The FDA and CDC has recommended that use of the Johnson & Johnson COVID-19 vaccine be paused after reports of blood clots in patients receiving the shot, the agencies announced Tuesday.

In a statement, FDA said 6.8 million doses of the J&J vaccine have been administered and the agency is investigating six reported cases of a rare and severe blood clot occurring in patients who received the vaccine.

The CDC will convene a meeting of the Advisory Committee on Immunization Practices on Wednesday to review the cases.

"This is important to ensure that the health care provider community is aware of the potential for these adverse effects and can plan due to the unique treatment required with this type of blood clot," the FDA said on Twitter.

Johnson & Johnson in a statement said, "We are aware of an extremely rare disorder involving people with blood clots in combination with low platelets in a small number of individuals who have received our COVID-19 vaccine. Out of an abundance of caution, the CDC and FDA have recommended a pause in the use of our vaccine."

This is a developing story and we will continue to update our team members as new information is available. In the meantime, the safety of the Pfizer and Moderna vaccines remains well established and we continue to encourage everyone to get vaccinated with one of these effective alternatives.

The following article from NPR is an excellent resource for more detailed information about the vaccine and blood clots, including advice for those who may have recently received the J&J vaccine.

Johnson & Johnson Vaccine And Blood Clots: What You Need to Know

Government health officials are recommending a "pause" in vaccinations with the Johnson & Johnson COVID-19 vaccine.

Federal health officials have called for a pause in the use of the Johnson & Johnson vaccine, after reports that six women who got the vaccine developed blood clots afterward. Close to 7 million people have gotten this vaccine in the U.S. to date.

The Centers for Disease Control and Prevention says the blood clots are extremely rare but that it is reviewing the cases. The agency says it expects this pause to last for "a matter of days."

The CDC's principle deputy director, Dr. Anne Schuchat says the pause is intended "to prepare the health care system to recognize and treat patients appropriately."

So how worried should you be about these rare cases? And how would you know if you might be at risk? We have answers.

Who is being affected by these blood clots?

The clots that have been reported so far are in women between the ages of 18 and 48. Among the six, one case was fatal and one patient is in critical condition. Their symptoms emerged six to 13 days after vaccination. However, at a press conference Tuesday, acting commissioner of the Food and Drug Administration, Janet Woodcock, said at this point there's not enough information to say whether any particular subgroup is more vulnerable.

The CDC's Schuchat added that there are too few cases at this point to determine what specific risk factors might predispose someone to developing these clots.

The FDA has suggested that health care providers pause the use of the vaccine while the side effects are being studied. However, providers are not prohibited from using the vaccine if they feel the benefits to an individual patient outweigh the risks. The government is convening an expert review panel which will hold a public meeting Wednesday. Officials hope to resolve these safety questions in a matter of days.

If you got your shot more than a month ago, your risk of developing these clots is "very low at this time," Schuchat says. The CDC and FDA say these events appear to be extremely rare but generally occur one week to "not longer than three weeks" after vaccination.

Schuchat says people who got the vaccine within the last couple of weeks should be on the lookout for severe headache, abdominal pain, leg pain or shortness of breath. If you develop these symptoms, seek medical treatment — with your doctor or by going to an urgent care clinic or the ER — and let doctors know you were recently vaccinated.

Officials note that these symptoms are different from the mild flu-like symptoms, like fever and mild headaches, that you might experience a few days after getting the vaccine.

Dr. Peter Marks, the director of the Center for Biologics Evaluation and Research at the FDA adds, "It would be more important if someone reported to an emergency room with a very severe headache or blood clots."

Health officials emphasize that these clots should not be treated the way other clots often are. Most importantly, Marks says doctors should avoid using heparin, a standard blood-thinning treatment, because in these clots it "can cause tremendous harm, or the outcome can be fatal."

But there is no simple substitute. Treatment needs to be individualized, the CDC's Schuchat says, because these patients don't simply have blood clots, they also have lower levels of platelets. And that can raise a person's risk of increased heavy bleeding, because it makes it harder for blood to clot.

Marks at the FDA says ideally, patients with this rare condition should be referred to physicians experienced in treating blood clots. The need for this specialized treatment is one reason the CDC and the FDA saw an urgent need to get the word out about this rare combination of side effects.

Scientists have a working hypothesis, but don't have complete answers. Marks at the FDA says the leading hypothesis is that, on rare occasions, the vaccine can trigger an undesirable immune response. So instead of simply prompting the body to produce antibodies that protect against the coronavirus, people also generate antibodies that affect blood platelets. That could explain why they are depleted among people with this rare condition.

Researchers in Europe noted this phenomenon among people who suffered similar side effects after receiving the AstraZeneca vaccine.

It's not happening with the other vaccines authorized for use in the United States, the Pfizer and the Moderna vaccines, according to the FDA. Those vaccines are based on a different technology, called mRNA, while the J&J uses what's called viral vector technology.

However it is similar to side effects seen with the AstraZeneca vaccine, which is not approved for use in the U.S. but is used widely in other parts of the world. Like the J&J vaccine, the AstraZeneca vaccine uses a modified virus to activate the immune system's response.

Health officials say the blood clotting side effects of the AstraZeneca vaccine appear to be more frequent than what has been reported for J&J. One estimate is they affect one person out of every 100,000 vaccines. So far for the J&J vaccine, this condition has been identified in about one in a million people, though health officials say there may be a small number of cases that haven't yet been reported.

The White House said it expects no significant impact on its vaccination plan because most of the vaccines used in the U.S. come from Pfizer and Moderna.

"This announcement will not have a significant impact on our vaccination plan," said Jeff Zients, the White House COVID-19 response coordinator. "Johnson & Johnson vaccine makes up less than 5% of the recorded shots in arms in the United States to date."

Americans scheduled for a J&J vaccine will be quickly rescheduled to receive a Pfizer or Moderna vaccine, Zients said.