Lei Yan, PhD
Associate Research Scientist in BiostatisticsCards
About
Research
Overview
Public Health Interests
Survival Analysis; Epidemiology Methods; COVID-19; Infectious Diseases; HIV/AIDS
Publications
Featured Publications
Respiratory syncytial virus vaccine effectiveness among US veterans, September, 2023 to March, 2024: a target trial emulation study
Bajema K, Yan L, Li Y, Argraves S, Rajeevan N, Fox A, Vergun R, Berry K, Bui D, Huang Y, Lin H, Hynes D, Lucero-Obusan C, Schirmer P, Cunningham F, Huang G, Aslan M, Ioannou G. Respiratory syncytial virus vaccine effectiveness among US veterans, September, 2023 to March, 2024: a target trial emulation study. The Lancet Infectious Diseases 2025 PMID: 39848264, DOI: 10.1016/s1473-3099(24)00796-5.Peer-Reviewed Original ResearchRespiratory syncytial virusRespiratory syncytial virus vaccinePositive RSV testVaccine effectivenessRSV testCare encountersSecondary outcomesEmergency departmentRSV-associated hospitalisationsMedian follow-upUS Food and Drug AdministrationHealth-care useVeterans Health AdministrationRespiratory illness seasonMatched index dateElectronic health recordsLower respiratory tract diseaseRSV-related illnessFood and Drug AdministrationDepartment of Veterans Affairs Cooperative Studies ProgramVeterans Affairs Cooperative Studies ProgramCooperative Studies ProgramRSV infectionMedian ageUS DepartmentSeverity and Long-Term Mortality of COVID-19, Influenza, and Respiratory Syncytial Virus
Bajema K, Bui D, Yan L, Li Y, Rajeevan N, Vergun R, Berry K, Huang Y, Lin H, Aslan M, Ioannou G. Severity and Long-Term Mortality of COVID-19, Influenza, and Respiratory Syncytial Virus. JAMA Internal Medicine 2025, 185: 324-334. PMID: 39869355, PMCID: PMC11773409, DOI: 10.1001/jamainternmed.2024.7452.Peer-Reviewed Original ResearchConceptsRespiratory syncytial virusLong-term mortalitySARS-CoV-2Syncytial virusCohort studyAssociated with higher long-term mortalityRisk differenceIntensive care unit admissionSeasonal influenza vaccineRetrospective cohort studyDisease severity of COVID-19Long-term deathAssociated with more severe disease outcomesRisk of deathCompare disease severitySevere disease outcomesRisk of hospitalizationSeverity of COVID-19Same-day testingInfluenza vaccineInverse probability weightingUnit admissionCumulative incidenceMortality of COVID-19Primary outcomeEffectiveness of dolutegravir-based regimens compared to raltegravir-, elvitegravir-, bictegravir, and darunavir-based regimens among older adults with HIV in the Veterans Aging Cohort Study (VACS)
Yan L, Henegar C, Marconi V, Gordon K, Hicks C, Vannappagari V, Justice A, Aslan M. Effectiveness of dolutegravir-based regimens compared to raltegravir-, elvitegravir-, bictegravir, and darunavir-based regimens among older adults with HIV in the Veterans Aging Cohort Study (VACS). AIDS Research And Therapy 2024, 21: 96. PMID: 39709467, PMCID: PMC11662819, DOI: 10.1186/s12981-024-00681-w.Peer-Reviewed Original ResearchMeSH KeywordsAgedAmidesAnti-HIV AgentsCohort StudiesDarunavirDrug Therapy, CombinationFemaleHeterocyclic Compounds, 3-RingHeterocyclic Compounds, 4 or More RingsHIV InfectionsHIV Integrase InhibitorsHumansMaleMiddle AgedOxazinesPiperazinesPyridazinesPyridonesQuinolonesRaltegravir PotassiumTreatment OutcomeVeteransViral