A systematic review of antimicrobial resistance in Salmonella enterica serovar Typhi, the etiological agent of typhoid

BACKGROUND

The temporal and spatial change in trends of antimicrobial resistance (AMR) in typhoid have not been systematically studied, and such information will be critical for defining intervention, as well as planning sustainable prevention strategies.

METHODOLOGY AND FINDINGS

To identify the phenotypic trends in AMR, 13,833 individual S. Typhi isolates, reported from 1973 to 2018 in 62 publications, were analysed to determine the AMR preponderance over time. Separate analyses of molecular resistance determinants present in over 4,000 isolates reported in 61 publications were also conducted. Multi-drug resistant (MDR) typhoid is in decline in Asia in a setting of high fluoroquinolone resistance while it is on the increase in Africa. Mutations in QRDRs in gyrA (S83F, D87N) and parC (S80I) are the most common mechanisms responsible for fluoroquinolone resistance. Cephalosporin resistant S. Typhi, dubbed extensively drug-resistant (XDR) is a real threat and underscores the urgency in deploying the Vi-conjugate vaccines.

CONCLUSION

From these observations, it appears that AMR in S. Typhi will continue to emerge leading to treatment failure, changes in antimicrobial policy and further resistance developing in S. Typhi isolates and other Gram-negative bacteria in endemic regions. The deployment of typhoid conjugate vaccines to control the disease in endemic regions may be the best defence.

Epidemiology and Immune Pathogenesis of Viral Sepsis

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Sepsis can be caused by a broad range of pathogens; however, bacterial infections represent the majority of sepsis cases. Up to 42% of sepsis presentations are culture negative, suggesting a non-bacterial cause. Despite this, diagnosis of viral sepsis remains very rare. Almost any virus can cause sepsis in vulnerable patients (e.g., neonates, infants, and other immunosuppressed groups). The prevalence of viral sepsis is not known, nor is there enough information to make an accurate estimate. The initial standard of care for all cases of sepsis, even those that are subsequently proven to be culture negative, is the immediate use of broad-spectrum antibiotics. In the absence of definite diagnostic criteria for viral sepsis, or at least to exclude bacterial sepsis, this inevitably leads to unnecessary antimicrobial use, with associated consequences for antimicrobial resistance, effects on the host microbiome and excess healthcare costs. It is important to understand non-bacterial causes of sepsis so that inappropriate treatment can be minimised, and appropriate treatments can be developed to improve outcomes. In this review, we summarise what is known about viral sepsis, its most common causes, and how the immune responses to severe viral infections can contribute to sepsis. We also discuss strategies to improve our understanding of viral sepsis, and ways we can integrate this new information into effective treatment.

A naturally protective epitope of limited variability as an influenza vaccine target

Current antigenic targets for influenza vaccine development are either highly immunogenic epitopes of high variability or conserved epitopes of low immunogenicity. This requires continuous update of the variable epitopes in the vaccine formulation or boosting of immunity to invariant epitopes of low natural efficacy. Here we identify a highly immunogenic epitope of limited variability in the head domain of the H1 haemagglutinin protein. We show that a cohort of young children exhibit natural immunity to a set of historical influenza strains which they could not have previously encountered and that this is partially mediated through the epitope. Furthermore, vaccinating mice with these epitope conformations can induce immunity to human H1N1 influenza strains that have circulated since 1918. The identification of epitopes of limited variability offers a mechanism by which a universal influenza vaccine can be created; these vaccines would also have the potential to protect against newly emerging influenza strains.

The relative invasive disease potential of Streptococcus pneumoniae among children after PCV introduction: A systematic review and meta-analysis

OBJECTIVES

Burden of pneumococcal disease depends on the prevalence and invasive disease potential of serotypes. We aimed to estimate the invasive disease potential of serotypes in children under 5 years of age by combining data from different settings with routine immunisation with pneumococcal conjugate vaccines (PCV).

METHODS

We conducted a systematic review, supplemented by unpublished data, to identify data on the frequency of pneumococcal serotypes in carriage and invasive pneumococcal disease (IPD). We estimated the invasive disease potential of serotypes as the ratio of IPD in relation to carriage (odds ratio and 95%CI) compared with 19A (reference serotype) by meta-analysis. We report results based on a random effects model for children aged 0-23, 24-29, and 0-59 months and by invasive clinical syndromes.

