Exploring the relationship between environmental enteric dysfunction and oral vaccine responses

Variability of vaccine responsiveness in early life

Vaccinations in early life elicit variable antibody and cellular immune responses, sometimes leaving fully vaccinated children unprotected against life-threatening infectious diseases. Specific immune cell populations and immune networks may have a critical period of development and calibration in a window of opportunity occurring during the first 100 days of early life. Among the early life determinants of vaccine responses, this review will focus on modifiable factors involving development of the infant microbiota and metabolome: antibiotic exposure, breast versus formula feeding, and Caesarian section versus vaginal delivery of newborns. How microbiota may serve as natural adjuvants for vaccine responses and how microbiota-derived metabolites influence vaccine responses are also reviewed. Early life poor vaccine responsiveness can be linked to increased infection susceptibility because both phenotypes share similar immunity dysregulation profiles. An early life pre-vaccination endotype, when interventions have the highest potential for success, should be sought that predicts vaccine response trajectories.

Genetic variation in environmental enteropathy and stunting in Zambian children: A pilot genome wide association study using the H3Africa chip

PURPOSE

Stunting is known to be heavily influenced by environmental factors, so the genetic contribution has received little attention. Here we report an exploration of genetic influences in stunted Zambian children with environmental enteropathy.

METHOD

Children with stunting (LAZ < -2) were enrolled and given nutritional therapy. Those that were non-responsive to therapy were designated as cases, and children with good growth (LAZ > -1) from the same community as controls. Blood and stool samples were taken to measure biomarkers of intestinal inflammation, epithelial damage, and microbial translocation. Single nucleotide polymorphism array genotyping was carried out on saliva samples using the H3Africa consortium array.

RESULTS

Genome wide associations were analysed in 117 cases and 41 controls. While no significant associations with stunting were observed at P<5x10-8, likely due to the small sample size, interesting associations were observed at lower thresholds. SNPs associated with stunting were in genomic regions known to modulate neuronal differentiation and fatty acid biosynthesis. SNPs associated with increased microbial translocation were associated with non-integrin membrane ECM interactions, tight junctions, hemostasis, and G-alpha signalling events. SNPs associated with increased inflammation were associated with, ECM interactions, purine metabolism, axon guidance, and cell motility. SNPs negatively associated with inflammation overlapped genes involved in semaphoring interactions. We explored the existing coeliac disease risk HLA genotypes and found present: DQ2.5 (7.5%), DQ8 (3.5%) and DQ2.2 (3.8%); however, no children were positive for coeliac antibodies. We detected HLA-DRB:1301 and HLA-C:1802 with high odds ratios and P<0.05 in stunted children compared to controls.

CONCLUSION

Genetic variations associated with stunting and the enteropathy underlying it, include variants associated with multiple pathways relating to gene expression, glycosylation, nerve signalling, and sensing of the nutritional and microbiological milieu.

Lack of Associations between Environmental Exposures and Environmental Enteric Dysfunction among 18-Month-Old Children in Rural Malawi

Environmental enteric dysfunction (EED) is common and contributes to linear growth faltering (stunting) and mortality among children in low-resource settings. A few studies on the environmental causes of EED have been conducted but the exact exposures that cause or predispose children to EED are context-specific and not clear. This study aimed to assess associations between selected environmental exposures and EED markers among 620 18-month-old children. This was a secondary analysis of data from Malawian children who participated in a randomized controlled trial (iLiNS-DYAD, registered at clinicaltrials.gov as NCT01239693) from birth to 18 months of age. Data on environmental exposures, including drinking water source, sanitation, exposure to animals, housing materials, season, residential area, and food insecurity were collected at enrolment. Biomarkers of EED included concentrations of calprotectin, regenerating 1B protein (REG1B), and alpha-1-antitrypsin from stool samples to assess intestinal inflammation, repair, and permeability, respectively. We performed bivariate and multivariable analyses to assess associations between environmental exposures and EED biomarkers. Adjusting for possible confounders, we did not find associations between the selected environmental exposures and the three biomarkers. These results do not provide support for our hypothesis that the studied adverse environmental exposures are associated with increased concentrations of children's EED markers in rural Malawi.

Single-cell profiling of environmental enteropathy reveals signatures of epithelial remodeling and immune activation

Environmental enteropathy (EE) is a subclinical condition of the small intestine that is highly prevalent in low- and middle-income countries. It is thought to be a key contributing factor to childhood malnutrition, growth stunting, and diminished oral vaccine responses. Although EE has been shown to be the by-product of a recurrent enteric infection, its full pathophysiology remains unclear. Here, we mapped the cellular and molecular correlates of EE by performing high-throughput, single-cell RNA-sequencing on 33 small intestinal biopsies from 11 adults with EE in Lusaka, Zambia (eight HIV-negative and three HIV-positive), six adults without EE in Boston, United States, and two adults in Durban, South Africa, which we complemented with published data from three additional individuals from the same clinical site. We analyzed previously defined bulk-transcriptomic signatures of reduced villus height and decreased microbial translocation in EE and showed that these signatures may be driven by an increased abundance of surface mucosal cells-a gastric-like subset previously implicated in epithelial repair in the gastrointestinal tract. In addition, we determined cell subsets whose fractional abundances associate with EE severity, small intestinal region, and HIV infection. Furthermore, by comparing duodenal EE samples with those from three control cohorts, we identified dysregulated WNT and MAPK signaling in the EE epithelium and increased proinflammatory cytokine gene expression in a T cell subset highly expressing a transcriptional signature of tissue-resident memory cells in the EE cohort. Together, our work elucidates epithelial and immune correlates of EE and nominates cellular and molecular targets for intervention.

Investigating the Impact of Moringa oleifera Supplemented to Kenyan Breastfeeding Mothers on Maternal and Infant Health: A Cluster Randomized Single-Blinded Controlled Pilot Trial Protocol

Undernutrition contributes to up to 45% of deaths globally in children <5 years, with an optimal time for intervention before 24 months of age. Breastmilk microbiome helps establish the infant intestinal microbiome and impacts infant intestinal and nutritional health. Inadequacies in breastmilk composition such as low vitamin A contribute to infant nutrient deficiencies. Changes in milk fatty acid composition (reduced saturated and increased unsaturated fatty acids) may reduce susceptibility to enteric infection and increase protective intestinal bacteria. Moringa oleifera leaves (moringa) provide high nutrient concentrations (including protein, iron, vitamin A) and increase milk production; this may enhance breastmilk quantity and quality and improve infant health.

Objective

To investigate the role of moringa supplementation to improve maternal and infant nutritional and intestinal health via changes in maternal milk quantity and quality.

Methods

Fifty mother-infant pairs exclusively breastfeeding will be enrolled in a single-blinded randomized controlled trial in Kombewa County Hospital and Chulaimbo SubCounty Hospital, Kisumu, Kenya.

Intervention

Dietary Supplementation of 20 g of Moringa oleifera leaf powder divided twice daily in corn porridge consumed daily for 3 months while control comparator will receive porridge daily for 3 months.

