“Vaccine induced prothrombotic immune thrombocytopenia,” or VIPIT, is a condition of blood clots associated with low platelet counts, that occurs following receipt of the vaccine.
The likely mechanism is antibodies that induce massive platelet activation, reducing platelet count and causing thrombosis although the full mechanism remains to be elucidated.
This syndrome is thought to mimic “heparin-induced thrombocytopenia” (HIT), in both cases antibodies to PF4 (Platelet factor 4) are present. Both Astra Zeneca and J & J use adenoviruses as the vector carrying the spike protein.
Moderna and Pfizer use mRNA and no adenoviruses.
VIPIT has not been seen with Moderna or Pfizer.
Thus far only 15 cases of VIPIT have been found with more than eight million doses administered of J & J. All have been in women: 13 in women ages 18 - 49 and 2 in women > age 50.
Starting 6-13 days after vaccination, 9 have involved the venous sinuses of the brain leading to hematoma and brain bleed. At least 4 have died despite treatment.
The Rx consists of steroids , immune globulins and Factor Xa inhibitors like apixaban. After considerable debate the CDC has removed the pause and said that all people over age 18 are eligible to receive the J & J vaccine. The risk of COVID-19 causing cots is multiple times higher than clots from the vaccine.
IMHO, there seems to be a connection of the formation of clots with estrogen given the occurrence in women and in the younger age group .
We know that estrogen activates the immune system while testosterone does the reverse. That is a theory why more women have side effects after the (second) Moderna or Pfizer vaccine than men.
Given that to be the case, I would advise young women, if possible, to avoid the adenovirus vaccines and opt for the mRNA vaccine. Only if the option exists and there is a choice.
Better to get any vaccine than none at all.