US halts J&J one-shot COVID-19 vaccinations over "extremely rare" clot risk

US immunizations with the Johnson & Johnson COVID-19 vaccine have been put on hold, as the CDC and FDA assesses six reported cases of rare blood clotting in America. The J&J Jannsen vaccine has been administered more than 6.8 million times in the US so far, since the one-shot drug received authorization under the FDA's pandemic EUA program.

It follows similar investigations kicking off in Europe, where the European Medicines Agency's PRAC safety committee responded to concerns about the vaccine's potential link to unusual blood clots. The drug is not currently in use in Europe, though was granted authorization were on March 11, and deployment had been expected within the next few weeks.

Now, injections in the US will cease, at least for a short period. On Wednesday, the CDC will hold a meeting of the Advisory Committee on Immunization Practices (ACIP) to review the six reported cases in the US. The FDA will also review that analysis, as it undertakes its own investigations.

"In these cases, a type of blood clot called cerebral venous sinus thrombosis (CVST) was seen in combination with low levels of blood platelets (thrombocytopenia)," the CDC and FDA explain. "All six cases occurred among women between the ages of 18 and 48, and symptoms occurred 6 to 13 days after vaccination."

Still, the risk of the side-effects are considered very low: to reiterate, only six incidents have been reported, among over 6.8 million doses of the vaccine administered. The hold on use is described by the agencies as "an abundance of caution."

"People who have received the J&J vaccine who develop severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination should contact their health care provider," the CDC and FDA warn. The pause will also give healthcare providers a chance to catch up with the recommended treatment, should blood clots arise, and how to spot them first.

That's important, because the way to treat these particular CVST clots is different from what might ordinarily be the go-to approach. "Treatment of this specific type of blood clot is different from the treatment that might typically be administered," the agencies point out. "Usually, an anticoagulant drug called heparin is used to treat blood clots. In this setting, administration of heparin may be dangerous, and alternative treatments need to be given."

In a statement today, Johnson & Johnson acknowledged the decision, and said it was working with regulators in both the US and Europe.

"The safety and well-being of the people who use our products is our number one priority," Johnson & Johnson said. "We are aware of an extremely rare disorder involving people with blood clots in combination with low platelets in a small number of individuals who have received our COVID-19 vaccine. The United States Centers for Disease Control (CDC) and Food and Drug Administration (FDA) are reviewing data involving six reported U.S. cases out of more than 6.8 million doses administered. Out of an abundance of caution, the CDC and FDA have recommended a pause in the use of our vaccine."

In Europe, meanwhile, J&J has voluntarily delayed the rollout of the vaccine.

More details on the impact of the decision today will be shared during a press conference later today. The advice to those with a vaccination scheduled using Johnson & Johnson's one-shot COVID-19 vaccine is to contact the healthcare provider, as it appears many are switching appointments to other drugs – such as Moderna or Pfizer's vaccines – while the J&J option is on hold.

Update: According to Acting FDA Commissioner Janet Woodcock, the halt on the J&J vaccine is expected to last "a matter of days" during the investigation.