3rd Dose of mRNA COVID Vaccines Improves Effectiveness Against Delta and Omicron Variants During Surge Periods

A 3rd mRNA COVID-19 vaccine dose improved the effectiveness of Moderna and Pfizer/BioNTech vaccines against infection with Delta or Omicron variants in a recent multistate analysis conducted between August 26, 2021, and January 5, 2022. Estimates of vaccine effectiveness were higher among adults who received a 3rd dose of an mRNA COVID-19 vaccine, compared with adults who only received 2 doses, during both Delta- and Omicron-predominant periods. This research highlights the importance of getting a 3rd dose when recommended for adults who have received mRNA vaccines.

Researchers analyzed 220,000+ emergency department and urgent care clinic encounters as well as 87,000+ hospitalizations among adults 18 years and older by ascertaining patients’ vaccination status and SARS-CoV-2 test results using large electronic health record (EHR) databases and immunization registries.

The data have been published in the Centers for Disease Control and Prevention’s (CDC’s) Morbidity and Mortality Weekly Report (MMWR): 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.

The research was sponsored by CDC’s COVID VISION Project, which integrates medical, laboratory, pharmacy, and vaccination records to examine medical events, care trajectories, and outcomes associated with COVID-19 illness. Westat supports the clinical sites in this work. Our researchers were among the report’s coauthors: Elizabeth A. Rowley, Dr.P.H.; Sarah E. Reese, Ph.D.; Matthew E. Levy, Ph.D.; Duck-Hye Yang, Ph.D.; Margaret M. Dunne, M.Sc.; and Sarah W. Ball, Sc.D.