Outcomes

Change in infant growth and maternal milk output (primary); maternal and infant vitamin A and iron status, changes in infant and maternal intestinal health (secondary).

Participating Centers

Pamoja Community Based Organization, Kombewa Sub-County Hospital, and Chulaimbo Sub-County Hospital.

13C-sucrose breath test for the non-invasive assessment of environmental enteropathy in Zambian adults

Objectives

Environmental enteropathy (EE) is a subclinical disorder highly prevalent in tropical and disadvantaged populations and is thought to play a role in growth faltering in children, poor responses to oral vaccines, and micronutrient deficiencies. This study aims to evaluate the potential of a non-invasive breath test based on stable isotopes for evaluation of impaired digestion and absorption of sucrose in EE.

Methods

We optimized a ¹³C-sucrose breath test (¹³C-SBT) in 19 young adults in Glasgow, United Kingdom. In a further experiment (in 18 adults) we validated the ¹³C-SBT using Reducose, an intestinal glucosidase inhibitor. We then compared the ¹³C-SBT to intestinal mucosal morphometry, immunostaining for sucrose-isomaltase (SI) expression, and SI activity in 24 Zambian adults with EE.

Results

Fully labeled sucrose (0.3 mg/kg) provided clear breath enrichment signals over 2–3 h in both British and Zambian adults, more than fivefold higher than naturally enriched sucrose. Reducose dramatically impaired ¹³C-sucrose digestion, reducing 4 h ¹³CO₂ breath recovery by > 50%. Duodenal biopsies in Zambian adults confirmed the presence of EE, and SI immunostaining was present in 16/24 adults. The kinetics of ¹³CO₂ evolution were consistently faster in participants with detectable SI immunostaining. Although sucrase activity was strongly correlated with villus height (r = 0.72; P < 0.05) after adjustment for age, sex and body mass index, there were no correlations between ¹³C-SBT and villus height or measured sucrase activity in pinch biopsies.

Conclusion

A ¹³C-SBT was developed which was easy to perform, generated clear enrichment of ¹³CO₂ in breath samples, and clearly reports sucrase activity. Further work is needed to validate it and understand its applications in evaluating EE.

Changes in Systemic Regulatory T Cells, Effector T Cells, and Monocyte Populations Associated With Early-Life Stunting

Stunting and environmental enteric dysfunction (EED) may be responsible for altered gut and systemic immune responses. However, their impact on circulating immune cell populations remains poorly characterized during early life. A detailed flow cytometry analysis of major systemic immune cell populations in 53 stunted and 52 non-stunted (2 to 5 years old) children living in Antananarivo (Madagascar) was performed. Compared to age-matched non-stunted controls, stunted children aged 2-3 years old had a significantly lower relative proportion of classical monocytes. No significant associations were found between stunting and the percentages of effector T helper cell populations (Th1, Th2, Th17, Th1Th17, and cTfh). However, we found that HLA-DR expression (MFI) on all memory CD4⁺ or CD8⁺ T cell subsets was significantly lower in stunted children compared to non-stunted controls. Interestingly, in stunted children compared to the same age-matched non-stunted controls, we observed statistically significant age-specific differences in regulatory T cells (Treg) subsets. Indeed, in 2- to 3-year-old stunted children, a significantly higher percentage of memory Treg, whilst a significantly lower percentage of naive Treg, was found. Our results revealed that both innate and adaptive systemic cell percentages, as well as activation status, were impacted in an age-related manner during stunting. Our study provides valuable insights into the understanding of systemic immune system changes in stunted children.

Association of Anti-Rotavirus IgA Seroconversion with Growth, Environmental Enteric Dysfunction and Enteropathogens in Rural Pakistani Infants

Background

The underperformance of oral vaccines in children of low- and middle-income countries is partly attributable to underlying environmental enteric dysfunction (EED).

Methodology

We conducted a longitudinal, community-based study to evaluate the association of oral rotavirus vaccine (Rotarix®) seroconversion with growth anthropometrics, EED biomarkers and intestinal enteropathogens in Pakistani infants. Children were enrolled between three to six months of their age based on their nutritional status. We measured serum anti-rotavirus immunoglobulin A (IgA) at enrollment and nine months of age with EED biomarkers and intestinal enteropathogens.

Results

A total of 391 infants received two doses of rotavirus (RV) vaccine. 331/391 provided paired blood samples. Of these 331 children, 45% seroconverted at 9 months of age, 35% did not seroconvert and 20% were seropositive at baseline. Non-seroconverted children were more likely to be stunted, wasted and underweight at enrollment. In univariate analysis, insulin-like growth factor (IGF) concentration at 6 months were higher in seroconverters, median (25th, 75th percentile): 26.3 (16.5, 43.5) ng/ml vs. 22.5 (13.6, 36.3) ng/ml for non-seroconverters, p-value = 0.024. At nine months, fecal myeloperoxidase (MPO) concentrations were significantly lower in seroconverters, 3050(1250, 7587) ng/ml vs. 4623.3 (2189, 11650) ng/ml in non-seroconverted children, p-value = 0.017. In multivariable logistic regression analysis, alpha-1 acid glycoprotein (AGP) and IGF-1 concentrations were positively associated with seroconversion at six months. The presence of sapovirus and rotavirus in fecal samples at the time of rotavirus administration, was associated with non-seroconversion and seroconversion, respectively.

Conclusion

We detected high baseline RV seropositivity and impaired RV vaccine immunogenicity in this high-risk group of children. Healthy growth, serum IGF-1 and AGP, and fecal shedding of rotavirus were positively associated with RV IgA seroconversion following immunization, whereas the presence of sapovirus was more common in non-seroconverters.

Trial registration: Clinical Trials ID: NCT03588013.

From Kiyoshi Shiga to Present-Day Shigella Vaccines: A Historical Narrative Review

We are at an exciting moment in time with the advancement of many vaccines, including a shigella vaccine for the world. It is instructive to look at the long road that some vaccines have traveled to recognize the remarkable accomplishments of those who were pioneers, appreciate the evolution of scientific and applied technology, and inform the future history of a vaccine that would have great potential for global health. To achieve this valuable retrospective, a narrative historical literature review was undertaken utilizing PubMed and Embase databases with relevant search terms. Retrieved articles were reviewed and information was organized into historical themes, landmark discoveries, and important vaccine development parallels. The literature reviewed was synthesized into major eras of shigella vaccine development from pathogen discovery and first attempts to empirical approaches of killed whole-cell and live-attenuated approaches, and a modern era that applied recombinant DNA engineering and structural vaccinology. The history of shigella vaccine development has largely followed the evolutionary path of vaccine development over the last 120 years, but with important lessons learned that should be considered as we embark on the future chapters of bringing to the world a safe and effective vaccine for global health.

