Effectiveness of a Third Dose of mRNA Vaccines Against COVID-19–Associated Emergency Department and Urgent Care Encounters and Hospitalizations Among Adults During Periods of Delta and Omicron Variant Predominance — VISION Network, 10 States, August 2021–January 2022

To January 5, 2022. Analyses were stratified by the period before and after the Omicron variant became the predominant strain (>50% of sequenced viruses) at each study site. During the period of Delta predominance across study sites in the United States (August-mid-December 2021), VE against laboratory-confirmed COVID-19-associated ED and UC encounters was 86% 14-179 days after dose 2, 76% ≥180 days after dose 2, and 94% ≥14 days after dose 3. Estimates of VE for the same intervals after vaccination during Omicron variant predominance were 52%, 38%, and 82%, respectively. During the period of Delta variant predominance, VE against laboratory-confirmed COVID-19-associated hospitalizations was 90% 14-179 days…

• IH
  Intermountain Healthcare
• P
  Pfizer
• G
  GlaxoSmithKline
• S
  Sanofi
• KP
  Kaiser Permanente
• VU
  Vanderbilt University
• BD
  BioFire Diagnostics
• CF
  Centers for Disease Control and Prevention
• SO
  School of Medicine, Indiana University
• IM
  Irving Medical Center, Columbia University
• SP
  Sanofi Pasteur