RESULTS

In comparison with 19A, serotypes 1, 7F, and 12F had a significantly higher invasive disease potential in children aged 0-23 and 0-59 months for all IPD and clinical syndromes (OR > 5). Several non-vaccine types (NVTs) (6C, 15A, 15BC, 16F, 23B, in these two age groups) had a lower invasive disease potential than 19A (OR 0.1-0.3). NVTs 8, 12F, 24F, and 33F were at the upper end of the invasiveness spectrum.

CONCLUSIONS

There is substantial variation among pneumococcal serotypes in their potential to cause IPD and disease presentation, which is influenced by age and time after PCV introduction. Surveillance of IPD and carriage is critical to understand the expected effectiveness of current PCVs (in the longer term) and guide the development of future vaccines.

Duration of intravenous antibiotic therapy for children with acute osteomyelitis or septic arthritis: a feasibility study

BACKGROUND

There is little current consensus regarding the route or duration of antibiotic treatment for acute osteomyelitis (OM) and septic arthritis (SA) in children.

OBJECTIVE

To assess the overall feasibility and inform the design of a future randomised controlled trial (RCT) to reduce the duration of intravenous (i.v.) antibiotic use in paediatric OM and SA.

DESIGN

(1) A prospective service evaluation (cohort study) to determine the current disease spectrum and UK clinical practice in paediatric OM/SA; (2) a prospective cohort substudy to assess the use of targeted polymerase chain reaction (PCR) in diagnosing paediatric OM/SA; (3) a qualitative study to explore families' views and experiences of OM/SA; and (4) the development of a core outcome set via a systematic review of literature, Delphi clinician survey and stakeholder consensus meeting.

SETTING

Forty-four UK secondary and tertiary UK centres (service evaluation).

PARTICIPANTS

Children with OM/SA.

INTERVENTIONS

PCR diagnostics were compared with culture as standard of care. Semistructured interviews were used in the qualitative study.

RESULTS

Data were obtained on 313 cases of OM/SA, of which 218 (61.2%) were defined as simple disease and 95 (26.7%) were defined as complex disease. The epidemiology of paediatric OM/SA in this study was consistent with existing European data. Children who met oral switch criteria less than 7 days from starting i.v. antibiotics were less likely to experience treatment failure (9.6%) than children who met oral switch criteria after 7 days of i.v. therapy (16.1% when switch was between 1 and 2 weeks; 18.2% when switch was > 2 weeks). In 24 out of 32 simple cases (75%) and 8 out of 12 complex cases (67%) in which the targeted PCR was used, a pathogen was detected. The qualitative study demonstrated the importance to parents and children of consideration of short- and long-term outcomes meaningful to families themselves. The consensus meeting agreed on the following outcomes: rehospitalisation or recurrence of symptoms while on oral antibiotics, recurrence of infection, disability at follow-up, symptom free at 1 year, limb shortening or deformity, chronic OM or arthritis, amputation or fasciotomy, death, need for paediatric intensive care, and line infection. Oral switch criteria were identified, including resolution of fever for ≥ 48 hours, tolerating oral food and medicines, and pain improvement.

LIMITATIONS

Data were collected in a 6-month period, which might not have been representative, and follow-up data for long-term complications are limited.

CONCLUSIONS

A future RCT would need to recruit from all tertiary and most secondary UK hospitals. Clinicians have implemented early oral switch for selected patients with simple disease without formal clinical trial evidence of safety. However, the current criteria by which decisions to make the oral switch are made are not clearly established or evidence based.

FUTURE WORK

A RCT in simple OM and SA comparing shorter- or longer-course i.v. therapy is feasible in children randomised after oral switch criteria are met after 7 days of i.v. therapy, excluding children meeting oral switch criteria in the first week of i.v. therapy. This study design meets clinician preferences and addresses parental concerns not to randomise prior to oral switch criteria being met.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Compositional and Functional Differences in the Human Gut Microbiome Correlate with Clinical Outcome following Infection with Wild-Type Salmonella enterica Serovar Typhi

