CDC website: “recent reports indicate a plausible causal relationship between the J&J/Janssen COVID-19 Vaccine and TTS, a rare and serious adverse event—blood clots with low platelets—which has caused death”
https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/adverse-events.html
Per the linked source:
A preprint study by the University of Oxford examined the records of more than 500,000 COVID-19 patients and used that data to estimate that cerebral venous thrombosis blood clots would occurred in about 39 of every 1 million people with COVID-19.
CVT has been reported to occur in about 5 per million people after a first dose of the AstraZeneca/Oxford vaccine. In more than 480,000 people receiving either the Pfizer/BioNTech or Moderna vaccines, CVT occurred in 4 per million.
The researchers said that compared to the Pfizer or Moderna vaccines, the risk of CVT from COVID-19 was about 10 times greater.