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Japanese encephalitis (JE) is a significant public health concern in Asia, particularly in children, where vaccination plays a crucial role in prevention. In this study, we investigated the immunogenicity and safety of two different live-attenuated JE vaccines used as primary and booster doses. Fifty healthy participants aged 1-3 years, who were primed with the chimeric JE vaccine IMOJEV® a year earlier, received a booster dose of the SA14-14-2 JE vaccine CD.JEVAX®. To evaluate the immune response, JE-neutralizing antibody titers were assessed on day 0 (pre-booster), day 30, and annually from 1 to 5 years post-booster using the 50% plaque reduction neutralization test (JEPRNT50). The assessment revealed strong immunogenicity 30 d post-booster, with a geometric mean titer of 2092.4 [95% confidence interval (CI): 1473.9-2970.5] and a seroprotection rate of 100%, which gradually decreased to 97.5% at 5 years post-booster. No severe adverse events were observed. The most common reaction within 7 d of vaccination was fever (20%; 95% CI: 10.7-32.3). These results indicate that a booster dose of CD.JEVAX® elicits a strong immune response in children previously vaccinated with IMOJEV® while maintaining a good safety profile, thus supporting the interchangeability of these two live-attenuated JE vaccines. Registered at www.thaiclinicaltrials.org (TCTR ID: TCTR20221102003), our study suggests that CD.JEVAX® can be a viable option for booster vaccination in JE prevention programs, potentially enhancing vaccine flexibility and accessibility.

Vaccine safety and immunogenicity data in human immunodeficiency virus (HIV)-exposed uninfected (HEU) children are important for decision-making in HIV and typhoid co-endemic countries. In an open-label study, we recruited Malawian HEU and HIV unexposed uninfected (HUU) infants aged 9 - 11 months. HEU participants were randomized to receive Vi-tetanus toxoid conjugate vaccine (Vi-TT) at 9 months, Vi-TT at 15 months, or Vi-TT at 9 and 15 months. HUU participants received Vi-TT at 9 and 15 months. Safety outcomes included solicited and unsolicited adverse events (AE) and serious AEs (SAEs) within 7 days, 28 days, and 6 months of vaccination, respectively. Serum was collected before and at day 28 after each vaccination to measure anti-Vi IgG antibodies by enzyme-linked immunosorbent assay (ELISA). Cohort 1 (66 participants) enrollment began 02 December 2019, and follow-up was terminated before completion due to the COVID-19 pandemic. Cohort 2 (100 participants) enrollment began 25 March 2020. Solicited AEs were mostly mild, with no significant differences between HEU and HUU participants or one- and two-dose groups. All six SAEs were unrelated to vaccination. Anti-Vi geometric mean titers (GMT) increased significantly from 4.1 to 4.6 ELISA units (EU)/mL at baseline to 2572.0 - 4117.6 EU/mL on day 28 post-vaccination, and similarly between HEU and HUU participants for both one- and two-dose schedules. All participants seroconverted (>4-fold increase in GMT) by the final study visit. Our findings of comparable safety and immunogenicity of Vi-TT in HUU and HEU children support country introductions with single-dose Vi-TT in HIV-endemic countries.

Introduction: Zebrafishes represent a proven model for human diseases and systems biology, exhibiting physiological and genetic similarities and having innate and adaptive immune systems. However, they are underexplored for human vaccinology, vaccine development, and testing. Here we summarize gaps and challenges., Areas Covered: Zebrafish models have four potential applications: 1) Vaccine safety: The past successes in using zebrafishes to test xenobiotics could extend to vaccine and adjuvant formulations for general safety or target organs due to the zebrafish embryos' optical transparency. 2) Innate immunity: The zebrafish offers refined ways to examine vaccine effects through signaling via Toll-like or NOD-like receptors in zebrafish myeloid cells. 3) Adaptive immunity: Zebrafishes produce IgM, IgD,and two IgZ immunoglobulins, but these are understudied, due to a lack of immunological reagents for challenge studies. 4) Systems vaccinology: Due to the availability of a well-referenced zebrafish genome, transcriptome, proteome, and epigenome, this model offers potential here., Expert Opinion: It remains unproven whether zebrafishes can be employed for testing and developing human vaccines. We are still at the hypothesis-generating stage, although it is possible to begin outlining experiments for this purpose. Through transgenic manipulation, zebrafish models could offer new paths for shaping animal models and systems vaccinology.

Introduction: Pseudoviruses are recombinant, replication-incompetent, viral particles designed to mimic the surface characteristics of native enveloped viruses. They are a safer, and cost-effective research alternative to live viruses. With the potential emergence of the next major infectious disease, more vaccine scientists must become familiar with the pseudovirus platform as a vaccine development tool to mitigate future outbreaks., Areas Covered: This review aims at vaccine developers to provide a basic understanding of pseudoviruses, list their production methods, and discuss their utility to assess vaccine efficacy against enveloped viral pathogens. We further illustrate their usefulness as wet-lab simulators for emerging mutant variants, and new viruses to help prepare for current and future viral outbreaks, minimizing the need for gain-of-function experiments with highly infectious or lethal enveloped viruses., Expert Opinion: With this platform, researchers can better understand the role of virus-receptor interactions and entry in infections, prepare for dangerous mutations, and develop effective vaccines.

Affordable, polyvalent meningococcal vaccines are needed for use in emergency reactive immunization campaigns. A phase IV randomized, observer-blind, controlled study compared the safety and immunogenicity of a quadrivalent meningococcal polysaccharide vaccine (MPV-4, MPV ACYW135) and quadrivalent meningococcal ACWY conjugate vaccine (MCV-4, Menactra®). Healthy, 2- to 10-year-old children in Bamako, Mali, were randomized 1:1 to receive one dose of MPV-4 or MCV-4. Safety outcomes were evaluated for 6 months post-immunization. Immunogenicity for all serogroups was assessed for non-inferiority between MPV-4 and MCV-4 30 days post immunization by serum bactericidal antibody assay using baby rabbit complement (rSBA). From December 2020 to July 2021, 260 healthy subjects were consented and randomized. At Day 30 post-immunization, the proportions of subjects with rSBA titers ≥ 128 for all serogroups in the MPV-4 group were non-inferior to those in MCV-4 group. The proportions of subjects with rSBA ≥ 4-fold increase and rSBA titers ≥ 8 for all serogroups were similar among vaccine groups ( P  > .05). Geometric Mean Titers and Geometric Mean Fold Increases for all serogroups in both vaccine groups were similar ( P  > .05). Few local and systemic post-immunization reactions of similar severity and duration were observed within 7 days and were similar in both groups ( P  > .05). All resolved without sequelae. Unsolicited adverse events were similar in both groups regarding relationship to study vaccine, severity and duration. No serious adverse events were reported during the study period. MPV ACYW135 showed a non-inferior immunogenicity profile and a comparable reactogenicity profile to MCV-4 in Malian children aged 2-10 years. Clinical Trial Registration : NCT04450498.

