Steve April 13, 2021

Federal health authorities recommended Tuesday that providers temporarily stop administering the Johnson & Johnson Covid-19 vaccine while they investigate a potential link to very rare blood clots.

Six women between the ages of 18 and 48 developed blood clots after receiving the Johnson & Johnson vaccine. One person died, and another is in critical condition, the Food and Drug Administration said.

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“We are recommending this pause while we work together to fully understand these events, and also so we can get information out to health care providers and vaccine recipients,” Dr. Janet Woodcock, acting FDA commissioner, said during a briefing Tuesday.

The review is expected to be completed quickly, lasting “a matter of days,” officials said.

The clots are considered extremely rare. Overall, more than 6.8 million people in the U.S. have received the Johnson & Johnson vaccine.

No such issues have been reported with the Covid-19 vaccines made by Pfizer-BioNTech or Moderna, health officials said.

In a statement, Johnson & Johnson said it was aware that blood clots had been reported with some Covid-19 vaccines, but that “no clear causal relationship has been established between these rare events” and its shot.

“We continue to work closely with experts and regulators to assess the data and support the open communication of this information to healthcare professionals and the public,” the company said.

The pause “will not have a significant impact” on the country’s vaccination plan, Jeff Zients, the White House Covid-19 Response Coordinator, said in a statement, adding that there is “more than enough supply” to meet President Joe Biden’s “goal of 200 million shots by his 100th day in office.”

The Centers for Disease Control and Prevention will convene its vaccine advisory committee on Wednesday to look into the possible link between the Johnson & Johnson vaccine and blood clots.

“I know that the information we’re providing today is going to be very concerning to Americans who have already received the Johnson & Johnson vaccine,” Dr. Anne Schuchat, principal deputy director for CDC, said during the briefing. “For people who got the vaccine more than a month ago, the risk is very low.”

For those who recently got the Johnson & Johnson vaccine, Schuchat advised to be aware of sudden, severe headaches, abdominal pain or shortness of breath.

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The six people who experienced clots were all women whose symptoms began six to 13 days after vaccination, the FDA and CDC said. They developed a type of blood clot in the brain called a cerebral venous sinus thrombosis, or CVST, as well as low levels of blood platelets.

Usually, people with blood clots are treated with a blood thinner called heparin. But in rare cases, the immune system reacts to the drug in a phenomenon called heparin-induced thrombocytopenia, which increases the risk for clotting.

For this reason, giving those who develop CVST heparin might actually be dangerous. Other blood thinners or medications may be more appropriate, officials said.

The call for a pause mirrors a situation that played out in Europe last month.

Some European governments paused the rollout of the Oxford University-AstraZeneca vaccine after a similarly tiny number of people suffered CVST blood clots. The AstraZeneca vaccine uses the same type of technology as the Johnson & Johnson shot.

Most European countries have since resumed administering the shot, but with a messy patchwork of different age restrictions and other guidelines. There is some evidence that as a result of this widely publicized fear, public trust in this vaccine is lower than others that are available.

The situation in Europe has divided experts, with some saying that governments could not ignore the possible link, and others saying that the pause may have increased infections and hesitancy, damage that far outweighs the dangers from these extremely rare side-effects.

Meanwhile, Johnson & Johnson also announced it will “proactively delay the rollout of our vaccine in Europe” while the company reviews potential cases overseas.

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Image: Alexander SmithAlexander Smith

Alexander Smith is a senior reporter for NBC News Digital based in London.

Image: Erika EdwardsErika Edwards

Erika Edwards is a health and medical news writer and reporter for NBC News and “TODAY.”

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