Insights into disease susceptibility as well as the efficacy of vaccines against typhoid and other enteric pathogens may be informed by better understanding the relationship between the effector immune response and the gut microbiota. In the present study, we characterized the composition (16S rRNA gene profiling) and function (RNA sequencing [RNA-seq]) of the gut microbiota following immunization and subsequent exposure to wild-type Salmonella enterica serovar Typhi in a human challenge model to further investigate the central hypothesis that clinical outcomes may be linked to the gut microbiota. Metatranscriptome analysis of longitudinal stool samples collected from study subjects revealed two stable patterns of gene expression for the human gut microbiota, dominated by transcripts from either Methanobrevibacter or a diverse representation of genera in the Firmicutes phylum. Immunization with one of two live oral attenuated vaccines against S. Typhi had minimal effects on the composition or function of the gut microbiota. It was observed that subjects harboring the methanogen-dominated transcriptome community at baseline displayed a lower risk of developing symptoms of typhoid following challenge with wild-type S. Typhi. Furthermore, genes encoding antioxidant proteins, metal homeostasis and transport proteins, and heat shock proteins were expressed at a higher level at baseline or after challenge with S. Typhi in subjects who did not develop symptoms of typhoid. These data suggest that functional differences relating to redox potential and ion homeostasis in the gut microbiota may impact clinical outcomes following exposure to wild-type S. Typhi.IMPORTANCES. Typhi is a significant cause of systemic febrile morbidity in settings with poor sanitation and limited access to clean water. It has been demonstrated that the human gut microbiota can influence mucosal immune responses, but there is little information available on the impact of the human gut microbiota on clinical outcomes following exposure to enteric pathogens. Here, we describe differences in the composition and function of the gut microbiota in healthy adult volunteers enrolled in a typhoid vaccine trial and report that these differences are associated with host susceptibility to or protection from typhoid after challenge with wild-type S Typhi. Our observations have important implications in interpreting the efficacy of oral attenuated vaccines against enteric pathogens in diverse populations.

Use of weighted multivariate estimates in trials of multi-serotype vaccines to simplify interpretation of treatment differences

Background

Many vaccines contain multiple components. Licensed pneumococcal conjugate vaccines (PCV) contain polysaccharides from 7, 10, or 13 different serotypes of Streptococcus pneumoniae. The main outcomes in randomised trials of pneumococcal vaccines are serotype-specific antibody measures. Comparisons are made between groups for each serotype, resulting in multiple separate comparisons of treatment effects which can be complicated to interpret. We investigated methods for computing the overall difference between vaccine groups across all serotypes.

Methods

Pneumococcal antibody concentrations were obtained from a randomised controlled trial of ten-valent pneumococcal vaccine, conducted in Kathmandu, Nepal. Infants received either 2 priming doses of vaccine at 6 and 14 weeks of age followed by a booster (2+1), or 3 priming doses at 6, 10, and 14 weeks of age with no booster (3+0). The overall difference between vaccine schedules across all serotypes was computed at each visit using a multivariate linear model with equal weights for each serotype. Alternative weights were derived from invasive pneumococcal disease cases in Nepal, Bangladesh and Pakistan, and from estimates of the relative invasiveness of each serotype and used in sensitivity analyses.

Results

When 10 separate estimates of treatment differences were computed the ratio of antibody responses for each serotype in the 2+1 group compared with the 3+0 group at 10 months of age varied greatly, with serotype-specific GMRs ranging from 2.80 for serotype 14, to 9.14 for serotype 18C. Using equal weights for each serotype, the overall geometric mean ratio (GMR) was 5.02 (95% CI 4.06−6.22) at 10 months of age, and 1.46 (95% CI 1.14−1.88) at 3 years of age. Using weights based on disease incidence gave GMRs ranging from 5.15 to 6.63 at 10 months of age, and 1.47 to 1.78 at 3 years of age. Using weights based on relative invasiveness gave estimates of 6.81 and 1.59, at 10 months and 3 years respectively.

Conclusion

PCV clinical trial data have a multivariate structure with correlated outcomes for different serotypes. When analysing each serotype separately, the multiple estimates of the treatment effect can complicate the interpretation of trial results. Reporting a single overall estimate which accounts for the correlation between outcomes can simplify such interpretation. Treatment effects can be weighted equally or alternative weights derived from independent data can be used.

Many modern vaccines have multiple components, such as quadrivalent meningococcal group ACWY vaccine or four-component group B meningococcal vaccine, thus these methods are widely applicable.