Introduction: The development of a yeast-expressed recombinant protein-based vaccine technology co-developed with LMIC vaccine producers and suitable as a COVID-19 vaccine for global access is described. The proof-of-concept for developing a SARS-CoV-2 spike protein receptor-binding domain (RBD) antigen as a yeast-derived recombinant protein vaccine technology is described., Areas Covered: Genetic Engineering: The strategy is presented for the design and genetic modification used during cloning and expression in the yeast system. Process and Assay Development: A summary is presented of how a scalable, reproducible, and robust production process for the recombinant protein COVID-19 vaccine antigen was developed. Formulation and Pre-clinical Strategy: We report on the pre-clinical and formulation strategy used for the proof-of-concept evaluation of the SARS-CoV-2 RBD vaccine antigen. Technology Transfer and Partnerships: The process used for the technology transfer and co-development with LMIC vaccine producers is described. Clinical Development and Delivery: The approach used by LMIC developers to establish the industrial process, clinical development, and deployment is described., Expert Opinion: Highlighted is an alternative model for developing new vaccines for emerging infectious diseases of pandemic importance starting with an academic institution directly transferring their technology to LMIC vaccine producers without the involvement of multinational pharma companies.

Introduction: Malaria, a devastating febrile illness caused by protozoan parasites, sickened 247,000,000 people in 2021 and killed 619,000, mostly children and pregnant women in sub-Saharan Africa. A highly effective vaccine is urgently needed, especially for Plasmodium falciparum (Pf), the deadliest human malaria parasite., Areas Covered: Sporozoites (SPZ), the parasite stage transmitted by Anopheles mosquitoes to humans, are the only vaccine immunogen achieving >90% efficacy against Pf infection. This review describes >30 clinical trials of PfSPZ vaccines in the U.S.A., Europe, Africa, and Asia, based on first-hand knowledge of the trials and PubMed searches of 'sporozoites,' 'malaria,' and 'vaccines.', Expert Opinion: First generation (radiation-attenuated) PfSPZ vaccines are safe, well tolerated, 80-100% efficacious against homologous controlled human malaria infection (CHMI) and provide 18-19 months protection without boosting in Africa. Second generation chemo-attenuated PfSPZ are more potent, 100% efficacious against stringent heterologous (variant strain) CHMI, but require a co-administered drug, raising safety concerns. Third generation, late liver stage-arresting, replication competent (LARC), genetically-attenuated PfSPZ are expected to be both safe and highly efficacious. Overall, PfSPZ vaccines meet safety, tolerability, and efficacy requirements for protecting pregnant women and travelers exposed to Pf in Africa, with licensure for these populations possible within 5 years. Protecting children and mass vaccination programs to block transmission and eliminate malaria are long-term objectives.

Japanese encephalitis is the main cause of viral encephalitis in Asia. In a previous single-arm vaccine trial, an inactivated chromatographically purified Japanese encephalitis Vero cell vaccine (CVI-JE; JEVAC TM ) was safe and immunogenic in 152 Thai children aged 1-3 years receiving a 2-dose primary immunization and booster dose 1 year later. We conducted a 5-year follow-up assessment of the persistence of the immune response the 144 children remaining in this cohort after first booster dose. Immunity was assessed by 50% plaque reduction neutralization test annually for up to 5 years post-booster. Seroprotection rates (95%CI) decreased from 100% (97.1-100) at 1 year post-booster to 93% (85.0-98.3) at 5 years post-booster. No serious vaccine-related adverse events or Japanese encephalitis infections were reported. A 2-dose primary immunization and booster 1 year later with CVI-JE provided long-lasting immunity in the majority of children.

Introduction: Transmitted by ticks, Lyme disease is the most common vector-borne disease in the Northern hemisphere. Despite the geographical expansion of human Lyme disease cases, no effective preventive strategies are currently available. Developing an efficacious and safe vaccine is therefore urgently needed. Efforts have previously been taken to identify vaccine targets in the causative pathogen ( Borrelia burgdorferi sensu lato) and arthropod vector ( Ixodes spp.). However, progress was impeded due to a lack of consumer confidence caused by the myth of undesired off-target responses, low immune responses, a limited breadth of immune reactivity, as well as by the complexities of the vaccine process development., Area Covered: In this review, we summarize the antigen engineering approaches that have been applied to overcome those challenges and the underlying mechanisms that can be exploited to improve both safety and efficacy of future Lyme disease vaccines., Expert Opinion: Over the past two decades, several new genetically redesigned Lyme disease vaccine candidates have shown success in both preclinical and clinical settings and built a solid foundation for further development. These studies have greatly informed the protective mechanisms of reducing Lyme disease burdens and ending the endemic of this disease.

Introduction: Chronic infection with the protozoal parasite Trypanosoma cruzi leads to a progressive cardiac disease, known as chronic Chagasic cardiomyopathy (CCC). A new therapeutic Chagas disease vaccine is in development to augment the existing antiparasitic chemotherapy drugs., Areas Covered: We report on our current understanding of the underlying immunologic and physiologic mechanisms that lead to CCC, including parasite immune escape mechanisms that allow persistence and the subsequent inflammatory and fibrotic processes that lead to clinical disease. We report on vaccine design and the observed immunotherapeutic effects including induction of a balanced T H 1/T H 2/T H 17 immune response that leads to reduced parasite burdens and tissue pathology. Furthermore, we report vaccine-linked chemotherapy, a dose-sparing strategy to further reduce parasite burdens and tissue pathology., Expert Opinion: Our vaccine-linked chemotherapeutic approach is a multimodal treatment strategy, addressing both the parasite persistence and the underlying deleterious host inflammatory and fibrotic responses that lead to cardiac dysfunction. In targeting treatment towards patients with chronic indeterminate or early determinate Chagas disease, this vaccine-linked chemotherapeutic approach will be highly economical and will reduce the global disease burden and deaths due to CCC.

Human papillomavirus (HPV) is one of the most common sexually transmitted infections in men and women. Most HPV studies have focused on vaccination toward women to prevent consequences of developing cervical cancer. However, persistent infections can cause penile, anal, and oropharyngeal cancers in men. Therefore, recent public health recommendations toward vaccination in men have been raised. There is limited HPV prevalence data among men in many countries, including Thailand. We conducted HPV sera IgG ELISA testing on a repository sera of Thai men (average age 21 years old) entering the Royal Thai Army as recruits in 2013 (n = 1000). HPV IgG antibodies against virus-like particles of HPV- type 6, 11, 16e, and 18 were evaluated using a commercial ELISA kit. Overall, the anti-HPV IgG was 47% (95% CI: 44%-50%). HPV seroprevalence was significantly associated with residence regions with the highest prevalence in South (64%), but not associated with educational level, marital status, or type of residence. This data suggested that almost half of the Thai men in this cohort were exposed to HPV by the age of 21. Thus, HPV vaccination provided to male adolescents should be considered for disease prevention and minimizing transmission to sexual partners.

