CDC Study Examines Incidence of, and Health Problems Associated with, Rare Blood Clotting Conditions

Blood clot in 3D brain illustration

In 2021, several European countries reported cases of unusual, life-threatening blood clots in the brain, known as cerebral venous sinus thrombosis (CVST), in people who had received the Oxford-AstraZeneca vaccine for coronavirus disease 2019 (COVID-19). Many of these people also had thrombocytopenia, a condition that occurs when there are low platelet levels in the blood. Platelets are blood cells that help the body form clots to stop bleeding. In the United States, a number of cases of CVST and thrombocytopenia were also reported in people who had received the Johnson & Johnson/Janssen COVID-19 vaccine.

CDC’s Advisory Committee on Immune Practices (ACIP) urgently needed data on CVST and CVST with thrombocytopenia as committee members considered the safety of the Johnson & Johnson/Janssen vaccine. However, very little information on CVST was available. Previous studies had small sample sizes not representative of the general population, and many did not determine which factors increased the risk for CVST. Up-to-date, comprehensive analyses were critically needed to inform both vaccine safety and what is known about the causes and health outcomes of CVST more generally. Therefore, researchers from the Centers for Disease Control and Prevention (CDC) designed a study to fill these information gaps.

About This Study

Researchers from the CDC conducted analyses of people hospitalized for CVST in the United States using three large, independent datasets:

  • 2018 Healthcare Cost and Utilization Project National Inpatient Sample (NIS)
  • 2019 IBM® MarketScan® Commercial and Medicare Supplemental Claims Database
  • 2019 IBM® MarketScan® Multi-state Medicaid Database

Using three datasets allowed researchers to compare findings from each sample.

Researchers examined

  • The incidence (new cases within a time period) of CVST and CVST with thrombocytopenia,
  • The severity of illness, and
  • Factors associated with increasing one’s risk for developing CVST and CVST with thrombocytopenia.

Read the full scientific article.

Main Findings from This Study


  • Incidence estimates for CVST were similar among each of the three samples, ranging from 2.5 to 3.2 per 100,000 people.
  • In all samples, incidence estimates increased with age. However, there were differences by sex.
    • Among both males and females, incidence was lowest among those who were younger than 18 years old.
    • Among females, incidence estimates were significantly higher by age 18 and were similar across all adult age groups.
    • In males, incidence estimates were lower in younger adults and higher among adults ages 40 and older.
  • Incidence for CVST with thrombocytopenia was significantly lower than for CVST overall, about 0.2 per 100,000 people from all three samples.
  • Only one dataset had a sample size large enough to examine CVST with thrombocytopenia by age and sex. Incidence among both males and females was highest for those ages 40 and older. There were no differences by sex.

Severe Disease or Death

  • Stroke and other types of blood clots were common among people with CVST and CVST with thrombocytopenia.
  • About 4% (1 in 25) of patients with CVST died while hospitalized and nearly 10% (1 in 10) of those with CVST with thrombocytopenia died while hospitalized.

Risk Factors

  • Several conditions were more common among people hospitalized for CVST (overall and with thrombocytopenia) than among people hospitalized for other reasons. These conditions include meningitis, encephalitis, head or neck infection, cancer, head injury, connective tissue disorders, bleeding disorders, and prior history of blood clots.
  • Women ages 18 to 49 years with CVST had a higher prevalence of recent pregnancy than same-aged women in the general population.
  • Women ages 18 to 64 with CVST had higher use of estrogen hormone medications, such as birth control pills or hormone replacement therapy, than same-aged women in the general population.

Future Directions

The findings from this study informed the work of an advisory committee evaluating vaccine safety. However, the study has broader applicability. This is one of the most comprehensive studies of CVST to date. It is important that more research on rare but potentially deadly conditions, such as CVST, be carried out, so clinicians and the wider public health community have access to current and complete data for informed decision-making.

Paper Reference

Payne AB, Adamski A, Abe K, Reyes NL, Richardson LC, Hooper WC, Schieve LA. Epidemiology of cerebral venous sinus thrombosis and cerebral venous sinus thrombosis with thrombocytopenia in the United States, 2018 and 2019. Res Pract Thromb Haemost. 2022 Mar 7;6(2):e12682. doi: 10.1002/rth2.12682. PMID: 35284775; PMCID: PMC8901465.