The association between previous SARS-CoV-2 infection and incidence of stroke.

Objectives: To define the association between prior SARS-CoV-2 infection and incidence of stroke.

Methods: We conducted a case-control study combining the Qatar stroke database and the Qatar National COVID-19 databases. Cases with stroke diagnosis were matched 1:1 on demographics, comorbidities, and vaccination status to controls who tested negative for SARS-CoV-2 during the same week.

Effectiveness of ChAdOx1 nCoV-19 (Vaxzevria) primary series vaccine against SARS-CoV-2 beta and delta variants: a nationwide study.

Background: This study assessed the real-world effectiveness of the ChAdOx1 nCoV-19 vaccine in adults against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, symptomatic infection, and severe coronavirus disease 2019 (COVID-19) during periods of Beta and Delta variant dominance in Qatar.

Methods: A national, matched, test-negative case-control study was conducted using 186,130 PCR-positive tests (cases) and 667,289 PCR-negative tests (controls) collected between January 1 and December 18, 2021. Subgroup analyses were performed to evaluate vaccine effectiveness across key strata.

Comparative effectiveness of one versus two doses of COVID-19 vaccines in Qatar: Evidence of converging protection over time.

Background: Supply constraints during the coronavirus disease 2019 (COVID-19) pandemic led to vaccination strategies that prioritized first-dose coverage. To evaluate the merit of this approach, this study compared the development of protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and severe COVID-19 following a single dose versus two doses across three widely used vaccine platforms.

Methods: National, matched, test-negative case-control analyses were conducted in Qatar between December 1, 2020, and December 18, 2021, to evaluate vaccine effectiveness.

A prospective cluster randomized trial of an interventions bundle to reduce inappropriate antibiotic use for upper respiratory tract infections in the outpatient setting.

Background: Antibiotic overuse and increasing antimicrobial resistance are global public health threats. We determined the impact of a multicomponent intervention in reducing inappropriate antibiotic use for upper respiratory tract infections (URTIs) in the outpatient setting.

Methods: DESIGN: Prospective, cluster-randomized trial.

Immune histories and natural infection protection during the omicron era.

Background: Past immunological events can either enhance or compromise an individual's future immune protection. This study investigated how different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) natural infection histories before an omicron infection, with or without vaccination, influence protection against subsequent omicron reinfection.

Methods: Three national, matched, retrospective cohort studies were conducted in Qatar from February 28, 2020, to August 12, 2024 to compare incidence of omicron reinfection between individuals with two omicron infections (omicron double-infection cohort) and those with one (omicron single-infection cohort); the omicron double-infection cohort with individuals who had a pre-omicron infection followed by an omicron reinfection (pre-omicron-omicron double-infection cohort); and the pre-omicron-omicron double-infection cohort with the omicron single-infection cohort.

Hepatocellular Carcinoma Among Patients With Metabolic Dysfunction Associated Steatotic Liver Disease.

Background And Aims: Metabolic dysfunction-associated steatotic liver disease (MASLD) has emerged as the leading cause of cirrhosis and hepatocellular carcinoma (HCC). We decided to determine factors associated with cirrhosis and HCC among patients with MASLD in order to help develop a better HCC surveillance strategy.

Methods: We retrieved Veterans Affairs data and identified patients with MASLD.

Assessing healthy vaccinee effect in COVID-19 vaccine effectiveness studies: a national cohort study in Qatar.

Background: This study investigated the presence of the healthy vaccinee effect-the imbalance in health status between vaccinated and unvaccinated individuals-in two rigorously conducted COVID-19 vaccine effectiveness studies involving primary series and booster vaccinations. It also examined the temporal patterns and variability of this effect across different subpopulations by analyzing the association between COVID-19 vaccination and non-COVID-19 mortality in Qatar.

Methods: Two matched, retrospective cohort studies assessed the incidence of non-COVID-19 death in national cohorts of individuals with a primary series vaccination versus no vaccination (two-dose analysis), and individuals with three-dose (booster) vaccination versus primary series vaccination (three-dose analysis), from January 5, 2021, to April 9, 2024.

Mitochondrial DNA Haplogroups, Biomarkers of Inflammation and Immune Activation, and Risk of Diabetes in Veterans with and without HIV.

Background: Type 2 diabetes mellitus (DM) is common among people with HIV (PWH). We previously reported that DM risk was greater in women of African ancestry with HIV who had mitochondrial DNA (mtDNA) haplogroup L3. We examined haplogroup associations with DM and selected soluble and cellular immune biomarkers among PWH and those without HIV in the Veterans Aging Cohort Study (VACS) Biomarker Cohort.

Evaluating Hospital Admission Data as Indicators of COVID-19 Severity: A National Assessment in Qatar.

Background: Accurately assessing SARS-CoV-2 infection severity is essential for understanding the health impact of the infection and evaluating the effectiveness of interventions. This study investigated whether SARS-CoV-2-associated hospitalizations can reliably measure true COVID-19 severity.

Methods: The diagnostic accuracy of SARS-CoV-2-associated acute care and ICU hospitalizations as indicators of infection severity was assessed in Qatar from 6 September 2021 to 13 May 2024.

Differential protection against SARS-CoV-2 reinfection pre- and post-Omicron.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly evolved over short timescales, leading to the emergence of more transmissible variants such as Alpha and Delta. The arrival of the Omicron variant marked a major shift, introducing numerous extra mutations in the spike gene compared with earlier variants. These evolutionary changes have raised concerns regarding their potential impact on immune evasion, disease severity and the effectiveness of vaccines and treatments.

Gastrointestinal illness among attendees of the FIFA Football World Cup 2022 in Qatar.

