The U.S. FDA on Tuesday recommended an immediate halt of the use of Johnson & Johnson's COVID-19 vaccine, citing cases of a rare blood clot disorder that six women developed within two weeks of receiving the shot.

The latest: Acting FDA Commissioner Janet Woodcock said at a briefing that she expects the pause to only last "a matter of days," as health officials investigate the data surrounding the "extremely rare" blood clots.

Driving the news: The FDA's recommendation was issued "out of an abundance of caution" and to prepare health providers to recognize and treat patients appropriately, since these types of blood clots require a different kind of treatment.

• The White House said in a statement Tuesday that the pause "will not have a significant impact" on the administration's vaccination plans, noting that it has secured enough Moderna and Pfizer doses for 300 million Americans.
• Nonetheless, some White House officials are concerned that the FDA's decision could increase vaccine hesitancy.

The big picture: Nearly 7 million Johnson & Johnson doses have been administered in the U.S., and another 9 million have been shipped out to the states.

• The six women who developed the blood clots were between the ages of 18 and 48, according to the FDA.
• While people who have received a J&J shot more than a month ago have a relatively low risk of developing any complications, the FDA recommends people vaccinated in the last three weeks contact their health care provider if they are experiencing severe headache, abdominal pain, leg pain or shortness of breath.
• The FDA authorized the vaccine for emergency use on Feb. 27. The U.S. will stop administering the vaccine at federal sites and recommends that states do the same.

What they're saying: "Right now, these adverse events appear to be extremely rare," the FDA and the CDC wrote in a statement.

• "Treatment of this specific type of blood clot is different from the treatment that might typically be administered."
• The agencies noted that the vaccine pause is important "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."

Between the lines: The CDC said there are too few cases to determine whether there are any subpopulations particularly at risk. The health agencies are not ready to single out any subgroups at this time.

What to watch: A CDC expert committee will convene on Wednesday to "review these cases and assess their potential significance."