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of diarrheal disease in developing nations where it accounts for a significant disease burden in children between the ages of 0 to 59 months. It is also the number one bacterial causative agent of traveler's diarrhea. ETEC infects hosts through the fecal-oral route and utilizes colonization factors (CF) to adhere within the small intestine. Over 25 CFs have been identified; 7 are considered major CFs and a vaccine targeting these is predicted to provide protection against up to 66% of ETEC associated disease. Coli Surface Antigen 6 (CS6) is a major CF and is associated with disease-causing ETEC isolates. Analysis of the CS6 operon sequence led to the identification of two regions of variability among clinical isolates which we predicted exert effects on CS6 transcript and protein expression. A total of 7 recombinant E. coli strains were engineered to encode the CS6 operon in wild-type, hybrid, and mutant configurations. Western blot analysis and RT-qPCR provided evidence to support the importance of an intergenic hairpin structure on CS6 expression. Our results reveal the significance of CS6 sequence selection regarding ETEC vaccine development and present novel information regarding CS6 sequence variation in WT ETEC strains.

The foot-and-mouth disease virus (FMDV) is the causative agent of FMD, a highly infectious and devastating viral disease of domestic and wild cloven-hoofed animals. FMD affects livestock and animal products' national and international trade, causing severe economic losses and social consequences. Currently, inactivated vaccines play a vital role in FMD control, but they have several limitations. The genetic code expansion technology provides powerful strategies for generating premature termination codon (PTC)-harbouring virus as a live but replication-incompetent viral vaccine. However, this technology has not been explored for the design and development of new FMD vaccines. In this study, we first expanded the genetic code of the FMDV genome via a transgenic cell line containing an orthogonal translation machinery. We demonstrated that the transgenic cells stably integrated the orthogonal pyltRNA/pylRS pair into the genome and enabled efficient, homogeneous incorporation of unnatural amino acids into target proteins in mammalian cells. Next, we constructed 129 single-PTC FMDV mutants and four dual-PTC FMDV mutants after considering the tolerance, location, and potential functions of those mutated sites. Amber stop codons individually substituted the selected amino acid codons in four viral proteins (3D, L, VP1, and VP4) of FMDV. We successfully rescued PTC-FMDV mutants, but the amber codon unexpectedly showed a highly degree of mutation rate during PTC-FMDV packaging and replication. Our findings highlight that the genetic code expansion technology for the generation of PTC-FMD vaccines needs to be further improved and that the genetic stability of amber codons during the packaging and replication of FMDV is a concern.

Malaria vaccines hold significant promise for life-saving benefit, especially to children who bear the major burden of malaria mortality. The RTS,S/AS01 malaria vaccine provides moderate efficacy and is being tested in implementation studies. In parallel, multiple strategies are being advanced to test next-generation malaria vaccines, including novel approaches that build on principles learned from RTS,S development, vaccination with radiation-attenuated sporozoites, and development of monoclonal antibodies targeting immunogenic peptides. Novel vaccine delivery approaches are also being advanced, including self-amplifying RNA vaccine delivery, self-assembling protein nanoparticle methods, circumsporozoite protein-based approaches, and whole organism vaccination. Techniques employed for COVID-19 vaccine development should also be considered for malaria vaccination, including sustained release polymer nanoparticle hydrogel vaccination and charge-altering releasable transporters. As vaccine science advances and new approaches optimize knowledge gained, highly effective malaria vaccines that provide sustained protection are within reach.

In 2017, the World Health Organization (WHO) named A. baumannii as one of the three antibiotic-resistant bacterial species on its list of global priority pathogens in dire need of novel and effective treatment. With only polymyxin and tigecycline antibiotics left as last-resort treatments, the need for novel alternative approaches to the control of this bacterium becomes imperative. Vaccines against numerous bacteria have had impressive records in reducing the burden of the respective diseases and addressing antimicrobial resistance; as in the case of Haemophilus influenzae type b  . A similar approach could be appropriate for A. baumannii . Toward this end, several potentially protective antigens against A. baumannii were identified and evaluated as vaccine antigen candidates. A licensed vaccine for the bacteria, however, is still not in sight. Here we explore and discuss challenges in vaccine development against A. baumannii and the promising approaches for improving the vaccine development process.

There is an urgent need for an accessible and low-cost COVID-19 vaccine suitable for low- and middle-income countries. Here, we report on the development of a SARS-CoV-2 receptor-binding domain (RBD) protein, expressed at high levels in yeast ( Pichia pastoris ), as a suitable vaccine candidate against COVID-19. After introducing two modifications into the wild-type RBD gene to reduce yeast-derived hyperglycosylation and improve stability during protein expression, we show that the recombinant protein, RBD219-N1C1, is equivalent to the wild-type RBD recombinant protein (RBD219-WT) in an in vitro ACE-2 binding assay. Immunogenicity studies of RBD219-N1C1 and RBD219-WT proteins formulated with Alhydrogel® were conducted in mice, and, after two doses, both the RBD219-WT and RBD219-N1C1 vaccines induced high levels of binding IgG antibodies. Using a SARS-CoV-2 pseudovirus, we further showed that sera obtained after a two-dose immunization schedule of the vaccines were sufficient to elicit strong neutralizing antibody titers in the 1:1,000 to 1:10,000 range, for both antigens tested. The vaccines induced IFN-γ IL-6, and IL-10 secretion, among other cytokines. Overall, these data suggest that the RBD219-N1C1 recombinant protein, produced in yeast, is suitable for further evaluation as a human COVID-19 vaccine, in particular, in an Alhydrogel® containing formulation and possibly in combination with other immunostimulants.

Severe acute respiratory syndrome CoV-2 (SARS-CoV-2) is currently causing a worldwide pandemic with high morbidity and mortality. Development of animal models that recapitulate important aspects of coronavirus disease 2019 (COVID-19) is critical for the evaluation of vaccines and antivirals, and understanding disease pathogenesis. SARS-CoV-2 has been shown to use the same entry receptor as SARS-CoV-1, human angiotensin-converting enzyme 2 (hACE2) [1-3]. Due to amino acid differences between murine and hACE2, inbred mouse strains fail to support high titer viral replication of SARS-CoV-2 virus. Therefore, a number of transgenic and knock-in mouse models, as well as viral vector-mediated hACE2 delivery systems have been developed. Here we compared the K18-hACE2 transgenic model to adenovirus-mediated delivery of hACE2 to the mouse lung. We show that K18-hACE2 mice replicate virus to high titers in the nasal turbinates, lung and brain, with high lethality, and cytokine/chemokine production. In contrast, adenovirus-mediated delivery results in viral replication to lower titers limited to the nasal turbinates and lung, and no clinical signs of infection. The K18-hACE2 model provides a stringent model for testing vaccines and antivirals, whereas the adenovirus delivery system has the flexibility to be used across multiple genetic backgrounds and modified mouse strains.

