Potential for Maternally Administered Vaccine for Infant Group B Streptococcus.

BACKGROUND: Natural history studies have correlated serotype-specific anti-capsular polysaccharide (CPS) IgG in newborns with a reduced risk of group B streptococcal disease. A hexavalent CPS-cross-reactive material 197 glycoconjugate vaccine (GBS6) is being developed as a maternal vaccine to prevent invasive group B streptococcus in young infants. METHODS: In an ongoing phase 2, placebo-controlled trial involving pregnant women, we assessed the safety and immunogenicity of a single dose of various GBS6 formulations and analyzed maternally transferred anti-CPS antibodies. In a parallel seroepidemiologic study that was conducted in the same population, we assessed serotype-specific anti-CPS IgG concentrations that were associated with a reduced risk of invasive disease among newborns through 89 days of age to define putative protective thresholds. RESULTS: Naturally acquired anti-CPS IgG concentrations were associated with a reduced risk of disease among infants in the seroepidemiologic study. IgG thresholds that were determined to be associated with 75 to 95% reductions in the risk of disease were 0.184 to 0.827 µg per milliliter. No GBS6-associated safety signals were observed among the mothers or infants. The incidence of adverse events and of serious adverse events were similar across the trial groups for both mothers and infants; more local reactions were observed in the groups that received GBS6 containing aluminum phosphate. Among the infants, the most common serious adverse events were minor congenital anomalies (umbilical hernia and congenital dermal melanocytosis). GBS6 induced maternal antibody responses to all serotypes, with maternal-to-infant antibody ratios of approximately 0.4 to 1.3, depending on the dose. The percentage of infants with anti-CPS IgG concentrations above 0.184 µg per milliliter varied according to serotype and formulation, with 57 to 97% of the infants having a seroresponse to the most immunogenic formulation. CONCLUSIONS: GBS6 elicited anti-CPS antibodies against group B streptococcus in pregnant women that were transferred to infants at levels associated with a reduced risk of invasive group B streptococcal disease. (Funded by Pfizer and the Bill and Melinda Gates Foundation; C1091002 ClinicalTrials.gov number, NCT03765073.).

Efficacy and Safety of a Bivalent RSV Prefusion F Vaccine in Older Adults.

BACKGROUND: Respiratory syncytial virus (RSV) infection causes considerable illness in older adults. The efficacy and safety of an investigational bivalent RSV prefusion F protein-based (RSVpreF) vaccine in this population are unknown. METHODS: In this ongoing, phase 3 trial, we randomly assigned, in a 1:1 ratio, adults (≥60 years of age) to receive a single intramuscular injection of RSVpreF vaccine at a dose of 120 µg (RSV subgroups A and B, 60 µg each) or placebo. The two primary end points were vaccine efficacy against seasonal RSV-associated lower respiratory tract illness with at least two or at least three signs or symptoms. The secondary end point was vaccine efficacy against RSV-associated acute respiratory illness. RESULTS: At the interim analysis (data-cutoff date, July 14, 2022), 34,284 participants had received RSVpreF vaccine (17,215 participants) or placebo (17,069 participants). RSV-associated lower respiratory tract illness with at least two signs or symptoms occurred in 11 participants in the vaccine group (1.19 cases per 1000 person-years of observation) and 33 participants in the placebo group (3.58 cases per 1000 person-years of observation) (vaccine efficacy, 66.7%; 96.66% confidence interval [CI], 28.8 to 85.8); 2 cases (0.22 cases per 1000 person-years of observation) and 14 cases (1.52 cases per 1000 person-years of observation), respectively, occurred with at least three signs or symptoms (vaccine efficacy, 85.7%; 96.66% CI, 32.0 to 98.7). RSV-associated acute respiratory illness occurred in 22 participants in the vaccine group (2.38 cases per 1000 person-years of observation) and 58 participants in the placebo group (6.30 cases per 1000 person-years of observation) (vaccine efficacy, 62.1%; 95% CI, 37.1 to 77.9). The incidence of local reactions was higher with vaccine (12%) than with placebo (7%); the incidences of systemic events were similar (27% and 26%, respectively). Similar rates of adverse events through 1 month after injection were reported (vaccine, 9.0%; placebo, 8.5%), with 1.4% and 1.0%, respectively, considered by the investigators to be injection-related. Severe or life-threatening adverse events were reported in 0.5% of vaccine recipients and 0.4% of placebo recipients. Serious adverse events were reported in 2.3% of participants in each group through the data-cutoff date. CONCLUSIONS: RSVpreF vaccine prevented RSV-associated lower respiratory tract illness and RSV-associated acute respiratory illness in adults (≥60 years of age), without evident safety concerns. (Funded by Pfizer; RENOIR ClinicalTrials.gov number, NCT05035212; EudraCT number, 2021-003693-31.).

