WASHINGTON – Federal health officials warned doctors and patients Tuesday to watch for symptoms that could indicate an extremely rare but serious form of blood clot in the brain suffered by six women who received Johnson & Johnson’s coronavirus vaccine. So what should you look for if you are one of the 6.8 million people who have received Johnson & Johnson’s one-dose vaccine, or are scheduled to receive it soon?

The symptoms include headaches, leg pain, abdominal pain and shortness of breath that begins six to 13 days after receipt of the vaccine, officials said. Those symptoms are different from the much more common flu-like aches and lethargy that can occur a day after receiving the shot, which are generally harmless side-effects of inoculation against the coronavirus.

Vaccine recipients with those symptoms that start a week or so after immunization should seek medical attention to determine whether they have a low count of blood-clotting platelets in their blood. All six of the women known to have suffered cerebral venous sinus thrombosis had low platelet counts, leading experts to speculate that the vaccine somehow, in rare cases,activates platelets and leads to blood clots in the channels that help route blood away from the brain. The clots can cause strokes or similar damage to the brain.

“If someone ends up with a very severe headache or any kind of shortness of breath, pain in their legs, pain in their abdomen . . . they would want to seek medical attention, and if there are low platelets at that time” further discussion with a health-care provider is necessary, said Peter Marks, director of the Center for Biologics Evaluation and Research (CBER) at the Food and Drug Administration, who spoke at a media briefing Tuesday morning.

In guidance sent to health care providers later Tuesday, the Centers for Disease Control and Prevention also included backache, new neurological symptoms, leg swelling and new or easy bruising among possible symptoms. They also warned physicians not to treat the condition with heparin, a common anticoagulant, which in this case could do more harm.

All the people affected are women between the ages of 18 and 48. One died and one is in critical condition, officials said. The development led states across the nation to pause immunization with the Johnson & Johnson vaccine while a federal expert panel examines the problem. Authorities said they hoped the development would not lead to fewer people accepting vaccines for coronavirus, which has caused more than 562,000 deaths in the United States so far.


Though the known cases are all among women of childbearing age, “at this time it’s not clear that there is any association with the oral contraceptive pill,” Marks said. Of course, it’s difficult to make any generalizations based on six cases. One woman who suffered a clot was using oral birth control medication, according to Anne Schuchat, principal deputy director of the CDC.

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Gowthami Arepally, associate professor of pathology at Duke University School of Medicine, said that cases of cerebral venous sinus thrombosis are something she is used to seeing, often among women using hormonal forms of birth control that raises the risk of such clots.

What makes the cases so unusual is the pairing with low platelets, the blood cells involved in clotting. Blood clots are thick collections of blood cells that can be caused by injuries, illness and long periods of sitting, among other reasons.

“It happens in very sick people, hospitalized people, not in healthy people,” Arepally said. What is being seen in the otherwise healthy patients resembles a rare immune reaction to the drug heparin, she said.

Among people with normal platelet counts, the disease affects 2 to 14 per million people per year. The Johnson & Johnson vaccine has been distributed for only six weeks. The blood clots also appear to be similar to problems caused by the AstraZeneca vaccine in Europe.


European regulators said it was “plausible” that the clots were linked to that vaccination. Johnson & Johnson disclosed Tuesday that the cases were being reviewed with European regulators and said the company was delaying its rollout there.

The clots have not been associated with the Pfizer-BioNTech or Moderna vaccines. They use different technologies than the Johnson & Johnson and AstraZeneca vaccines.

Angela Rasmussen, a virologist affiliated with Georgetown University, urged people not to overreact and wait for additional information.

“I am a woman between the ages of 18 and 48 who got the Johnson & Johnson vaccine eight days ago, and I recommend that people do what I’m doing, which is not panic,” she said. “First of all, we don’t know if these six cases are actually associated with the vaccine. We don’t know if those six cases had some other conditions that would have predisposed them to having blood clots like this. We don’t know a lot about it, which is why there’s a pause.”

Schuchat said at the news conference there may have been underlying conditions among some of the six women who suffered these blood clots.

Lisa Maragakis, an associate professor of medicine, infectious-disease and epidemiology at Johns Hopkins University School of Medicine added that “any time a message like this comes out, particularly for those who are within that two week window, there’s a concern about ‘What does this mean for me?'” Maragakis said. “I feel like overwhelmingly the message should be one of reassurance that we don’t yet know if these events are even associated with a vaccine. But even if they are, we know that serious events can happen with vaccine. These events are serious but appear to be, at least at this point, very rare.”


Six reports of this condition out of nearly 7 million shots delivered, Rasmussensaid, is “1 in 1,000,000 basically, or 1 in more than 1,000,000.”

She added, “I’m not worried that I’m going to have a blood clot. “

Acting FDA commissioner Janet Woodcock stressed that the risk of clots is tiny in comparison with the danger posed by the pandemic. Vaccines are the best protection against the coronavirus, she said.

“We’re recommending a pause out of an abundance of caution, but on an individual basis, a provider and a patient can make a decision on whether to receive the vaccine,” she said.

With millions of Americans still hesitant to receive the available coronavirus vaccines or rejecting them altogether, Maragakis said “it is very unfortunate that this pause is necessary right now.” She added that the move likely will cause additional concern about the Johnson & Johnson vaccine.

“I hope it doesn’t spill over more generally to the other types of vaccines because they are lifesaving and we’re seeing overwhelming data that they’re preventing serious disease from covid-19,” she said.

The recommendation to pause should not be an indication that the vaccines are unsafe or unregulated, Rasmussen said. She added that she is already seeing some vaccine opponents citing the Johnson & Johnson development as a reason to not take the shots.

“This is exactly how we know that these vaccines are safe, because when we get any kind of indication, even if it’s rare, even if it’s a tiny little blip like six cases, they will investigate to make sure that these vaccines are safe,” she said. “People should feel confident in this process.”

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The Washington Post’s Carolyn Y. Johnson contributed to this report.