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Background: Breakthrough infections after SARS-CoV-2 vaccination have been reported. Clinical outcomes in these persons are not widely known. Methods: We evaluated all vaccinated persons with breakthrough infection ≥14 days after the second vaccine dose and unvaccinated controls matched on age, sex, nationality, and reason for testing between December 23, 2020 and March 28, 2021 in Qatar. Our primary outcome was severe disease defined as hospitalization, mechanical ventilation, or death. Results: Among 456 persons cases of breakthrough infection and 456 unvaccinated matched controls with confirmed infection, median age was 45 years, 60.7% were males, and ≥1 comorbid condition was present in 61.2% of the vaccinated and 47.8% of the unvaccinated persons (P=0.009). Severe disease was recorded in 48 (10.5%) of the vaccinated and 121 (26.5%) of the unvaccinated group (P<0.001). Factors associated with severe disease included increasing age (HR vs. <40 years old: >40–60 years, HR 2.32; >60–70 years, HR 4.34; >70 years, HR 5.43); presence of symptoms at baseline (HR 2.42, 95%CI 1.44-4.07); and being unvaccinated (HR 2.84, 95%CI 1.80-4.47). Conclusions: In persons with breakthrough SARS-CoV-2 infection, increasing age is associated with a higher risk of severe disease or death, while vaccination is associated with a lower risk. Presence of comorbidities was not associated with severe disease or death among persons with breakthrough infection.

Background: Qatar experienced a large severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemic that disproportionately affected the craft and manual workers (CMWs) who constitute 60% of the population. This study aimed to investigate level of immunity in communities within this population as well as infection exposure required to achieve herd immunity. Methods: Anti-SARS-CoV-2 seropositivity was assessed in ten CMW communities between June 21 and September 9, 2020. PCR positivity, infection positivity (antibody and/or PCR positive), and infection severity rate were also estimated. Associations with anti-SARS-CoV-2 positivity were investigated using regression analyses. Results: Study included 4,970 CMWs who were mostly men (95.0%) and <40 years of age (71.5%). Seropositivity ranged from 54.9% (95% CI: 50.2-59.4%) to 83.8% (95% CI: 79.1-87.7%) in the different CMW communities. Pooled mean seropositivity across all communities was 66.1% (95% CI: 61.5-70.6%). PCR positivity ranged from 0.0% to 10.5% (95% CI: 7.4-14.8%) in the different CMW communities. Pooled mean PCR positivity was 3.9% (95% CI: 1.6-6.9%). Median cycle threshold (Ct) value was 34.0 (range: 15.8-37.4). The majority (79.5%) of PCR-positive individuals had Ct value >30 indicative of earlier rather than recent infection. Infection positivity (antibody and/or PCR positive) ranged from 62.5% (95% CI: 58.3-66.7%) to 83.8% (95% CI: 79.1-87.7%) in the different CMW communities. Pooled mean infection positivity was 69.5% (95% CI: 62.8-75.9%). Only five infections were ever severe and one was ever critical, an infection severity rate of 0.2% (95% CI: 0.1-0.4%). Conclusions: Based on an extended range of epidemiological measures, active infection is rare in these communities with limited if any sustainable infection transmission for clusters to occur. At least some CMW communities in Qatar have reached or nearly reached herd immunity for SARS-CoV-2 infection at a proportion of ever infection of 65-70%.

Background and objective The risk factors for breakthrough infections among healthcare workers (HCW) after completion of a full course of vaccination are poorly understood. Our objective was to determine the risk factors for breakthrough SARS-CoV-2 infection among HCWs at a national healthcare system in Qatar. Methods We identified all HCWs at Hamad Medical Corporation in Qatar between December 20, 2020 and May 18, 2021 with confirmed SARS-CoV-2 RT-PCR infection >14 days after the second vaccine dose. For each case thus identified, we identified one control with a negative test after December 20, 2020, matched on age, sex, nationality, job family and date of SARS-CoV-2 testing. We excluded those with a prior positive test and temporary workers. We used Cox regression analysis to determine factors associated with breakthrough infection. Results Among 22,247 fully vaccinated HCW, we identified 164 HCW who had breakthrough infection and matched them to 164 controls to determine the factors associated with SARS-CoV-2 breakthrough infection. In the breakthrough infection group the nursing and midwifery job family constituted the largest group, spouse was identified as the most common positive contact followed by a patient. Exposure to a confirmed case, presence of symptoms and all other job families except Allied Health Professionals when compared with nursing and Midwifery staff independently predicted infection. Conclusion Presence of symptoms and contact with a confirmed case are major risk factors for breakthrough SARS-CoV-2 infection after vaccination, and these groups should be prioritized for screening even after full vaccination.