Bivalent Prefusion F Vaccine in Pregnancy to Prevent RSV Illness in Infants.

BACKGROUND: Whether vaccination during pregnancy could reduce the burden of respiratory syncytial virus (RSV)-associated lower respiratory tract illness in newborns and infants is uncertain. METHODS: In this phase 3, double-blind trial conducted in 18 countries, we randomly assigned, in a 1:1 ratio, pregnant women at 24 through 36 weeks' gestation to receive a single intramuscular injection of 120 µg of a bivalent RSV prefusion F protein-based (RSVpreF) vaccine or placebo. The two primary efficacy end points were medically attended severe RSV-associated lower respiratory tract illness and medically attended RSV-associated lower respiratory tract illness in infants within 90, 120, 150, and 180 days after birth. A lower boundary of the confidence interval for vaccine efficacy (99.5% confidence interval [CI] at 90 days; 97.58% CI at later intervals) greater than 20% was considered to meet the success criterion for vaccine efficacy with respect to the primary end points. RESULTS: At this prespecified interim analysis, the success criterion for vaccine efficacy was met with respect to one primary end point. Overall, 3682 maternal participants received vaccine and 3676 received placebo; 3570 and 3558 infants, respectively, were evaluated. Medically attended severe lower respiratory tract illness occurred within 90 days after birth in 6 infants of women in the vaccine group and 33 infants of women in the placebo group (vaccine efficacy, 81.8%; 99.5% CI, 40.6 to 96.3); 19 cases and 62 cases, respectively, occurred within 180 days after birth (vaccine efficacy, 69.4%; 97.58% CI, 44.3 to 84.1). Medically attended RSV-associated lower respiratory tract illness occurred within 90 days after birth in 24 infants of women in the vaccine group and 56 infants of women in the placebo group (vaccine efficacy, 57.1%; 99.5% CI, 14.7 to 79.8); these results did not meet the statistical success criterion. No safety signals were detected in maternal participants or in infants and toddlers up to 24 months of age. The incidences of adverse events reported within 1 month after injection or within 1 month after birth were similar in the vaccine group (13.8% of women and 37.1% of infants) and the placebo group (13.1% and 34.5%, respectively). CONCLUSIONS: RSVpreF vaccine administered during pregnancy was effective against medically attended severe RSV-associated lower respiratory tract illness in infants, and no safety concerns were identified. (Funded by Pfizer; MATISSE ClinicalTrials.gov number, NCT04424316.).

Identification of a Novel Keto Sugar Component in Streptococcus pneumoniae Serotype 12F Capsular Polysaccharide and Impact on Vaccine Immunogenicity.

Implementation of conjugate vaccine technology revolutionized the ability to effectively elicit long-lasting immune responses to bacterial capsular polysaccharides. Although expansion of conjugate vaccine serotype coverage is designed to target residual disease burden to pneumococcal serotypes not contained in earlier vaccine versions, details of polysaccharide Ag structure, heterogeneity, and epitope structure components contributing to vaccine-mediated immunity are not always clear. Analysis of Streptococcus pneumoniae serotype 12F polysaccharide by two-dimensional nuclear magnetic resonance spectroscopy and mass spectrometry revealed a partial substitution of N-acetyl-galactosamine by the keto sugar 2-acetamido-2,6-dideoxy-xylo-hexos-4-ulose (Sug) in up to 25% of the repeat units. This substitution was not described in previous published structures for 12F. Screening a series of contemporary 12F strains isolated from humans (n = 17) identified Sug incorporation at varying levels in all strains examined. Thus, partial Sug substitution in S. pneumoniae serotype 12F may have always been present but is now detectable by state-of-the-art analytical techniques. During the steps of conjugation, the serotype 12F Sug epitope is modified by reduction, and both polysaccharide PPSV23 and conjugate PCV20 vaccines contain 12F Ags with little to no Sug epitope. Both PCV20 and PPSV23 vaccines were evaluated for protection against circulating 12F strains with varying amounts of Sug in their repeat unit based on an opsonophagocytic killing assay involving HL-60 cells and rabbit complement. Both vaccines elicited human-derived neutralizing Abs against serotype 12F, independent of Sug level between ∼2 and 25 mol%. These findings suggest that the newly identified serotype 12F Sug epitope is likely not an essential epitope for vaccine-elicited protection.

