A simplified pneumonia severity index (PSI) for clinical outcome prediction in COVID-19.

BACKGROUND: The Pneumonia Score Index (PSI) was developed to estimate the risk of dying within 30 days of presentation for community-acquired pneumonia patients and is a strong predictor of 30-day mortality after COVID-19. However, three of its required 20 variables (skilled nursing home, altered mental status and pleural effusion) are not discreetly available in the electronic medical record (EMR), resulting in manual chart review for these 3 factors. The goal of this study is to compare a simplified 17-factor version (PSI-17) to the original (denoted PSI-20) in terms of prediction of 30-day mortality in COVID-19. METHODS: In this retrospective cohort study, the hospitalized patients with confirmed SARS-CoV-2 infection between 2/28/20-5/28/20 were identified to compare the predictive performance between PSI-17 and PSI-20. Correlation was assessed between PSI-17 and PSI-20, and logistic regressions were performed for 30-day mortality. The predictive abilities were compared by discrimination, calibration, and overall performance. RESULTS: Based on 1,138 COVID-19 patients, the correlation between PSI-17 and PSI-20 was 0.95. Univariate logistic regression showed that PSI-17 had performance similar to PSI-20, based on AUC, ICI and Brier Score. After adjusting for confounding variables by multivariable logistic regression, PSI-17 and PSI-20 had AUCs (95% CI) of 0.85 (0.83-0.88) and 0.86 (0.84-0.89), respectively, indicating no significant difference in AUC at significance level of 0.05. CONCLUSION: PSI-17 and PSI-20 are equally effective predictors of 30-day mortality in terms of several performance metrics. PSI-17 can be obtained without the manual chart review, which allows for automated risk calculations within an EMR. PSI-17 can be easily obtained and may be a comparable alternative to PSI-20.

Integrative systems biology reveals NKG2A-biased immune responses correlate with protection in infectious disease, autoimmune disease, and cancer.

Infection, autoimmunity, and cancer are principal human health challenges of the 21st century. Often regarded as distinct ends of the immunological spectrum, recent studies hint at potential overlap between these diseases. For example, inflammation can be pathogenic in infection and autoimmunity. T resident memory (TRM) cells can be beneficial in infection and cancer. However, these findings are limited by size and scope; exact immunological factors shared across diseases remain elusive. Here, we integrate large-scale deeply clinically and biologically phenotyped human cohorts of 526 patients with infection, 162 with lupus, and 11,180 with cancer. We identify an NKG2A+ immune bias as associative with protection against disease severity, mortality, and autoimmune/post-acute chronic disease. We reveal that NKG2A+ CD8+ T cells correlate with reduced inflammation and increased humoral immunity and that they resemble TRM cells. Our results suggest NKG2A+ biases as a cross-disease factor of protection, supporting suggestions of immunological overlap between infection, autoimmunity, and cancer.

SARS-CoV-2 Antiviral Prescribing Gaps Among Non-Hospitalized High-Risk Adults.

Within a multi-state clinical cohort, SARS-CoV-2 antiviral prescribing patterns were evaluated from April 2022-June 2023 among non-hospitalized SARS-CoV-2-infected patients with risk factors for severe COVID-19. Among 3,247 adults, only 31.9% were prescribed an antiviral agent (87.6% nirmatrelvir/ritonavir, 11.9% molnupiravir, 0.5% remdesivir), highlighting the need to identify and address treatment barriers.

Disease diagnostics using machine learning of immune receptors.

Clinical diagnosis typically incorporates physical examination, patient history, and various laboratory tests and imaging studies, but makes limited use of the human system's own record of antigen exposures encoded by receptors on B cells and T cells. We analyzed immune receptor datasets from 593 individuals to develop MAchine Learning for Immunological Diagnosis (Mal-ID) , an interpretive framework to screen for multiple illnesses simultaneously or precisely test for one condition. This approach detects specific infections, autoimmune disorders, vaccine responses, and disease severity differences. Human-interpretable features of the model recapitulate known immune responses to SARS-CoV-2, Influenza, and HIV, highlight antigen-specific receptors, and reveal distinct characteristics of Systemic Lupus Erythematosus and Type-1 Diabetes autoreactivity. This analysis framework has broad potential for scientific and clinical interpretation of human immune responses.

