All six cases occurred among women between 18 and 48, and symptoms occurred 6 to 13 days after vaccination, FDA officials said in a joint statement.
More than 6.8 million doses of the one-dose vaccine had been administered in the U.S.
All Pennsylvania teachers and administrators were given the J&J vaccine. Out of the 200,000 offered the vaccine about 125,000 received it. No incidents of blood clots have been reported according to the Pennsylvania Department of Health.
"CDC will convene a meeting of the Advisory Committee on Immunization Practices (ACIP) on Wednesday to further review these cases and assess their potential significance," CDC Principal Deputy Director Dr. Anne Schuchat and FDA Center for Biologics Evaluation and Research Dr. Peter Marks said.
"FDA will review that analysis as it also investigates these cases. Until that process is complete, we are recommending a pause in the use of this vaccine out of an abundance of caution.
"This is important, in part, to ensure that the health care provider community is aware of the potential for these adverse events and can plan for proper recognition and management due to the unique treatment required with this type of blood clot."
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