A Phase 2 Extension Study Evaluating the Immunogenicity, Safety, and Tolerability of 3 or 4 Doses of a Clostridioides difficile Vaccine in Healthy US Adults Aged 65 to 85 Years.

BACKGROUND: This phase 2 extension explored the long-term antibody persistence of an investigational Clostridioides difficile vaccine and the safety, tolerability, and immunogenicity of dose 4 approximately 12 months post-dose 3. METHODS: One year post-dose 3, healthy US 65- to 85-year-olds (N = 300) were randomized to dose 4 of vaccine at previously received antigen levels (100 or 200 µg) or placebo. Assessments included safety and percentages of participants achieving neutralizing antibody titers above prespecified thresholds (≥219 and ≥2586 neutralization units/mL for toxins A and B, respectively). RESULTS: In participants previously given three 200-µg doses and placebo in the extension, toxin A and B neutralizing antibodies were above prevaccination levels 48 months post-dose 3 (36 months after placebo); 24.0% and 26.0% had toxin A and B antibodies at or above prespecified thresholds, respectively. Neutralizing antibodies increased post-dose 4 (12 months post-dose 3) and persisted to 36 months post-dose 4. Thirty days post-dose 4, all participants had toxin A and 86.5% to 100% had toxin B titers at or above prespecified thresholds. Local reactions were more frequent in vaccine recipients. Systemic and adverse event frequencies were similar across groups. CONCLUSIONS: C difficile vaccine immune responses persisted 48 months post-dose 3. Dose 4 was immunogenic and well tolerated, supporting continued development. Clinical Trials Registration. ClinicalTrials.gov NCT02561195.

Efficacy of a 4-Antigen Staphylococcus aureus Vaccine in Spinal Surgery: The STaphylococcus aureus suRgical Inpatient Vaccine Efficacy (STRIVE) Randomized Clinical Trial.

BACKGROUND: Staphylococcus aureus is a global pathogen that is frequently responsible for healthcare-associated infections, including surgical site infections (SSIs). Current infection prevention and control approaches may be limited, with S. aureus antibiotic resistance remaining problematic. Thus, a vaccine to prevent or reduce S. aureus infection is critically needed. We evaluated the efficacy and safety of an investigational 4-antigen S. aureus vaccine (SA4Ag) in adults undergoing elective open posterior spinal fusion procedures with multilevel instrumentation. METHODS: In this multicenter, site-level, randomized, double-blind trial, patients aged 18-85 years received a single dose of SA4Ag or placebo 10-60 days before surgery. SA4Ag efficacy in preventing postoperative S. aureus bloodstream infection and/or deep incisional or organ/space SSIs was the primary end point. Safety evaluations included local reactions, systemic events, and adverse events (AEs). Immunogenicity and colonization were assessed. RESULTS: Study enrollment was halted when a prespecified interim efficacy analysis met predefined futility criteria. SA4Ag showed no efficacy (0.0%) in preventing postoperative S. aureus infection (14 cases in each group through postoperative day 90), despite inducing robust functional immune responses to each antigen compared with placebo. Colonization rates across groups were similar through postoperative day 180. Local reactions and systemic events were mostly mild or moderate in severity, with AEs reported at similar frequencies across groups. CONCLUSIONS: In patients undergoing elective spinal fusion surgical procedures, SA4Ag was safe and well tolerated but, despite eliciting substantial antibody responses that blocked key S. aureus virulence mechanisms, was not efficacious in preventing S. aureus infection. Clinical Trials Registration. NCT02388165.

Safety and Immunogenicity of Bivalent RSVpreF Vaccine Coadministered with Seasonal Inactivated Influenza Vaccine in Older Adults.

