Top 5 Takeaways

  1. Bivalent mRNA COVID-19 Vaccine Effectiveness: The bivalent mRNA COVID-19 vaccine was found to be 47% effective in preventing thromboembolic events in immunocompetent persons aged ≥65 years and 51% effective in adults aged ≥18 years with end stage renal disease (ESRD) receiving dialysis, compared to the original monovalent vaccines.
  2. Study Population and Method: Two retrospective cohort studies were conducted among Medicare fee-for-service enrollees aged ≥65 years and those aged ≥18 years with ESRD on dialysis, using Medicare Parts A and B data from September 2022 to March 2023.
  3. Context of Previous Vaccine Safety Concerns: These findings provide context to a preliminary safety signal regarding ischemic stroke post Pfizer-BioNTech bivalent vaccination in persons aged ≥65, which attenuated over time and was not consistently evident in further studies.
  4. Vaccine Effectiveness Over Time: The effectiveness of the bivalent vaccine appears to wane over time, with lower effectiveness observed ≥60 days post-vaccination compared to 7-59 days post-vaccination.
  5. Public Health Implications: The study emphasizes the importance of staying up to date with COVID-19 vaccinations, particularly for older adults and those with ESRD, to prevent COVID-19-related complications including thromboembolic events.

Original Article Author and Citation

Corresponding Author

Amanda B. Payne, PhD,

Suggested Citation

Payne AB, Novosad S, Wiegand RE, et al. Effectiveness of Bivalent mRNA COVID-19 Vaccines in Preventing COVID-19–Related Thromboembolic Events Among Medicare Enrollees Aged ≥65 Years and Those with End Stage Renal Disease — United States, September 2022–March 2023. MMWR Morb Mortal Wkly Rep 2024;73:16–23. DOI:


The study examined the effectiveness of bivalent mRNA COVID-19 vaccines in preventing thromboembolic events such as ischemic stroke, venous thromboembolism, and myocardial infarction. The research used retrospective cohort studies among Medicare enrollees to compare the effectiveness of bivalent vaccines with original monovalent vaccines.


The study involved two retrospective cohort studies focusing on Medicare enrollees aged ≥65 years and those aged ≥18 years with ESRD on dialysis. Data was collected from Medicare Parts A and B enrollment and claims records.


The findings indicated that the bivalent COVID-19 vaccine offers substantial protection against thromboembolic events, with a slight decrease in effectiveness over time. This study provides important insights into the vaccine’s ongoing effectiveness, especially in light of previous safety concerns.


The study underscores the importance of COVID-19 vaccinations in preventing thromboembolic complications, particularly in older adults and those with ESRD. It highlights the role of the bivalent vaccine in offering added protection compared to the monovalent vaccine.

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