COVID-19 Vaccine Safety Technical (VaST) 

Work Group 

VaST assessment

H. Keipp Talbot, MD MPH (VaST Chair)

Robert H. Hopkins, Jr., MD (NVAC Chair)

Advisory Committee on Immunization Practices

February 24, 2023
COVID-19 Vaccine Safety Technical (VaST) Work Group

Objectives

 Review, evaluate, and interpret post-authorization/approval COVID-19 

vaccination safety data

 Serve as the central hub for technical subject matter expertise from 

federal agencies conducting post-authorization/approval safety 

monitoring

 Advise on analyses, interpretation, and presentation of vaccine safety data

 Provide updates to the ACIP COVID-19 Vaccines Work Group and the 

entire ACIP on COVID-19 vaccine safety

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Activities

 From December 21, 2020 through February 24, 2023

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71 independent meetings to review vaccine safety data

17 joint meetings with ACIP COVID-19 Vaccines Work Group

22 ACIP meeting presentations or reports with VaST assessments

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COVID-19 Vaccine Safety Technical (VaST) Work Group
VaST assessment

 Statistical signal for ischemic stroke in the Vaccine Safety Datalink 

following bivalent COVID-19 booster vaccination 

 Myocarditis/pericarditis following mRNA COVID-19 vaccination 

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 The statistical signal among persons aged ≥ 65 years for ischemic stroke/transient 

ischemic attack (TIA) following bivalent Pfizer-BioNTech COVID-19 booster vaccination 

in VSD is based on limited data and has been attenuating over time. 

 A signal has not been observed in two other U.S. active vaccine safety monitoring 

systems1, nor in data from other countries2. 

– The U.S. systems differ from each other; the VSD and VA analyses included TIA 

with ischemic stroke, while FDA CMS analysis did not.

– VSD is the only U.S. system that uses concurrent comparator groups.

– The VA and FDA CMS analyses have not evaluated simultaneous administration 

with influenza vaccination.

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VaST assessment – statistical signal for ischemic 

stroke/TIA in the Vaccine Safety Datalink (VSD)

1FDA analysis of Centers for Medicare and Medicaid Services (CMS) data, and Department of Veterans Affairs (VA) rapid cycle analyses

2Israel and European countries
 No increased rate ratio for ischemic stroke/TIA following bivalent Moderna COVID-19 

booster vaccination. 

 Previous surveillance in VSD and other U.S. systems found no evidence of increased 

risk of ischemic stroke/TIA after the primary series or monovalent COVID-19 booster 

vaccination for either Pfizer-BioNTech or Moderna products. 

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VaST assessment – statistical signal for ischemic 

stroke/TIA in the Vaccine Safety Datalink (VSD)
 The cause of the increased rate ratio is unclear; potential contributing factors include 

simultaneous administration of bivalent COVID-19 booster and influenza vaccines* or 

unmeasured confounding or bias.

 VaST would like to review additional data on simultaneous administration of bivalent 

COVID-19 booster and influenza vaccination. 

 VaST highlighted several areas for further exploration:

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Assess the impact of recent respiratory viral illness (e.g., COVID-19, influenza) on 

risk of ischemic stroke/TIA.

Analyses in VSD highlighted potential reasons for the lower rate of ischemic 

stroke/TIA in the vaccinated comparator group, which could be contributing to the 

increased rate ratio. These should be explored further. 

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VaST assessment – statistical signal for ischemic 

stroke/TIA in the Vaccine Safety Datalink (VSD)

*Most VSD participants aged≥ 65 years received high-dose influenza vaccine in 2022-23 season
 VaST has reviewed data on myocarditis/pericarditis following COVID-19 vaccination 

since April 2021 and provided several assessments at ACIP meetings.

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Rates after the monovalent primary series, monovalent booster doses and 

bivalent booster doses have been assessed. 

Rates highest in adolescent and young adult males following primary series 

dose 2 and first monovalent booster dose.

Outcomes after the monovalent primary series and monovalent booster doses 

have also been assessed.

 Data on rates after bivalent COVID-19 booster vaccination are limited. 

Current data in VSD do not raise additional concerns about myocarditis 

following bivalent COVID-19 booster vaccination. 

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VaST assessment – myocarditis/pericarditis following 

mRNA COVID-19 vaccination 
 The ACIP COVID-19 Vaccines Work Group will continue to review safety data

 VaST is preparing to transition review of vaccine safety data to the ACIP COVID-19 

Vaccines Work Group

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VaST – future plans
VaST Members

VaST Members

Keipp Talbot (ACIP)

Robert Hopkins (NVAC)

Matt Daley

Grace Lee

Veronica McNally

Kathy Edwards

Lisa Jackson

Jennifer Nelson

Laura Riley

Robert Schechter

Patricia Whitley-Williams

CDC Co-Leads

Lauri Markowitz

Melinda Wharton

Ex Officio and Liaison Representatives 

Tatiana Beresnev (NIH)

Karen Farizo; Hui Lee Wong (FDA)

Valerie Marshall (OIDP)

Jeffrey Kelman (CMS)

Matthew Clark (IHS)

Timothy Styles (HRSA)

Fran Cunningham (VA)

Margaret Ryan (DoD)

Administrative Support

Jared Woo

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