BACKGROUND: Respiratory syncytial virus (RSV) and influenza are both typically seasonal diseases, with winter peaks in temperate climates. Coadministration of an RSV vaccine and influenza vaccine could be a benefit, requiring 1 rather than 2 visits to a healthcare provider for individuals receiving both vaccines. METHODS: The primary immunogenicity objective of this phase 3, 1:1 randomized, double-blind, placebo-controlled study in healthy ≥65-year-olds in Australia was to demonstrate noninferiority of immune responses with coadministration of the stabilized RSV prefusion F protein-based vaccine (RSVpreF) and seasonal inactivated influenza vaccine (SIIV) versus SIIV or RSVpreF administered alone, using a 1.5-fold noninferiority margin (lower bound 95% CI >0.667). Safety and tolerability were evaluated by collecting reactogenicity and adverse event data. RESULTS: Of 1403 participants randomized, 1399 received vaccinations (median [range] age, 70 [65‒91] years). Local reactions and systemic events were mostly mild or moderate when RSVpreF was coadministered with SIIV or administered alone. No vaccine-related serious adverse events were reported. Geometric mean ratios were 0.86 for RSV-A and 0.85 for RSV-B neutralizing titers at 1 month after RSVpreF administration and 0.77 to 0.90 for strain-specific hemagglutination inhibition assay titers at 1 month after SIIV. All comparisons achieved the prespecified 1.5-fold noninferiority margin. CONCLUSION: The primary study objectives were met, demonstrating noninferiority of RSVpreF and SIIV immune responses when RSVpreF was coadministered with SIIV and that RSVpreF had an acceptable safety and tolerability profile when coadministered with SIIV. The results of this study support coadministration of RSVpreF and SIIV in an older adult population. CLINICAL TRIAL REGISTRATION: NCT05301322.

A Bivalent Omicron-BA.4/BA.5-Adapted BNT162b2 Booster in ≥12-Year-Olds.

BACKGROUND: Protection against contemporary SARS-CoV-2 variants requires sequence-adapted vaccines. METHODS: In this ongoing phase 2/3 trial, 12-17-year-olds (n=108), 18-55-year-olds (n=313), and >55-year-olds (n=306) who previously received 3 original BNT162b2 30-µg doses, received a fourth dose (second booster) of 30-µg bivalent original/Omicron-BA.4/BA.5-adapted BNT162b2 (BNT162b2-Omi.BA.4/BA.5). For comparisons with original BNT162b2, participants were selected from another phase 3 trial. Immunologic superiority 1-month post-vaccination, with respect to 50% neutralizing titers (GMR lower bound [LB] 2-sided 95%CI >1), and noninferiority with respect to seroresponse rates (rate-difference LB 2-sided 95%CI >-5%), for Omicron BA.4/BA.5 were assessed in >55-year-olds versus original BNT162b2 as a second booster. Noninferiority with respect to neutralizing titer level (GMR LB 2-sided 95%CI >0.67) and seroresponse rate (rate-difference LB 2-sided 95%CI >-10%) of Omicron BA.4/BA.5 immune response for BNT162b2-Omi.BA.4/BA.5 in 18‒55-year-olds versus >55-year-olds was assessed. RESULTS: One-month post-vaccination in >55-year-olds, model-adjusted GMR of Omicron BA.4/BA.5 neutralizing titers for the BNT162b2-Omi.BA.4/BA.5 versus BNT162b2 group (2.91; 95%CI 2.45-3.44) demonstrated superiority of BNT162b2-Omi.BA.4/BA.5. Adjusted difference in percentages of >55-year-olds with seroresponse (26.77%; 95%CI 19.59-33.95) showed noninferiority of BNT162b2-Omi.BA.4/BA.5 to BNT162b2. Noninferiority of BNT162b2-Omi.BA.4/BA.5 in 18‒55-year-olds to >55-year-olds was met for model-adjusted GMR and seroresponse. GMTs in 12-17-year-olds increased from baseline to 1-month post-vaccination. The BNT162b2-Omi.BA.4/BA.5 safety profile was similar to booster doses of bivalent Omicron BA.1-modified BNT162b2 and original BNT162b2 reported in previous studies. CONCLUSIONS: Based on immunogenicity and safety data up to 1-month post-vaccination in participants who previously received 3 original BNT162b2 doses, a BNT162b2-Omi.BA.4/BA.5 30 µg booster has a favorable benefit-risk profile. CLINICAL TRIAL REGISTRATION: NCT05472038.

Human Infection Challenge with Serotype 3 Pneumococcus.