Principles for the Physician-Led Patient-Centered Medical Home and Other Approaches to Team-Based Care: A Position Paper From the American College of Physicians.

Team-based care models such as the Patient-Centered Medical Home are associated with improved patient health outcomes, better team coordination and collaboration, and increased well-being among health care professionals. Despite these attributes, hindrances to wider adoption remain. In addition, some health care professionals have sought to practice independent of the physician-led health care team, potentially undermining patient access to physicians who have the skills and training to deliver whole-person, comprehensive, and longitudinal care. In this paper, the American College of Physicians reaffirms the importance of the physician-led health care team and offers policy recommendations on professionalism, payment models, training, licensure, and research to support the expansion of dynamic clinical care teams.

Organ-specific immunity: A tissue analysis framework for investigating local immune responses to SARS-CoV-2.

Local immune activation at mucosal surfaces, mediated by mucosal lymphoid tissues, is vital for effective immune responses against pathogens. While pathogens like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can spread to multiple organs, patients with coronavirus disease 2019 (COVID-19) primarily experience inflammation and damage in their lungs. To investigate this apparent organ-specific immune response, we develop an analytical framework that recognizes the significance of mucosal lymphoid tissues. This framework combines histology, immunofluorescence, spatial transcript profiling, and mathematical modeling to identify cellular and gene expression differences between the lymphoid tissues of the lung and the gut and predict the determinants of those differences. Our findings indicate that mucosal lymphoid tissues are pivotal in organ-specific immune response to SARS-CoV-2, mediating local inflammation and tissue damage and contributing to immune dysfunction. The framework developed here has potential utility in the study of long COVID and may streamline biomarker discovery and treatment design for diseases with differential pathologies at the organ level.

An NKG2A biased immune response confers protection for infection, autoimmune disease, and cancer.

Infection, autoimmunity, and cancer are the principal human health challenges of the 21st century and major contributors to human death and disease. Often regarded as distinct ends of the immunological spectrum, recent studies have hinted there may be more overlap between these diseases than appears. For example, pathogenic inflammation has been demonstrated as conserved between infection and autoimmune settings. T resident memory (TRM) cells have been highlighted as beneficial for infection and cancer. However, these findings are limited by patient number and disease scope; exact immunological factors shared across disease remain elusive. Here, we integrate large-scale deeply clinically and biologically phenotyped human cohorts of 526 patients with infection, 162 with lupus, and 11,180 with cancer. We identify an NKG2A+ immune bias as associative with protection against disease severity, mortality, and autoimmune and post-acute chronic disease. We reveal that NKG2A+ CD8+ T cells correlate with reduced inflammation, increased humoral immunity, and resemble TRM cells. Our results suggest that an NKG2A+ bias is a pan-disease immunological factor of protection and thus supports recent suggestions that there is immunological overlap between infection, autoimmunity, and cancer. Our findings underscore the promotion of an NKG2A+ biased response as a putative therapeutic strategy.

Researching COVID to Enhance Recovery (RECOVER) adult study protocol: Rationale, objectives, and design.

