WASHINGTON (NewsNation Now) — The Food and Drug Administration and Centers for Disease Control and Prevention Tuesday recommended pausing the use of Johnson & Johnson’s COVID-19 vaccine for at least a few days to investigate reports of rare but potentially dangerous blood clots.

The one-shot J&J was considered an important addition in bringing the vaccine into harder-to-reach populations since it does not require cold storage or a second appointment. More than 6.8 million doses of J&J have been administered, according to the FDA.

Here’s what you need to know about the shot and the pause:

Who has this affected?

Six women under age 50 developed rare blood clots after receiving the shot, according to a joint statement issued by the CDC and FDA Tuesday morning.

All six women were between the ages of 18 and 48, with symptoms occurring six to 13 days after the vaccination. One person died and all of the cases remain under investigation.

The clots occurred in veins that drain blood from the brain and occurred together with low platelets, the fragments in blood that normally form clots.

The type of blood clot is called cerebral venous sinus thrombosis. The clots occur in veins that drain blood from the brain and occurred together with low platelets. 

This particular type of blood clot, health experts emphasize, must be treated differently than other types — with different blood thinners or antibody infusions rather than the typical heparin treatment.

WHAT IF I ALREADY GOT THE j &j SHOT?

Deputy director of the CDC, Dr. Anne Schuchat, said for those who have received their vaccines at least a month ago or more, the risk of developing the clots is “very low at this time.”

Those who may have gotten their Johnson & Johnson shots in the last couple of weeks should monitor their symptoms.

The clots have usually occurred about a week after the shots and not longer than three weeks with a median of about nine days after vaccination.

What are the symptoms? Fauci says be aware but don’t freak out

The agencies are recommending that people who were given the J&J vaccine who are experiencing severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after receiving the shot contact their health care provider.

Dr. Anthony Fauci, the nation’s top infectious diseases expert, echoed the agencies Tuesday saying the chances of the blood clots occurring are less than one in a million but Americans should pay attention if they received the vaccine.

“It’s less than one in a million.” Fauci adds people should “pay attention” to symptoms associated with the blood clots, particularly between one and three weeks after the shot.

“Don’t get an anxiety reaction,” Fauci said Tuesday.

ARE THE OTHER vaccines SAFE?

CDC’s Dr. Anne Schuchat said authorities have not seen similar clots after the use of the two other authorized vaccines: Pfizer or Moderna vaccines. Schuchat said people should continue to get vaccinated with those shots.

“There have been no red flag signals from those,” Fauci said Tuesday.

CAN I STILL GET A VACCINE?

Jeff Zients, the White House COVID-19 response coordinator, said the J&J pause will not have a “significant impact” on the country’s vaccination plan, adding that J&J vaccines make up less than 5 percent of the recorded shots in arms in the U.S. to date.

“We have more than enough supply of Pfizer and Moderna vaccines to continue the current pace of about 3 million shots per day, and that puts us well on pace to meet the President’s goal of 200 million shots by his first 100 days in office,” Zients said.

About 74.1 million people, or 22.3% of the U.S. population, have been fully inoculated with COVID-19 vaccines made by Pfizer Inc/ BioNTech SE, Moderna Inc and Johnson & Johnson, according to CDC data. 36.4% of the U.S. population or 120.8 million adults had received at least one dose of a COVID-19 vaccine.

WHAT’S NEXT AND HOW LONG WILL THIS LAST?

CDC’s Advisory Committee on Immunization Practices will meet Wednesday to discuss the cases and the FDA has also launched an investigation of the cases.

“Until that process is complete, we are recommending a pause in the use of this vaccine out of an abundance of caution,” said Schuchat and the FDA’s Dr. Peter Marks in a joint statement.

The FDA said the cases under investigation appear similar to unusual clots that European authorities say are possibly linked to another COVID-19 vaccine not yet cleared in the U.S., from AstraZeneca. European regulators have stressed that the AstraZeneca risk appears to be lower than the possibility of developing clots from birth control pills.

J&J said in a statement it was aware of the reports of blood clots, but that no link to its vaccine had been established. The company also said it is delaying the rollout of its vaccine in Europe as a precaution.

Fauci says the pause by regulators is a “testimony to how seriously we take safety” and says he expects the pause to last days to weeks. Acting FDA commissioner, Dr. Janet Woodcock, also said the recommended pause on the vaccine will likely last just a matter of days.

“It really allows both the FDA and the CDC to further investigate these cases to try and understand,” Dr. Fauci said.

The Associated Press, Nexstar Media Wire and Reuters contributed to this report.