There is a need for development of an effective vaccine against Francisella tularensis , as this potential bioweapon has a high mortality rate and low infectious dose when delivered via the aerosol route. Moreover, this Tier 1 agent has a history of weaponization. We engineered targeted mutations in the Type A strain F. tularensis subspecies tularensis Schu S4 in aro genes encoding critical enzymes in aromatic amino acid biosynthesis. F. tularensis Schu S4 ΔaroC , Schu S4Δ aroD , and Schu S4Δ aroC Δ aroD mutant strains were attenuated for intracellular growth in vitro and for virulence in vivo and, conferred protection against pulmonary wild-type (WT) F. tularensis Schu S4 challenge in the C57BL/6 mouse model. F. tularensis Schu S4Δ aroD was identified as the most promising vaccine candidate, demonstrating protection against high-dose intranasal challenge; it protected against 1,000 CFU Schu S4, the highest level of protection tested to date. It also provided complete protection against challenge with 92 CFU of a F. tularensis subspecies holarctica strain (Type B). Mice responded to vaccination with Schu S4Δ aroD with systemic IgM and IgG2c, as well as the production of a functional T cell response as measured in the splenocyte-macrophage co-culture assay. This vaccine was further characterized for dissemination, histopathology, and cytokine/chemokine gene induction at defined time points following intranasal vaccination which confirmed its attenuation compared to WT Schu S4. Cytokine, chemokine, and antibody induction patterns compared to wild-type Schu S4 distinguish protective vs . pathogenic responses to F. tularensis and elucidate correlates of protection associated with vaccination against this agent.

Enteric bacterial pathogens cause significant morbidity and mortality globally. Studies in tissue culture and animal models shaped our initial understanding of these host-pathogen interactions. However, intrinsic shortcomings in these models limit their application, especially in translational applications like drug screening and vaccine development. Human intestinal enteroid and organoid models overcome some limitations of existing models and advance the study of enteric pathogens. In this review, we detail the use of human enteroids and organoids to investigate the pathogenesis of invasive bacteria Shigella, Listeria , and Salmonella , and noninvasive bacteria pathogenic Escherichia coli, Clostridium difficile , and Vibrio cholerae . We highlight how these studies confirm previously identified mechanisms and, importantly, reveal novel ones. We also discuss the challenges for model advancement, including platform engineering to integrate environmental conditions, innate immune cells and the resident microbiome, and the potential for pre-clinical testing of recently developed antimicrobial drugs and vaccines.

A SARS-CoV receptor-binding domain (RBD) recombinant protein was developed and manufactured under current good manufacturing practices in 2016. The protein, known as RBD219-N1 when formulated on Alhydrogel®, induced high-level neutralizing antibodies and protective immunity with minimal immunopathology in mice after a homologous virus challenge with SARS-CoV (MA15 strain). We examined published evidence in support of whether the SARS-CoV RBD219-N1 could be repurposed as a heterologous vaccine against Coronavirus Infectious Disease (COVID)-19. Our findings include evidence that convalescent serum from SARS-CoV patients can neutralize SARS-CoV-2. Additionally, a review of published studies using monoclonal antibodies (mAbs) raised against SARS-CoV RBD and that neutralizes the SARS-CoV virus in vitro finds that some of these mAbs bind to the receptor-binding motif (RBM) within the RBD, while others bind to domains outside this region within RBD. This information is relevant and supports the possibility of developing a heterologous SARS-CoV RBD vaccine against COVID-19, especially due to the finding that the overall high amino acid similarity (82%) between SARS-CoV and SARS-CoV-2 spike and RBD domains is not reflected in RBM amino acid similarity (59%). However, the high sequence similarity (94%) in the region outside of RBM offers the potential of conserved neutralizing epitopes between both viruses.

Malaria is an illness caused by Plasmodium parasites transmitted to humans by infected mosquitoes. Of the five species that infect humans, P. falciparum exacts the highest toll in terms of human morbidity and mortality, and therefore represents a major public health threat in endemic areas. Recent advances in control efforts have reduced malaria incidence and prevalence, including rapid diagnostic testing, highly effective artemisinin combination therapy, use of insecticide-treated bednets, and indoor residual spraying. But, reductions in numbers of cases have stalled over the last few years, and incidence may have increased. As this concerning trend calls for new tools to combat the disease, the RTS,S vaccine has arrived just in time. The vaccine was created in 1987 and began pilot implementation in endemic countries in 2019. This first-generation malaria vaccine demonstrates modest efficacy against malaria illness and holds promise as a public health tool, especially for children in high-transmission areas where mortality is high.

The development, clinical advancement and licensure of vaccines, and monitoring of vaccine effectiveness could be expedited and simplified by the ability to measure immunological endpoints that can predict a favorable clinical outcome. Antigen-specific and functional antibodies have been described in the context of naturally acquired immunity and vaccination against Shigella , and their presence in serum has been associated with reduced risk of disease in human subjects. The relevance of these antibodies as correlates of protective immunity, their mechanistic contribution to protection (e.g. target antigens, interference with pathogenesis, and participation in microbial clearance), and factors that influence their magnitude and makeup (e.g. host age, health condition, and environment) are important considerations that need to be explored. In addition to facilitating vaccine evaluation, immunological correlates of protection could be useful for identifying groups at risk and advancing immune therapies. Herein we discuss the precedent and value of functional antibodies as immunological endpoints to predict vaccine efficacy and the relevance of functional antibody activity to evaluate protective immunity against shigellosis.

Introduction : Rift Valley fever (RVF) outbreaks can cause devastating economic loss and public health concerns. RVF virus (RVFV: genus Phlebovirus family Phenuiviridae ) is transmitted by mosquitoes, causes abortion in sheep, cattle, and goats, and severe diseases in humans including hemorrhagic fever, encephalitis, or retinitis. RVFV has spread from sub-Saharan Africa into Madagascar, Egypt, Saudi Arabia, and Yemen. Area covered : There are a few licensed veterinary RVF vaccines in endemic countries, whereas no licensed RVF vaccines are available for human use. There are two Investigational New Drug (IND) RVF candidate vaccines used in clinical trials. This review will discuss the development of two IND vaccines for RVF over the past 20-40 years, and further innovation for future RVF vaccines applicable for the use in endemic areas. Expert opinion : Vaccination for human RVF can protect at-risk personnel against severe RVF illness. Formalin-inactivated RVF candidate vaccine requires three doses to induce protective immunity, whereas the live-attenuated MP-12 candidate vaccine retains strong immunogenicity. Further innovation in safety, immunogenicity, and thermostability will facilitate future RVF vaccines for humans.

