The AstraZeneca vaccine, which is not yet authorized for any use in the U.S., has been linked to rare occurrences of blood clots in Europe and the United Kingdom.
These warnings came as a study published in the New England Journal of Medicine linked the AstraZeneca vaccine to reports of rare blood clots in 11 patients — nine of them women — in their 20s, 30s and 40s in Germany and Austria.
In the AstraZeneca vaccine, the modified virus comes from chimpanzees; in Johnson & Johnson's, the virus comes from humans.
No such clotting issues have been reported with the Covid-19 vaccines made by Pfizer-BioNTech or Moderna, health officials said.Experts hypothesize that in very rare instances, the adenoviruses used in the Johnson & Johnson and the AstraZeneca Covid-19 vaccines might prompt the body to make antibodies similar to what's seen in heparin-induced thrombocytopenia.But current evidence suggests the risk of blood clots is exceedingly rare."There is a larger risk of getting Covid-19 disease, and a presumably lesser risk of this blood clotting disorder.".
There are a handful of other vaccines that use the adenovirus technology, including Johnson & Johnson's Ebola vaccine