Rationale: Streptococcus pneumoniae serotype 3 (SPN3) is a cause of invasive pneumococcal disease and associated with low carriage rates. Following the introduction of pediatric 13-valent pneumococcal conjugate vaccine (PCV13) programs, SPN3 declines are less than other vaccine serotypes and incidence has increased in some populations coincident with a shift in predominant circulating SPN3 clade, from I to II. A human challenge model provides an effective means for assessing the impact of PCV13 on SPN3 in the upper airway. Objectives: To establish SPN3's ability to colonize the nasopharynx using different inoculum clades and doses, and the safety of an SPN3 challenge model. Methods: In a human challenge study involving three well-characterized and antibiotic-sensitive SPN3 isolates (PFESP306 [clade Ia], PFESP231 [no clade], and PFESP505 [clade II]), inoculum doses (10,000, 20,000, 80,000, and 160,000 cfu/100 µl) were escalated until maximal colonization rates were achieved, with concurrent acceptable safety. Measurement and Main Results: Presence and density of experimental SPN3 nasopharyngeal colonization in nasal wash samples, assessed using microbiological culture and molecular methods, on Days 2, 7, and 14 postinoculation. A total of 96 healthy participants (median age 21, interquartile range 19-25) were inoculated (n = 6-10 per dose group, 10 groups). Colonization rates ranged from 30.0-70.0% varying with dose and isolate. 30.0% (29/96) reported mild symptoms (82.8% [24/29] developed a sore throat); one developed otitis media requiring antibiotics. No serious adverse events occurred. Conclusions: An SPN3 human challenge model is feasible and safe with comparable carriage rates to an established Serotype 6B human challenge model. SPN3 carriage may cause mild upper respiratory symptoms.

Preclinical Immunogenicity and Efficacy of Optimized O25b O-Antigen Glycoconjugates To Prevent MDR ST131 E. coli Infections.

Multivalent O-antigen polysaccharide glycoconjugate vaccines are under development to prevent invasive infections caused by pathogenic Enterobacteriaceae. Sequence type 131 (ST131) Escherichia coli of serotype O25b has emerged as the predominant lineage causing invasive multidrug-resistant extraintestinal pathogenic E. coli (ExPEC) infections. We observed the prevalence of E. coli O25b ST131 among a contemporary collection of isolates from U.S. bloodstream infections from 2013 to 2016 (n = 444) and global urinary tract infections from 2014 to 2017 (n = 102) to be 25% and 24%, respectively. To maximize immunogenicity of the serotype O25b O antigen, we investigated glycoconjugate properties, including CRM197 carrier protein cross-linking (single-end versus cross-linked "lattice") and conjugation chemistry (reductive amination chemistry in dimethyl sulfoxide [RAC/DMSO] versus ((2-((2-oxoethyl)thio)ethyl)carbamate [eTEC] linker). Using opsonophagocytic assays (OPAs) to measure serum functional antibody responses to vaccination, we observed that higher-molecular-mass O25b long-chain lattice conjugates showed improved immunogenicity in mice compared with long- or short-chain O antigens conjugated via single-end attachment. The lattice conjugates protected mice from lethal challenge with acapsular O25b ST131 strains as well as against hypervirulent O25b isolates expressing K5 or K100 capsular polysaccharides. A single 1-µg dose of long-chain O25b lattice conjugate constructed with both chemistries also elicited robust serum IgG and OPA responses in cynomolgus macaques. Our findings show that key properties of the O-antigen carrier protein conjugate such as saccharide epitope density and degree of intermolecular cross-linking can significantly enhance functional immunogenicity.