Laboratory and molecular surveillance of paediatric typhoidal Salmonella in Nepal: Antimicrobial resistance and implications for vaccine policy

Background

Children are substantially affected by enteric fever in most settings with a high burden of the disease, including Nepal. However pathogen population structure and transmission dynamics are poorly delineated in young children, the proposed target group for immunization programs. Here we present whole genome sequencing and antimicrobial susceptibility data on 198 S. Typhi and 66 S. Paratyphi A isolated from children aged 2 months to 15 years of age during blood culture surveillance at Patan Hospital, Nepal, 2008–2016.

Principal findings

S. Typhi was the dominant agent and comprised several distinct genotypes, dominated by 4.3.1 (H58). The heterogeneity of genotypes in children under five was reduced compared to data from 2005–2006, attributable to ongoing clonal expansion of H58. Most isolates (86%) were non-susceptible to fluoroquinolones, associated mainly with S. Typhi H58 lineage II and S. Paratyphi A harbouring mutations in the quinolone resistance-determining region (QRDR); non-susceptible strains from these groups accounted for 50% and 25% of all isolates. Multi-drug resistance (MDR) was rare (3.5% of S. Typhi, 0 S. Paratyphi A) and restricted to chromosomal insertions of resistance genes in H58 lineage I strains. Temporal analyses revealed a shift in dominance from H58 Lineage I to H58 Lineage II, with the latter being significantly more common after 2010. Comparison to global data sets showed the local S. Typhi and S. Paratyphi A strains had close genetic relatives in other South Asian countries, indicating regional strain circulation. Multiple imports from India of ciprofloxacin-resistant H58 lineage II strains were identified, but these were rare and showed no evidence of clonal replacement of local S. Typhi.

Significance

These data indicate that enteric fever in Nepal continues to be a major public health issue with ongoing inter- and intra-country transmission, and highlights the need for regional coordination of intervention strategies. The absence of a S. Paratyphi A vaccine is cause for concern, given its prevalence as a fluoroquinolone resistant enteric fever agent in this setting.

An Appraisal of the Clinical Features of Pediatric Enteric Fever: Systematic Review and Meta-analysis of the Age-Stratified Disease Occurrence

Children bear a substantial proportion of the enteric fever disease burden in endemic areas. Controversy persists regarding which age groups are most affected, leading to uncertainty about optimal intervention strategies. We performed a systematic review and meta-analysis of studies in Asia and Africa to compare the relative proportion of children with enteric fever in the age groups <5 years, 5–9 years, and 10–14 years. Overall, studies conducted in Africa showed a relatively smaller occurrence of disease in the youngest age group, whereas in Asia the picture was more mixed with a very large degree of heterogeneity in estimates. The clinical features of enteric fever reviewed here differ between younger and older children and adults, likely leading to further uncertainty over disease burden. It is evident from our review that preschool children and infants also contribute a significant proportion of disease burden but have not been adequately targeted via vaccination programs, which have been focusing primarily on school-based vaccination campaigns.

Nanoscale chemical imaging of solid-liquid interfaces using tip-enhanced Raman spectroscopy

Tip-enhanced Raman spectroscopy (TERS) is a powerful tool for non-destructive and label-free surface molecular mapping at the nanoscale. However, to date nanoscale resolution chemical imaging in a liquid environment has not been possible, in part due to the lack of robust TERS probes that are stable when immersed in a liquid. In this work, we have addressed this challenge by developing plasmonically-active TERS probes with a multilayer metal coating structure that can be successfully used within a liquid environment. Using these novel TERS probes, we have compared the plasmonic enhancement of TERS signals in air and water environments for both gap mode and non-gap mode configurations and show that in both cases the plasmonic enhancement decreases in water. To better understand the signal attenuation in water, we have performed numerical simulations that revealed a negative correlation between the electric field enhancement at the TERS probe-apex and the refractive index of the surrounding medium. Finally, using these robust probes we demonstrate TERS imaging with nanoscale spatial resolution in a water environment for the first time by employing single-wall carbon nanotubes as a model sample. Our findings are expected to broaden the scope of TERS to a range of scientific disciplines in which nanostructured solid-liquid interfaces play a key role.

