Efficacy and safety of human gut-derived multi-strain probiotics in patients with irritable bowel syndrome: A prospective open-label observation study.

This study aimed to investigate the efficacy and safety of human gut-derived multi-strain probiotics in patients with irritable bowel syndrome (IBS). This was an open-label, prospective, observational study. Patients with IBS were administered human gut-derived multi-strain probiotics for 4 weeks. The primary and secondary outcomes were based on the overall responder rate of the total IBS severity scoring system (IBS-SSS) score (>50-point decrease) and the IBS quality of life (IBS-QOL) score and IBS-SSS1 subscore (>10-point decrease in both scores), respectively. The estimated response rate is 55%. Of 44 patients, the total IBS-SSS score responder rate was 18.2% and 63.6% of patients at 2 and 4 weeks, respectively (P = .018). Compared with baseline, a significant improvement in the IBS-QOL score was observed in 27.3% and 63.6% of patients at 2 and 4 weeks, respectively (P = .001). Overall improvement rates in the IBS-SSS1 subscore were observed in 29.5% and 61.4% of patients at 2 and 4 weeks, respectively (P < .001). Primary and secondary outcomes were higher at 4 weeks (total IBS-SSS score, 63.6%; IBS-QOL score, 63.6%; IBS-SSS1 subscore, 61.4%) than the estimated responder rate (55%). Human gut-derived multi-strain probiotics have the potential to become an effective and safe treatment option for IBS patients.

Korean Amberjack Skin-Inspired Hyaluronic Acid Bioink for Reconstruction of Human Skin.

Decellularized extracellular matrix (dECM) has been extensively employed as tissue engineering scaffolds because its components can greatly enhance the migration and proliferation of cultivating cells. In this study, we decellularized Korean amberjack skin and incorporated soluble fractions in hyaluronic acid hydrogels with 3D-printed tissue engineering hydrogels to overcome any limitation of animal-derived dECM. The hydrolyzed fish-dECM was mixed with methacrylated hyaluronic acid and chemically crosslinked to 3D-printed fish-dECM hydrogels, where fish-dECM contents affected both printability and injectability of the hydrogels. Swelling ratios and mass erosion of the 3D-printed hydrogels were dependent on fish-dECM contents, where higher fish-dECM in the hydrogel increased swelling ratios and mass erosion rates. The higher content of fish-dECM considerably enhanced the viability of the incorporated cells in the matrix for 7 days. Artificial human skin was constructed by seeding human dermal fibroblasts and keratinocytes in the 3D-printed hydrogels, and a formation of a bilayered skin was visualized with tissue staining. Thus, we envision that 3D-printed hydrogels containing fish-dECM can be an alternative bioink composed of a non-mammal-derived matrix.

Feasibility of in vivo swine models using guide wire-assisted intraductal radiofrequency ablation for benign biliary stricture.

Several in vivo swine models of benign biliary stenosis (BBS) have been recently reported for preclinical studies of novel endoscopic techniques and devices. The aim of this study was to evaluate the efficacy and feasibility of large animal models of BBS by using intraductal radiofrequency ablation (RFA) assisted by guide wire. Six in vivo swine models were made by using an intraductal RFA for cauterization at 10 W, 80 °C, 90 s in the common bile duct (CBD). Endoscopic retrograde cholangiopancreatography (ERCP) was performed with cholangiography and histologic evaluation was done for the common bile duct. Blood tests were examined before, after, and at the final follow-up. Guide wire assisted RFA electrode produced BBS in all (6/6, 100%) animal models without severe complications. Fluoroscopy findings at 2 weeks after intraductal RFA in every model revealed BBS in the common bile duct. In histologic evaluations, fibrosis and chronic inflammatory changes were noted. After the procedure, ALP, GGT, and CRP were elevated and decreased after an appropriate drain. A swine model of BBS is developed by inducing intraductal thermal injury using intraductal RFA assisted by guide wire. This novel technique for inducing BBS in swine is effective and feasible.

Research progress and future directions on intraductal papillary mucinous neoplasm: A bibliometric and visualized analysis of over 30 years of research.

