Effectiveness of mRNA COVID-19 Vaccine Boosters Against Infection, Hospitalization, and Death: A Target Trial Emulation in the Omicron (B.1.1.529) Variant Era.

Journal Article (Journal Article)

BACKGROUND: The effectiveness of a third mRNA COVID-19 vaccine dose (booster dose) against the Omicron (B.1.1.529) variant is uncertain, especially in older, high-risk populations. OBJECTIVE: To determine mRNA booster vaccine effectiveness (VE) against SARS-CoV-2 infection, hospitalization, and death in the Omicron era by booster type, primary vaccine type, time since primary vaccination, age, and comorbidity burden. DESIGN: Retrospective matched cohort study designed to emulate a target trial of booster vaccination versus no booster, conducted from 1 December 2021 to 31 March 2022. SETTING: U.S. Department of Veterans Affairs health care system. PARTICIPANTS: Persons who had received 2 mRNA COVID-19 vaccine doses at least 5 months earlier. INTERVENTION: Booster monovalent mRNA vaccination (Pfizer-BioNTech's BNT162b2 or Moderna's mRNA-1273) versus no booster. MEASUREMENTS: Booster VE. RESULTS: Each group included 490 838 well-matched persons, who were predominantly male (88%), had a mean age of 63.0 years (SD, 14.0), and were followed for up to 121 days (mean, 79.8 days). Booster VE more than 10 days after a booster dose was 42.3% (95% CI, 40.6% to 43.9%) against SARS-CoV-2 infection, 53.3% (CI, 48.1% to 58.0%) against SARS-CoV-2-related hospitalization, and 79.1% (CI, 71.2% to 84.9%) against SARS-CoV-2-related death. Booster VE was similar for different booster types (BNT162b2 or mRNA-1273), age groups, and primary vaccination regimens but was significantly higher with longer time since primary vaccination and higher comorbidity burden. LIMITATION: Predominantly male population. CONCLUSION: Booster mRNA vaccination was highly effective in preventing death and moderately effective in preventing infection and hospitalization for up to 4 months after administration in the Omicron era. Increased uptake of booster vaccination, which is currently suboptimal, should be pursued to limit the morbidity and mortality of SARS-CoV-2 infection, especially in persons with high comorbidity burden. PRIMARY FUNDING SOURCE: U.S. Department of Veterans Affairs.

Full Text

Duke Authors

Cited Authors

  • Ioannou, GN; Bohnert, ASB; O'Hare, AM; Boyko, EJ; Maciejewski, ML; Smith, VA; Bowling, CB; Viglianti, E; Iwashyna, TJ; Hynes, DM; Berry, K; COVID-19 Observational Research Collaboratory (CORC),

Published Date

  • December 2022

Published In

Volume / Issue

  • 175 / 12

Start / End Page

  • 1693 - 1706

PubMed ID

  • 36215715

Pubmed Central ID

  • PMC9575390

Electronic International Standard Serial Number (EISSN)

  • 1539-3704

Digital Object Identifier (DOI)

  • 10.7326/M22-1856


  • eng

Conference Location

  • United States