A Randomized Controlled Trial of Dietary Rice Bran Intake on Microbiota Diversity, Enteric Dysfunction, and Fecal Secretory IgA in Malian and Nicaraguan Infants

BACKGROUND

Malnutrition and diarrhea are leading causes of death in children aged <5 y. Rice bran is a nutrient-dense prebiotic available globally.

OBJECTIVES

The objective of this secondary analysis was to evaluate the effects of daily rice bran supplementation on environmental enteric dysfunction (EED) markers, total fecal secretory IgA (sIgA), and microbiota in infants at high risk of malnutrition.

METHODS

Six-month-old Malian and Nicaraguan infants were randomly assigned to control or daily rice bran supplementation cohorts (1 to 5 g/d). Feces were collected monthly for 6 mo to evaluate fecal sIgA, markers of EED, and microbiota diversity. Statistical methods included linear mixed models, generalized mixed models, Spearman correlation, and Wilcoxon rank-sum tests.

RESULTS

Six-month-old Malian infants had significantly elevated sIgA (4.0× higher, P < 0.001), fecal myeloperoxidase (31.6× higher, P < 0.001), fecal α1-antitrypsin (1.8× higher, P = 0.006), and lower fecal neopterin (0.13× higher, P < 0.001) than the age-matched Nicaraguan infants. In the Nicaraguan rice bran cohort from 6 to 12 mo of age, there was a significant decrease in sIgA concentrations (0.4×, P < 0.05) and a correlation between sIgA and the EED marker α1-antitrypsin (0.523, P < 0.0001) at 12 mo of age. In Malian infants, daily rice bran ingestion resulted in decreased EED scores (0.71×, P = 0.02) and a stable sIgA concentration over time. The rice bran group of Malian infants also had correlation between sIgA and the EED marker neopterin (0.544, P < 0.001) at 12 mo of age and a significant (P < 0.05) increase in microbiota α-diversity at a younger age (9 mo with rice bran compared with 10 mo in control group), which supports earlier microbiota maturation.

CONCLUSIONS

These results support rice bran as a functional food ingredient targeting gut mucosa in children at high-risk of malnutrition.

Epithelial Abnormalities in the Small Intestine of Zambian Children With Stunting

Background

Environmental enteropathy (EE) contributes to impaired linear growth (stunting), in millions of children worldwide. We have previously reported that confocal laser endomicroscopy (CLE) shows fluorescein leaking from blood to gut lumen in vivo in adults and children with EE. We set out to identify epithelial lesions which might explain this phenomenon in Zambian children with stunting non-responsive to nutritional support.

Methods

We performed confocal laser endomicroscopy (CLE) in 75 children and collected intestinal biopsies for histology in 91 children. CLE videos were evaluated, employing the Watson score to determine severity of leakiness. Morphometry was carried out on well-orientated mucosa and 3 biopsies were examined by electron microscopy.

Results

Confocal laser endomicroscopy demonstrated substantial leakage from circulation to gut lumen in 73 (97%) children. Histology consistently showed characteristic changes of EE: villus blunting, lamina propria and epithelial inflammation, and depletion of secretory cells (Paneth cells and goblet cells). Epithelial abnormalities included marked variability in epithelial height, disorganised and shortened microvilli, dilated intercellular spaces, pseudostratification, formation of synechiae between epithelium on adjacent villi, crypt destruction, and abundant destructive lesions which may correspond to the microerosions identified on CLE.

Conclusion

Epithelial abnormalities were almost universal in Zambian children with non-responsive stunting, including epithelial microerosions, cell-cell adhesion anomalies, and defects in secretory cells which may all contribute to impairment of mucosal barrier function and microbial translocation.

Impact of maternal antibodies and microbiota development on the immunogenicity of oral rotavirus vaccine in African, Indian, and European infants

Identifying risk factors for impaired oral rotavirus vaccine (ORV) efficacy in low-income countries may lead to improvements in vaccine design and delivery. In this prospective cohort study, we measure maternal rotavirus antibodies, environmental enteric dysfunction (EED), and bacterial gut microbiota development among infants receiving two doses of Rotarix in India (n = 307), Malawi (n = 119), and the UK (n = 60), using standardised methods across cohorts. We observe ORV shedding and seroconversion rates to be significantly lower in Malawi and India than the UK. Maternal rotavirus-specific antibodies in serum and breastmilk are negatively correlated with ORV response in India and Malawi, mediated partly by a reduction in ORV shedding. In the UK, ORV shedding is not inhibited despite comparable maternal antibody levels to the other cohorts. In both India and Malawi, increased microbiota diversity is negatively correlated with ORV immunogenicity, suggesting that high early-life microbial exposure may contribute to impaired vaccine efficacy.

Associations between biomarkers of environmental enteric dysfunction and oral rotavirus vaccine immunogenicity in rural Zimbabwean infants

BACKGROUND

Oral rotavirus vaccines (RVV) are poorly immunogenic in low-income countries. Environmental enteric dysfunction (EED) resulting from poor water, sanitation and hygiene (WASH) may contribute. We therefore tested associations between EED and RVV immunogenicity, and evaluated the effect of improved WASH on EED.

METHODS

We measured nine biomarkers of EED among Zimbabwean infants born to mothers enrolled in a cluster-randomised 2 × 2 factorial trial of improved WASH and improved feeding between November 2012 and March 2015 (NCT01824940). We used multivariable regression to determine associations between EED biomarkers and RVV seroconversion, seropositivity and geometric mean titer. Log-binomial regression was used to evaluate the effect of improved WASH on EED.

FINDINGS

Among 303 infants with EED biomarkers and immunogenicity data, plasma intestinal fatty-acid binding protein and stool myeloperoxidase were positively associated with RVV seroconversion; adjusted RR 1.63 (95%CI 1.04, 2.57) and 1.29 (95%CI 1.01, 1.65), respectively. There were no other associations between RVV immunogenicity and either individual biomarkers or EED domains (intestinal permeability, intestinal damage, intestinal inflammation and microbial translocation). EED biomarkers did not differ between randomised WASH and non-WASH groups.

INTERPRETATION

We found no evidence that EED was associated with poor RVV immunogenicity. Contrary to our hypothesis, there was weak evidence that EED was associated with increased seroconversion. EED biomarkers were not affected by a package of household-level WASH interventions.

A Modern-World View of Host-Microbiota-Pathogen Interactions

The microbiota-the diverse set of commensal microbes that normally colonize humans-represents the first line of defense against infectious diseases. In this review, we summarize the direct and indirect mechanisms by which the microbiota modulates susceptibility to, and severity of, infections, with a focus on immunological mechanisms. Moreover, we highlight some of the ways that modern-world lifestyles have influenced the structure-function relationship between the microbiota and infectious diseases. Ultimately, understanding how the microbiota influences infectious risks will facilitate development of microbiota-derived therapeutics that bolster host defenses.

