The US Centers for Disease Control and Prevention and the US Food and Drug Administration are recommending that the United States pause the use of Johnson & Johnson's Covid-19 vaccine over six reported US cases of a "rare and severe" type of blood clot.

One person is currently in critical condition and another, a 45-year-old Virginia woman, died. The six reported cases were among more than 6.8 million doses of the Johnson & Johnson vaccine administered in the United States.

All six cases occurred among women between the ages of 18 and 48, and symptoms occurred 6 to 13 days after vaccination, according to a joint statement on Tuesday from Dr Anne Schuchat, principal deputy director of the CDC and Dr Peter Marks, director of the FDA's Center for Biologics Evaluation and Research.

"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," the statement 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."