LoadConceptsVeterans Aging Cohort StudyRAL-based regimenAntiretroviral therapyAging Cohort StudyCohort studyOdds of virologic suppressionIntegrase strand transfer inhibitorsDarunavir-based regimensDolutegravir-based regimensDTG-based regimensAntiretroviral therapy experienceHuman immunodeficiency virusDTG-based regimenInverse probability of treatment weightingStrand transfer inhibitorsBackgroundReal-world dataProbability of treatment weightingMethodsThis cohort studyVirologic suppressionVirological failureVirological effectImmunodeficiency virusDarunavir/ritonavirClinical outcomesRegimen initiationIdentifying Veterans Who Benefit From Nirmatrelvir-Ritonavir: A Target Trial Emulation
Yan L, Bui D, Li Y, Rajeevan N, Rowneki M, Berry K, Argraves S, Huang Y, Hynes D, Cunningham F, Huang G, Aslan M, Ioannou G, Bajema K. Identifying Veterans Who Benefit From Nirmatrelvir-Ritonavir: A Target Trial Emulation. Clinical Infectious Diseases 2024, 79: 643-651. PMID: 38864601, DOI: 10.1093/cid/ciae202.Peer-Reviewed Original ResearchRisk quartileVeterans Health AdministrationLowest risk quartileHighest risk quartileTarget trial emulationRisk prediction modelUntreated veteransRisk of deathOlder veteransYounger veteransHealth AdministrationTrial emulationMeasure incidenceNirmatrelvir-ritonavirVeteransHospitalUntreated participantsCOVID-19QuartileRiskSevere coronavirus disease 2019ParticipantsPersonsCoronavirus disease 2019Severe COVID-19
2025
Deconstructing fertilizer price spikes: Evidence from Chinese urea fertilizer market
Hu Z, Yan L, Yuan J, Etienne X (2025). Deconstructing fertilizer price spikes: Evidence from Chinese urea fertilizer market. Food Policy, 133.Peer-Reviewed Original ResearchEffectiveness of the 2023-to-2024 XBB.1.5 COVID-19 Vaccines Over Long-Term Follow-up : A Target Trial Emulation.
Ioannou G, Berry K, Rajeevan N, Li Y, Yan L, Huang Y, Lin H, Bui D, Hynes D, Rowneki M, Bohnert A, Boyko E, Iwashyna T, Maciejewski M, Smith V, Berkowitz T, O'Hare A, Viglianti E, Aslan M, Bajema K. Effectiveness of the 2023-to-2024 XBB.1.5 COVID-19 Vaccines Over Long-Term Follow-up : A Target Trial Emulation. Annals Of Internal Medicine 2025, 178: 348-359. PMID: 39903865, DOI: 10.7326/annals-24-01015.Peer-Reviewed Original ResearchConceptsU.S. Department of Veterans AffairsDepartment of Veterans AffairsMatched index dateVaccine effectivenessTarget trial emulationSARS-CoV-2-associated deathsRandomized controlled trialsCOVID-19 vaccineSARS-CoV-2-related outcomesSARS-CoV-2 testingVeterans AffairsResidual confoundingAbsence of randomized controlled trialsLong-term follow-upDocumented SARS-CoV-2 infectionTrial emulationUnvaccinated personsIndex datePositive resultsControlled trialsCOVID-19SARS-CoV-2 infectionIncomplete captureHospitalDocumented infection
2024
Development of a prediction model for 30-day COVID-19 hospitalization and death in a national cohort of Veterans Health Administration patients–March 2022—April 2023
