evidence: You asked, we answered: Do the COVID-19 vaccines cause blood clots or heart problems? [...] As with any vaccine, rare adverse events have been reported after COVID-19 vaccination. For example, some people who received the Johnson & Johnson and AstraZeneca vaccines reported blood clots. The condition is known as thrombosis with thrombocytopenia syndrome or TTS. Out of more than 18 million people who got J&J vaccines in the U.S., 60 cases of TTS were reported, and nine people died. Most people who developed these problems were female, ages 18 to 49. For women, the risk of blood clots after the J&J vaccine is estimated to be 5.8 per million. For men, the risk of blood clots after J&J is 2.2 per million. [...] No evidence indicates that the Pfizer-BioNTech and Moderna mRNA COVID-19 vaccines are associated with the same risk of blood clots. However, data from multiple studies show a slight risk for myocarditis and pericarditis following the mRNA COVID-19 vaccines. These cases occurred most frequently in males, ages 16 years and older, within seven days of receiving the second dose of an mRNA COVID-19 vaccine.