Ischemic stroke after COVID-19 bivalent vaccine administration in patients aged 65 years and older: analysis of nation-wide patient electronic health records in the United States
Authors: Gorenflo Maria P. , Davis Pamela B. , Kaelber David C. , Xu Rong 
Published: February 2023

AbstractImportanceThe Centers for Disease Control and Prevention (CDC) announced in January 2023 that they were investigating a potential connection between administration of the Pfizer novel coronavirus disease-2019 (COVID-19) bivalent vaccine booster and ischemic stroke (IS).ObjectiveTo explore the relationship between Pfizer bivalent booster administration and IS in older patients in the United States and compare it to other COVID-19 vaccines.DesignA retrospective cohort study was conducted to compare hazard of IS among patients aged 65 years or over who received the Pfizer bivalent, Moderna bivalent, or Pfizer/Moderna monovalent COVID-19 booster vaccine 1-21 and 22-42 days after vaccination.SettingPatient data were collected from TriNetX, a cloud-based analytics platform that includes electronic health record data from over 90 million unique patients in the United States.ParticipantsPatients in the United States aged 65 years or over at the time of administration of a Pfizer bivalent (n = 43,216), Moderna bivalent (n = 4,267), or Pfizer/Moderna monovalent (n = 100,583) booster were included for analysis. Cohorts were propensity-score matched by demographic factors and risk factors for IS and severe COVID-19.ExposuresPfizer bivalent, Moderna bivalent, or Pfizer/Moderna monovalent COVID-19 booster administration.Main outcomesThe hazard ratio (HR) and 95% confidence interval (CI) for IS in the cohorts at 1-21 and 22-42 days after administration.ResultsAfter matching, the Pfizer bivalent cohort included 4,267 patients, with an average age of 73.7 years (44.43% male, 76.59% white). The Moderna bivalent cohort included 4,267 patients, with an average age of 74.0 years (44.08% male, 77.39% white). There was no significant difference in the hazard of IS encounters between the Pfizer bivalent versus Moderna bivalent cohorts at 1-21- or 22-42-days post-administration: HR = 0.59 (0.31, 1.11), 0.73 (0.33, 1.60). The hazard for IS was lower in the Pfizer bivalent cohort than in the Pfizer/Moderna monovalent cohort at both timepoints: HR = 0.24 (0.19, 0.29), 0.25 (0.20, 0.31).Conclusions and relevanceOlder adults administered the Pfizer bivalent booster had similar hazard for IS encounters compared to those administered the Moderna bivalent booster vaccine, but lower hazard than those administered the Pfizer/Moderna monovalent boosters.Key PointsQuestionWhat is the comparative hazard of ischemic stroke in American patients ages 65 years and over after administration of the Pfizer bivalent, Moderna bivalent, or Pfizer/Moderna monovalent COVID-19 booster vaccine?FindingsA retrospective cohort study was conducted. There was no significant difference in the hazard of ischemic stroke encounters between the Pfizer bivalent versus Moderna bivalent cohorts, but lower hazard for the Pfizer bivalent than the monovalent boosters at 1-21 or 22-42 days post-administration.MeaningThere is no evidence from these results that the Pfizer bivalent booster is associated with increased hazard for ischemic stroke.