IMPORTANCE: SARS-CoV-2 infection can result in ongoing, relapsing, or new symptoms or other health effects after the acute phase of infection; termed post-acute sequelae of SARS-CoV-2 infection (PASC), or long COVID. The characteristics, prevalence, trajectory and mechanisms of PASC are ill-defined. The objectives of the Researching COVID to Enhance Recovery (RECOVER) Multi-site Observational Study of PASC in Adults (RECOVER-Adult) are to: (1) characterize PASC prevalence; (2) characterize the symptoms, organ dysfunction, natural history, and distinct phenotypes of PASC; (3) identify demographic, social and clinical risk factors for PASC onset and recovery; and (4) define the biological mechanisms underlying PASC pathogenesis. METHODS: RECOVER-Adult is a combined prospective/retrospective cohort currently planned to enroll 14,880 adults aged ≥18 years. Eligible participants either must meet WHO criteria for suspected, probable, or confirmed infection; or must have evidence of no prior infection. Recruitment occurs at 86 sites in 33 U.S. states, Washington, DC and Puerto Rico, via facility- and community-based outreach. Participants complete quarterly questionnaires about symptoms, social determinants, vaccination status, and interim SARS-CoV-2 infections. In addition, participants contribute biospecimens and undergo physical and laboratory examinations at approximately 0, 90 and 180 days from infection or negative test date, and yearly thereafter. Some participants undergo additional testing based on specific criteria or random sampling. Patient representatives provide input on all study processes. The primary study outcome is onset of PASC, measured by signs and symptoms. A paradigm for identifying PASC cases will be defined and updated using supervised and unsupervised learning approaches with cross-validation. Logistic regression and proportional hazards regression will be conducted to investigate associations between risk factors, onset, and resolution of PASC symptoms. DISCUSSION: RECOVER-Adult is the first national, prospective, longitudinal cohort of PASC among US adults. Results of this study are intended to inform public health, spur clinical trials, and expand treatment options. REGISTRATION: NCT05172024.

Large libraries of single-chain trimer peptide-MHCs enable antigen-specific CD8+ T cell discovery and analysis.

The discovery and characterization of antigen-specific CD8+ T cell clonotypes typically involves the labor-intensive synthesis and construction of peptide-MHC tetramers. We adapt single-chain trimer (SCT) technologies into a high throughput platform for pMHC library generation, showing that hundreds can be rapidly prepared across multiple Class I HLA alleles. We use this platform to explore the impact of peptide and SCT template mutations on protein expression yield, thermal stability, and functionality. SCT libraries were an efficient tool for identifying T cells recognizing commonly reported viral epitopes. We then construct SCT libraries to capture SARS-CoV-2 specific CD8+ T cells from COVID-19 participants and healthy donors. The immunogenicity of these epitopes is validated by functional assays of T cells with cloned TCRs captured using SCT libraries. These technologies should enable the rapid analyses of peptide-based T cell responses across several contexts, including autoimmunity, cancer, or infectious disease.

Prediction of HLA genotypes from single-cell transcriptome data.

The human leukocyte antigen (HLA) locus plays a central role in adaptive immune function and has significant clinical implications for tissue transplant compatibility and allelic disease associations. Studies using bulk-cell RNA sequencing have demonstrated that HLA transcription may be regulated in an allele-specific manner and single-cell RNA sequencing (scRNA-seq) has the potential to better characterize these expression patterns. However, quantification of allele-specific expression (ASE) for HLA loci requires sample-specific reference genotyping due to extensive polymorphism. While genotype prediction from bulk RNA sequencing is well described, the feasibility of predicting HLA genotypes directly from single-cell data is unknown. Here we evaluate and expand upon several computational HLA genotyping tools by comparing predictions from human single-cell data to gold-standard, molecular genotyping. The highest 2-field accuracy averaged across all loci was 76% by arcasHLA and increased to 86% using a composite model of multiple genotyping tools. We also developed a highly accurate model (AUC 0.93) for predicting HLA-DRB345 copy number in order to improve genotyping accuracy of the HLA-DRB locus. Genotyping accuracy improved with read depth and was reproducible at repeat sampling. Using a metanalytic approach, we also show that HLA genotypes from PHLAT and OptiType can generate ASE ratios that are highly correlated (R2 = 0.8 and 0.94, respectively) with those derived from gold-standard genotyping.

Therapeutic trials for long COVID-19: A call to action from the interventions taskforce of the RECOVER initiative.