A comparative analysis of SARS-CoV-2 antivirals characterizes 3CLpro inhibitor PF-00835231 as a potential new treatment for COVID-19.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiological agent of Coronavirus Disease 2019 (COVID-19). There is a dire need for novel effective antivirals to treat COVID-19, as the only approved direct-acting antiviral to date is remdesivir, targeting the viral polymerase complex. A potential alternate target in the viral life cycle is the main SARS-CoV-2 protease 3CLpro (Mpro). The drug candidate PF-00835231 is the active compound of the first anti-3CLpro regimen in clinical trials. Here, we perform a comparative analysis of PF-00835231, the pre-clinical 3CLpro inhibitor GC-376, and the polymerase inhibitor remdesivir, in alveolar basal epithelial cells modified to express ACE2 (A549+ACE2 cells). We find PF-00835231 with at least similar or higher potency than remdesivir or GC-376. A time-of-drug-addition approach delineates the timing of early SARS-CoV-2 life cycle steps in A549+ACE2 cells and validates PF-00835231's early time of action. In a model of the human polarized airway epithelium, both PF-00835231 and remdesivir potently inhibit SARS-CoV-2 at low micromolar concentrations. Finally, we show that the efflux transporter P-glycoprotein, which was previously suggested to diminish PF-00835231's efficacy based on experiments in monkey kidney Vero E6 cells, does not negatively impact PF-00835231 efficacy in either A549+ACE2 cells or human polarized airway epithelial cultures. Thus, our study provides in vitro evidence for the potential of PF-00835231 as an effective SARS-CoV-2 antiviral and addresses concerns that emerged based on prior studies in non-human in vitro models.Importance:The arsenal of SARS-CoV-2 specific antiviral drugs is extremely limited. Only one direct-acting antiviral drug is currently approved, the viral polymerase inhibitor remdesivir, and it has limited efficacy. Thus, there is a substantial need to develop additional antiviral compounds with minimal side effects and alternate viral targets. One such alternate target is its main protease, 3CLpro (Mpro), an essential component of the SARS-CoV-2 life cycle processing the viral polyprotein into the components of the viral polymerase complex. In this study, we characterize a novel antiviral drug, PF-00835231, which is the active component of the first-in-class 3CLpro-targeting regimen in clinical trials. Using 3D in vitro models of the human airway epithelium, we demonstrate the antiviral potential of PF-00835231 for inhibition of SARS-CoV-2.

The impact of human vaccines on bacterial antimicrobial resistance. A review.

At present, the dramatic rise in antimicrobial resistance (AMR) among important human bacterial pathogens is reaching a state of global crisis threatening a return to the pre-antibiotic era. AMR, already a significant burden on public health and economies, is anticipated to grow even more severe in the coming decades. Several licensed vaccines, targeting both bacterial (Haemophilus influenzae type b, Streptococcus pneumoniae, Salmonella enterica serovar Typhi) and viral (influenza virus, rotavirus) human pathogens, have already proven their anti-AMR benefits by reducing unwarranted antibiotic consumption and antibiotic-resistant bacterial strains and by promoting herd immunity. A number of new investigational vaccines, with a potential to reduce the spread of multidrug-resistant bacterial pathogens, are also in various stages of clinical development. Nevertheless, vaccines as a tool to combat AMR remain underappreciated and unfortunately underutilized. Global mobilization of public health and industry resources is key to maximizing the use of licensed vaccines, and the development of new prophylactic vaccines could have a profound impact on reducing AMR.

A Phase 2 Study Evaluating the Safety, Tolerability, and Immunogenicity of Two 3-Dose Regimens of a Clostridium difficile Vaccine in Healthy US Adults Aged 65 to 85 Years.

BACKGROUND: Clostridium difficile causes toxin-mediated nosocomial diarrhea and community-acquired infections; no preventive vaccine is licensed. In this phase 2 study, we explored safety, tolerability, and immunogenicity in older US adults of an investigational bivalent C. difficile vaccine that contains equal dosages of genetically and chemically detoxified toxins A and B. METHODS: Conducted from July 2015 through March 2017, 855 healthy adults aged 65-85 years from 15 US centers were randomized 3:3:1 to receive vaccine (100 or 200 µg) or placebo at 0, 1, and 6 months (month regimen) or 1, 8, and 30 days (day regimen). Serum toxin A- and B-specific neutralizing antibodies were measured. Participant-reported local reactions (LRs) and systemic events (SEs), adverse events (AEs), serious AEs, newly diagnosed chronic medical conditions, and immediate AEs were recorded. RESULTS: The 200-µg dose level elicited higher immune responses than the 100-µg dose level across regimens. Compared with the day regimen, the month regimen induced stronger and more persistent immune responses that remained elevated 12 months after dose 3. Responses peaked at month 7 (month regimen) and day 37 (day regimen). LRs (primarily injection site pain) were more frequent in vaccine recipients than controls; SE frequency was similar across groups. More related AEs were reported in the day regimen group than the month regimen group. CONCLUSIONS: The C. difficile vaccine was safe, well tolerated, and immunogenic in healthy US adults aged 65-85 years. Immune responses were particularly robust in the 200-µg month regimen group. These results support continued vaccine development. CLINICAL TRIALS REGISTRATION: NCT02561195.