Rotavirus Infection, Illness, and Vaccine Performance in Malnourished Children: A Review of the Literature

Live, oral rotavirus vaccines are more effective at preventing rotavirus disease in countries with low child mortality compared with high child mortality. Among several hypotheses, poorer protection in malnourished children, who are more prevalent in countries with high child mortality, may partially explain this difference. We conducted a literature search to identify articles with a laboratory-confirmed rotavirus endpoint that evaluated differences by malnutrition status in rotavirus vaccine effectiveness and vaccine efficacy (VE) or the prevalence of rotavirus infection or illness among children <5 years old. We identified 7 analyses from 11 countries published from 2007 to 2019 that stratified rotavirus VE by malnutrition status. Among well-nourished children, VE point estimates ranged from 71% to 84% in observational studies and 26% to 61% in clinical trials. Among malnourished children, they ranged from -28% to 45% in observational studies and -3% to 61% in clinical trials. The relative difference between VE in well-nourished and malnourished children by length-for-age ranged from 37% to 64%, by weight-for-age ranged from 0% to 107%, and by weight-for-height ranged from -65% to 137%. We identified 3 cohort and 6 cross-sectional studies of natural rotavirus infection and illness and none reported that malnourished children were more susceptible to rotavirus infection or illness than well-nourished children. Overall, rotavirus vaccines may offer less protection to children with malnutrition than well-nourished children. As malnourished children often have worse outcomes from diarrhea, high rotavirus vaccine coverage and a better understanding of the performance of oral rotavirus vaccines in this population is important, though our finding that malnourished children may be less susceptible to rotavirus provides important context and information for vaccine evaluation design.

Intestinal Biopsies for the Evaluation of Environmental Enteropathy and Environmental Enteric Dysfunction

Environmental enteric dysfunction (EED) is a syndrome characterized by impairments of digestion and absorption and intestinal barrier failure in people living in insanitary or tropical environments. There is substantial evidence that it contributes to impaired linear growth of millions of children in low- and middle-income countries, to slowed neurocognitive development, and to diminished responses to oral vaccines. It represents the functional consequences of environmental enteropathy, an asymptomatic inflammatory disorder of the mucosa, and there is considerable overlap with the enteropathy observed in severe clinical malnutrition. The majority of studies of EED have employed functional tests based on lactulose permeation to define the presence of abnormal leak in the gut. However, where intestinal biopsies can safely be collected the opportunity then arises to study the underlying enteropathy in cellular and molecular detail, as well as to measure important functional elements such as enzyme expression. The purpose of this narrative review is to summarize the current understanding of environmental enteropathy obtained from small intestinal biopsies, and prospects for future work. We review histology, electron microscopy, transcription and protein expression, physiological measures, and the microbiome. We conclude that while noninvasive biomarkers of enteropathy and intestinal dysfunction permit large-scale studies of unquestionable value, intestinal biopsies are still required to investigate pathophysiology in depth.

Enterotoxigenic Escherichia coli (ETEC) vaccines: Priority activities to enable product development, licensure, and global access

Diarrhoeal disease attributable to enterotoxigenic Escherichia coli (ETEC) causes substantial morbidity and mortality predominantly in paediatric populations in low- and middle-income countries. In addition to acute illness, there is an increasing appreciation of the long-term consequences of enteric infections, including ETEC, on childhood growth and development. Provision of potable water and sanitation and appropriate clinical care for acute illness are critical to reduce the ETEC burden. However, these interventions are not always practical and may not achieve equitable and sustainable coverage. Vaccination may be the most cost-effective and equitable means of primary prevention; however, additional data are needed to accelerate the investment and guide the decision-making process for ETEC vaccines. First, to understand and quantify the ETEC disease burden, additional data are needed on the association between ETEC infection and physical and cognitive stunting as well as delayed educational attainment. Furthermore, the role of inappropriate or inadequate antibiotic treatment of ETEC-attributable diarrhoea may contribute to the development of antimicrobial resistance (AMR) and needs further elucidation. An ETEC vaccine that mitigates acute diarrhoeal illness and minimizes the longer-term disease manifestations could have significant public health impact and be a cost-effective countermeasure. Herein we review the ETEC vaccine pipeline, led by candidates compatible with the general parameters of the Preferred Product Characteristics (PPC) recently developed by the World Health Organization. Additionally, we have developed an ETEC Vaccine Development Strategy to provide a framework to underpin priority activities for researchers, funders and vaccine manufacturers, with the goal of addressing globally unmet data needs in the areas of research, product development, and policy, as well as commercialization and delivery. The strategy also aims to guide prioritization and co-ordination of the priority activities needed to minimize the timeline to licensure and use of ETEC vaccines, especially in in low- and middle-income countries, where they are most urgently needed.

Quantification of trivalent non-replicating rotavirus vaccine antigens in the presence of aluminum adjuvant

Parenterally administered rotavirus vaccines may overcome the low efficacy observed in resource-poor regions that use live oral formulations. We have reported work on a trivalent nonreplicating rotavirus vaccine (NRRV) for parenteral administration consisting of the recombinant tetanus toxoid P2 CD4 epitope fused to a truncated VP8* fragment (P2-VP8*) for the P[4], P[6], and P[8] serotypes of rotavirus adjuvanted with aluminum. An essential part of developing this vaccine candidate was devising quantification methods for each antigen in the trivalent NRRV in the presence of aluminum adjuvant. This report describes the development of quantitative inhibition enzyme-linked immunosorbent assays (ELISAs) for in vitro antigenicity determination of the adjuvanted trivalent NRRV using serotype-specific monoclonal antibodies (mAbs) against each of the P2-VP8* antigens. Adjuvanted trivalent vaccine samples are titrated and incubated with a constant concentration of specific mAbs against each NRRV P2-VP8* antigen variant. Unbound mAbs are measured by ELISA to indirectly quantify the amount of each antigen present in the trivalent vaccine. Sensitive, specific, and reproducible inhibition ELISAs were developed and qualified for each antigen and used for final product quantification and release testing without desorption of the vaccine antigen.

The contribution of environmental enteropathy to the global problem of micronutrient deficiency

Sometimes referred to as hidden hunger, micronutrient deficiencies persist on a global scale. For some micronutrients this appears to be due to inadequate intake, for others intake may not match increased requirements. However, for most micronutrient deficiencies there is uncertainty as to the dominant driver, and the question about the contribution of malabsorption is open. Environmental enteropathy (EE), formerly referred to as tropical enteropathy and also referred to as environmental enteric dysfunction, is an asymptomatic disorder of small intestinal structure and function which is very highly prevalent in many disadvantaged populations. Recent studies of the pathology and microbiology of this disorder suggest that it is driven by very high pathogen burdens in children and adults living in insanitary environments and is characterised by major derangements of the epithelial cells of the intestinal mucosa. Transcriptomic data suggest that it may lead to impaired digestion and absorption of macronutrients. Given the very high prevalence of EE, marginal malabsorption could have large impacts at population scales. However, the relative contributions of inadequate soil and crop micronutrient contents, inadequate intake, malabsorption and increased requirements are unknown. Malabsorption may compromise attempts to improve micronutrient status, but with the exception of zinc there is currently little evidence to confirm that malabsorption contributes to micronutrient deficiency. Much further research is required to understand the role of malabsorption in hidden hunger, especially in very disadvantaged populations where these deficiencies are most prevalent.

