Understanding the global burden of enterotoxigenic E. coli (ETEC) and Shigella diarrhea as well as estimating the cost effectiveness of vaccines to control these two significant pathogens have been hindered by the lack of a diagnostic test that is rapid, simple, sensitive, and can be applied to the endemic countries. We previously developed a simple and rapid assay, Rapid Loop mediated isothermal amplification based Diagnostic Test (RLDT) for the detection of ETEC and Shigella spp. (Shigella). In this study, the RLDT assay was evaluated in comparison with quantitative PCR (qPCR), culture and conventional PCR for the detection of ETEC and Shigella. This validation was performed using previously collected stool samples from endemic countries, from the travelers to the endemic countries, as well as samples from a controlled human infection model study of ETEC. The performance of RLDT from dried stool spots was also validated. RLDT resulted in excellent sensitivity and specificity compared to qPCR (99% and 99.2% respectively) ranging from 92.3 to 100% for the individual toxin genes of ETEC and 100% for Shigella. Culture was less sensitive compared to RLDT. No significant differences were noted in the performance of RLDT using samples from various sources or stool samples from moderate to severe diarrhea or asymptomatic infections. RLDT performed equally well in detection of ETEC and Shigella from the dried stool samples on filter papers. This study established that RLDT is sufficiently sensitive and specific to be used as a simple and rapid diagnostic assay to detect ETEC and Shigella in endemic countries to determine disease burden of these pathogens in the national and subnational levels. This information will be important to guide public health and policy makers to prioritize resources for accelerating the development and introduction of effective preventative and/or treatment interventions against these enteric infections.

Inactivated whole-cell vaccines present a full repertoire of antigens to the immune system. Formalin treatment, a standard method for microbial inactivation, can modify or destroy protein antigenic epitopes. We tested the hypothesis that photochemical inactivation with psoralen and UVA light (PUVA), which targets nucleic acid, would improve the immunogenicity of an Enterotoxigenic E. coli (ETEC) vaccine relative to a formalin-inactivated counterpart. Exposure of ETEC H10407 to PUVA using the psoralen drug 4′-Aminomethyltrioxsalen hydrochloride (AMT) yielded replication-incompetent bacteria that retained their metabolic activity. CFA/I-mediated mannose-resistant hemagglutination (MRHA) was equivalent for PUVA-inactivated and live ETEC, but was severely reduced for formalin–ETEC, indicating that PUVA preserved fimbrial protein functional integrity. The immunogenicity of PUVA–ETEC and formalin–ETEC was compared in mice ± double mutant heat-labile enterotoxin (dmLT) adjuvant. Two weeks after an intramuscular prime/boost, serum anti-ETEC IgG titers were similar for the two vaccines and were increased by dmLT. However, the IgG responses raised against several conserved ETEC proteins were greater after vaccination with PUVA–ETEC. In addition, PUVA–ETEC generated IgG specific for heat-labile toxin (LT) in the absence of dmLT, which was not a property of formalin–ETEC. These data are consistent with PUVA preserving ETEC protein antigens in their native-like form and justify the further testing of PUVA as a vaccine platform for ETEC using murine challenge models.

For the first time in over 20 years, an Enterotoxigenic Escherichia coli (ETEC) vaccine candidate, ETVAX^®, has advanced into a phase 2b field efficacy trial for children 6–18 months of age in a low-income country. ETVAX^® is an inactivated whole cell vaccine that has gone through a series of clinical trials to provide a rationale for the design elements of the Phase 2b trial. This trial is now underway in The Gambia and will be a precursor to an upcoming pivotal phase 3 trial. To reach this point, numerous findings were brought together to define factors such as safe and immunogenic doses for children, and the possible benefit of a mucosal adjuvant, double mutant labile toxin (dmLT). Considering the promising but still underexplored potential of inactivated whole cells in oral vaccination, we present a perspective compiling key observations from past ETVAX^® trials that informed The Gambian trial design. This report will update the trial’s status and explore future directions for ETEC vaccine trials. Our aim is to provide not only an update on the most advanced ETEC vaccine candidate but also to offer insights beneficial for the development of other much-needed oral whole-cell vaccines against enteric and other pathogens.

