The Massachusetts Department of Public Health on Tuesday directed all providers to pause administration of Johnson & Johnson COVID-19 vaccines, responding to a federal recommendation that those particular shots not be given while the Food and Drug Administration and Center for Disease Control review six cases of a rare and severe blood clot reported in women who had received the vaccine.

With more than 6.8 million J&J doses administered in the U.S. as of Monday, the CDC and FDA said they were making the move out of an abundance of caution. State data show that 181,034 people in Massachusetts had received the J&J vaccine as of Monday.

"Right now, these adverse events appear to be extremely rare. COVID-19 vaccine safety is a top priority for the federal government, and we take all reports of health problems following COVID-19 vaccination very seriously," the CDC's Dr. Anne Schuchat and FDA's Dr. Peter Marks said in a joint statement. "People who have received the J&J vaccine who develop severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination should contact their health care provider."

A spokesperson for the state's COVID-19 command center said none of the six cases are known to be linked to Massachusetts, and that individuals who have received a J&J shot should contact their physicians if they have any concerns.

People who are scheduled to receive a J&J vaccine are encouraged to contact the provider with whom they booked the shot with any questions about their upcoming appointments.

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"In response to today's recommendation from the FDA and CDC to pause J&J vaccines due to an extremely rare condition reported in 6 individuals nationwide, the Department of Public Health directed all providers to immediately pause administration of the J&J vaccine until federal health experts investigate this matter," command center communications director Kate Reilly said in a statement.

The FDA plans a 10 a.m. news conference, and the CDC on Wednesday plans to convene its Advisory Committee on Immunization Practices on Wednesday to review the cases.

According to the two federal agencies, six women between the ages of 18 and 48 developed a type of blood clot called cerebral venous sinus thrombosis, in combination with low levels of blood platelets, and symptoms occurred six to 13 days after vaccination.

The CDC and FDA are advising providers that this type of clot requires different treatment than might typically be given, as use of the anticoagulant drug heparin may be dangerous.

Gov. Charlie Baker often talks about the Johnson & Johnson vaccine as a game-changer for the state's vaccine distribution strategy, describing the single-dose shot as a way to accelerate vaccination speed and capacity.