A Bivalent Meningococcal B Vaccine in Adolescents and Young Adults.

BACKGROUND: MenB-FHbp is a licensed meningococcal B vaccine targeting factor H-binding protein. Two phase 3 studies assessed the safety of the vaccine and its immunogenicity against diverse strains of group B meningococcus. METHODS: We randomly assigned 3596 adolescents (10 to 18 years of age) to receive MenB-FHbp or hepatitis A virus vaccine and saline and assigned 3304 young adults (18 to 25 years of age) to receive MenB-FHbp or saline at baseline, 2 months, and 6 months. Immunogenicity was assessed in serum bactericidal assays that included human complement (hSBAs). We used 14 meningococcal B test strains that expressed vaccine-heterologous factor H-binding proteins representative of meningococcal B epidemiologic diversity; an hSBA titer of at least 1:4 is the accepted correlate of protection. The five primary end points were the proportion of participants who had an increase in their hSBA titer for each of 4 primary strains by a factor of 4 or more and the proportion of those who had an hSBA titer at least as high as the lower limit of quantitation (1:8 or 1:16) for all 4 strains combined after dose 3. We also assessed the hSBA responses to the primary strains after dose 2; hSBA responses to the 10 additional strains after doses 2 and 3 were assessed in a subgroup of participants only. Safety was assessed in participants who received at least one dose. RESULTS: In the modified intention-to-treat population, the percentage of adolescents who had an increase in the hSBA titer by a factor of 4 or more against each primary strain ranged from 56.0 to 85.3% after dose 2 and from 78.8 to 90.2% after dose 3; the percentages of young adults ranged from 54.6 to 85.6% and 78.9 to 89.7%, after doses 2 and 3, respectively. Composite responses after doses 2 and 3 in adolescents were 53.7% and 82.7%, respectively, and those in young adults were 63.3% and 84.5%, respectively. Responses to the 4 primary strains were predictive of responses to the 10 additional strains. Most of those who received MenB-FHbp reported mild or moderate pain at the vaccination site. CONCLUSIONS: MenB-FHbp elicited bactericidal responses against diverse meningococcal B strains after doses 2 and 3 and was associated with more reactions at the injection site than the hepatitis A virus vaccine and saline. (Funded by Pfizer; ClinicalTrials.gov numbers, NCT01830855 and NCT01352845 ).

A Novel Hexavalent Capsular Polysaccharide Conjugate Vaccine (GBS6) for the Prevention of Neonatal Group B Streptococcal Infections by Maternal Immunization.

BACKGROUND: Group B streptococcus (GBS) causes serious diseases in newborn infants, often resulting in lifelong neurologic impairments or death. Prophylactic vaccination of pregnant women prior to delivery could provide comprehensive protection, as early onset and late-onset disease and maternal complications potentially could be addressed. METHODS: Capsular polysaccharide conjugate vaccine GBS6 was designed using surveillance data yielded by whole-genome sequencing of a global collection of recently recovered GBS isolates responsible for invasive neonatal GBS disease. Capsular polysaccharides were isolated, oxidized using sodium periodate, and conjugated to CRM197 by reductive amination in dimethyl sulfoxide. Immune responses in mice and rhesus macaques were measured in a multiplex Luminex immunoglobulin G (IgG) assay and opsonophagocytic activity assays. RESULTS: The optimized conjugates were immunogenic, alone and in combination, in mice and rhesus macaques, inducing IgG antibodies that mediated opsonophagocytic killing. Active immunization of murine dams with GBS6 prior to mating resulted in serotype-specific protection of pups from a lethal challenge with GBS. Protection following passive administration of serotype-specific IgG monoclonal antibodies to dams demonstrated conclusively that anticapsular polysaccharide IgG alone is sufficient for protection. CONCLUSIONS: The findings support the ongoing clinical evaluation of maternal GBS6 vaccination as a potential alternative method to prevent GBS disease in infants.

High Resolution Mapping of Bactericidal Monoclonal Antibody Binding Epitopes on Staphylococcus aureus Antigen MntC.

