A small number of patients have developed immune thrombocytopenia (ITP) after receiving the Pfizer/BioNTech and Moderna coronavirus vaccines. Whether the onset of the condition was related to the vaccine is unknown.
As of February 8, more than 31 million people in the U.S. had received at least one dose of the vaccine, with 36 cases of ITP reported to the Vaccine Adverse Event Reporting System by the end of January.
"I think it is possible that there is an association," James Bussel, MD, a hematologist and professor emeritus at Weill Cornell Medicine told The New York Times. "I'm assuming there's something that made the people who developed thrombocytopenia susceptible, given what a tiny percentage of recipients they are." He added, "Having it happen after a vaccine is well-known and has been seen with many other vaccines. Why it happens, we don't know."
U.S. Food and Drug Administration and Centers for Disease Control and Prevention officials said they were investigating the reports, but that the rates of ITP in vaccinated patients did not appear higher than that of the general U.S. population. The vaccine is considered safe overall, and the cases of ITP could be coincidental.