Although most individuals recover from acute SARS-CoV-2 infection, a significant number continue to suffer from Post-Acute Sequelae of SARS-CoV-2 (PASC), including the unexplained symptoms that are frequently referred to as long COVID, which could last for weeks, months, or even years after the acute phase of illness. The National Institutes of Health is currently funding large multi-center research programs as part of its Researching COVID to Enhance Recover (RECOVER) initiative to understand why some individuals do not recover fully from COVID-19. Several ongoing pathobiology studies have provided clues to potential mechanisms contributing to this condition. These include persistence of SARS-CoV-2 antigen and/or genetic material, immune dysregulation, reactivation of other latent viral infections, microvascular dysfunction, and gut dysbiosis, among others. Although our understanding of the causes of long COVID remains incomplete, these early pathophysiologic studies suggest biological pathways that could be targeted in therapeutic trials that aim to ameliorate symptoms. Repurposed medicines and novel therapeutics deserve formal testing in clinical trial settings prior to adoption. While we endorse clinical trials, especially those that prioritize inclusion of the diverse populations most affected by COVID-19 and long COVID, we discourage off-label experimentation in uncontrolled and/or unsupervised settings. Here, we review ongoing, planned, and potential future therapeutic interventions for long COVID based on the current understanding of the pathobiological processes underlying this condition. We focus on clinical, pharmacological, and feasibility data, with the goal of informing future interventional research studies.

Transplant of organs from donors with positive SARS-CoV-2 nucleic acid testing: A report from the organ procurement and transplantation network ad hoc disease transmission advisory committee.

BACKGROUND: Decisions to transplant organs from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleic acid test-positive (NAT+) donors must balance risk of donor-derived transmission events (DDTE) with the scarcity of available organs. METHODS: Organ Procurement and Transplantation Network (OPTN) data were used to compare organ utilization and recipient outcomes between SARS-CoV-2 NAT+ and NAT- donors. NAT+ was defined by either a positive upper or lower respiratory tract (LRT) sample within 21 days of procurement. Potential DDTE were adjudicated by OPTN Disease Transmission Advisory Committee. RESULTS: From May 27, 2021 (date of OTPN policy for required LRT testing of lung donors) to January 31, 2022, organs were recovered from 617 NAT+ donors from all OPTN regions and 53 of 57 (93%) organ procurement organizations. NAT+ donors were younger and had higher organ quality scores for kidney and liver. Organ utilization was lower for NAT+ donors compared to NAT- donors. A total of 1241 organs (776 kidneys, 316 livers, 106 hearts, 22 lungs, and 21 other) were transplanted from 514 NAT+ donors compared to 21 946 organs from 8853 NAT- donors. Medical urgency was lower for recipients of NAT+ liver and heart transplants. The median waitlist time was longer for liver recipients of NAT+ donors. The match run sequence number for final acceptor was higher for NAT+ donors for all organ types. Outcomes for hospital length of stay, 30-day mortality, and 30-day graft loss were similar for all organ types. No SARS-CoV-2 DDTE occurred in this interval. CONCLUSIONS: Transplantation of SARS-CoV-2 NAT+ donor organs appears safe for short-term outcomes of death and graft loss and ameliorates the organ shortage. Further study is required to assure comparable longer term outcomes.

Association of Remdesivir Treatment With Mortality Among Hospitalized Adults With COVID-19 in the United States.

Importance: SARS-CoV-2, which causes COVID-19, poses considerable morbidity and mortality risks. Studies using data collected during routine clinical practice can supplement randomized clinical trials to provide needed evidence, especially during a global pandemic, and can yield markedly larger sample sizes to assess outcomes for important patient subgroups. Objective: To evaluate the association of remdesivir treatment with inpatient mortality among patients with COVID-19 outside of the clinical trial setting. Design, Setting, and Participants: A retrospective cohort study in US hospitals using health insurance claims data linked to hospital chargemaster data from December 1, 2018, to May 3, 2021, was conducted among 24 856 adults hospitalized between May 1, 2020, and May 3, 2021, with newly diagnosed COVID-19 who received remdesivir and 24 856 propensity score-matched control patients. Exposure: Remdesivir treatment. Main Outcomes and Measures: All-cause inpatient mortality within 28 days of the start of remdesivir treatment for the remdesivir-exposed group or the matched index date for the control group. Results: A total of 24 856 remdesivir-exposed patients (12 596 men [50.7%]; mean [SD] age, 66.8 [15.4] years) and 24 856 propensity score-matched control patients (12 621 men [50.8%]; mean [SD] age, 66.8 [15.4] years) were included in the study. Median follow-up was 6 days (IQR, 4-11 days) in the remdesivir group and 5 days (IQR, 2-10 days) in the control group. There were 3557 mortality events (14.3%) in the remdesivir group and 3775 mortality events (15.2%) in the control group. The 28-day mortality rate was 0.5 per person-month in the remdesivir group and 0.6 per person-month in the control group. Remdesivir treatment was associated with a statistically significant 17% reduction in inpatient mortality among patients hospitalized with COVID-19 compared with propensity score-matched control patients (hazard ratio, 0.83 [95% CI, 0.79-0.87]). Conclusions and Relevance: In this retrospective cohort study using health insurance claims and hospital chargemaster data, remdesivir treatment was associated with a significantly reduced inpatient mortality overall among patients hospitalized with COVID-19. Results of this analysis using data collected during routine clinical practice and state-of-the-art methods complement results from randomized clinical trials. Future areas of research include assessing the association of remdesivir treatment with inpatient mortality during the circulation of different variants and relative to time from symptom onset.