Introduction : Klebsiella pneumoniae (KP) are a leading cause of healthcare-associated infections. The dramatic increase in microbial resistance to third-generation cephalosporin and carbapenem 'front line' antimicrobial agents and the paucity of new antimicrobials have left clinicians with few therapeutic options and resulted in increased morbidity and mortality. Vaccines may reduce the incidence of infections thereby reducing the necessity for antimicrobials and are not subject to antimicrobial resistance mechanisms. Areas covered : We review whole cell, subunit, capsular polysaccharide (CPS), O polysaccharide (OPS) and conjugate vaccines against KP infection, as well as alternative KP vaccine platforms. Expert opinion : Vaccine-induced antibodies to KP CPS have been protective in preclinical studies, but the number of CPS types (>77) makes vaccines against this virulence factor less feasible. Since four OPS serotypes account of ~80% of invasive KP infections and anti-OPS antibodies are also protective in preclinical studies, both OPS-based conjugate and multiple antigen presenting system (MAPS) vaccines are in active development. Vaccines based on other KP virulence factors, such as outer membrane proteins, type 3 fimbriae (MrkA) and siderophores are at earlier stages of development. Novel strategies for the clinical testing of KP vaccines need to be developed.

Introduction : Influenza vaccines are safe and effective, yet they are infrequently used in low- and middle-income countries (LMICs). Areas covered : We examine influenza vaccine programs for children from within a framework of new vaccine adoption in LMICs. We review the available evidence on disease burden and vaccine introduction, the current global and financing policies, and the current status of vaccine availability, and country readiness for implementation. Expert commentary : Access to appropriate formulations of influenza vaccines and existing immunization infrastructures must be strengthened if influenza vaccine programs are to be expanded in LMICs. While WHO recommends that implementation of influenza vaccine programs should be a country decision based on national goals, capacities, and data review, vaccine decision makers from many LMICs will likely need more evidence to inform the value proposition of program investment for pediatric vaccination, particularly related to alternative immunization strategies that align with current vaccine delivery platforms, anticipated program impact on severe illness endpoints, and program costs and economic benefits. Targeted research and development to address the specific needs of LMICs may be needed to demonstrate the value proposition of influenza vaccines and to expand influenza vaccine programs in these settings.

Introduction: Chagas disease, caused by infection with the parasite Trypanosoma cruzi, represents a huge public health problem in the Americas, where millions of people are affected. Despite the availability of two drugs against the infection (benznidazole and nifurtimox), multiple factors impede their effective usage: (1) gaps in patient and healthcare provider awareness; (2) lack of access to diagnosis; (3) drug toxicity and absence of treatment algorithms to address adverse effects; (4) failures in drug supply and distribution; and (5) inconsistent drug efficacy against the symptomatic chronic stage. Areas covered: We review new approaches and technologies to enhance access to diagnosis and treatment to reduce the disease burden. We also provide an updated picture of recently published and ongoing anti-T. cruzi drug clinical trials. Although there has been progress improving the research and development (R&D) landscape, it is unclear whether any new treatments will emerge soon. Literature search methodologies included multiple queries to public databases and the use of own-built libraries. Expert opinion: Besides R&D, there is a major need to continue awareness and advocacy efforts by patient associations, local and national governments, and international agencies. Overall, health systems strengthening is essential to ensure vector control commitments, as well as patient access to diagnosis and treatment.

CD4+ and CD8+ T subsets are essential components of the adaptive immune system which act in concert at the site of infections to effectively protect against pathogens. Very limited data is available in humans regarding the relationship between CD4+ and CD8+ S . Typhi responsive cells in the terminal ileum mucosa (TI) and peripheral blood following Ty21a oral typhoid immunization. Here, we compared TI lamina propria mononuclear cells (LPMC) and peripheral blood CD4+ and CD8+ T memory (T M ) subsets responses and their relationship by Spearman's correlation following Ty21a immunization in volunteers undergoing routine colonoscopy. We observed that Ty21a immunization (i) influences the homing and accumulation of both CD4+ and CD8+ T cells in the TI, particularly integrin α4β7+ CCR9+ CD8+ T cells, (ii) elicits significantly higher frequencies of LPMC S . Typhi-responsive CD8+ T multifunctional (CD107a, IFNγ, IL-17A and/or MIP1β) cells than their CD4+ T counterparts, and (iii) results in the correlation of LPMC CD4+ Teffector/memory (T EM ) S . Typhi responses (CD107a, IFNγ, TNFα, IL-17A and/or MIP1β) to their LPMC CD8+ T EM counterparts. Moreover, we demonstrated that these positive correlations between CD4+ and CD8+ T EM occur primarily in TI LPMC but not in PBMC, suggesting important differences in responses between the mucosal and systemic compartments following oral Ty21a immunization. This study provides the first demonstration of the correlation of S . Typhi-specific CD4+ and CD8+ T M responses in the human terminal ileum mucosa and provides valuable information regarding the generation of mucosal and systemic immune responses following oral Ty21a-immunization which might impact future vaccine design and development.

Nontyphoidal Salmonella (NTS) are important human enteric pathogens globally. Among the different serovars associated with human NTS disease, S . Newport (a serogroup C 2 -C 3 ) accounts for a measurable proportion of cases. However, to date there are no licensed human NTS vaccines. NTS lipopolysaccharide-associated O polysaccharides are virulence factors and protective antigens in animal models. As isolated molecules, bacterial polysaccharides are generally poorly immunogenic, a limitation overcome by conjugation to a protein carrier. We report herein the development of a candidate serogroup C Salmonella ) accounts for a measurable proportion of cases. However, to date there are no licensed human NTS vaccines. NTS lipopolysaccharide-associated O polysaccharides are virulence factors and protective antigens in animal models. As isolated molecules, bacterial polysaccharides are generally poorly immunogenic, a limitation overcome by conjugation to a protein carrier. We report herein the development of a candidate serogroup C 2 glycoconjugate vaccine based on 3 glycoconjugate vaccine based on S . Newport Core-O polysaccharide (COPS) and phase 1 flagellin (FliC). S . Newport COPS and FliC were purified from genetically engineered reagent strains, and conjugated at the polysaccharide reducing end to FliC protein lysines with thioether chemistry. S . Newport COPS:FliC immunization in mice improved anti-polysaccharide immune responses, generated high anti-FliC IgG titers, and mediated robust protection against challenge with both the homologous serovar as well another serogroup C 2 -C 3 serovar ( S . Newport COPS:FliC induced sera found that the anti-COPS IgG antibodies were specific for serogroup C S . Newport COPS:FliC induced sera found that the anti-COPS IgG antibodies were specific for serogroup C 2 -C 3 lipopolysaccharide, and could promote bactericidal killing by complement and uptake into phagocytes. These preclinical studies establish the protective capacity of serogroup C 2 OPS glycoconjugates, and provide a path forward for the development of a multivalent 3 vaccine for humans that includes serogroup C Salmonella vaccine for humans that includes serogroup C 2 -C 3 .