Summary Pediatric recipients of living‐donor liver transplants (LDLT) can often discontinue immunosuppression (IS). We examined factors affecting development of operational tolerance (OT), defined as off IS for >1 year, in this population. A historic cohort analysis was conducted in 134 pediatric primary semi‐allogeneic LDLT. Multivariate logistic regression analysis was used. The frequency of peripheral regulatory T cells (Tregs) was determined at >10 years post‐Tx by FACS analysis. IS was successfully discontinued in 84 tolerant patients (Gr‐tol), but not in 50 intolerant patients (Gr‐intol). The Gr‐intol consisted of 24 patients with rejection (Gr‐rej) and 26 with fibrosis of grafts (Gr‐fib). The absence of early rejection [odds ratio (OR) 2.79, 95% CI 1.11–7.02, P = 0.03], was a positive independent predictor, whereas HLA‐A mismatch (0.18, 0.03–0.91, P = 0.04) was a negative predictor. HLA‐DR mismatches did not affect OT. The Treg frequency was significantly decreased in Gr‐intol (4.9%) compared with Gr‐tol (7.6%) (P = 0.003). There were increased levels of tacrolimus in the first week in Gr‐Tol (P = 0.02). Although HLA‐B mismatch (8.73, 1.09–70.0, P = 0.04) was a positive independent predictor of OT, its clinical significance remains doubtful. In this large cohort of pediatric LDLT recipients, absence of early rejection, HLA‐A match and the later predominance of Tregs are factors associated with OT.

Infection after pediatric living donor liver transplantation (LDLT) is a major cause of morbidity and mortality. Here, we sought to determine the incidence, timing, location, and risk factors for bacterial and fungal infections. We retrospectively investigated infection for 3 postoperative months in 345 consecutive pediatric patients (56.2% were females) who underwent primary LDLT at Kyoto University Hospital, Japan. A total of 179 patients (51.9%) developed at least 1 bacterial and/or fungal infection episode, with an infection rate of 2.5 per patient. The predominant infection site was the surgical site (52%). Most of the bacterial and fungal infection occurred within the first month. Enterococcus species followed by multidrug-resistant Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus were the predominant bacterial pathogens. All fungal isolates were Candida species. Prolonged preoperative hospital stay more than 7 days (P ¼ 0.025) and bile leak (P ¼ 0.047) were independent predictors of bacterial infection. Preoperative ascites (P ¼ 0.009) and prolonged insertion of intravascular catheters (P ¼ 0.001) independently predicted fungal infections. Bacterial and fungal infections were responsible for 42.9% of the causes of death in our study. To avoid bacterial and fungal infections after LDLT, broader-spectrum prophylaxis to cover the range of organisms seen in these infections should be considered as a more favorable treatment regimen to prevent prophylaxis failure, especially for patients with a preoperative hospital stay more than 7 days or operative complications in the form of a bile leak. Early drain removal and prophylactic antifungal drugs should be considered for patients with preoperative ascites. Cooperation between attending physicians and infectious disease physicians can improve the outcome of patients after LDLT. Liver Transpl 17:976-984, 2011. V C 2011 AASLD.Received September 28, 2010; accepted January 15, 2011.Liver transplantation (LT) is the treatment of choice for end-stage liver disease.1 Living donor liver transplantation (LDLT) is one way to perform LT and the most effective alternative for patients in areas where there is a shortage of available deceased donors for LT, e.g., Japan.2 Infection represents a major cause of

This is the first report providing detailed evidence that donor-specific naïve-Tregs were generated and their suppressive properties were upregulated in the peripheral blood of tolerant patients, whereas their frequency was downregulated in intolerant patients. Therefore, we speculate that not only conventional-Tregs play a role in Tx tolerance but also the role of naïve-Tregs is critical.

A unique Vδ1-bearing T-cell clone accumulates within accepted human liver grafts. It might be useful as a biomarker of tolerance and the identification of its ligand might aid in the development of a novel strategy for tolerance induction.