BACKGROUND: Malignant change from low-grade dysplasia to high-grade dysplasia and invasive carcinoma following an adenoma-carcinoma sequence is becoming more common in intraductal papillary mucinous neoplasm (IPMN) of the pancreas. The aim of this study is to analyze their main characteristics and recent research trends in IPMNs and consequently create better understandings of the current situation and trends. METHODS: A comprehensive search was performed in The Science Citation Index Expanded of the Web of Science. All articles between 1990 and 2021 were searched. VOS viewer (Leiden University, Leiden, Netherlands) was used for a qualitative and quantitative analysis of keywords, constituting maps based on co-occurrence matrix. RESULTS: A total of 1658 eligible articles were screened among the 3950 identified articles for this subject. Finally, 879 articles were included in this study. Many articles on IPMN have been published in Japan and South Korea. Tanaka published the highest number of articles (n = 26, citations = 11,143). The Pancreas published the highest number of articles. (n = 100, citations = 2533). These articles were grouped into 4 clusters including basic research, disease overview, management/prognosis and malignant IPMN by using bibliometric keywords network analysis. Overlay visualization demonstrates, a trend of the studies has been changed from basic research or disease to management or prognosis. CONCLUSIONS: In this study, we found and highlight the most cited and influential articles related to IPMN. Plus, this study analyzed global research trends in IPMN over the past 30 years and provides insight into the features and research hotspots of the articles in IPMN research.

Prevalence and prognosis of acute pancreatitis in critically ill patients with COVID-19.

BACKGROUND: Coronavirus disease 2019 (COVID-19) is a global pandemic issue. In addition to the well-known respiratory and fever symptoms, gastrointestinal symptoms have also been reported. This study aimed to evaluate the prevalence and prognosis of patients with COVID-19 infection complicated with acute pancreatitis in intensive care unit (ICU). METHODS: This was a retrospective observational cohort study, and patients aged 18 years or older, admitted into the ICU in a single tertiary center from January 1, 2020, to April 30, 2022 were enrolled. Patients were identified by electronic medical records and reviewed manually. The primary outcome was the prevalence of acute pancreatitis among ICU patients with COVID-19. The secondary outcomes were the length of hospital stay, need for mechanical ventilation (MV), need for continuous renal replacement therapy (CRRT), and in-hospital mortality. RESULTS: A total of 4133 patients, admitted into the ICU, were screened. Among these patients, 389 were infected by COVID-19, and 86 were diagnosed with acute pancreatitis. COVID-19 positive patients were more likely to present with acute pancreatitis than COVID-19 negative patients (odds ratio = 5.42, 95% confidence interval: 2.35-6.58, P < 0.01). However, the length of hospital stay, need for MV, need for CRRT, and in-hospital mortality were not significantly different between acute pancreatitis patients with and without COVID-19 infection. CONCLUSIONS: Severe COVID-19 infections may cause acute pancreas damage in critically ill patients. However, the prognosis may not differ between acute pancreatitis patients with and without COVID-19 infection.

Comparison of Clinical and Imaginal Features According to the Pathological Grades of Dysplasia in Branch-Duct Intraductal Papillary Mucinous Neoplasm (BD-IPMN) for Personalized Medicine.

Background: In patients with BD-IPMN, surgical indications have been focused on finding malignant lesions (HGD, high-grade dysplasia/IC, invasive carcinoma). The aim of this study was to compare the preoperative factors that distinguish HGD from LGD (low-grade dysplasia) and HGD from IC to find the optimal pathologic target for surgery according to individuals, considering surgical risks and outcomes. Methods: We retrospectively analyzed 232 patients with BD-IPMN diagnosed based on pathology after surgery and preoperative images. The primary outcome was identifying preoperative factors distinguishing HGD from LGD, and HGD from IC. Results: In patients with LGD/HGD, a solid component or an enhancing mural nodule ≥ 5 mm (OR = 9.29; 95% CI: 3.3−54.12; p < 0.000) and thickened/enhancing cyst walls (OR = 6.95; 95% CI: 1.68−33.13; p = 0.008) were associated with HGD. In patients with malignant lesions (HGD/IC), increased serum CA 19-9 (OR = 12.59; 95% CI: 1.81−87.44; p = 0.006) was associated with IC. Conclusions: The predictive factors for HGD were the presence of a solid component or an enhancing mural nodule ≥ 5 mm and thickened/enhancing cyst walls compared with LGD, and if accompanied by increased CA 19-9, it might be necessary to urgently evaluate the lesion due to the possibility of progression to IC. Based on this finding, we need to find HGD as the optimal pathologic target for surgery to improve survival in low-surgical-risk patients, and IC could be assumed to be the optimal pathologic target for surgery in high-surgical-risk patients because of high morbidity and mortality associated with surgery.

A novel bipolar electrocautery-enhanced delivery system with a lumen-apposing metal stent for EUS-guided drainage: A porcine study.