Large libraries of single-chain trimer peptide-MHCs enable rapid antigen-specific CD8+ T cell discovery and analysis.

CD8 + cytotoxic T cell responses against viral infection represent a major element of the adaptive immune response. We describe the development of a peptide antigen - major histompatibility complex (pMHC) library representing the full SARS-CoV-2 viral proteome, and comprised of 634 pMHC multimers representing the A*02.01, A*24.02, and B*07.02 HLA alleles, as well as specific antigens associated with the cytomegalovirus (CMV). These libraries were used to capture non-expanded CD8 + T cells from blood samples collected from 64 infected individuals, and then analyzed using single cell RNA-seq. The discovery and characterization of antigen-specific CD8 + T cell clonotypes typically involves the labor-intensive synthesis and construction of peptide-MHC tetramers. We adapted single-chain trimer (SCT) technologies into a high throughput platform for pMHC library generation, showing that hundreds can be rapidly prepared across multiple Class I HLA alleles. We used this platform to explore the impact of peptide and SCT template mutations on protein expression yield, thermal stability, and functionality. SCT libraries were an efficient tool for identifying T cells recognizing commonly reported viral epitopes. We then constructed SCT libraries designed to capture SARS-CoV-2 specific CD8 + T cells from COVID-19 participants and healthy donors. The immunogenicity of these epitopes was validated by functional assays of T cells with cloned TCRs captured using SCT libraries. These technologies should enable the rapid analyses of peptide-based T cell responses across several contexts, including autoimmunity, cancer, or infectious disease.

COVID-19 and Cancer: Special Considerations for Patients Receiving Immunotherapy and Immunosuppressive Cancer Therapies.

Patients with cancer generally have a higher risk of adverse outcomes from COVID-19, with higher age, male sex, poor performance status, cancer type, and uncontrolled malignant disease as the main risk factors. However, the influence of specific cancer therapies varies and raises concerns during the pandemic. In patients undergoing cancer immunotherapy or other immunosuppressive cancer treatments, we summarize the evidence on outcomes from COVID-19; address the safety, immunogenicity, and efficacy of COVID-19 vaccination; and review COVID-19 antiviral therapeutics for the patient with cancer. Despite higher mortality for patients with cancer, treatment with immune checkpoint inhibitors does not seem to increase mortality risk based on observational evidence. Inhibitory therapies directed toward B-cell lineages, including monoclonal antibodies against CD20 and CAR T-cell therapies, are associated with poor outcomes in COVID-19; however, the data are sparse. Regarding vaccination in patients receiving immune checkpoint inhibitors, clinical efficacy comparable to that in the general population can be expected. In patients undergoing B-cell-depleting therapy, immunogenicity and clinical efficacy are curtailed, but vaccination is not futile, which is thought to be due to the cellular response. Vaccine reactogenicity and toxicity in all groups of patients with cancer are comparable to that of the general population. Preexposure prophylaxis with monoclonal antibodies directed against the viral spike may provide passive immunity for those not likely to mount an adequate vaccine response. If infected, prompt treatment with monoclonal antibodies or oral small molecule antivirals is beneficial, though with oral antiviral therapies, care must be taken to avoid drug interactions in patients with cancer.

Risk factors for severe COVID-19 differ by age for hospitalized adults.