Enterotoxigenic Escherichia coli (ETEC) is a major cause of travelers' diarrhea and of diarrhea among young children in developing countries. Experimental challenge studies in adult volunteers have played a pivotal role in establishing ETEC as an enteric pathogen, elucidating its pathogenesis by identifying specific virulence attributes, characterizing the human immune response to clinical and sub-clinical ETEC infection and assessing preliminarily the clinical acceptability, immunogenicity and efficacy of prototype ETEC vaccines. This review provides a historical perspective of experimental challenge studies with ETEC. It summarizes pioneering early studies carried out by investigators at the University of Maryland School of Medicine to show how those studies provided key information that influenced the directions taken by many research groups to develop vaccines to prevent ETEC. In addition, key experimental challenge studies undertaken at other institutions will also be cited.

Estradiol, a major female steroid produced during pregnancy, has been reported to protect ovariectomized animals against H1N1 influenza infections via its anti-inflammatory effects. However, it remains unclear why pregnant women with high gestational estradiol levels are highly susceptible to influenza infections. This study was aimed to investigate the effects of pregnancy level of estradiol on female immunity against H5N1 infection in Balb/c mice. A sex-dependent susceptibility to H5N1 infection (higher morbidity and higher mortality) was observed in both pregnant and non-pregnant female mice as compared to male mice. Subcutaneous implantation of estradiol pellets increased serum estradiol concentrations of non-pregnant female mice to the pregnancy level. These mice were protected from H5N1 infection through downregulation of pulmonary pro-inflammatory cytokines. However, the production of virus-specific antibodies after infection was significantly delayed in estradiol-implanted mice when compared to placebos. Virus-specific IgG-secreting and IL-4-secreting cells were also reduced in estradiol-implanted mice. Similarly, lower antibody titers to seasonal vaccine antigens were found in pregnant women as compared to non-pregnant females without hormone usage. Our results indicate that estradiol levels equivalent to those found during pregnancy have divergent effects on female immunity against influenza, highlighting the importance of vaccination during pregnancy to prevent severe influenza infections.

Non-typhoidal Salmonella (NTS) are a leading cause of foodborne infections worldwide, and serogroups B, C 1 , C 2- C 3 and D are the most common serogroups associated with human disease. While live vaccine candidates that protect against S. Typhimurium (serogroup B) and S. Enteritidis (serogroup D) have been described by us and others, far less effort has been directed towards vaccines that target either serogroup C 1 or C 2- C 3 Salmonella Newport-based live-attenuated vaccine (serogroup C Salmonella Newport-based live-attenuated vaccine (serogroup C 2- C 3 ). Deletion of the genes clpX or rfaL , previously used in live vaccines to attenuate S. Typhimurium and/or S. Enteritidis, failed to attenuate S. Newport. However, we found that deletion of either guaBA or htrA . Newport in an intraperitoneal infection model in BALB/c mice. Our live-attenuated vaccine candidate CVD 1966 ( S . Newport in an intraperitoneal infection model in BALB/c mice. Our live-attenuated vaccine candidate CVD 1966 ( S. Newport Δ guaBA Δ htrA . Newport, we observed vaccine efficacies of 53% for immunization via the intraperitoneal route and 47% for immunization via the oral route. Following intraperiteonal immunization, the vaccine also significantly reduced the bacterial burden of challenge organisms in the liver and spleen. Interestingly, reducing the LPS chain length by deleting S . Newport, we observed vaccine efficacies of 53% for immunization via the intraperitoneal route and 47% for immunization via the oral route. Following intraperiteonal immunization, the vaccine also significantly reduced the bacterial burden of challenge organisms in the liver and spleen. Interestingly, reducing the LPS chain length by deleting rfaL did not induce a stronger immune response towards surface antigens, and failed to elicit any protection against lethal homologous challenge. In conclusion, we have developed a live-attenuated Salmonella serogroup C 2- vaccine that we are further evaluating.3 vaccine that we are further evaluating.

Shigella is one of the major enteric pathogens worldwide. We present a murine model of S. flexneri infection and investigate the role of zinc deficiency (ZD). C57BL/6 mice fed either standard chow (HC) or ZD diets were pretreated with an antibiotic cocktail and received S. flexneri strain 2457T orally. Antibiotic pre-treated ZD mice showed higher S. flexneri colonization than non-treated mice. ZD mice showed persistent colonization for at least 50 days post-infection (pi). S. flexneri -infected mice showed significant weight loss, diarrhea and increased levels of fecal MPO and LCN in both HC and ZD fed mice. S. flexneri preferentially colonized the colon, caused epithelial disruption and inflammatory cell infiltrate, and promoted cytokine production which correlated with weight loss and histopathological changes. Infection with S. flexneri ΔmxiG (critical for type 3 secretion system) did not cause weight loss or diarrhea, and had decreased stool shedding duration and tissue burden. Several biochemical changes related to energy, inflammation and gut-microbial metabolism were observed. Zinc supplementation increased weight gains and reduced intestinal inflammation and stool shedding in ZD infected mice. In conclusion, young antibiotic-treated mice provide a new model of oral S. flexneri infection, with ZD promoting prolonged infection outcomes.

A therapeutic vaccine for human Chagas disease (American trypanosomiasis caused by Trypanosoma cruzi) is under development based on the success of vaccinating mice with DNA constructs expressing the antigens Tc24 and Tc-TSA-1. However, because DNA and nucleic acid vaccines produce less than optimal responses in humans, our strategy relies on administering a recombinant protein-based vaccine, together with adjuvants that promote Th1-type immunity. Here we describe a process for the purification and refolding of recombinant TSA-1 expressed in Escherichia coli. The overall yield (20-25%) and endotoxin level of the purified recombinant TSA-1 (rTSA-1) is suitable for pilot scale production of the antigen for use in phase 1 clinical trials. Mice infected with T. cruzi were treated with rTSA-1, either alone or with Toll-like receptor 4 (TLR-4) agonist adjuvants including monophosphoryl lipid A (MPLA), glucopyranosyl lipid A (GLA, IDRI), and E6020 (EISEI, Inc). TSA-1 with the TLR-4 agonists was effective at reducing parasitemia relative to rTSA-1 alone, although it was difficult to discern a therapeutic effect compared to treatment with TLR-4 agonists alone. However, rTSA-1 with a 10 ug dose of MPLA optimized reductions in cardiac tissue inflammation, which were significantly reduced compared to MPLA alone. It also elicited the lowest parasite burden and the highest levels of TSA-1-specific IFN-gamma levels and IFN-gamma/IL-4 ratios. These results warrant the further evaluation of rTSA-1 in combination with rTc24 in order to maximize the therapeutic effect of vaccine-linked chemotherapy in both mice and non-human primates before advancing to clinical development.