BACKGROUND: An electrocautery-enhanced delivery system with a lumen-apposing metal stent (LAMS) is available for one-step endoscopic ultrasound-guided transmural drainage (EUS-TD). Bipolar electrosurgery has several potential clinical advantages, including reduced collateral thermal damage, enhanced hemostasis, and no requirement for a return electrode plate. In this study, we compared the technical feasibility and safety of a newly developed bipolar electrocautery-enhanced delivery system with a conventional delivery system for EUS-TD using a LAMS in a porcine model. METHOD: Ten days before the study, 12 mini pigs underwent common bile duct ligation for EUS-guided gallbladder drainage. Transenteric puncture was performed, followed by placement of a guidewire. In six pigs, a bipolar electrocautery-enhanced delivery system with LAMS (Hot SPAXUS) was inserted over the guidewire and advanced into the gallbladder, without prior dilation of the tract, by applying a bipolar cut current. In the remaining six pigs, a conventional delivery system with LAMS (Cold SPAXUS) was inserted after tract dilatation using a cystotome. The stent was removed after 4 weeks. RESULTS: In all pigs, the stent was successfully inserted and deployed in the gallbladder without adverse events. The mean procedure time of EUS-TD was significantly lower in the Hot SPAXUS group than that of the Cold SPAXUS group (mean ± standard deviation: 188.7 ± 5.2 vs 449.5 ± 97.5 s, P = .0019). Stent migration was not observed, and all stents were removed successfully. CONCLUSIONS: Endoscopic ultrasound-guided transmural drainage using a bipolar electrocautery-enhanced LAMS is feasible for reducing the procedure time while maintaining the high success rate and safety of conventional LAMS.

Analysis of Mortality in Intracerebral Hemorrhage Patients with Hyperacute Ischemic Stroke Treated Using Thrombolytic Therapy: A Nationwide Population-based Cohort Study in South Korea.

This study investigated the impact of intracerebral hemorrhage (ICH) on the cumulative mortality of patients with hyperacute ischemic stroke. This population-based retrospective cohort study used claims data from the National Health Insurance Service customized database of South Korea. The recruitment period was 2005−2018. The study population included patients with hyperacute ischemic stroke who had received intravenous thrombolysis. The primary endpoint was 12-month cumulative mortality, which was analyzed in both the ICH and no-ICH groups. Of the 50,550 patients included, 2567 (5.1%) and 47,983 (94.9%) belonged to the ICH and no-ICH groups, respectively. In the univariable analysis for 12-month mortality, ICH patients were substantially more prevalent among dead patients than among patients who survived (11.6% versus 3.6%; p < 0.001). The overall 12-month cumulative mortality rate was 18.8%. Mortality in the ICH group was higher than that in the no-ICH group (42.8% versus 17.5%; p < 0.001). In the multivariable analysis, the risk of 12-month cumulative mortality was 2.97 times higher in the ICH group than in the no-ICH group (95% confidence interval, 2.79−3.16). The risk of 12-month cumulative mortality in hyperacute ischemic stroke can increase approximately threefold after the occurrence of spontaneous ICH following intravenous thrombolysis.

Clinical Utility of Personalized Serum IgG Subclass Ratios for the Differentiation of IgG4-Related Sclerosing Cholangitis (IgG4-SC) from Primary Sclerosing Cholangitis (PSC) and Cholangiocarcinoma (CCA).

BACKGROUND: The differential diagnosis of immunoglobulin G4-sclerosing cholangitis (IgG4-SC) from primary sclerosing cholangitis (PSC) or cholangiocarcinoma (CCA) is important. In this study, we aimed to find the best combinations of serum IgG subclasses and IgG4 levels for differentiating IgG4-SC from PSC or CCA. METHODS: In total, 31 patients with IgG4-SC, 27 patients with PSC, and 40 patients with CCA were enrolled from 2003 to 2017 at a single tertiary referral center. We retrospectively assessed the IgG4, IgG4/IgG1, IgG4/(IgG1+IgG3), and (IgG4+IgG2)/(IgG1+IgG3) in each of the patients. ROC curves were established to obtain the optimal cutoff value for each parameter. McNemar's test was used to compare the sensitivities, specificities, and accuracies of diagnostic algorithms. RESULTS: In differentiating IgG4-SC from PSC, the accuracies of IgG4/IgG1 ≥ 0.087 and of IgG4/(IgG1+IgG3) ≥ 0.081 were significantly higher than that of IgG4 ≥ 135 mg/dL alone (78% vs. 66%, p = 0.025). Serum IgG4 ≥ 52 mg/dL showed the best accuracy for differentiation of IgG4-SC from CCA, with a sensitivity and specificity of 80% and 82%, respectively, but this was statistically not significant (p = 0.405). CONCLUSIONS: The serum IgG4/IgG1 or IgG4/(IgG1+IgG3) level may help to differentiate IgG4-SC from PSC. IgG4 alone is the most accurate serologic marker for the differentiation of IgG4-SC from CCA.