The Staphylococcus aureus manganese transporter protein MntC is under investigation as a component of a prophylactic S.aureus vaccine. Passive immunization with monoclonal antibodies mAB 305-78-7 and mAB 305-101-8 produced using MntC was shown to significantly reduce S. aureus burden in an infant rat model of infection. Earlier interference mapping suggested that a total of 23 monoclonal antibodies generated against MntC could be subdivided into three interference groups, representing three independent immunogenic regions. In the current work binding epitopes for selected representatives of each of these interference groups (mAB 305-72-5 - group 1, mAB 305-78-7 - group 2, and mAB 305-101-8 - group 3) were mapped using Hydrogen-Deuterium Exchange Mass Spectrometry (DXMS). All of the identified epitopes are discontinuous, with binding surface formed by structural elements that are separated within the primary sequence of the protein but adjacent in the context of the three-dimensional structure. The approach was validated by co-crystallizing the Fab fragment of one of the antibodies (mAB 305-78-7) with MntC and solving the three-dimensional structure of the complex. X-ray results themselves and localization of the mAB 305-78-7 epitope were further validated using antibody binding experiments with MntC variants containing substitutions of key amino acid residues. These results provided insight into the antigenic properties of MntC and how these properties may play a role in protecting the hostagainst S. aureus infection by preventing the capture and transport of Mn2+, a key element that the pathogen uses to evade host immunity.

A Vaccine Approach for the Prevention of Infections by Multidrug-resistant Enterococcus faecium.

The incidence of multidrug-resistant Enterococcus faecium hospital infections has been steadily increasing. With the goal of discovering new vaccine antigens, we systematically fractionated and purified four distinct surface carbohydrates from E. faecium endocarditis isolate Tx16, shown previously to be resistant to phagocytosis in the presence of human serum. The two most abundant polysaccharides consist of novel branched heteroglycan repeating units that include signature sugars altruronic acid and legionaminic acid, respectively. A minor high molecular weight polysaccharide component was recognized as the fructose homopolymer levan, and a glucosylated lipoteichoic acid (LTA) was identified in a micellar fraction. The polysaccharides were conjugated to the CRM197 carrier protein, and the resulting glycoconjugates were used to immunize rabbits. Rabbit immune sera were evaluated for their ability to kill Tx16 in opsonophagocytic assays and in a mouse passive protection infection model. Although antibodies raised against levan failed to mediate opsonophagocytic killing, the other glycoconjugates induced effective opsonic antibodies, with the altruronic acid-containing polysaccharide antisera showing the greatest opsonophagocytic assay activity. Antibodies directed against either novel heteroglycan or the LTA reduced bacterial load in mouse liver or kidney tissue. To assess antigen prevalence, we screened a diverse collection of blood isolates (n = 101) with antibodies to the polysaccharides. LTA was detected on the surface of 80% of the strains, and antigens recognized by antibodies to the two major heteroglycans were co-expressed on 63% of these clinical isolates. Collectively, these results represent the first steps toward identifying components of a glycoconjugate vaccine to prevent E. faecium infection.

Comparison of Phenotypic and Genotypic Approaches to Capsule Typing of Neisseria meningitidis by Use of Invasive and Carriage Isolate Collections.

Neisseria meningitidis serogroup B (MnB) is a leading cause of bacterial meningitis; however, MnB is most commonly associated with asymptomatic carriage in the nasopharyngeal cavity, as opposed to the disease state. Two vaccines are now licensed for the prevention of MnB disease; a possible additional benefit of these vaccines could be to protect against disease indirectly by disrupting nasopharyngeal carriage (e.g., herd protection). To investigate this possibility, accurate diagnostic approaches to characterize MnB carriage isolates are required. In contrast to invasive meningococcal disease (IMD) isolates, which can be readily serogrouped, carriage isolates often lack capsule expression, making standard phenotypic assays unsuitable for strain characterization. Several antibody-based methods were evaluated for their abilities to serogroup isolates and were compared with two genotyping methods (real-time PCR [rt-PCR] and whole-genome sequencing [WGS]) to identify which approach would most accurately ascertain the polysaccharide groups associated with carriage isolates. WGS and rt-PCR were in agreement for 99% of IMD isolates, including those with coding sequences for MnB, MnC, MnW, and MnY, and the phenotypic methods correctly identified serogroups for 69 to 98% of IMD isolates. In contrast, only 47% of carriage isolates were groupable by genotypic methods, due to mutations within the capsule operon; of the isolates identified by genotypic methods, ≤43% were serogroupable with any of the phenotypic methods tested. These observations highlight the difficulties in the serogrouping and capsular genogrouping of meningococcal carriage isolates. Based on our findings, WGS is the most suitable approach for the characterization of meningococcal carriage isolates.