The pause in using Johnson & Johnson's COVID-19 vaccine should continue until more is known about the development of blood clots in recent weeks by six women who received the vaccine, a federal advisory committee said Wednesday.

The Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control and Prevention (CDC) held an emergency meeting Wednesday to discuss the cases. Panel members decided they needed more time to assess the data and risks and wouldn't vote on a recommendation until they meet again in a week or 10 days.

The extremely rare blood clots have been reported in seven of the 7.2 million Americans who have gotten the J&J vaccine. The six recent cases were reported in women ages 18 to 48, and symptoms occurred six to 13 days after vaccination. One man in an earlier clinical trial also developed blood clots.

One woman died and three remain hospitalized. All of them also had low platelet counts within two weeks of receiving the J&J vaccine. An eighth case with similar symptoms is under investigation.

ACIP is a panel of independent experts who advise the CDC on its vaccine policies. At the public meeting Wednesday, experts reviewed and debated data from the rare blood clots and heard comments from the public before voting on how to proceed.

"Right now, we believe these events to be extremely rare, but we are also not yet certain we have heard about all possible cases, as this syndrome may not be easily recognized as one associated with the vaccine," Dr Rochelle Walensky, the CDC director, said at a White House news conference on the pandemic on Wednesday.

Jeffrey Zients, the White House's pandemic coordinator, said that the pause wouldn't generally interrupt the momentum of the country's vaccination campaign.

"In the very short term, we do expect some impact on daily averages as sites and appointments transition from Johnson & Johnson to Moderna and Pfizer vaccines," he said. "We have more than enough Pfizer and Moderna vaccine supply to continue or even accelerate the current pace of vaccinations."

More than 7 million people in the US had received the J&J shot as of Tuesday, and 10 million doses have been shipped out to states, according to CDC data.

On Tuesday, all 50 states, Washington DC and Puerto Rico quickly paused or recommended that providers suspend the administration of the vaccine. The US military, federally run vaccination sites and private companies, including CVS, Walgreens, Rite Aid, Walmart and Publix also paused the injections.

The clotting disorder in the vaccine recipients is different and much rarer than typical blood clots, which develop in hundreds of thousands of people every year.

The women not only had clotting in the brain, but a notably low level of platelets, which are components of blood that help form normal clots. Three also had large, dangerous clots in other parts of the body.

The specific combination of blood clots and low platelets also has been observed after use of the AstraZeneca vaccine in Europe.

Use of the J&J vaccine began on March 2, and the first case of blood clots in the brain was reported on March 19. About 1.4 million women ages 20 to 50 — the age range of those who had the clots — received the vaccine.

Experts noted that patients with the condition need to be treated as soon as possible because the clots are very serious. Some patients needed invasive procedures to remove large clots from blood vessels in their brains.

Agencies contributed to this story.