Update on rotavirus vaccine underperformance in low- to middle-income countries and next-generation vaccines

In the decade since oral rotavirus vaccines (ORV) were recommended by the World Health Organization for universal inclusion in all national immunization programs, significant yet incomplete progress has been made toward reducing the burden of rotavirus in low- to middle-income countries (LMIC). ORVs continue to demonstrate effectiveness and impact in LMIC, yet numerous factors hinder optimal performance and evaluation of these vaccines. This review will provide an update on ORV performance in LMIC, the increasing body of literature regarding factors that affect ORV response, and the status of newer and next-generation rotavirus vaccines as of early 2020. Fully closing the gap in rotavirus prevention between LMIC and high-income countries will likely require a multifaceted approach accounting for biological and methodological challenges and evaluation and roll-out of newer and next-generation vaccines.

Safety and Ethics in Endoscopic Studies in Children: Evidence From the BEECH Study in Zambia

BACKGROUND

Environmental enteropathy is an example of a poorly-understood intestinal disorder affecting millions of children worldwide, characterized by malabsorption and stunting. Although there is increasing interest in non-invasive means of assessing intestinal structure and function, the potential value of intestinal biopsy for histology, immunostaining, RNA sequencing and epigenetic work means that endoscopic biopsy remains extremely valuable. We here report our experience in the BEECH (Biomarkers of Environmental Enteropathy in CHildren) study of stunting in Zambia, in the belief that it may help address the knowledge gap regarding the safety of endoscopic biopsy in vulnerable young children.

METHODS

We report our experience of safety in 119 children undergoing endoscopic biopsy in the BEECH study in Lusaka Children's Hospital, Lusaka, and discuss ethical considerations in this light.

RESULTS

Upper gastrointestinal endoscopy was performed on children with stunting (length-for-age z score -2 or less) not responsive to nutritional interventions. Conscious sedation was provided by anaesthetists. Of 119 children, 5 (4%) developed transient desaturation, but no serious adverse events were experienced; no clinical, demographic or anaesthetic characteristics were identified as predictive of desaturation. Two children derived clinically useful information from the endoscopy, one life-saving. Of 105 lactase tests, 59 (54%) showed hypolactasia.

DISCUSSION

Children with stunting underwent endoscopy safely, and some derived clinical benefit. Safety and the possibility of clinical benefit are usually felt to be preconditions for the ethical justification for endoscopy for research in children, and we believe that these conditions were met in this study.

Intussusception after Rotavirus Vaccine Introduction in India

BACKGROUND

A three-dose, oral rotavirus vaccine (Rotavac) was introduced in the universal immunization program in India in 2016. A prelicensure trial involving 6799 infants was not large enough to detect a small increased risk of intussusception. Postmarketing surveillance data would be useful in assessing whether the risk of intussusception would be similar to the risk seen with different rotavirus vaccines used in other countries.

METHODS

We conducted a multicenter, hospital-based, active surveillance study at 27 hospitals in India. Infants meeting the Brighton level 1 criteria of radiologic or surgical confirmation of intussusception were enrolled, and rotavirus vaccination was ascertained by means of vaccination records. The relative incidence (incidence during the risk window vs. all other times) of intussusception among infants 28 to 365 days of age within risk windows of 1 to 7 days, 8 to 21 days, and 1 to 21 days after vaccination was evaluated by means of a self-controlled case-series analysis. For a subgroup of patients, a matched case-control analysis was performed, with matching for age, sex, and location.

RESULTS

From April 2016 through June 2019, a total of 970 infants with intussusception were enrolled, and 589 infants who were 28 to 365 days of age were included in the self-controlled case-series analysis. The relative incidence of intussusception after the first dose was 0.83 (95% confidence interval [CI], 0.00 to 3.00) in the 1-to-7-day risk window and 0.35 (95% CI, 0.00 to 1.09) in the 8-to-21-day risk window. Similar results were observed after the second dose (relative incidence, 0.86 [95% CI, 0.20 to 2.15] and 1.23 [95% CI, 0.60 to 2.10] in the respective risk windows) and after the third dose (relative incidence, 1.65 [95% CI, 0.82 to 2.64] and 1.08 [95% CI, 0.69 to 1.73], respectively). No increase in intussusception risk was found in the case-control analysis.

CONCLUSIONS

The rotavirus vaccine produced in India that we evaluated was not associated with intussusception in Indian infants. (Funded by the Bill and Melinda Gates Foundation and others.).

Nutritional status, environmental enteric dysfunction, and prevalence of rotavirus diarrhoea among children in Zambia

BACKGROUND

Rotavirus is the most common cause of fatal diarrhoeal disease among children under the age of five globally and is responsible for millions of hospitalizations each year. Although nutritional status and environmental enteric dysfunction (EED) are recognized as important predictors of susceptibility to diarrhoeal disease, no research to date has examined the mechanisms by which undernutrition and EED may protect against prevalence of rotavirus infection.

METHODS

We utilized data collected from a study evaluating the effectiveness of Rotarix™ vaccine against severe gastroenteritis among children under the age of 5 in Zambia. The prevalence of malnutrition, wasting, and stunting at the time of study enrollment was calculated using WHO child growth standards. Commercial ELISA kits were used to assess levels of faecal biomarkers for EED: alpha-1-antitrypsin and myeloperoxidase, and calprotectin. Separate multivariate logistic regression models were used to examine each measure of nutritional status and rotavirus diarrhoea including and excluding adjustment for EED.

RESULTS

In models that did not include adjustment for EED, malnourished children had 0.66 times the odds of having rotavirus diarrhoea compared to children with normal nutritional status (95% CI: 0.42, 1.0; p = 0.07). EED severity score was significantly higher among controls asymptomatic for diarrhoeal disease compared to cases with rotavirus diarrhoea (p = 0.02).

CONCLUSION

The morphological changes associated with EED may confer protection against rotavirus infection and subsequent diarrhoeal disease among children. Further research is critically needed to better understand the complex mechanisms by which nutritional status and EED may impact susceptibility to rotavirus in early life.

The Impact of Improved Water, Sanitation, and Hygiene on Oral Rotavirus Vaccine Immunogenicity in Zimbabwean Infants: Substudy of a Cluster-randomized Trial

BACKGROUND

Oral vaccines have lower efficacy in developing compared to developed countries. Poor water, sanitation, and hygiene (WASH) may contribute to reduced oral vaccine immunogenicity.

