The Clinical Epidemiology Center (CEC) is a center of data analytics focused on solving major health problems affecting veterans and the world. We translate complex health data into actionable insights that drive medical innovation and improve patient outcomes within the VA St. Louis Health Care System and beyond.
Our Mission
Our mission is to conduct pioneering epidemiological research that enhances the health and well-being of our nation’s veterans. By leveraging large-scale data and advanced analytical methods, we aim to uncover the root causes of disease, identify effective treatments, and inform public health policy.
We aim to advance the health and healthcare of U.S. Veterans by generating high-quality evidence through innovative clinical research, rigorous epidemiologic methods, and collaborative scientific inquiry.
VISION
To be a leading center of excellence in clinical epidemiology, shaping the future of health care through research that improves outcomes for Veterans and informs policy and practice nationwide.
About the Center
The Clinical Epidemiology Center is dedicated to advancing research that improves health outcomes for U.S. Veterans. The Center is directed by Dr. Ziyad Al-Aly, an internationally recognized leader in clinical epidemiology and pharmacoepidemiology (TIME100 Health honoree; Clarivate Highly Cited Researcher). Our team conducts and supports high-quality patient-oriented investigations that address critical questions in clinical care, population health, and healthcare delivery.
Our researchers leverage large-scale electronic health record data and advanced epidemiologic and causal inference methods to generate evidence with real-world clinical impact. Through collaboration with investigators, healthcare systems, and partners, the Center aims to accelerate scientific discovery and translation into improved care for Veterans.
Research and Impact
The Center’s research portfolio addresses major health challenges affecting Veterans, with particular emphasis on:
- Long COVID and other post infection illness
- Medication effectiveness and safety
- Diabetes and metabolic disease
- Chronic Kidney Disease
- GLP-1 receptor agonists and emerging therapeutics
Our investigators have a strong publication record in leading scientific journals, including Nature, Science, Nature Medicine, NEJM, JAMA, BMJ, and other high-impact publications. Their research is frequently featured in major national and international media outlets including New York Times, Wall Street Journal, Washington Post, NPR, BBC, CNN, and several others.
INSTITUTIONAL DEVELOPMENT
Supported by new funding initiatives, the Center is expanding its research programs and collaborative partnerships. We work closely with clinicians, investigators, and trainees to advance innovative research and translate findings into improved healthcare outcomes for Veterans.
Core Focus Areas
Leadership
Dr. Ziyad Al-Aly
Director, Clinical Epidemiology Centerziyad.al-aly@va.gov(314) 289-6333Dr. Al-Aly is a renowned clinical epidemiologist whose work has significantly advanced our understanding of the long-term health consequences of various diseases. His leadership guides the center’s strategic direction and research initiatives.
The Center is directed by Ziyad Al-Aly, MD, whose research focuses on the long-term effects of COVID-19, medication effectiveness, kidney disease, and diabetes. Under this leadership, the Center is expanding its research portfolio, strengthening interdisciplinary collaboration, and advancing methodological innovation in clinical epidemiology.
Research Team
Yan Xie
Director of Pharmacoepidemiologyyan.xie3@va.govYan Xie, PhD, is a clinical epidemiologist specializing in leveraging big data such as electronic health records to address some of the world’s most pressing and impactful research questions. He currently serves as Director of Pharmacoepidemiology at the Clinical Epidemiology Center, VA St. Louis Health Care System, and as an Assistant Professor at Washington University School of Medicine in St. Louis.
Dr. Xie’s research addresses critical public health issues, including acute and chronic disease epidemiology, comparative effectiveness, and environmental epidemiology. With over 60 peer-reviewed publications in leading journals such as NEJM, JAMA, The BMJ, and Nature Medicine, his research has garnered extensive international recognition with over 19000 citations, and an h-index of 52. Dr. Xie’s research has been featured in more than 6000 news stories internationally. He was featured on Clarivate (Web of Science) global list of the top 1% of Highly Cited Researchers in 2024 and 2025 and has been ranked among the top 2% of global scientists by Stanford/Elsevier.
Taeyoung Choi
Biostatistician/Data ScientistTaeyoung.choi@va.govTaeyoung Choi is a Biostatistician and Data Scientist with over five years of experience at the VA St. Louis Health Care System.
He specializes in clinical epidemiology and pharmacoepidemiology. His research focus often involves high-impact medical data, and he has co-authored numerous studies in prestigious journals, including: The New England Journal of Medicine (NEJM), Nature Medicine, The BMJ, JAMA, and The Lancet.
