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On August 31, 2022, the FDA authorized use of the ancestral strain/Omicron BA.5 COVID-19 mRNA vaccine (“bivalent vaccine”), but additional Omicron variants soon emerged. The CDC's VISION network used a test-negative study design to evaluate the bivalent vaccine's effectiveness (VE) against emergency department/urgent care visits (ED/UC) for COVID-19–like illness and COVID-19–related hospitalization compared with no vaccination or vaccination with 2, 3, or 4 monovalent doses in immunocompetent adults from September 13 to November 18, 2022. The ED/UC cohort included 9009 cases (positive for SARS-CoV-2) and 69,294 controls (negative). Bivalent vaccine recipients were older than monovalent vaccine recipients (median age, 68 vs. 55), and most (5…