MAIT cell clonal expansion and TCR repertoire shaping in human volunteers challenged with Salmonella Paratyphi A

Mucosal-associated invariant T (MAIT) cells are innate-like T cells that can detect bacteria-derived metabolites presented on MR1. Here we show, using a controlled infection of humans with live Salmonella enterica serovar Paratyphi A, that MAIT cells are activated during infection, an effect maintained even after antibiotic treatment. At the peak of infection MAIT cell T-cell receptor (TCR)β clonotypes that are over-represented prior to infection transiently contract. Select MAIT cell TCRβ clonotypes that expand after infection have stronger TCR-dependent activation than do contracted clonotypes. Our results demonstrate that host exposure to antigen may drive clonal expansion of MAIT cells with increased functional avidity, suggesting a role for specific vaccination strategies to increase the frequency and potency of MAIT cells to optimize effector function.

Salmonella Typhi Bactericidal Antibodies Reduce Disease Severity but Do Not Protect against Typhoid Fever in a Controlled Human Infection Model

Effective vaccines against Salmonella Typhi, a major cause of febrile illness in tropical regions, can have a significant effect as a disease control measure. Earlier work has shown that immunization with either of two Salmonella Typhi vaccines, licensed Ty21a or candidate M01ZH09, did not provide full immunity in a controlled human infection model. Here, we describe the human humoral immune responses to these oral vaccines and their functional role in protection after challenge with S. Typhi. Serum, obtained from healthy volunteers before and after vaccination with Ty21a or M01ZH09 or placebo and before and after oral challenge with wild-type S. Typhi, was assessed for bactericidal activity. Single-dose vaccination with M01ZH09 induced an increase in serum bactericidal antibodies (p = 0.001) while three doses of Ty21a did not. No association between bactericidal activity and protection against typhoid after challenge was seen in either vaccine arm. Bactericidal activity after vaccination correlated significantly with delayed disease onset (p = 0.013), lower bacterial burden (p = 0.006), and decreased disease severity scores (p = 0.021). Depletion of antibodies directed against lipopolysaccharide significantly reduced bactericidal activity (p = 0.009). We conclude that antibodies induced after ingestion of oral live-attenuated typhoid vaccines or after challenge with wild-type S. Typhi exhibit bactericidal activity. This bactericidal activity is mediated by anti-O:LPS antibodies and significantly reduces clinical symptoms but does not provide sterile immunity. This directs future vaccine studies toward other antigens or mechanisms of protection against typhoid.

Change in viral bronchiolitis management in primary care in the UK after the publication of NICE guideline

The aim of this study was to investigate changes in general practitioner (GP) management before and after the publication of the National Institute for Health and Care Excellence bronchiolitis guideline. In March 2015 and May 2016, an electronic questionnaire was sent to GPs. It was completed by 1001 GPs in 2015 and 1009 in 2016. There were small but significant improvements in proportions of GPs using a guideline, measuring oxygen saturations and providing written guidance, and appropriate reductions in those prescribing medications. Thirty-five per cent had read the guideline and 25% changed their practice since guideline publication. There were modest but significant improvements in reported management by GPs after guideline publication.

Prevention of enteric fever in travellers with typhoid conjugate vaccines

The 2018 WHO position paper on typhoid vaccines indicates preference for the use of new generation typhoid conjugate vaccines over existing parenteral Vi-polysaccharide (Vi-PS) and oral attenuated Ty21a vaccines

Transcriptomics in Human Challenge Models

Human challenge models, in which volunteers are experimentally infected with a pathogen of interest, provide the opportunity to directly identify both natural and vaccine-induced correlates of protection. In this review, we highlight how the application of transcriptomics to human challenge studies allows for the identification of novel correlates and gives insight into the immunological pathways required to develop functional immunity. In malaria challenge trials for example, innate immune pathways appear to play a previously underappreciated role in conferring protective immunity. Transcriptomic analyses of samples obtained in human challenge studies can also deepen our understanding of the immune responses preceding symptom onset, allowing characterization of innate immunity and early gene signatures, which may influence disease outcome. Influenza challenge studies demonstrate that these gene signatures have diagnostic potential in the context of pandemics, in which presymptomatic diagnosis of at-risk individuals could allow early initiation of antiviral treatment and help limit transmission. Furthermore, gene expression analysis facilitates the identification of host factors contributing to disease susceptibility, such as C4BPA expression in enterotoxigenic Escherichia coli infection. Overall, these studies highlight the exceptional value of transcriptional data generated in human challenge trials and illustrate the broad impact molecular data analysis may have on global health through rational vaccine design and biomarker discovery.