Bui D, Bajema K, Huang Y, Yan L, Li Y, Rajeevan N, Berry K, Rowneki M, Argraves S, Hynes D, Huang G, Aslan M, Ioannou G. Development of a prediction model for 30-day COVID-19 hospitalization and death in a national cohort of Veterans Health Administration patients–March 2022—April 2023. PLOS ONE 2024, 19: e0307235. PMID: 39365775, PMCID: PMC11451987, DOI: 10.1371/journal.pone.0307235.Peer-Reviewed Original ResearchConceptsVeterans Health AdministrationCOVID-19 hospitalizationArea under the receiver operating characteristic curveComprehensive electronic health recordNational cohortElectronic health recordsAll-cause mortalityNational cohort of patientsFull modelHealth recordsHealth AdministrationReceipt of COVID-19 vaccineMortality riskEpidemiology of COVID-19COVID-19High-risk patientsBrier scoreCohort of patientsAnti-SARS-CoV-2 treatmentCOVID-19 vaccineReceiver operating characteristic curveCalibration interceptHospitalAntiviral treatmentAvailability of effective vaccinesRegional variation in financial hardship among US veterans during the COVID-19 pandemic
Hauschildt K, Bui D, Govier D, Eaton T, Viglianti E, Ettman C, McCready H, Smith V, O’Hare A, Osborne T, Boyko E, Ioannou G, Maciejewski M, Bohnert A, Hynes D, Iwashyna T, Chai W, Bowling B, Maciejewski M, Womer J, Iwashyna T, Anderson S, Bernstein T, Cabrales A, Hauschildt K, Admon A, Byrd K, Cano J, Curtis J, DelMonico E, Horowitz D, Kamphius L, Korpela P, Kumbier K, Langa K, Prescott H, Rouse M, Saini S, Seelye S, Sussman J, Wawrin N, Monahan M, Bohnert A, Viglianti E, Akgun K, Aslan M, Cheung K, Li Y, Mutalik P, Rajeevan N, Yan L, Anderson L, Berkowitz T, Bogdan J, Bosworth H, Boucher N, Cummin G, Dennis P, Floyd B, Hastings S, Kaufman B, Meyer C, Miles A, Naylor J, Shepherd-Banigan M, Smith V, Smith B, Woods C, Dobalian A, Goetz M, Ikuta K, Ong M, Shaukat A, Backus L, Ferguson J, Osborne T, Shahoumian T, Veigulis Z, Zulman D, Bajema K, Bui D, Chen J, Govier D, Helfand M, Hickok A, Hough C, McCready H, Moss A, Newell S, Niederhausen M, Nugent S, Saha S, Slatore C, Takata Y, Teo A, Tuepker A, Vranas K, Winchell K, Hynes D, Boyko E, Au D, Baraff A, Berry Wyatt K, Borgerding J, Burwick N, Crothers K, Davis M, Doll J, Dominitz J, Eastment M, Fan V, Fox A, Hawkins E, Hebert P, Hu E, Korpak A, Morelli D, Peterson A, Reddy A, Shah J, Showalter W, Smith N, Suri P, Thomas E, Turner A, Vig E, Wicks K, Wong E, Wysham K, Ioannou G, O'Hare A, Jones B, Jones M, Knight S. Regional variation in financial hardship among US veterans during the COVID-19 pandemic. Health Affairs Scholar 2024, 2: qxae075. PMID: 38938272, PMCID: PMC11210296, DOI: 10.1093/haschl/qxae075.Peer-Reviewed Original ResearchSelf-Reported Everyday Functioning After COVID-19 Infection
Iwashyna T, Smith V, Seelye S, Bohnert A, Boyko E, Hynes D, Ioannou G, Maciejewski M, O’Hare A, Viglianti E, Berkowitz T, Pura J, Womer J, Kamphuis L, Monahan M, Bowling C, Admon A, Akgun K, Anderson S, Aslan M, Au D, Backus L, Bajema K, Baraff A, Batten L, Berkowitz T, Bernstein T, Berry Wyatt K, Bogdan J, Bosworth H, Boucher N, Burwick N, Cabrales A, Cano J, Chai W, Chen J, Cheung K, Crothers K, Curtis J, Davis M, Del Monico E, Dobalian A, Doll J, Dominitz J, Eastment M, Fan V, Ferguson J, Floyd B, Fox A, Goetz M, Govier D, Green P, Hastings S, Hauschildt K, Hawkins E, Hebert P, Helfand M, Hickok A, Horowitz D, Hough C, Hu E, Ikuta K, Jones B, Jones M, Kamphuis L, Kaufman B, Knight S, Korpak A, Korpela P, Kumbier K, Langa K, Laundry R, Lavin S, Li Y, Linquist J, McCready H, Michel M, Miles A, Milne J, Monahan M, Morelli D, Mutalik P, Naylor J, Neiderhausen M, Newell S, Nugent S, Ong M, Osborne