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U.S. Pauses J&J Vaccinations to Probe 'Extremely Rare' Blood Clots

6 cases reported after 6.8 million doses of Johnson & Johnson COVID-19 vaccine administered

Johnson & Johnson Janssen COVID-19 vaccine box and vial

Paul Hennessy/SOPA Images/LightRocket via Getty Images

En español | Federal health officials on Tuesday called for a pause in the use of Johnson & Johnson's (J&J) single-dose coronavirus vaccine “out of an abundance of caution.”

The recommendation, issued in a joint statement by the Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA), comes as the agencies review six cases of a rare but serious type of blood clot, called cerebral venous sinus thrombosis, in individuals after receiving the J&J vaccine. As of April 12, more than 6.8 million doses of the one-shot vaccine have been administered in the U.S.

When to See Your Doctor

Seek medical attention if within three weeks of receiving the J&J vaccine you experience:

  • Severe headache
  • Abdominal pain
  • Leg pain
  • Shortness of breath

Source: FDA/CDC

All six cases occurred in women between the ages of 18 and 48, the agencies said, and symptoms developed six to 13 days after vaccination. One case was fatal, and one person is in critical condition, Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, confirmed during a media briefing.

Blood clot requires unique treatment

The CDC will convene a meeting of its vaccine advisory committee on April 14 to review the cases “and assess their potential significance.” The FDA will also conduct an investigation, and both agencies are recommending that states halt the vaccine's use until the process is complete.

"This is important, in part, to ensure that the health care provider community is aware of the potential for these adverse events and can plan for proper recognition and management due to the unique treatment required with this type of blood clot,” Anne Schuchat, principal deputy director of the CDC, and the FDA's Marks said in the joint statement.

Blood clots are commonly treated with heparin, an anticoagulant drug often referred to as a blood thinner. A big reason for the J&J pause: Cerebral venous sinus thrombosis can require a different treatment approach. “In this setting, administration of heparin may be dangerous, and alternative treatments need to be given,” Schuchat and Marks said.

Health care providers who see patients with low blood platelets or blood clots should inquire about recent vaccination “and then act accordingly in the diagnosis and management of those individuals,” Marks added. Schuchat and Marks did not specify a course of treatment in their statement.

Clotting cases ‘extremely rare'

Officials stress that the occurrence of these blood clots after vaccination “appear to be extremely rare,” but encourage people who have received the J&J vaccine and go on to develop severe headache, abdominal pain, leg pain or shortness of breath within three weeks after their shot to contact their health care provider.


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The symptoms associated with the blood clots are different from the mild flu-like symptoms that many people experience after vaccination, Schuchat emphasized. Typical reactions from the J&J vaccine include injection site pain and swelling, tiredness, headache, muscle pain, chills, fever and nausea. These symptoms usually start within a day or two of getting the vaccine, the CDC says.

Experts don't have an explanation for the possible association between the rare blood clots and the vaccine, but speculate it may be tied to an immune response “that occurs very, very rarely after some people receive the vaccine,” Marks explained. “And that immune response leads to activation of the platelets and these extremely rare blood clots.” J&J's vaccine utilizes a viral vector to stimulate an immune response in the body; so does AstraZeneca's vaccine, which has also been linked to blood clots in Europe. (AstraZeneca has not applied for FDA authorization in the U.S.)


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The vaccines from Pfizer-BioNTech and Moderna use a different type of technology, called mRNA. To date, no cases of cerebral venous sinus thrombosis have been reported for these vaccines, Marks confirmed. And people who have vaccine appointments for these two vaccines should continue with their appointments, Schuchat added.

U.S. vaccine supply ample without J&J

The pause comes as cases of COVID-19 are climbing. The U.S. is averaging about 66,000 daily cases — up about 3 percent from the previous seven-day average, CDC Director Rochelle Walensky announced on April 12. Hospitalizations from the disease are also increasing, especially among people under 65.

However, Jeff Zients, the White House COVID-19 Response Coordinator, said the pause of J&J's vaccine “will not have a significant impact on our vaccination plan,” since the shot makes up less than 5 percent of vaccinations, to date.

Nearly 121 million Americans have received at least one dose of a coronavirus vaccine; about 74 million are fully vaccinated, or about 20 percent of the U.S. population. The majority of vaccines administered have come from Pfizer-BioNTech (97,978,125 doses) and Moderna (84,694,388 doses), data from the CDC show.

"Based on actions taken by the President earlier this year, the United States has secured enough Pfizer and Moderna doses for 300 million Americans. 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,” Zients said in an April 13 statement. “This is more than enough supply to continue the current pace of vaccinations of 3 million shots per day and meet the President's goal of 200 million shots by his 100th day in office — and continue on to reach every adult who wants to be vaccinated.”

Zients added that health officials are working with state and federal partners to quickly reschedule people in line for a J&J vaccine for a Pfizer-BioNTech or Moderna vaccine.

In a news release, Johnson & Johnson said the company is “working closely with medical experts and health authorities” and that it strongly supports “the open communication of this information to health care professionals and the public.” It's also reviewing blood clot cases with European health authorities and is delaying the rollout of the vaccine in Europe.

Rachel Nania joined AARP as a health and medicine writer in 2019 after spending several years as a radio reporter and editor in Washington, D.C. She is the recipient of a 2018 Gracie Award and a 2019 regional Edward R. Murrow Award, and participated in a 2019 dementia fellowship with the National Press Foundation.

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