Pfizer’s COVID-19 Vaccine Linked to Blood Clotting: FDA Pfizer’s COVID-19 vaccine has been linked to blood clotting 4 in older individuals, according to the U.S. Food and Drug Administration (FDA).

FDA researchers, crunching data from a database of elderly persons in the United States, found that pulmonary embolism—blood clotting in the lungs—met the initial threshold for a statistical signal and continued meeting the criteria after a more in-depth evaluation.

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