Coronavirus Disease-2019 (COVID-19) vaccine acceptance is variable. We surveyed participants in the COVID-19 Community Research Partnership from 17 December 2020 to 13 January 2021 to assess vaccine receptiveness. Vaccine uptake was then monitored until 15 May 2021; 20,232 participants responded to the receptiveness survey with vaccination status accessed in 18,874 participants via daily follow-up surveys (participants not completing daily surveys ≥30 days to 15 May 2021, were excluded). In the initial survey, 4802 (23.8%) were vaccine hesitant. Hesitancy was most apparent in women (Adjusted RR 0.93, p < 0.001), Black Americans (Adjusted RR 1.39, 1.41, 1.31 to non-Hispanic Whites, Other, and Hispanic or Latino, respectively p < 0.001), healthcare workers (Adjusted RR 0.93, p < 0.001), suburbanites (ref. Urban Adjusted RR 0.85, 0.90 to urban and rural dwellers, respectively, p < 0.01), and those previously diagnosed with COVID-19 (RR 1.20, p < 0.01). Those <50 years were also less accepting of vaccination. Subsequent vaccine uptake was 99% in non-hesitant participants. For those who were unsure, preferred not to answer, or answered “no”, vaccination rates were 80% (Adjusted RR 0.86, p < 0.0001), 78% (Adjusted RR 0.83, p < 0.0001), and 52.7% (Adjusted RR 0.65, p < 0.0001), respectively. These findings suggest that initial intent did not correlate with vaccine uptake in our cohort.

Enterotoxigenic Escherichia coli (ETEC) causes 75 million diarrhoea episodes with up to 42 000 deaths annually in children. To prevent ETEC in children, we aimed to evaluate the safety, immunogenicity, and efficacy of ETVAX, an oral, inactivated, whole-cell ETEC vaccine with toxoid and double-mutant heat-labile toxin adjuvant. In this phase 2b, double-blind, placebo-controlled trial, Gambian children aged 6-18 months were recruited from four enrolment centres and block-randomised (1:1) via a computer-generated sequence, stratified by enrolment centres, to receive ETVAX or placebo on days 1, 15, and 90. Parents, staff, investigators assessing outcomes, and investigators analysing the data were masked to group assignment. An immunogenicity subset was assessed for serum antibody responses to ETEC colonisation factors and heat-labile toxin. The primary safety endpoint was serious adverse events, assessed in all children who received at least one intervention dose. The primary efficacy endpoint was vaccine efficacy against moderate-to-severe ETEC-positive diarrhoea (MSD-ETEC), excluding co-infections with Cryptosporidium spp, norovirus genogroup II, rotavirus, or Shigella spp, assessed in the per-protocol population. Secondary endpoints included vaccine efficacy against MSD-ETEC regardless of copathogens and against moderate-to-severe diarrhoea (MSD) regardless of cause. Exploratory vaccine efficacy analyses were against MSD-ETEC excluding only enteroparasitic copathogens (Giardia lamblia and Cryptosporidium) and against MSD-ETEC regardless of copathogens when first dose was given before age 9 months. This trial was registered with the Pan African Clinical Trials Registry (PACTR20201081921856). Between Feb 22, 2021, and June 24, 2022, 5253 children were screened and 4936 (2499 [51%] girls, 2437 [49%] boys) were randomly assigned (2468 to ETVAX, 2468 to placebo). Serious adverse events occurred in 24 (1·0%) of 2474 in the vaccine group and 32 (1·3%) of 2462 in the placebo group, with none related to the investigational product. Immunogenicity was assessed in 122 children. ETVAX increased antibodies to colonisation factors (CFA/I, CS3) and heat-labile toxins. Vaccine efficacy was 26·6% (95% CI -58·3 to 66·0; p=0·43) for the primary endpoint, 48·2% (p=0·053) against MSD-ETEC regardless of copathogens, and 80·6% (p=0·0092) when excluding enteroparasitic copathogens. Vaccine efficacy against all MSD-ETEC reached 67·8% (p=0·026) when dosing started before age 9 months. Vaccine efficacy against MSD regardless of cause was 21·4% (p=0·032). ETVAX was safe and immunogenic. Although the primary endpoint was not met, the secondary and exploratory findings suggest ETVAX protects Gambian children against ETEC-positive MSD particularly when administered before age 9 months and when children were not co-infected with enteroparasites. ETVAX also showed a reduction in all-cause MSD. These results support advancing ETVAX to a pivotal phase 3 trial. European & Developing Countries Clinical Trials Partnership.