Objectives: Mass gathering events may facilitate the transmission of foodborne diseases. We determined the presentations and causative organisms of gastrointestinal illness among the attendees of the Fédération Internationale de Football Association Football World Cup 2022 (FIFA 2022).

Methods: The study was conducted at Hamad Medical Corporation in Qatar, which served as the national reference laboratory for all microbiology testing.

BNT162b2 Versus mRNA-1273 Vaccines: Comparative Analysis of Long-Term Protection Against SARS-CoV-2 Infection and Severe COVID-19 in Qatar.

Background: This study provides a head-to-head comparison of the protection provided by the BNT162b2 and mRNA-1273 vaccines against SARS-CoV-2 infection and against severe COVID-19, covering primary series and third dose/booster vaccinations over up to 3 years of follow-up, both before and after the emergence of the omicron variant.

Methods: Two national, matched, retrospective cohort studies were conducted on Qatar's vaccinated population from December 16, 2020, to February 18, 2024. Subgroup analyses by pre-vaccination SARS-CoV-2 infection history, as well as sensitivity analyses, were also conducted.

The impact of COVID-19 on the clinical course and outcome of patients with cirrhosis: An observational study.

Background And Aims: Severe outcomes of COVID-19 are associated with advancing age and comorbidities. The specific aim of our study was to determine the impact of COVID-19 on the clinical course and outcome of patients with cirrhosis.

Methods: We retrieved data from VA national repository and identified patients tested for SARS-CoV-2 RNA who had cirrhosis.

Nirmatrelvir/ritonavir or Molnupiravir for treatment of non-hospitalized patients with COVID-19 at risk of disease progression.

Background: In randomized controlled trials, Nirmatrelvir/ritonavir (NMV/r) and Molnupiravir (MPV) reduced the risk of severe/fatal COVID-19 disease. Real-world data are limited, particularly studies directly comparing the two agents.

Methods: Using the VA National COVID-19 database, we identified previously uninfected, non-hospitalized individuals with COVID-19 with ≥1 risk factor for disease progression who were prescribed either NMV/r or MPV within 3 days of a positive test.

Spectrum of infection and outcomes in individuals with Candida auris infection in Qatar.

Background: We investigated the spectrum of infection and risk factors for invasive fungal disease due to Candida auris (CA) in Qatar.

Methods: We performed structured chart reviews on individuals with any positive CA culture between May 2019 and December 2022 at three tertiary care hospitals in Qatar. Invasive CA disease (ICAD) was defined as a positive sterile site culture, or any positive culture for CA with appropriate antifungal prescription.

Association between COVID-19 vaccination and stroke: a nationwide case-control study in Qatar.

Objective: This study investigated the association between Coronavirus Disease 2019 mRNA vaccination and stroke in Qatar.

Methods: Between December 1, 2020, and April 11, 2023, a matched case-control study was conducted to investigate the association between 3036 acute stroke cases and 3036 controls drawn from the entire population of Qatar.

Results: The adjusted odds ratio (aOR) for vaccination among cases compared to controls was 0.

Effectiveness of two and three doses of COVID-19 mRNA vaccines against infection, symptoms, and severity in the pre-omicron era: A time-dependent gradient.

Background: Vaccines were developed and deployed to combat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. This study aimed to characterize patterns in the protection provided by the BNT162b2 and mRNA-1273 mRNA vaccines against a spectrum of SARS-CoV-2 infection symptoms and severities.

Methods: A national, matched, test-negative, case-control study was conducted in Qatar between January 1 and December 18, 2021, utilizing a sample of 238,896 PCR-positive tests and 6,533,739 PCR-negative tests.

Protection of natural infection against reinfection with SARS-CoV-2 JN.1 variant.

Overall effectiveness of infection in preventing reinfection with SARS-CoV-2 JN.1 variant was estimated at 1.8% (95% CI: −9.

Addressing bias in the definition of SARS-CoV-2 reinfection: implications for underestimation.

Introduction: Reinfections are increasingly becoming a feature in the epidemiology of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, accurately defining reinfection poses methodological challenges. Conventionally, reinfection is defined as a positive test occurring at least 90 days after a previous infection diagnosis.

SARS-CoV-2 infection and effects of age, sex, comorbidity, and vaccination among older individuals: A national cohort study.

Background: We investigated the contribution of age, coexisting medical conditions, sex, and vaccination to incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and of severe, critical, or fatal COVID-19 in older adults since pandemic onset.

Methods: A national retrospective cohort study was conducted in the population of Qatar aged ≥50 years between February 5, 2020 and June 15, 2023. Adjusted hazard ratios (AHRs) for infection and for severe coronavirus disease 2019 (COVID-19) outcomes were estimated through Cox regression models.

Turning point in COVID-19 severity and fatality during the pandemic: a national cohort study in Qatar.

Objective: To assess the evolution of COVID-19 severity and fatality in a unique setting that consistently applied, throughout the pandemic, rigorous and standardised criteria for defining severe COVID-19 outcomes.

Methods And Analysis: We conducted a national cohort study on 312 109 Qatari citizens to investigate incidence of severe, critical or fatal COVID-19 classified according to the WHO criteria between 28 February 2020 and 21 April 2023. Incidence rates for severe, critical or fatal COVID-19 were estimated during the pre-omicron phase, first omicron wave, combined phases and throughout the pandemic.

History of primary-series and booster vaccination and protection against Omicron reinfection.

Laboratory evidence suggests a possibility of immune imprinting for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We investigated the differences in the incidence of SARS-CoV-2 reinfection in a cohort of persons who had a primary Omicron infection, but different vaccination histories using matched, national, retrospective, cohort studies. Adjusted hazard ratio for reinfection incidence, factoring adjustment for differences in testing rate, was 0.