Dynamic Recognition and Analysis of Gait Contour of Dance Movements Based on Generative Adversarial Networks.

With the generation of images, videos, and other data, how to identify the gait of the action in the video has gradually become the focus of research. Aiming at the problems of complex and changeable movements, strong coherence, and serious occlusion in dance video images, this paper proposes a dynamic recognition model of gait contour of dance movements based on GAN (generative adversarial networks). GAN method is used to convert the gait diagrams in any state into a group of gait diagrams in normal state with multiple angles, which are arranged in turn. In order to retain as much original feature information as possible, multiple loss strategy is adopted to optimize the network, increase the distance between classes, and reduce the distance within classes. Experimental results show that the average recognition rates of this model at 50°, 90°, and 120°are 93.24, 98.24, and 97.93, respectively, which shows that the recognition accuracy of dance movement recognition method is high. And this method can effectively improve the dynamic recognition of gait contour of dance movements.

SARS-CoV-2 Cross-Reactivity in Prepandemic Serum from Rural Malaria-Infected Persons, Cambodia.

Inhabitants of the Greater Mekong Subregion in Cambodia are exposed to pathogens that might influence serologic cross-reactivity with severe acute respiratory syndrome coronavirus 2. A prepandemic serosurvey of 528 malaria-infected persons demonstrated higher-than-expected positivity of nonneutralizing IgG to spike and receptor-binding domain antigens. These findings could affect interpretation of large-scale serosurveys.

Pre-pandemic SARS-CoV-2 serological reactivity in rural malaria-experienced Cambodians.

Greater Mekong inhabitants are exposed to pathogens, zoonotic and otherwise, that may influence SARS-CoV-2 seroreactivity. A pre-pandemic (2005 to 2011) serosurvey of from 528 malaria-experienced Cambodians demonstrated higher-than-expected (up to 13.8 %) positivity of non-neutralizing IgG to SARS-CoV-2 spike and RBD antigens. These findings have implications for interpreting large-scale serosurveys. ARTICLE SUMMARY LINE: In the pre-COVID19 pandemic years of 2005 to 2011, malaria experienced Cambodians from rural settings had higher-than-expected seroreactivity to SARS-CoV-2 spike and receptor binding domain proteins.

Feasibility study of endoscopic biliary drainage under direct peroral cholangioscopy by using an ultra-slim upper endoscope (with videos).

The therapeutic utility of peroral cholangioscopy (POC) is limited. Direct POC using an ultra­slim upper endoscope expands the therapeutic indications because of its larger working channel, of up to 2.2 mm. We evaluated the feasibility of selective biliary drainage using a plastic stent under direct POC. From April 2015 to March 2019, biliary drainage under endoscopic visualization was performed in the same endoscopic session as direct POC without exchanging the duodenoscope. After guidewire insertion through the stricture or stone, a 5 Fr plastic stent and/or nasobiliary drainage catheter was used for biliary drainage. Selective biliary drainage under direct POC was performed in 32 patients, including 17 with difficult bile duct stones. Biliary drainage was performed with a plastic stent in 29 patients, nasobiliary drainage in one, and combined drainage in two patients. The technical success rate for biliary drainage placement under direct POC was 100 % (32/32). No significant procedure-related complications occurred. In conclusion, biliary drainage with a plastic stent or catheter under direct POC using an ultra-slim upper endoscope is feasible and may be useful for lesions obstructing the bile duct.

Clinical Characteristics of Clonorchis sinensis-Associated Cholangiocarcinoma: A Large-Scale, Single-Center Study.

