All six cases occurred in women ages 18 to 48, with symptoms developing six to 13 days after they received the shot.
The blood-clotting disorder is called cerebral venous sinus thrombosis, and it was only reported in individuals who also had low levels of blood platelets, a condition called thrombocytopenia.
“The real thing that is so notable here is not just the cerebral venous sinus thrombosis or the thrombocytopenia,” Dr. Peter Marks, director of the Food and Drug Administration’s Center for Biologics Evaluation and Research, said during a separate media briefing. “Those two things can occur. It’s their occurrence together that makes a pattern, and that pattern is very, very similar to what was seen in Europe.”