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Daily Dose: Bivalent Boosters Protect Against Severe COVID-19 Disease

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Patient Care brings primary care clinicians a lot of medical news every day—it’s easy to miss an important study. The Daily Dose provides a concise summary of one of the website's leading stories you may not have seen.


On December 16, 2022, we reported on data from 2 real-world studies released by the Centers for Disease Control and Prevention (CDC) that suggested bivalent COVID-19 booster vaccinations may reduce the risk of hospitalization and emergency department (ED) visits by at least 50%.

The studies

The first study included more than 93 000 adults in 9 states who had either been hospitalized (15 500) or had an ED or urgent care encounter (78 000) for a COVID-like illness. Vaccine effectiveness was evaluated between September 13 and November 18, 2022, when the Omicron BA.5 variant was the predominate sublineage in circulation and additional variants also emerged. The vaccine effectiveness of a bivalent booster dose received after 2, 3, or 4 monovalent doses against ED/urgent care encounters for COVID-19–associated illness was 56% compared with no vaccination, 31% compared with a monovalent dose received 2–4 months earlier, and 50% compared with receipt of last monovalent dose ≥11 months earlier. Bivalent booster dose effectiveness against hospitalization for COVID-19–associated illness, again after receipt of 2, 3, or 4 monovalent doses, was 57% compared with no vaccination, and 45% compared with receipt of last monovalent doses ≥11 months earlier.


The second study was of 798 immunocompetent adults aged ≥65 years admitted for COVID-19-like illness to 22 hospitals in 18 US states also between between September and November 2022. When compared with unvaccinated patients, the vaccine effectiveness of a dose of bivalent mRNA vaccine in preventing COVID-19-associated hospitalization was 84%. Booster vaccine effectiveness was 73% when compared with patients who had received ≥2 monovalent-only mRNA vaccine doses ≥2 months before illness onset. Relative vaccine effectiveness of a bivalent booster dose was 78% and 83% when compared to patients whose last monovalent dose was 6 to 11 months and ≥12 months before illness onset, respectively.

Clinical implications

"All persons should stay up to date with recommended COVID-19 vaccinations, including receiving a bivalent booster dose if eligible."

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