Background: Clonorchis sinensis (CS) infection is considered a group 1 carcinogen of cholangiocarcinoma (CCA). There were very few studies regarding clinical characteristics of CS-associated CCA (CACC). This study aimed to investigate clinical characteristics of patients with CCA with or without CS infection. Methods: A total of 367 patients diagnosed with CCA who underwent diagnostic tests for CS infection were enrolled. CS infection was defined as follows: at least one positive serum ELISA test, skin test, stool microscopy, or bile microscopy. Results: There were 95 (26%) patients with CS infections. The median follow-up duration was 14.9 months (range, 6.07-36.17). The following significant differences were noted among patients with CACC compared to non-CACC; diagnosis at younger age (median 62 years vs. 65 years, p = 0.018), higher male to female ratio (83.2 vs. 61.8%, p < 0.001), and residence in CS-endemic area (46.3 vs. 25.4%, p = 0.014). Univariate analysis of prognostic factors indicated that tumor location, curative resection, tumor stage, and laboratory tests including CA 19-9, CEA, and bilirubin were significantly associated with overall survival, but CS infection was not. In multivariate analysis, tumor location, CEA, curative resection and tumor stage were identified as independent prognostic factors. Among patients under age 64, CACC group had lower survival rate than non-CACC group (p = 0.022). Conclusions: CACC had the following significant characteristics compared to non-CACC; diagnosis at younger age, higher male to female ratio, higher prevalence in CS endemic areas and poorer overall survival in patients under age 64.

The effect of calcium and magnesium on activity, immunogenicity, and efficacy of a recombinant N1/N2 neuraminidase vaccine.

Despite the importance of immunity against neuraminidase (NA), NA content and immunogenicity are neglected in current influenza vaccines. To address this, a recombinant N1/N2 NA vaccine (NAV) was developed. Stability assays were used to determine optimal temperature and buffer conditions for vaccine storage. The effect of divalent cation-related enhancement of NA stability and activity on N1 and N2 immunogenicity and efficacy against viral challenge was assessed. Differences in activity between N1 and N2 and cation-related activity enhancement did not translate into differences in immunogenicity or efficacy. NAV-vaccinated mice showed robust antibody titers against N1 and N2, and after challenge with influenza A (H1N1) virus, decreased viral titers and decreased antiviral and inflammatory responses by transcriptomic analysis. These findings provide guidance for optimal storage and assessment of NA-based vaccines and confirm the importance of NA in influenza vaccination strategies in attenuating viral replication and limiting inflammatory responses necessary to clear infection.

A novel electrocautery-enhanced delivery system for one-step endoscopic ultrasound-guided drainage of the gallbladder and bile duct using a lumen-apposing metal stent: a feasibility study.

BACKGROUND: The use of a lumen-apposing metal stent (LAMS) capable of one-step endoscopic ultrasound-guided transmural drainage (EUS-TD) can increase the effectiveness of the procedure. We evaluated the newly developed electrocautery-enhanced (EC) delivery system with a LAMS for one-step EUS-guided gallbladder drainage (EUS-GBD) or choledochoduodenostomy (EUS-CDS). METHODS: In the animal experiment, an EC-LAMS was advanced into the gallbladder without prior tract dilation in four pigs. A conventional LAMS was inserted in another four pigs as a control group. After the animal experiment, 17 patients underwent EUS-TD using the EC-LAMS (EUS-GBD in 10 patients, EUS-CDS in 7). The primary outcome was the technical success rate. RESULTS: In the animal study, the mean procedure time was significantly shorter in the EC-LAMS group than in the conventional LAMS group. In the human study, the overall technical success rate was 94.1 %, with one EUS-GBD failure. The clinical success rate was 100 %. The overall adverse event rate was 17.6 %. CONCLUSIONS: One-step EUS-GBD or EUS-CDS using the novel EC-LAMS is a feasible approach that achieves a high success rate and maintains safety.

Efficacy of a modified short fully covered self-expandable metal stent for perihilar benign biliary strictures.

BACKGROUND AND AIM: Endoscopic management of a benign biliary stricture (BBS) on the hilum is complicated and challenging. Although the placement of a fully covered self-expandable metal stent (FCSEMS) is possible to increase effectiveness, stent migration and stent-induced adverse events are problematic. We aimed to evaluate the usefulness of a modified short FCSEMS with a long lasso in patients with a difficult perihilar BBS. METHODS: Patients with perihilar BBS within 2 cm from the hilar confluence that failed initially with plastic stents were enrolled. A modified short FCSEMS was deployed and then removed 5-6 months later. The primary outcome was clinical success. Other technical success, adverse events, endoscopic success of stent removal, and recurrence of stricture during the follow-up period were measured. RESULTS: Endoscopic intraductal placement was technically successful in all patients (n = 19). Combined contralateral plastic stent placement was performed in 13 patients (68.4%). The median duration of stent placement was 163 days (range, 138-196 days). Endoscopic stent removal was successful in all patients except one spontaneous distal migration. Stricture resolution without de novo focal stricture occurrence was 100%. Endoscopic stone removal after stricture improvement was successful in all 13 patients with bile duct stones above the stricture. During a follow-up period (median 635 days) after stent removal, only one recurrence developed. CONCLUSIONS: Temporary placement of a modified intraductal short FCSEMS with or without a contralateral plastic stent improved perihilar BBS in patients that primarily failed by plastic stents. Combined biliary stones were also successfully removed after stricture resolution.