T, Peterson M, Peterson A, Prescott H, Rajeevan N, Reddy A, Rouse M, Rowneki M, Saha S, Saini S, Shah J, Shahoumian T, Shaukat A, Shepherd-Banigan M, Showalter W, Slatore C, Smith N, Smith B, Suri P, Sussman J, Takata Y, Teo A, Thomas E, Thomas L, Tuepker A, Veigulis Z, Vig E, Vranas K, Wang X, Wicks K, Winchell K, Wong E, Woods C, Wysham K, Yan L, Zulman D. Self-Reported Everyday Functioning After COVID-19 Infection. JAMA Network Open 2024, 7: e240869. PMID: 38427352, PMCID: PMC10907923, DOI: 10.1001/jamanetworkopen.2024.0869.Peer-Reviewed Original ResearchConceptsEveryday functioningActivities of daily livingSelf-reported everyday functioningCOVID-19 infectionImpact of COVID-19 infectionDaily livingVeterans AffairsCOVID-19 cohortDocumented COVID-19Instrumental activities of daily livingMatched pairs of participantsHealth-related quality of lifePairs of participantsCohort studyProportion of veteransControl cohortLife-space mobilityStudy of veteransCohort study of veteransUS Veterans AffairsHealth-related qualityDocumented COVID-19 infectionSelf-reportTarget trial emulationQuality of lifeChanges in Outpatient Health Care Use After COVID-19 Infection Among Veterans
Hebert P, Kumbier K, Smith V, Hynes D, Govier D, Wong E, Kaufman B, Shepherd-Banigan M, Rowneki M, Bohnert A, Ioannou G, Boyko E, Iwashyna T, O’Hare A, Bowling C, Viglianti E, Maciejewski M, Admon A, Akgun K, Anderson L, Anderson S, Aslan M, Au D, Backus L, Bajema K, Baraff A, Batten L, Berkowitz T, Bernstein T, Berry Wyatt K, Bogdan J, Borgerding J, Bosworth H, Boucher N, Burwick N, Byrd K, Cabrales A, Cano J, Chai W, Chen J, Cheung K, Crothers K, Cummin G, Curtis J, Davis M, Del Monico E, Dennis P, Dobalian A, Doll J, Dominitz J, Eastment M, Fan V, Ferguson J, Floyd B, Fox A, Goetz M, Green P, Hastings S, Hauschildt K, Hawkins E, Helfand M, Hickok A, Horowitz D, Hough C, Hu E, Ikuta K, Jones B, Jones M, Kamphius L, Knight S, Korpak A, Korpela P, Langa K, Laundry R, Lavin S, Li Y, Lindquist J, McCready H, Meyer C, Michel M, Miles A, Milne J, Monahan M, Morelli D, Mutalik P, Naylor J, Niederhausen M, Newell S, Nugent S, Ong M, Osborne T, Peterson M, Peterson A, Prescott H, Pura J, Rajeevan N, Reddy A, Rouse M, Saha S, Saini S, Seelye S, Shah J, Shahoumian T, Shaukat A, Showalter W, Slatore C, Smith B, Smith N, Streja E, Suri P, Sussman J, Takata Y, Teo A, Thomas E, Thomas L, Tuepker A, Turner A, Veigulis Z, Vig E, Vranas K, Wang X, Wicks K, Winchell K, Womer J, Woods C, Wysham K, Yan L, Zulman D. Changes in Outpatient Health Care Use After COVID-19 Infection Among Veterans. JAMA Network Open 2024, 7: e2355387. PMID: 38334995, PMCID: PMC10858406, DOI: 10.1001/jamanetworkopen.2023.55387.Peer-Reviewed Original ResearchConceptsOutpatient health care useHealth care useCare useOutpatient useOutpatient visitsPrimary care visitsCounts of outpatient visitsPrimary care patientsOutpatient care utilizationCategories of careVeterans Affairs Corporate Data WarehouseCorporate Data WarehouseIncreased outpatient visitsNegative binomial regression modelsBinomial regression modelsCare visitsCare utilizationPopulation surveillance studyRetrospective cohort studyCare patientsUninfected veteransCOVID-19 infectionMain OutcomesPeri-infection periodCohort study
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