METHODS

We conducted a cluster-randomized 2 × 2 factorial trial in rural Zimbabwe. Pregnant women and their infants were eligible if they lived in clusters randomized to (1) standard of care (52 clusters); (2) improved infant feeding (53 clusters); (3) WASH: ventilated improved pit latrine, 2 hand-washing stations, liquid soap, chlorine, infant play space, and hygiene counseling (53 clusters); or (4) feeding plus WASH (53 clusters). This substudy compared oral rotavirus vaccine (RVV) seroconversion (primary outcome), and seropositivity and geometric mean titer (GMT) (secondary outcomes), in WASH vs non-WASH infants by intention-to-treat analysis.

RESULTS

We included 801 infants with documented RVV receipt and postvaccine titer measurements (329 from 84 WASH clusters; 472 from 102 non-WASH clusters); 328 infants with prevaccination titers were included in the primary outcome. Thirty-three of 109 (30.3%) infants in the WASH group seroconverted following rotavirus vaccination, compared to 43 of 219 (19.6%) in the non-WASH group (absolute difference, 10.6% [95% confidence interval {CI}, .54%-20.7%]; P = .031). In the WASH vs non-WASH groups, 90 of 329 (27.4%) vs 107 of 472 (22.7%) were seropositive postvaccination (absolute difference, 4.7% [95% CI, -1.4% to 10.8%]; P = .130), and antirotavirus GMT was 18.4 (95% CI, 15.6-21.7) U/mL vs 14.9 (95% CI, 13.2-16.8) U/mL (P = .072).

CONCLUSIONS

Improvements in household WASH led to modest but significant increases in seroconversion to RVV in rural Zimbabwean infants.

CLINICAL TRIALS REGISTRATION

NCT01824940.

Markers of Environmental Enteric Dysfunction Are Associated with Poor Growth and Iron Status in Rural Ugandan Infants

BACKGROUND

Environmental enteric dysfunction (EED), characterized by altered intestinal permeability/inflammation, microbial translocation, and systemic inflammation (SI), may be a significant contributor to micronutrient deficiencies and poor growth in infants from low-resource settings.

OBJECTIVE

We examined associations among EED, SI, growth, and iron status at 6 mo of age.

METHODS

We performed a cross-sectional analysis of 6-mo-old infants (n = 548) enrolled in a Ugandan birth-cohort study (NCT04233944). EED was assessed via serum concentrations of anti-flagellin and anti- LPS immunoglobulins (Igs); SI was assessed via serum concentrations of ɑ1-acid glycoprotein (AGP) and C-reactive protein (CRP); iron status was assessed via serum concentrations of hemoglobin (Hb), soluble transferrin receptor (sTfR), and ferritin. Associations were assessed using adjusted linear regression analysis.

RESULTS

At 6 mo, ∼35% of infants were stunted [length-for-age z score (LAZ) < -2] and ∼53% were anemic [hemoglobin (Hb) <11.0 g/dL]. Nearly half (∼46%) had elevated AGP (>1 g/L) and ∼30% had elevated CRP (>5 mg/L). EED and SI biomarkers were significantly correlated (r = 0.142-0.193, P < 0.001 for all). In adjusted linear regression models, which included adjustments for SI, higher anti-flagellin IgA, anti-LPS IgA, and anti-LPS IgG concentrations were each significantly associated with lower LAZ [β (95% CI): -0.21 (-0.41, 0.00), -0.23 (-0.44, -0.03), and -0.33 (-0.58, -0.09)]. Furthermore, higher anti-flagellin IgA, anti-flagellin IgG, and anti-LPS IgA concentrations were significantly associated with lower Hb [β (95% CI): -0.24 (-0.45, -0.02), -0.58 (-1.13, 0.00), and -0.26 (-0.51, 0.00)] and higher anti-flagellin IgG and anti-LPS IgG concentrations were significantly associated with higher sTfR [β (95% CI): 2.31 (0.34, 4.28) and 3.13 (0.75, 5.51)].

CONCLUSIONS

EED is associated with both low LAZ and iron status in 6-mo-old infants. Further research on the mechanisms by which EED affects growth and micronutrient status is warranted.

Immune predictors of oral poliovirus vaccine immunogenicity among infants in South India

Identification of the causes of poor oral vaccine immunogenicity in low-income countries might lead to more effective vaccines. We measured mucosal and systemic immune parameters at the time of vaccination with oral poliovirus vaccine (OPV) in 292 Indian infants aged 6–11 months, including plasma cytokines, leukocyte counts, fecal biomarkers of environmental enteropathy and peripheral blood T-cell phenotype, focused on gut-homing regulatory CD4+ populations. We did not find a distinct immune phenotype associated with OPV immunogenicity, although viral pathogens were more prevalent in stool at the time of immunization among infants who failed to seroconvert (63.9% vs. 45.6%, p = 0.002). Using a machine-learning approach, we could predict seroconversion a priori using immune parameters and infection status with a median 58% accuracy (cross-validation IQR: 50–69%) compared with 50% expected by chance. Better identification of immune predictors of OPV immunogenicity is likely to require sampling of mucosal tissue and improved oral poliovirus infection models.

Predictors of oral rotavirus vaccine immunogenicity in rural Zimbabwean infants

BACKGROUND

Oral rotavirus vaccines (RVV) have poor immunogenicity in low-income countries, for reasons that remain unclear. This study identified the determinants of RVV immunogenicity among infants in rural Zimbabwe.

METHODS

Anti-rotavirus IgA titres were measured among a sub-group of infants enrolled in the Sanitation Hygiene Infant Nutrition Efficacy (SHINE) trial (NCT01824940). SHINE was a cluster-randomized trial of improved infant and young child feeding, and improved water, sanitation and hygiene (WASH) in two rural Zimbabwean districts. Infants received RVV as part of the national immunisation programme. Among HIV-unexposed infants in the non-WASH trial arms, we evaluated associations between potential risk factors (vaccine schedule and dose, maternal and infant nutritional status, infant diarrhoea, and household environment) and RVV immunogenicity (seroconversion, seropositivity and geometric mean titres) using multivariable regression.

RESULTS

Among 219 infants with seroconversion data, 43 (20%) successfully seroconverted and 176 (80%) failed to seroconvert to RVV. Seroconversion was positively associated with a higher length-for-age Z-score (LAZ) around the time of vaccination (adjusted RR 1.27 (95% CI 1.04, 1.55), P = 0.021), and negatively associated with concurrent OPV and RVV administration (adjusted RR 0.36 (0.19, 0.71), P = 0.003). Among 472 infants with post-vaccination titres, a higher LAZ score was associated with increased seropositivity (aRR 1.21 (95% CI 1.06, 1.38), P = 0.004), and higher birthweight was associated with increased IgA titres (0.45 (95%CI 0.18, 1.09) U/mL greater per 100 g gain in birthweight; P = 0.001).

CONCLUSIONS

Infant ponderal and linear growth were positively associated with RVV immunogenicity, while concurrent administration of OPV was negatively associated with RVV immunogenicity. Together, these findings suggest that improving foetal growth and separating RVV and OPV administration are plausible approaches to increasing RVV immunogenicity.

