FDA advises states to pause use of J&J Covid vaccine after rare blood-clotting issue affects 6 women, kills 1

The Food and Drug Administration asked states on Tuesday to temporarily halt using Johnson & Johnson's Covid-19 vaccine "out of an abundance of caution" after six women in the U.S. developed a rare blood-clotting disorder that left one woman dead and another in critical condition.

"Right now, these adverse events appear to be extremely rare," the FDA said in a joint statement with the Centers for Disease Control and Prevention. "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."

All six cases occurred in women ages 18 to 48, with symptoms developing six to 13 days after they received the shot. Doctors typically treat that type of blood clot with heparin, but health regulators noted that could be dangerous in this case and recommended a different treatment.

J&J said in a statement that "no clear causal relationship" has been identified between the blood clots and the vaccine, adding it is working closely with regulators to assess the data.

People who got the J&J vaccine more than a month ago are at very low risk for developing the blood clots, Dr. Anne Schuchat, the principal deputy director of the CDC, told reporters on a conference call Tuesday.

"For people who recently got the vaccine within the last couple weeks, they should be aware to look for any symptoms," she said. "If you've received the vaccine and developed severe headaches, abdominal pain, leg pain or shortness of breath you should contact your healthcare provider and seek medical treatment."

The blood clotting generally occurs about a week after vaccination, but not more than three weeks after, with a median time frame of nine days, Dr. Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, said on the call.

"We know that for these vaccines, that for the first several days after vaccination, there are flu-like symptoms that can include headache," he said, adding that those are likely common adverse events. "If someone presented to an emergency room with very severe headache or blood clots," doctors should ask whether they recently got a vaccine before putting together a plan of care. If the patient also has low platelets, doctors should consider that it may be related to the vaccine, he said.

Shares of J&J fell by almost 3% in intraday trading.

Out of the 120 million people in the U.S., roughly 6.9 million have received J&J's vaccine, White House chief medical advisor Dr. Anthony Fauci told reporters in a separate press conference Tuesday, noting that there haven't been any "red flag signals" from the Pfizer or Moderna vaccines that rely on MRNA technology in making their vaccines. Out of the 6.9 million people who got the J&J jab, 6 developed blood clots.

"We are totally aware that this is a rare event. We want to get this worked out as quickly as we possibly can and that's why you see the word 'pause,' in other words, you want to hold off for a bit," Fauci said. "We want to leave that up to the FDA and the CDC to investigate this carefully. I don't think it was pulling the trigger too quickly."

Fauci said the pause is expected to last a matter of days to a few weeks. He said it gives the FDA and CDC time to investigate the cases, try to understand what's going on and what the women have in common.

"It might shed some light on looking forward on what will happen and what we will do," he said.

The CDC will convene a meeting of the Advisory Committee on Immunization Practices on Wednesday to further review the cases, federal health regulators said Tuesday. The FDA is also investigating the cases.

Last week, Europe's medicines regulator said it found a possible link between the coronavirus vaccine developed by AstraZeneca and the University of Oxford and rare blood-clotting issues. AstraZeneca has not received authorization for use in the U.S.

Emer Cooke, executive director of the European Medicines Agency, said in a televised news conference last week that unusual blood clotting with low blood platelets would be added as a "very rare" side effect to the AstraZeneca vaccine's product information, along with a slew of other possible adverse reactions.

Isaac Bogoch, an infectious disease specialist who has sat on several drug data and safety monitoring boards, said J&J and AstraZeneca use the same platform for their vaccines. The J&J and AstraZeneca vaccines use an adenovirus, a common type of virus that typically causes mild cold symptoms.

"Clearly we don't have all the information and need to learn more about the mechanism and risk factors," he told CNBC. "But of course we can't sweep any potential adverse events under the rug and it needs to be investigated thoroughly."

Marks told reporters that researchers haven't yet found a specific cause for the blood clotting in J&J vaccine recipients, but they believed it was similar to other adeno viral vector vaccines.

"That is an immune response that occurs very, very rarely after some people receive the vaccine and that immune response leads to activation of the platelets and the extremely rare blood clots," Marks said.

J&J's Covid-19 vaccine, like Pfizer's and Moderna's shots, received an emergency use authorization from the FDA to start distributing the doses across the U.S. An EUA grants conditional clearance based on two months of safety data, pending another submission for full approval which usually requires at least six months of data.

J&J submitted its Covid vaccine data to the FDA in February, and no specific concerns were identified at the time when analyzed by age, race and comorbidities, according to the agency. The FDA said at the time the most common side effects reported were headache and fatigue, followed by muscle aches, nausea and fever.

It's unclear how the pause will impact J&J's goal to deliver 100 million doses to the U.S. by the end of May. The company has already been plagued by manufacturing issues after a plant run by Emergent BioSolutions ruined 15 million doses of the vaccine.

Dr. Kavita Patel, a former federal health official, told CNBC she believes the FDA's recommendation will likely have lasting impacts on the nation's efforts to combat the pandemic.

"This is a devastating blow to this J&J vaccine effort in the United States," Patel, a primary care physician in Washington, said in an interview on CNBC's "Squawk Box." Patel said the supply of the two-shot vaccines from Pfizer and Moderna won't be able to quickly make up the demand created by the J&J pause. This will delay U.S. vaccination efforts, she added.

Jeffrey Zients, President Joe Biden's Covid czar, said the White House was informed last night that the FDA would have an announcement this morning about the J&J shot.

He said the pause will not have a "significant impact" on the administration's goal to administer 200 million Covid shots within Biden's first 100 days in office. He said J&J's vaccine makes up less than 5% of the recorded shots in arms in the U.S. to date.

"Based on actions taken by the President earlier this year, the United States has secured enough Pfizer and Moderna doses for 300 million Americans," he said in a statement. "Over the last few weeks, we have made available more than 25 million doses of Pfizer and Moderna each week, and in fact this week we will make available 28 million doses of these vaccines."

— CNBC's Rich Mendez contributed to this article.