Pfizer’s COVID-19 vaccine has been linked to blood clotting 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.
Three other outcomes of interest—a lack of oxygen to the heart, a blood platelet disorder called immune thrombocytopenia, and another type of clotting called intravascular coagulation—initially raised red flags, researchers said. More in-depth evaluations, such as comparisons with populations who received influenza vaccines, showed those three as no longer meeting the statistical threshold for a signal.
Researchers looked at data covering 17.4 million elderly Americans who received a total of 34.6 million vaccine doses between Dec. 10, 2020, and Jan. 16, 2022.
The study was published by the journal Vaccine on Dec. 1.
The FDA said it was not taking any action on the results because they do not prove the vaccines cause any of the four outcomes, and because the findings “are still under investigation and require more robust study.”
Pfizer's COVID-19 Vaccine Linked to Blood Clotting: FDA