Enteropathogens and Rotavirus Vaccine Immunogenicity in a Cluster Randomized Trial of Improved Water, Sanitation and Hygiene in Rural Zimbabwe

BACKGROUND

Oral rotavirus vaccines (RVVs) are less efficacious in low-income versus high-income settings, plausibly due to more enteropathogen exposure through poor water, sanitation and hygiene (WASH). We explored associations between enteropathogens and RVV immunogenicity and evaluated the effect of improved WASH on enteropathogen carriage.

METHODS

We detected stool enteropathogens using quantitative molecular methods and measured anti-rotavirus immunoglobulin A by enzyme-linked immunosorbent assay in infants enrolled to a cluster randomized 2 × 2 factorial trial of improved WASH and improved infant feeding in Zimbabwe (NCT01824940). We used multivariable regression to explore associations between enteropathogens and RVV seroconversion, seropositivity and geometric mean titer. We evaluated effects of improved WASH on enteropathogen prevalence using linear and binomial regression models with generalized estimating equations.

RESULTS

Among 224 infants with enteropathogen and immunogenicity data, 107 (47.8%) had ≥1 pathogen and 39 (17.4%) had ≥2 pathogens detected at median age 41 days (interquartile range: 35-54). RVV seroconversion was low (23.7%). After adjusting for Sabin-poliovirus quantity, pan-enterovirus quantity was positively associated with RVV seroconversion (relative risk 1.61 per 10-fold increase in pan-enterovirus; 95% confidence interval: 1.35-1.91); in the same model, Sabin quantity was negatively associated with RVV seroconversion (relative risk: 0.76; 95% confidence interval: 0.60-0.96). There were otherwise no meaningful associations between individual or total pathogens (bacteria, viruses, parasites or all pathogens) and any measure of RVV immunogenicity. Enteropathogen detection did not differ between randomized WASH and non-WASH groups.

CONCLUSIONS

Enteropathogen infections were common around the time of rotavirus vaccination in rural Zimbabwean infants but did not explain poor RVV immunogenicity and were not reduced by a package of household-level WASH interventions.

Tryptophan, glutamine, leucine, and micronutrient supplementation improves environmental enteropathy in Zambian adults: a randomized controlled trial

BACKGROUND

Environmental enteropathy (EE) refers to villus blunting, reduced absorption, and microbial translocation in children and adults in tropical or deprived residential areas. In previous work we observed an effect of micronutrients on villus height (VH).

OBJECTIVE

We aimed to determine, in a randomized controlled trial, if amino acid (AA) or multiple micronutrient (MM) supplementation can improve intestinal structure or barrier dysfunction in Zambian adults with EE.

METHODS

AA (tryptophan, leucine, and glutamine) and/or MM supplements were given for 16 wk in a 2 × 2 factorial comparison against placebo. Primary outcomes were changes in VH, in vivo small intestinal barrier dysfunction assessed by confocal laser endomicroscopy (CLE), and mechanistic (or mammalian) target of rapamycin complex 1 (MTORC1) nutrient responsiveness in lamina propria CD4+ lymphocytes.

RESULTS

Over 16 wk AA, but not MM, supplementation increased VH by 16% (34.5 μm) compared with placebo (P = 0.04). Fluorescein leak, measured by CLE, improved only in those allocated to both AA and MM supplementation. No effect was seen on MTORC1 activation, but posttreatment MTORC1 and VH were correlated (ρ = 0.51; P = 0.001), and change in MTORC1 was correlated with change in VH in the placebo group (ρ = 0.63; P = 0.03). In secondary analyses no effect was observed on biomarkers of microbial translocation. Metabolomic analyses suggest alterations in a number of microbial- and host-derived metabolites including the leucine metabolite β-hydroxy-β-methylbutyrate, which was increased by AA supplementation and correlated with VH.

CONCLUSIONS

In this phase 2 trial, AA supplementation protected against a decline in VH over the supplementation period, and improved barrier function when combined with micronutrients. Leucine and MTORC1 metabolism may be involved in the mechanism of effect. This trial was registered at www.pactr.org as PACTR201505001104412.

The effect of increased inoculum on oral rotavirus vaccine take among infants in Dhaka, Bangladesh: A double-blind, parallel group, randomized, controlled trial

BACKGROUND

Oral, live-attenuated rotavirus vaccines suffer from impaired immunogenicity and efficacy in low-income countries. Increasing the inoculum of vaccine might improve vaccine response, but this approach has been inadequately explored in low-income countries.

METHODS

We performed a double-blind, parallel group, randomized controlled trial from June 2017 through June 2018 in the urban Mirpur slum of Dhaka, Bangladesh to compare vaccine take (primary outcome) among healthy infants randomized to receive either the standard dose or double the standard dose of oral Rotarix (GlaxoSmithKline) vaccine at 6 and 10 weeks of life. Infants with congenital malformations, birth or enrollment weight <2000 gm, known immunocompromising condition, enrollment in another vaccine trial, or other household member enrolled in the study were excluded. Infants were randomized using random permuted blocks. Vaccine take was defined as detection of post-vaccination fecal vaccine shedding by real-time reverse transcription polymerase chain reaction with sequence confirmation or plasma rotavirus-specific immunoglobulin A (RV-IgA) seroconversion 4 weeks following the second dose.

RESULTS

220 infants were enrolled and randomized (110 per group). 97 standard-dose and 92 high-dose infants completed the study per-protocol. For the primary outcome, no significant difference was observed between groups: vaccine take occurred in 62 (67%) high-dose infants versus 69 (71%) standard-dose infants (RR 0.92, 95% CI 0.67-1.24). However, in post-hoc analysis, children with confirmed vaccine replication had significantly increased RV-IgA responses, independent of the intervention. No significant adverse events related to study participation were detected.

CONCLUSIONS

Administration of double the standard dose of an oral, live-attenuated rotavirus vaccine (Rotarix) did not improve vaccine take among infants in urban Dhaka, Bangladesh. However, improved immunogenicity in children with vaccine replication irrespective of initial inoculum provides further evidence for the need to promote in-host replication and improved gut health to improve oral vaccine response in low-income settings. ClinicalTrials.gov: NCT02992197.

Enterotoxigenic Escherichia coli Infections

PURPOSE OF REVIEW

Review recent developments pertaining to the epidemiology, molecular pathogenesis, and sequelae of enterotoxigenic Escherichia coli (ETEC) infections in addition to discussion of challenges for vaccinology.

RECENT FINDINGS

ETEC are a major cause of diarrheal illness in resource poor areas of the world where they contribute to unacceptable morbidity and continued mortality particularly among young children; yet, precise epidemiologic estimates of their contribution to death and chronic disease have been difficult to obtain. Although most pathogenesis studies, and consequently vaccine development have focused intensively on canonical antigens, more recently identified molecules unique to the ETEC pathovar may inform our understanding of ETEC virulence, and the approach to broadly protective vaccines. ETEC undeniably continue to have a substantial impact on global health; however, further studies are needed to clarify the true impact of these infections, particularly in regions where access to care may be limited. Likewise, our present understanding of the relationship of ETEC infection to non-diarrheal sequelae is presently limited, and additional effort will be required to achieve a mechanistic understanding of these diseases and to fulfill Koch's postulates on a molecular level. Precise elucidation of the role played by novel virulence factors, the global burden of acute illness, and the contribution of these pathogens and/or their toxins to non-diarrheal morbidity remain important imperatives.

