Federal health agencies on Tuesday recommended pausing the use of the Johnson & Johnson vaccine after a small number of people experienced "a rare and severe type of blood clot" after receiving the shot.
Of these, six have experienced the clot, the agencies said, adding: "Right now, these adverse events appear to be extremely rare."
In a statement, Johnson & Johnson said it was aware that blood clots had been reported with some Covid-19 vaccines, but that "no clear causal relationship has been established between these rare events" and its shot.
The CDC will convene Wednesday a meeting of its Advisory Committee on Immunization Practices, which provides guidance on vaccines.
It said that committee would "further review these cases and assess their potential significance," while the FDA would also investigate.
Drug Administration, Centers for Disease Control, The New York Times, CDC, FDA