Affiliations:
-Clinical Epidemiology Center, Research and Development Service, VA Saint Louis Health Care System, Saint Louis, Missouri, USA
-Veterans Research and Education Foundation of Saint Louis, Saint Louis, Missouri, USA
-Division of Pharmacoepidemiology, Clinical Epidemiology Center, Research and Development Service, VA Saint Louis Health Care System, Saint Louis, Missouri, USA
Miao Cai
Biostatisticianmiao.cai@va.govDr. Cai is currently a biostatistician at the VA St. Louis Health Care System Clinical Epidemiology Center, where he studies the long-term consequences of COVID-19 and the effectiveness of vaccines and drug therapies, using large observational cohort studies involving millions of individuals and advanced causal inference methods. He has published more than 90 peer-reviewed articles, including multiple first-author papers in The New England Journal of Medicine, The BMJ, Nature Medicine, and Lancet Infectious Diseases. His research has been featured in Nature and Science, and covered by Reuters, Bloomberg, NPR, CNN, CBS, and TIME.
Kieran Maroney, PhD MPH
Postdoctoral Fellowkieran.maroney@va.govDr. Maroney joined the CEC in January 2026. As an epidemiologist at the CEC, he draws on his experience in real‑world evidence, observational research, and post‑market safety surveillance, shaped by roles in both academic research and FDA regulatory review.
The Center’s investigators bring expertise spanning clinical epidemiology, health outcomes research, causal inference, and data science, enabling a comprehensive and collaborative approach to complex health challenges.
The CEC hosts an ongoing lecture series featuring national and international experts in clinical research, epidemiology, and healthcare innovation. These events promote scientific exchange, collaboration, and professional development across disciplines.
Information about our upcoming lecture series and other important events will be available here soon. Please check back for updates.
Present at Our Lecture Series
The CEC maintains a selective, invitation-driven lecture series designed to highlight nationally recognized leaders whose scholarship advances clinical epidemiology, population health, and health policy.
While most speakers are invited, we welcome inquiries from established investigators and thought leaders whose work aligns with our mission and demonstrates substantial impact.
To be considered, please submit:
- Brief bio
- Proposed lecture title
Submissions may be sent to: STLCEC@va.gov
Upcoming Lectures
The CEC is undergoing significant expansion through new funding initiatives and growing research programs. We are actively building collaborations and creating opportunities for investigators, trainees, and staff to contribute to impactful research that improves Veteran health.
The Clinical Epidemiology Center seeks talented, thoughtful, and collaborative individuals who are committed to advancing rigorous , high-impact research that improves the health and healthcare of U.S. Veterans.
We value strong communication skills, intellectual curiosity, initiative, and the ability to work effectively within interdisciplinary research teams. Our work leverages large-scale electronic health records and advanced epidemiologic and causal inference methods to generate evidence with real-world impact.
Positions at the Center require the highest standards of professionalism and research integrity. Employees must meet institutional and VA requirements, including required training and background clearance.
We welcome inquiries regarding research collaborations and career opportunities. We also invite experts interested in presenting as part of our Lecture Series to reach out.
Published Work
- High-dimensional characterization of post-acute sequelae of COVID-19
- Postacute Sequelae of SARS-CoV-2 Infection in the Pre-Delta, Delta, and Omicron Eras
- Long-term outcomes following hospital admission for COVID-19 versus seasonal influenza: a cohort study
- Association of Treatment With Nirmatrelvir and the Risk of Post–COVID-19 Condition
- Molnupiravir and risk of post-acute sequelae of covid-19: cohort study
- Cases, Hospitalization, and Mortality in COVID-19 and Influenza Among Veterans in 2022-2025 Influenza Seasons
- Risk of Death in Patients Hospitalized for COVID-19 vs Seasonal Influenza in Fall-Winter 2022-2023
- Mortality in Patients Hospitalized for COVID-19 vs Influenza in Fall-Winter 2023-2024
- Rates of Hospitalization and Death due to COVID-19 in US Veterans With SARS-CoV-2 Infection in the XBB-, JN.1-, and KP-Predominant Eras
- Adverse cardiovascular and kidney outcomes in people with SARS-CoV-2 treated with SGLT2 inhibitors
- Mapping the effectiveness and risks of GLP-1 receptor agonists
- Glucagon-like peptide 1 receptor agonist discontinuation and risks of major adverse cardiovascular events in adults with type 2 diabetes: target trial emulation
- Glucagon-like peptide-1 receptor agonists and risk of substance use disorders among US veterans with type 2 diabetes: cohort study