Risk stratification for hospitalized adults with COVID-19 is essential to inform decisions about individual patients and allocation of resources. So far, risk models for severe COVID outcomes have included age but have not been optimized to best serve the needs of either older or younger adults. Models also need to be updated to reflect improvements in COVID-19 treatments. This retrospective study analyzed data from 6906 hospitalized adults with COVID-19 from a community health system across five states in the western United States. Risk models were developed to predict mechanical ventilation illness or death across one to 56 days of hospitalization, using clinical data available within the first hour after either admission with COVID-19 or a first positive SARS-CoV-2 test. For the seven-day interval, models for age ≥ 18 and < 50 years reached AUROC 0.81 (95% CI 0.71-0.91) and models for age ≥ 50 years reached AUROC 0.82 (95% CI 0.77-0.86). Models revealed differences in the statistical significance and relative predictive value of risk factors between older and younger patients including age, BMI, vital signs, and laboratory results. In addition, for hospitalized patients, sex and chronic comorbidities had lower predictive value than vital signs and laboratory results.

Delayed mortality among solid organ transplant recipients hospitalized for COVID-19.

INTRODUCTION: Most studies of solid organ transplant (SOT) recipients with COVID-19 focus on outcomes within one month of illness onset. Delayed mortality in SOT recipients hospitalized for COVID-19 has not been fully examined. METHODS: We used data from a multicenter registry to calculate mortality by 90 days following initial SARS-CoV-2 detection in SOT recipients hospitalized for COVID-19 and developed multivariable Cox proportional-hazards models to compare risk factors for death by days 28 and 90. RESULTS: Vital status at day 90 was available for 936 of 1117 (84%) SOT recipients hospitalized for COVID-19: 190 of 936 (20%) died by 28 days and an additional 56 of 246 deaths (23%) occurred between days 29 and 90. Factors associated with mortality by day 90 included: age > 65 years [aHR 1.8 (1.3-2.4), p =<0.001], lung transplant (vs. non-lung transplant) [aHR 1.5 (1.0-2.3), p=0.05], heart failure [aHR 1.9 (1.2-2.9), p=0.006], chronic lung disease [aHR 2.3 (1.5-3.6), p<0.001] and body mass index ≥ 30 kg/m 2 [aHR 1.5 (1.1-2.0), p=0.02]. These associations were similar for mortality by day 28. Compared to diagnosis during early 2020 (March 1-June 19, 2020), diagnosis during late 2020 (June 20-December 31, 2020) was associated with lower mortality by day 28 [aHR 0.7 (0.5-1.0, p=0.04] but not by day 90 [aHR 0.9 (0.7-1.3), p=0.61]. CONCLUSIONS: In SOT recipients hospitalized for COVID-19, >20% of deaths occurred between 28 and 90 days following SARS-CoV-2 diagnosis. Future investigations should consider extending follow-up duration to 90 days for more complete mortality assessment.

Daptomycin-Resistant Enterococcus Bacteremia Is Associated With Prior Daptomycin Use and Increased Mortality After Liver Transplantation.

BACKGROUND: Risk factors for acquisition of vancomycin-resistant Enterococcus (VRE) include immunosuppression, antibiotic exposure, indwelling catheters, and manipulation of the gastrointestinal tract, all of which occur in liver transplant recipients. VRE infections are documented in liver transplantation (LT); however, only one single center study has assessed the impact of daptomycin-resistant Enterococcus (DRE) in this patient population. METHODS: We conducted a retrospective multicenter cohort study comparing liver transplant recipients with either VRE or DRE bacteremia. The primary outcome was death within 1 year of transplantation. Multivariable logistic regression analyses were performed to calculate adjusted odds ratios for outcomes of interest. RESULTS: We identified 139 cases of Enterococcus bacteremia following LT, of which 78% were VRE and 22% were DRE. When adjusted for total intensive care unit days in the first transplant year, liver-kidney transplantation, and calcineurin inhibitor use, patients with DRE bacteremia were 2.65 times more likely to die within 1 year of transplantation (adjusted odds ratio [aOR], 2.648; 95% CI, 1.025-6.840; P = .044). Prior daptomycin exposure was found to be an independent predictor of DRE bacteremia (aOR, 30.62; 95% CI, 10.087-92.955; P < .001). CONCLUSIONS: In this multicenter study of LT recipients with Enterococcus bacteremia, DRE bacteremia was associated with higher 1-year mortality rates when compared with VRE bacteremia. Our data provide strong support for dedicated infection prevention and antimicrobial stewardship efforts for transplant patients. Further research is needed to support the development of better antibiotics for DRE and practical guidance focusing on identification and prevention of colonization and subsequent infection in liver transplant recipients at high risk for DRE bacteremia.

