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Effectiveness of COVID-19 Booster on the Risk of Hospitalization Among Medicare Beneficiaries

  • Hemalkumar B. Mehta
    Correspondence
    Correspondence: Hemalkumar B. Mehta, PhD, Johns Hopkins Bloomberg School of Public Health, Department of Epidemiology, 615 N. Wolfe Street E7640, Baltimore, MD 21205, Phone: 410 502 9763, Fax: 410 955 0863
    Affiliations
    Center for Drug Safety and Effectiveness, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland

    Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland
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  • Shuang Li
    Affiliations
    Sealy Center on Aging and Department of Internal Medicine, The University of Texas Medical Branch, Galveston
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  • James S. Goodwin
    Affiliations
    Sealy Center on Aging and Department of Internal Medicine, The University of Texas Medical Branch, Galveston
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      ABSTRACT

      Objective

      To determine the effectiveness of booster vaccinations on the risk of hospitalization with COVID-19, and how it varies by enrollee characteristics and interval from the initial vaccination to receipt of booster.

      Methods

      This cohort study used 100% Medicare claims from January 2020 through December 2021 and matched 3,940,475 individuals who received boosters to 3,940,475 controls based on week and type of original COVID-19 vaccine, and demographic and clinical characteristics. We compared the association of booster vs. no booster with COVID-19 hospitalization using Cox proportional hazards regression models controlling for patient characteristics. We also determined the association of time from original vaccine to booster with COVID-19 hospitalization.

      Results

      Over a maximum of 130 days of follow-up, boosted enrollees had 8.20 (95% CI, 7.81-8.60) COVID-19 hospitalizations per million days vs. 43.70 (42.79-44.64) for controls, 81% effectiveness. Effectiveness varied by race, prior hospitalizations, and certain comorbidities; for example, leukemia/lymphoma (53% effectiveness), autoimmune disease (73%) and dementia (73%). Boosters received between 6 and 9 months after original vaccination varied between 81% and 85% effectiveness, while boosters received at 5-6 months (62%) or <5 months (58%) were less effective.

      Conclusions

      Boosters are highly effective in the Medicare population. Approximately 69,225 hospitalizations would be prevented by boosters in the 15,000,000 individuals aged 65+ currently not boosted, in a period similar to the September 2020 through January 2021 period studied. Boosters provided the greatest benefits if they were received between six to nine months following original vaccinations. However, boosters were associated with substantial decreases in COVID-19 hospitalizations in all categories of enrollees.

      Keywords

      List of abbreviations:

      CI (confidence interval), FDA (Food and Drug Administration)