U.S. Calls For Pause on Johnson & Johnson Vaccine After Rare Cases of Blood Clots

Health officials are investigating six reports of a rare and serve blood clot among female recipients of the Johnson & Johnson COVID-19 vaccine in the U.S., one of whom died. On April 13, the Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC) recommended a pause in the administration of the single-dose vaccine while the investigation takes place.

Several states have already begun pausing Johnson & Johnson shots.

The blood clot is called cerebral venous sinus thrombosis (CVST) and prevents blood from draining out of the brain. The condition was seen in combination with low levels of blood platelets (thrombocytopenia), which means anticoagulation medication may not be suitable to treat the blood clot.

The CDC has asked its Advisory Committee on Immunization Practices (ACIP) to meet on Wednesday, April 14, to review the data on the rare events.

Why Is This Type of Blood Clot Happening?

In an April 13 briefing call with reporters, Dr. Peter Marks, MD, PhD, director of the FDA’s Center for Biologics Evaluation and Research, said a rare immune response could potentially be activating platelets, causing the extremely rare blood clots.

“What we’re debating is if an extremely rare side effect is proven to be linked to the vaccine,” Amesh Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security, tells Verywell. “This is certainly less than the risk of blood clots from getting COVID itself."

Similar infrequent events have been seen with the AstraZeneca COVID-19 vaccine, which is similar in design to the Johnson & Johnson vaccine. Both use adenovirus vectors—genetic pieces of the common cold that are unable to reproduce but can deliver genetic code from COVID-19 into the body.

“This vector may, in certain individuals, generate antibodies that interfere with platelet function and produce a condition similar to heparin-induced thrombocytopenia, which is diagnosable and treatable,” Adalja says.

The AstraZeneca vaccine has been approved for use in some countries, paused for use in others, and not yet authorized for use in the U.S.

Neither the FDA nor CDC answered questions today on how the Johnson & Johnson news might affect any authorization of the AstraZeneca vaccine, which Anthony Fauci, MD, deemed "imminent" in an April 12 briefing.

Symptoms to Look For

It cannot be overstated how rare these CVST cases are—six incidents after more than 6.8 million Johnson & Johnson doses were administered in the U.S. Still, the CDC and FDA are advising Johnson & Johnson vaccine recipients who develop any or all of the following symptoms within three weeks of vaccination to contact a healthcare provider:

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

Sending a Message to Healthcare Providers 

The CDC and FDA said a key reason for the pause is to alert healthcare providers to the clotting issue, since the treatment for CVST is different from the treatment that might typically be administered for blood clots. Usually, an anticoagulant drug called heparin is used to treat blood clots, but according to the agencies' statements: “in this setting, administration of heparin may be dangerous, and alternative treatments need to be given."

Public health experts are concerned that the reports could increase hesitancy for the millions of Americans not yet vaccinated against COVID-19, another issue healthcare providers will need to confront.

Adalja says he is concerned that the pause will do irreparable harm to the vaccine rollout and affect people's willingness to get any vaccine.

"I fear this risk-averse stance will likely cost lives and delay control of the pandemic,” he says. 

Adalja says he hopes that the ACIP “is able to rapidly adjudicate this issue and have [J &J] vaccinations resume," adding it will be important for the committee to "stress risk/benefit calculations, particularly in those at high-risk for severe disease, hospitalization, and death from COVID-19.”

An Important Safety Precaution

William Schaffner, MD, professor of health policy, preventive medicine and infectious diseases at the Vanderbilt School of Medicine in Nashville, Tennessee, tells Verywell that the U.S. vaccine safety surveillance is the best in the world.

"You can see that it is working because we had this signal of a concern that was detected very quickly," he says.

The rare events are only showing up now, Schaffner says, because they appear to occur in less than one case per million people vaccinated. Only 15,000 people were involved in the Johnson & Johnson clinical trial, “so you would not be able to detect any possible cases until the vaccine was in wide use," he says.

Schaffner says the U.S. safety system has not found the same clotting difficulty with the Moderna or Pfizer vaccines.

“I would encourage people not yet vaccinated to get Moderna or Pfizer, or hang tight for a few days to see the results of the investigation, as well as the FDA and CDC’s ultimate recommendation on the J&J vaccine."

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.