Efficacy and safety of baricitinib plus standard of care for the treatment of critically ill hospitalised adults with COVID-19 on invasive mechanical ventilation or extracorporeal membrane oxygenation: an exploratory, randomised, placebo-controlled trial.

BACKGROUND: The oral, selective Janus kinase 1/2 inhibitor baricitinib has shown efficacy in studies of hospitalised adults with COVID-19. COV-BARRIER (NCT04421027) was a multinational, phase 3, randomised, double-blind, placebo-controlled trial of baricitinib in patients with confirmed SARS-CoV-2 infection. We aimed to evaluate the efficacy and safety of baricitinib plus standard of care in critically ill hospitalised adults with COVID-19 requiring invasive mechanical ventilation or extracorporeal membrane oxygenation. METHODS: This exploratory trial followed the study design of COV-BARRIER in a critically ill cohort not included in the main phase 3 trial. The study was conducted across 18 hospitals in Argentina, Brazil, Mexico, and the USA. Participants (aged ≥18 years) hospitalised with laboratory-confirmed SARS-CoV-2 infection on baseline invasive mechanical ventilation or extracorporeal membrane oxygenation were randomly assigned (1:1) to baricitinib (4 mg) or placebo once daily for up to 14 days in combination with standard of care. Participants, study staff, and investigators were masked to study group assignment. Prespecified endpoints included all-cause mortality through days 28 and 60, number of ventilator-free days, duration of hospitalisation, and time to recovery through day 28. The efficacy analysis was done in the intention-to-treat population and the safety analysis was done in the safety population. This trial is registered with ClinicalTrials.gov, NCT04421027. FINDINGS: Between Dec 23, 2020, and April 10, 2021, 101 participants were enrolled into the exploratory trial and assigned to baricitinib (n=51) or placebo (n=50) plus standard of care. Standard of care included baseline systemic corticosteroid use in 87 (86%) participants. Treatment with baricitinib significantly reduced 28-day all-cause mortality compared with placebo (20 [39%] of 51 participants died in the baricitinib group vs 29 [58%] of 50 in the placebo group; hazard ratio [HR] 0·54 [95% CI 0·31-0·96]; p=0·030; 46% relative reduction; absolute risk reduction 19%). A significant reduction in 60-day mortality was also observed in the baricitinib group compared with the placebo group (23 [45%] events vs 31 [62%]; HR 0·56 [95% CI 0·33-0·97]; p=0·027; 44% relative reduction; absolute risk reduction 17%). In every six baricitinib-treated participants, one additional death was prevented compared with placebo at days 28 and 60. The number of ventilator-free days did not differ significantly between treatment groups (mean 8·1 days [SD 10·2] in the baricitinib group vs 5·5 days [8·4] in the placebo group; p=0·21). The mean duration of hospitalisation in baricitinib-treated participants was not significantly shorter than in placebo-treated participants (23·7 days [SD 7·1] vs 26·1 days [3·9]; p=0·050). The rates of infections, blood clots, and adverse cardiovascular events were similar between treatment groups. INTERPRETATION: In critically ill hospitalised patients with COVID-19 who were receiving invasive mechanical ventilation or extracorporeal membrane oxygenation, treatment with baricitinib compared with placebo (in combination with standard of care, including corticosteroids) reduced mortality, which is consistent with the mortality reduction observed in less severely ill patients in the hospitalised primary COV-BARRIER study population. However, this was an exploratory trial with a relatively small sample size; therefore, further phase 3 trials are needed to confirm these findings. FUNDING: Eli Lilly and Company.