Coaxial Electrospun Nanofibers with Different Shell Contents to Control Cell Adhesion and Viability.

Electrospun nanofibers are widely employed as cell culture matrices because their biomimetic structures resemble a natural extracellular matrix. However, due to the limited cell infiltration into nanofibers, three-dimensional (3D) construction of a cell matrix is not easily accomplished. In this study, we developed a method for the partial digestion of a nanofiber into fragmented nanofibers composed of gelatin and polycaprolactone (PCL). The PCL shells of the coaxial fragments were subsequently removed with different concentrations of chloroform to control the remaining PCL on the shell. The swelling and exposure of the gelatin core were manipulated by the remaining PCL shells. When cells were cultivated with the fragmented nanofibers, they were spontaneously assembled on the cell sheets. The cell adhesion and proliferation were significantly affected by the amount of PCL shells on the fragmented nanofibers.

Pre-existing immunity to influenza virus hemagglutinin stalk might drive selection for antibody-escape mutant viruses in a human challenge model.

The conserved region of influenza hemagglutinin (HA) stalk (or stem) has gained attention as a potent target for universal influenza vaccines1-5. Although the HA stalk region is relatively well conserved, the evolutionarily dynamic nature of influenza viruses6 raises concerns about the possible emergence of viruses carrying stalk escape mutation(s) under sufficient immune pressure. Here we show that immune pressure on the HA stalk can lead to expansion of escape mutant viruses in study participants challenged with a 2009 H1N1 pandemic influenza virus inoculum containing an A388V polymorphism in the HA stalk (45% wild type and 55% mutant). High level of stalk antibody titers was associated with the selection of the mutant virus both in humans and in vitro. Although the mutant virus showed slightly decreased replication in mice, it was not observed in cell culture, ferrets or human challenge participants. The A388V mutation conferred resistance to some of the potent HA stalk broadly neutralizing monoclonal antibodies (bNAbs). Co-culture of wild-type and mutant viruses in the presence of either a bNAb or human serum resulted in rapid expansion of the mutant. These data shed light on a potential obstacle for the success of HA-stalk-targeting universal influenza vaccines-viral escape from vaccine-induced stalk immunity.

Influenza A Reinfection in Sequential Human Challenge: Implications for Protective Immunity and "Universal" Vaccine Development.

BACKGROUND: Identification of correlates of protection against human influenza A virus infection is important in development of broadly protective ("universal") influenza vaccines. Certain assumptions underlie current vaccine developmental strategies, including that infection with a particular influenza A virus should offer long-term or lifelong protection against that strain, preventing reinfection. In this study we report observations made when 7 volunteers participated in sequential influenza challenge studies where they were challenged intranasally using the identical influenza A(H1N1)pdm09 virus approximately 1 year apart. We evaluate and describe the outcomes of these 7 rechallenge participants and discuss what these results may suggest about correlates of protection and development of more broadly protective influenza vaccines. METHODS: Seven participants were enrolled in 2 viral challenge studies at 7.5- to 18.5-month intervals. Both challenge studies used the identical lot of influenza A (H1N1)pdm09 virus administered intranasally. We evaluated pre- and postchallenge hemagglutination inhibition, neuraminidase inhibition, and stalk antibody titers; peripheral blood leukocyte host gene expression response profiles; daily viral detection via nasal wash; and clinical signs and symptoms. RESULTS: At least 3 of 7 participants demonstrated confirmed laboratory evidence of sequential infection, with 5 of 7 demonstrating clinical evidence. CONCLUSIONS: The data presented in this report demonstrate that sequential infection with the identical influenza A virus can occur and suggest it may not be rare. These data raise questions about immune memory responses in an acute superficial respiratory mucosal infection and their implications in development of broadly protective influenza vaccines. Further investigation of these observations is warranted. CLINICAL TRIALS REGISTRATION: NCT01646138; NCT01971255.