Neonatal vitamin A supplementation and immune responses to oral polio vaccine in Zimbabwean infants

Background

Micronutrient deficiencies may contribute to reduced oral vaccine immunogenicity in developing countries. We hypothesised that neonatal vitamin A supplementation (NVAS) would improve oral vaccine responses.

Methods

We performed a cross-sectional study of infants recruited at birth to the Zimbabwe Vitamin A for Mothers and Babies (ZVITAMBO) trial, a randomised controlled trial of single, high-dose NVAS vs placebo conducted in Zimbabwe between 1997–2001. We measured poliovirus-specific IgA to type 1–3 polio strains by semiquantitative capture ELISA in cryopreserved plasma samples collected at 6 months of age.

Results

A total of 181 infants fulfilled inclusion criteria, of whom 80 were randomised to NVAS and 101 to placebo. There were no significant differences in baseline characteristics between groups. At 6 months of age, median (IQR) vaccine titres for infants randomised to NVAS vs placebo were 932 (421–3001) vs 1774 (711–5431) for Sabin-1 (p=0.04); 1361 (705–3402) vs 2309 (1081–4283) for Sabin-2 (p=0.15); and 1584 (796–4216) vs 2260 (996–5723) for Sabin-3 (p=0.14), respectively. After adjusting for breast feeding status, birth weight, season and infant sex in a linear regression model, there was only weak evidence of difference in log mean titres between vitamin A and placebo groups for Sabin-1 (p=0.08) and no evidence of difference in log mean titres for Sabin-2 and Sabin-3.

Conclusions

NVAS did not augment oral polio vaccine responses in Zimbabwean infants. Further research is required to understand the impact of NVAS on responses to other oral vaccines.

The trial is registered with clinicaltrials.gov identifier: NCT00198718.

Environmental enteric dysfunction and growth

OBJECTIVE

To describe the current indicators of environmental enteric dysfunction and its association with linear growth deficit and the height-for-age anthropometric indicator.

DATA SOURCES

Narrative review with articles identified in PubMed and Scopus databases using combinations of the following words: environmental, enteric, dysfunction, enteropathy, and growth, as well as the authors' personal records.

DATA SYNTHESIS

In the last 15 years, new non-invasive markers have been investigated to characterize environmental enteric dysfunction; however, the best tests to be used have not yet been identified. There is evidence that, in environmental enteric dysfunction, a systemic inflammatory process may also occur as a consequence of increased intestinal permeability, in addition to intestinal mucosa abnormalities. Bacterial overgrowth in the small intestine and changes in fecal microbiota profile have also been identified. There is evidence indicating that environmental enteric dysfunction can impair not only full growth but also the neuropsychomotor development and response to orally administered vaccines. It is important to emphasize that the environmental enteric dysfunction is not a justification for not carrying out vaccination, which must follow the regular schedule. Another aspect to emphasize is the greater risk for those children who had height impairment in early childhood, possibly associated with environmental enteric dysfunction, to present overweight and obesity in adulthood when exposed to a high calorie diet, which has been called "triple burden."

CONCLUSIONS

According to the analyzed evidence, the control of environmental enteric dysfunction is very important for the full expression of growth, development, and vaccine response in the pediatric age group.

Interventions to improve oral vaccine performance: a systematic review and meta-analysis

BACKGROUND

Oral vaccines underperform in low-income and middle-income countries compared with in high-income countries. Whether interventions can improve oral vaccine performance is uncertain.

METHODS

We did a systematic review and meta-analysis of interventions designed to increase oral vaccine efficacy or immunogenicity. We searched Ovid-MEDLINE and Embase for trials published until Oct 23, 2017. Inclusion criteria for meta-analysis were two or more studies per intervention category and available seroconversion data. We did random-effects meta-analyses to produce summary relative risk (RR) estimates. This study is registered with PROSPERO (CRD42017060608).

FINDINGS

Of 2843 studies identified, 87 were eligible for qualitative synthesis and 66 for meta-analysis. 22 different interventions were assessed for oral poliovirus vaccine (OPV), oral rotavirus vaccine (RVV), oral cholera vaccine (OCV), and oral typhoid vaccines. There was generally high heterogeneity. Seroconversion to RVV was significantly increased by delaying the first RVV dose by 4 weeks (RR 1·37, 95% CI 1·16-1·62) and OPV seroconversion was increased with monovalent or bivalent OPV compared with trivalent OPV (RR 1·51, 95% CI 1·20-1·91). There was some evidence that separating RVV and OPV increased RVV seroconversion (RR 1·21, 95% CI 1·00-1·47) and that higher vaccine inoculum improved OCV seroconversion (RR 1·12, 95% CI 1·00-1·26). There was no evidence of effect for anthelmintics, antibiotics, probiotics, zinc, vitamin A, withholding breastfeeding, extra doses, or vaccine buffering.

INTERPRETATION

Most strategies did not improve oral vaccine performance. Delaying RVV and reducing OPV valence should be considered within immunisation programmes to reduce global enteric disease. New strategies to address the gap in oral vaccine efficacy are urgently required.

FUNDING

Wellcome Trust, Bill & Melinda Gates Foundation, UK Medical Research Council, and WHO Polio Research Committee.

Effective mucosal live attenuated Salmonella vaccine by deleting phosphotransferase system component genes ptsI and crr

Salmonella enterica is a major human pathogen that causes invasive non-typhoidal Salmonellosis (iNTS), resulting in significant morbidity and mortality. Although a number of pre-clinical and clinical studies have reported on the feasibility of developing a safe and effective vaccine against iNTS, there have been no licensed Salmonella vaccines available to protect against NTS strains. Vaccine formulations of highest priority for NTS are live attenuated vaccines, which can elicit effective induction of intestinal mucosal and intracellular bacteria-specific cell mediated immune responses. Since glucose is crucial for intracellular survival and replication in host cells, we constructed strains with mutations in components of the glucose uptake system, called the phosphotransferase system (PTS), and compared the relative virulence and immune responses in mice. In this study, we found that the strain with mutations in both ptsI and crr (KST0556) was the most attenuated strain among the tested strains, and proved to be highly effective in inducing a mucosal immune response that can protect against NTS infections in mice. Thus, we suggest here that KST0556 (ΔptsIΔcrr) is a potential live vaccine candidate for NTS, and may also be a candidate for a live delivery vector for heterologous antigens. Moreover, since PTS is a well-conserved glucose transporter system in both Gramnegative and Gram-positive bacteria, the ptsI and crr genes may be potential targets for creating live bacterial vectors or vaccine strains.