD, Merck &amp; Co., Inc.: Full time employee|Merck &amp; Co., Inc.: Stocks/Bonds (Public Company) Kevin Bakker, PhD, Merck &amp; Co., Inc.: Grant/Research Support|Merck &amp; Co., Inc.: Stocks/Bonds (Public Company)

Streptococcus pneumoniae (pneumococcus) is a common cause of respiratory and invasive infections in humans. PCV13, a pneumococcal conjugate vaccine used globally, is highly effective against diseases caused by pneumococcal serotypes included in its formulation. However, one of them, the serotype 3 (ST3) is still being relatively commonly isolated from patients, suggesting an escape from vaccine-induced immunity. The thick capsule produced by ST3 facilitates bacterial evasion from the immune system. Additionally, host immune responses may influence the outcome of ST3 infection. Here we evaluated the influence of inflammation in the adaptive immune responses and protection induced by PCV13 against ST3, using two outbred mice lines that were phenotypically selected for high (AIRmax) and low (AIRmin) inflammatory responses. AIRmin and AIRmax mice were immunized with PCV13. Inbred BALB/c mice were used as reference for vaccine efficacy. Induction of IgG against polysaccharides (PS) from pneumococcal serotype 1 (ST1) and ST3 were evaluated by ELISA. Protection was tested against invasive infections with ST1 and ST3 pneumococcal strains. Sera were compared by IgG binding to pneumococcal surface, induction of pneumococcal agglutination and opsonophagocytosis. The phagocytic capacity of mice-derived neutrophils was also evaluated. Immunization of AIRmin, AIRmax and BALB/c mice with PCV13 induced IgG against PS from ST1 and ST3 pneumococci. Despite vaccination, AIRmin mice were not protected against fatal infection with ST3. Sera from AIRmin mice immunized with PCV13 presented lower levels of anti-PS3 IgG, with reduced capacity to bind to pneumococcal surface. Reduced capacity to induce opsonophagocytosis of ST3 pneumococci in vitro was also observed. Conversely, PCV13 protected AIRmin mice against fatal infection with ST1 and this correlated with the capacity of the sera to induce ST1 opsonophagocytosis. Our results show that both host and bacterial features can influence the outcome of protection induced by PCV13 against ST3 pneumococcal infection.

Streptococcus suis is a worldwide pathogen that impacts the swine industry, causing severe clinical signs, including meningitis and arthritis, in postweaning piglets. A key virulence mechanism of S. suis is biofilm formation, which improves its persistence and resistance to external factors. Here, we assessed the in vitro biofilm formation of 240 S. suis isolates from Spanish swine farms and evaluated the effects of serovars (SVs) and coinfections with other porcine respiratory disease complex (PRDC) pathogens. Our study revealed significant heterogeneity in biofilm formation among S. suis SVs. Notably, SV2 resulted in the lowest degree of biofilm formation, in contrast with the high biofilm-forming capacities of SV1, SV7, and SV9. Other PRDC pathogens, including Actinobacillus pleuropneumoniae, Glaesserella parasuis, and Pasteurella multocida, formed biofilms, although they were generally less robust than those of S. suis (except for SV2), which contrasts with the high biofilm formation of Staphylococcus hyicus. Coinfections enhanced biofilm formation in mixed cultures of S. suis, particularly with P. multocida. Other coinfections revealed variable results in pathogen interactions, suggesting the potential of biofilms for increased persistence and pathogenicity in coinfections. In conclusion, this study underscores the importance of serovar-specific differences in biofilm formation among S. suis isolates, with significant implications for pathogenicity and persistence. The heterogeneous biofilm formation observed in coinfections with other PRDC pathogens reveals a complex interplay that could exacerbate disease severity. These findings provide a foundation for further research on biofilm mechanisms to mitigate the impact of PRDC in the swine industry.