AS03- and MF59-Adjuvanted Influenza Vaccines in Children

Influenza is a major cause of respiratory disease leading to hospitalization in young children. However, seasonal trivalent influenza vaccines (TIVs) have been shown to be ineffective and poorly immunogenic in this population. The development of live-attenuated influenza vaccines and adjuvanted vaccines are important advances in the prevention of influenza in young children. The oil-in-water emulsions MF59 and adjuvant systems 03 (AS03) have been used as adjuvants in both seasonal adjuvanted trivalent influenza vaccines (ATIVs) and pandemic monovalent influenza vaccines. Compared with non-adjuvanted vaccine responses, these vaccines induce a more robust and persistent antibody response for both homologous and heterologous influenza strains in infants and young children. Evidence of a significant improvement in vaccine efficacy with these adjuvanted vaccines resulted in the use of the monovalent (A/H1N1) AS03-adjuvanted vaccine in children in the 2009 influenza pandemic and the licensure of the seasonal MF59 ATIV for children aged 6 months to 2 years in Canada. The mechanism of action of MF59 and AS03 remains unclear. Adjuvants such as MF59 induce proinflammatory cytokines and chemokines, including CXCL10, but independently of type-1 interferon. This proinflammatory response is associated with improved recruitment, activation and maturation of antigen presenting cells at the injection site. In young children MF59 ATIV produced more homogenous and robust transcriptional responses, more similar to adult-like patterns, than did TIV. Early gene signatures characteristic of the innate immune response, which correlated with antibody titers were also identified. Differences were detected when comparing child and adult responses including opposite trends in gene set enrichment at day 3 postvaccination and, unlike adult data, a lack of correlation between magnitude of plasmablast response at day 7 and antibody titers at day 28 in children. These insights show the utility of novel approaches in understanding new adjuvants and their importance for developing improved influenza vaccines for children.

Influenza Vaccination Strategies Should Target Children

Strategies to increase influenza vaccination rates have typically targeted healthcare professionals (HCPs) and individuals in various high-risk groups such as the elderly. We argue that they should (instead or as well) focus on increasing vaccination rates in children. Because children suffer higher influenza incidence rates than any other demographic group, and are major drivers of seasonal influenza epidemics, we argue that influenza vaccination strategies that serve to increase uptake rates in children are likely to be more effective in reducing influenza-related morbidity and mortality than those targeting HCPs or the elderly. This is true even though influenza-related morbidity and mortality amongst children are low, except in the very young. Further, we argue that there are no decisive reasons to suppose that children-focused strategies are less ethically acceptable than elderly or HCP-focused strategies.

Efficacy and immunogenicity of a Vi-tetanus toxoid conjugate vaccine in the prevention of typhoid fever using a controlled human infection model of Salmonella Typhi: a randomised controlled, phase 2b trial

BACKGROUND

Salmonella enterica serovar Typhi (S Typhi) is responsible for an estimated 20 million infections and 200 000 deaths each year in resource poor regions of the world. Capsular Vi-polysaccharide-protein conjugate vaccines (Vi-conjugate vaccines) are immunogenic and can be used from infancy but there are no efficacy data for the leading candidate vaccine being considered for widespread use. To address this knowledge gap, we assessed the efficacy of a Vi-tetanus toxoid conjugate vaccine using an established human infection model of S Typhi.

METHODS

In this single-centre, randomised controlled, phase 2b study, using an established outpatient-based human typhoid infection model, we recruited healthy adult volunteers aged between 18 and 60 years, with no previous history of typhoid vaccination, infection, or prolonged residency in a typhoid-endemic region. Participants were randomly assigned (1:1:1) to receive a single dose of Vi-conjugate (Vi-TT), Vi-polysaccharide (Vi-PS), or control meningococcal vaccine with a computer-generated randomisation schedule (block size 6). Investigators and participants were masked to treatment allocation, and an unmasked team of nurses administered the vaccines. Following oral ingestion of S Typhi, participants were assessed with daily blood culture over a 2-week period and diagnosed with typhoid infection when meeting pre-defined criteria. The primary endpoint was the proportion of participants diagnosed with typhoid infection (ie, attack rate), defined as persistent fever of 38°C or higher for 12 h or longer or S Typhi bacteraemia, following oral challenge administered 1 month after Vi-vaccination (Vi-TT or Vi-PS) compared with control vaccination. Analysis was per protocol. This trial is registered with ClinicalTrials.gov, number NCT02324751, and is ongoing.