Translational science for new biotechnologies (e.g. drugs, vaccines, devices, or diagnostics) depend on the development of a robust ' business case' . This is driven by complex scientific, technical, logistical, financial and operational elements to determine the feasibility and probability of traversing the "valleys of death" leading to licensure. The potential results in terms of profitability and financial realization, called 'product value proposition' play a crucial role in establishing incentives for investment during and after development. With this review, our goal is to summarize the challenges in taking vaccines against neglected tropical diseases (NTDs) from development through licensure and provide a perspective that these vaccines can have measurable public health and economic profitability and market success. Understanding these processes and its challenges would open the opportunity to accelerate and advance these essential NTD vaccines through the last mile towards licensure and for the delivery to afflicted populations in low- and middle-income countries.

Inactivated mouse-brain-derived Japanese encephalitis vaccine has a worrisome safety profile and the live attenuated vaccine is unsuitable in immunodeficiency. This study aimed to evaluate the immunogenicity and safety of an inactivated chromatographically purified Vero-cell-derived JE vaccine (CVI-JE, Beijing P-3 strain) in children. 152 healthy Thai children, with an average (SD) age of 14.4 (3.8) months, received 3 doses of CVI-JE on days 0, 7-28, and one year. Homologous JE neutralizing antibody titers (NT) were measured. All subjects had seroprotection [geometric mean titer (GMT) 150] 28 days' post 2nd vaccination. The seroprotection rates at 1 year after primary series and and 1 month after the booster were 89.3% (GMT 49) and 100% (GMT 621), respectively. Local and systemic reactions-fever (17.6%), vomiting (8%), and poor appetite (5.3%)-were noted within 28 days' post-vaccination. All these symptoms were self-limited., Conclusions: CVI-JE is safe, immunogenic, and provided high NT.

There are two internationally available WHO-prequalified oral rotavirus vaccines (Rotarix and RotaTeq), two rotavirus vaccines licensed in India (Rotavac and Rotasiil), one in China (Lanzhou lamb rotavirus vaccine) and one in Vietnam (Rotavin-M1), and several candidates in development. Rotavirus vaccination has been rolled out in Latin American countries and is beginning to be deployed in sub-Saharan African countries but middle- and low-income Asian countries have lagged behind in rotavirus vaccine introduction. We provide a mini-review of the leading newer-generation rotavirus vaccines and compare them with Rotarix and RotaTeq. We discuss how the development and future availability of newer-generation rotavirus vaccines that address the programmatic needs of poorer countries may help scale-up rotavirus vaccination where it is needed.

Antipoverty vaccines are the vaccines targeting a group of approximately 20 neglected tropical diseases (NTDs), as currently defined by the World Health Organization (WHO). The "antipoverty" moniker refers to the fact that NTDs trap populations in poverty due to their chronic and deleterious effects on child intellect and worker productivity. Therefore, NTD vaccines can be expected to promote both global health and economic advancement. Unfortunately, antipoverty vaccine development has lagged behind vaccines for major childhood infections and pandemic threats, despite evidence for their cost-effectiveness and cost-savings. Currently, the only licensed vaccines for NTDs include those for yellow fever, dengue, and rabies, although several other NTD vaccines for hookworm disease, schistosomiasis, leishmaniasis, and Zika and Ebola virus infections are in different stages of clinical development, while others are at the preclinical development stage. With the exception of the viral NTD vaccines there so far has been minimal industry interest in the antipoverty vaccines, leaving their development to a handful of non-profit product development partnerships. The major scientific and geopolitical hurdles to antipoverty vaccine development are discussed, including a rising antivaccine ("antivax") movement now entering highly populated low- and middle-income countries.

There is a paucity of information on diarrheagenic enterotoxigenic Escherichia coli (ETEC)'s interaction with innate immune cells, in part due to the lack of reliable models that recapitulate infection in human gut. In a recent publication, we described the development of an ex vivo enteroid-macrophage co-culture model using human primary cells. We reported that macrophages residing underneath the epithelial monolayer acquired "resident macrophage" phenotype characterized by lower production of inflammatory cytokines and strong phagocytic activity. These macrophages extended projections across the epithelium, which captured ETEC applied to the apical side of the epithelium and reduced luminal bacterial load. Additional evidence presented in this addendum confirms these findings and further demonstrates that macrophage adaptation occurs regardless of the stage of differentiation of epithelial cells, and that ETEC uptake arises rapidly after infection. The enteroid-macrophage co-culture represents a novel and relevant tool to study host-cell interactions and pathogenesis of enteric infections in humans.

One combined measles-mumps-rubella (MMR) vaccine without Human Serum Albumin (HSA) is currently licensed in the USA (M-M-R II; Merck, USA) and another has been developed (Priorix™ [MMR-RIT, GSK, Belgium]). In this follow-up study, children from USA or Puerto Rico, who had received one dose of M-M-R II or MMR-RIT at 12-15 months of age in the primary study (NCT00861744), were followed-up for 2 y post-vaccination. Anti-measles and anti-rubella antibodies were measured using Enzyme-Linked Immunosorbent Assay (ELISA), and anti-mumps antibodies using ELISA and plaque reduction neutralization (PRN) assays. Serious adverse events (SAEs) were recorded during the entire follow-up. The according-to-protocol (ATP) persistence cohort included 752 children (M-M-R II = 186, MMR-RIT = 566), who received primary vaccination at a mean age of 12.3 ( ± 0.67) months. 104 children were revaccinated with MMR-containing vaccines; therefore, serology results for timepoints after revaccination were excluded from the analysis. Seropositivity for measles (Year 1≥ 98.3%; Year 2≥ 99.4%) and rubella (Year 1≥ 98.9%; Year 2 = 100%) remained as high at Year 2 as at Day 42. Similarly, seropositivity for mumps determined by ELISA (Year 1≥ 90.1%; Year 2≥ 94.1%) and PRN assays (Year 1≥ 87.5%; Year 2≥ 91.7%) persisted. Thirty-three SAEs were recorded in 23 children; 2 SAEs (inguinal adenitis and idiopathic thrombocytopenic purpura) and one SAE (febrile convulsion) were considered as potentially related to MMR-RIT and M-M-R II, respectively. This study showed that antibodies against measles, mumps and rubella persisted for up to 2 y post-vaccination with either MMR vaccine in children aged 12-15 months, and that both vaccines were well-tolerated during the follow-up period.