FINDINGS

Between Aug 18, 2015, and Nov 4, 2016, 112 participants were enrolled and randomly assigned; 34 to the control group, 37 to the Vi-PS group, and 41 to the Vi-TT group. 103 participants completed challenge (31 in the control group, 35 in the Vi-PS group, and 37 in the Vi-TT group) and were included in the per-protocol population. The composite criteria for typhoid diagnosis was met in 24 (77%) of 31 participants in the control group, 13 (35%) of 37 participants in the Vi-TT group, and 13 (35%) of 35 participants in the Vi-PS group to give vaccine efficacies of 54·6% (95% CI 26·8-71·8) for Vi-TT and 52·0% (23·2-70·0) for Vi-PS. Seroconversion was 100% in Vi-TT and 88·6% in Vi-PS participants, with significantly higher geometric mean titres detected 1-month post-vaccination in Vi-TT vaccinees. Four serious adverse events were reported during the conduct of the study, none of which were related to vaccination (one in the Vi-TT group and three in the Vi-PS group).

INTERPRETATION

Vi-TT is a highly immunogenic vaccine that significantly reduces typhoid fever cases when assessed using a stringent controlled model of typhoid infection. Vi-TT use has the potential to reduce both the burden of typhoid fever and associated health inequality.

FUNDING

The Bill & Melinda Gates Foundation and the European Commission FP7 grant, Advanced Immunization Technologies (ADITEC).

Issues in vaccinology: Present challenges and future directions

Vaccination is a principal and highly cost-effective means of controlling infectious diseases, providing direct protection against pathogens by conferring long-lasting immunological memory and inducing population-level herd immunity. Despite rapid ongoing progress in vaccinology, there remain many obstacles to the development and deployment of novel or improved vaccines; these include the underlying science of how to induce and sustain appropriate protective immune responses as well as bureaucratic, logistic and socio-political hurdles. The failure to distribute and administer existing vaccines to at-risk communities continues to account for a large proportion of infant mortality worldwide: almost 20 million children do not have access to basic vaccines and several million still die each year as a result. While emerging epidemic or pandemic diseases pose a significant threat to global health and prosperity, there are many infectious diseases which provide a continuous or cyclical burden on healthcare systems which also need to be addressed. Gaps in knowledge of the human immune system stand in the way of developing technologies to overcome individual and pathogenic variation. The challenges in tackling infectious disease and directions that the field of preventive medicine may take to improve the current picture of global health are the focus of this review.

Persistence of immunity after vaccination with a capsular group B meningococcal vaccine in 3 different toddler schedules

BACKGROUND

One schedule for the capsular group B meningococcal vaccine 4CMenB is 2 doses that are administered 2 months apart for children aged 12-23 months, with a booster dose 12-24 months later. Our objective was to provide data on persistence of human serum bactericidal antibody (hSBA) titres in children up to 4 years of age after initial doses at 12-24 months, and immunogenicity of a booster dose at 48 months of age compared with vaccine-naive children.

METHODS

Children previously immunized, as part of a randomized controlled trial, with 2 doses of 4CMenB vaccine at 12-24 months of age received a booster at 4 years of age. Vaccine-naive age-matched toddlers received 2 doses of 4CMenB. Human serum bactericidal antibody titres against reference strains H44/76, 5/99, NZ98/254 and M10713 were evaluated before and after innoculation with 4CMenB vaccine in 4-year-old children.

RESULTS

Of 332 children in the study, 123 had previously received 4CMenB and 209 were vaccine-naive controls. Before the booster, the proportions of participants (previously vaccinated groups compared with controls) with hSBA titres of 1:5 or more were as follows: 9%-11% v. 1% (H44/76), 84%-100% v. 4% (5/99), 0%-18% v. 0% (NZ98/254) and 59%-60% v. 60% (M10713). After 1 dose of 4CMenB in previously immunized children, the proportions of participants achieving hSBA titres of 1:5 or more were 100% (H44/76 and 5/99), 70%-100% (NZ98/254) and 90%-100% (M10713).

INTERPRETATION

We found that waning of hSBA titres by 4 years of age occurred after 2 doses of 4CMenB vaccine administered at 12-24 months, and doses at 12-24 months have a priming effect on the immune system. A booster may be necessary to maintain hSBA titres of 1:5 or more among those children with increased disease risk. Trial registration: ClinicalTrials.gov, no. NCT01717638.