Introduction: Rift Valley fever (RVF) is a mosquito-borne zoonotic viral disease endemic to Africa and the Arabian Peninsula. High rates of abortion among infected ruminants and hemorrhagic fever in infected humans are major public health concerns. Commercially available veterinary RVF vaccines are important for preventing the spread of the Rift Valley fever virus (RVFV) in endemic countries; however, RVFV outbreaks continue to occur frequently in endemic countries in the 21st century. In the U.S., the live-attenuated MP-12 vaccine has been developed for both animal and human vaccination. This vaccine strain is well attenuated, and a single dose induces neutralizing antibodies in both ruminants and humans. Areas covered: This review describes scientific evidences of MP-12 vaccine efficacy and safety, as well as MP-12 variants recently developed by reverse genetics, in comparison with other RVF vaccines. Expert commentary: The containment of active RVF outbreaks and long-term protection from RVF exposure to infected mosquitoes are important goals for RVF vaccination. MP-12 vaccine will allow immediate vaccination of susceptible animals in case of an unexpected RVF outbreak in the U.S., whereas MP-12 vaccine may be also useful for the RVF control in endemic regions.

A therapeutic vaccine for human Chagas disease is under development by the Sabin Vaccine Institute Product Development Partnership. The aim of the vaccine is to significantly reduce the parasite burden of Trypanosoma cruzi in humans, either as a standalone product or in combination with conventional chemotherapy. Vaccination of mice with Tc24 formulated with monophosphoryl-lipid A (MPLA) adjuvant results in a Th1 skewed immune response with elevated IgG2a and IFNγ levels and a statistically significant decrease in parasitemia following T. cruzi challenge. Tc24 was therefore selected for scale-up and further evaluation. During scale up and downstream process development, significant protein aggregation was observed due to intermolecular disulfide bond formation. To prevent protein aggregation, cysteine codons were replaced with serine codons which resulted in the production of a non-aggregated and soluble recombinant protein, Tc24-C4. No changes to the secondary structure of the modified molecule were detected by circular dichroism. Immunization of mice with wild-type Tc24 or Tc24-C4, formulated with E6020 (TLR4 agonist analog to MPLA) emulsified in a squalene-oil-in-water emulsion, resulted in IgG2a and antigen specific IFNγ production levels from splenocytes that were not significantly different, indicating that eliminating putative intermolecular disulfide bonds had no significant impact on the immunogenicity of the molecule. In addition, vaccination with either formulated wild type Tc24 or Tc24-C4 antigen also significantly increased survival and reduced cardiac parasite burden in mice. Investigations are now underway to examine the efficacy of Tc24-C4 formulated with other adjuvants to reduce parasite burden and increase survival in pre-clinical studies.

Introduction: Cholera remains a problem in developing countries and a risk for travelers. Hypochlorhydria, blood group O, cardiac and renal disease increase the risk of developing cholera gravis. Oral vaccines containing inactivated Vibrio cholerae and requiring two doses are available in some countries. No cholera vaccine had been available for U.S. travelers for decades until 2016 when CVD 103-HgR (VAXCHORA™), an oral live attenuated vaccine, was licensed by the U.S. FDA. Areas covered: Enduring protection following wild-type cholera provided the rationale to develop a single-dose live oral vaccine. CVD 103-HgR is well-tolerated and protects against cholera caused by V. cholerae O1 of either serotype (Inaba, Ogawa) and biotype (El Tor, Classical). Since 90% vaccine efficacy is evident 10 days post-ingestion of a single dose, CVD 103-HgR can rapidly protect travelers. Vibriocidal antibody seroconversion correlates with protection; >90% of U.S. adult (including elderly) vaccinees seroconvert. The U.S. Public Health Service's Advisory Committee on Immunization Practices recommends CVD 103-HgR for U.S. travelers to areas of ongoing cholera transmission. Expert commentary: Next steps include evaluations in children, post-licensure safety and effectiveness monitoring, diminishing cold chain constraints, optimizing a 'high-dose' formulation for developing countries, and diminishing/eliminating the need for water to administer a dose.

Rift Valley fever is a mosquito-borne zoonotic disease affecting ruminants and humans. Rift Valley fever virus (RVFV: family Bunyaviridae, genus Phlebovirus) causes abortions and fetal malformations in ruminants, and hemorrhagic fever, encephalitis, or retinitis in humans. The live-attenuated MP-12 vaccine is conditionally licensed for veterinary use in the US. However, this vaccine lacks a marker for the differentiation of vaccinated from infected animals (DIVA). NSs gene is dispensable for RVFV replication, and thus, rMP-12 strains lacking NSs gene is applicable to monitor vaccinated animals. However, the immunogenicity of MP-12 lacking NSs was not as high as parental MP-12. Thus, chimeric MP-12 strains encoding NSs from either Toscana virus (TOSV), sandfly fever Sicilian virus (SFSV) or Punta Toro virus Adames strain (PTA) were characterized previously. Although chimeric MP-12 strains are highly immunogenic, the attenuation through the S-segment remains unknown. Using pathogenic ZH501 strain, we aimed to demonstrate the attenuation of ZH501 strain through chimeric S-segment encoding either the NSs of TOSV, SFSV, PTA, or Punta Toro virus Balliet strain (PTB). In addition, we characterized rZH501 encoding a human dominant-negative PKR (PKRΔE7), which also enhances the immunogenicity of MP-12. Study done on mice revealed that attenuation of rZH501 occurred through the S-segment encoding either PKRΔE7 or SFSV NSs. However, rZH501 encoding either TOSV, PTA, or PTB NSs in the S-segment uniformly caused lethal encephalitis. Our results indicated that the S-segments encoding PKRΔE7 or SFSV NSs are attenuated and thus applicable toward next generation MP-12 vaccine candidates that encode a DIVA marker.

Shigella flexneri is a Gram-negative pathogen that invades the colonic epithelium and causes millions of cases of watery diarrhea or bacillary dysentery predominately in children under the age of 5 years in developing countries. The effector Shigella enterotoxin 2 (ShET2), or OspD3, is encoded by the sen or ospD3 gene on the virulence plasmid. Previous literature has suggested that ospD3 is in an operon downstream of the ospC1 gene, and expression of both genes is controlled by a promoter upstream of ospC1. Since the intergenic region is 328 bases in length and contains several putative promoter regions, we hypothesized the genes are independently expressed. Here we provide data that ospD3 and ospC1 are not co-transcribed and that OspC1 is not required for OspD3/ShET2 function. Most importantly, we identified strong promoter activity in the intergenic region and demonstrate that OspD3/ShET2 can be expressed and secreted independently of OspC1. This work increases our understanding of the synthesis of a unique virulence factor and provides further insights into Shigella pathogenesis.