Doctors Explain the Johnson & Johnson Vaccine’s Link to Extremely Rare Blood Clots

Korin Miller
·7 min read
Photo credit: Evgenii Kovalev - Getty Images
Photo credit: Evgenii Kovalev - Getty Images

The Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) are recommending a “pause” in the use of the Johnson & Johnson COVID-19 vaccine.

“As of April 12, more than 6.8 million doses of the Johnson & Johnson (Janssen) vaccine have been administered in the U.S. The CDC and FDA are reviewing data involving six reported U.S. cases of a rare and severe type of blood clot in individuals after receiving the J&J vaccine,” a joint statement from the agencies reads. “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).”

All six cases occurred in women between the ages of 18 and 48, with symptoms emerging six to 13 days after vaccination. The agencies stress that the clots “appear to be extremely rare.”

The CDC plans to have a meeting of the Advisory Committee on Immunization Practices (ACIP) on April 14 to review the cases and determine their potential significance. The FDA will also review that analysis. “Until that process is complete, we are recommending a pause in the use of this vaccine out of an abundance of caution,” the statement says.

“This is an extremely rare risk that they’re talking about,” says Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security, who is concerned that the statement will “put people into a panic” before medical experts have investigated the matter thoroughly.

The White House responded to the news with a statement from Jeff Zients, White House COVID-19 response coordinator. “This announcement will not have a significant impact on our vaccination plan: Johnson & Johnson vaccine makes up less than 5% of the recorded shots in arms in the United States to date,” Zients said. “Based on actions taken by the president earlier this year, the United States has secured enough Pfizer and Moderna doses for 300 million Americans.”

At the current pace of production there 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 said, adding that the White House is working with state and federal partners to get anyone scheduled for a Johnson & Johnson vaccine “quickly rescheduled” for a Pfizer or Moderna vaccine.

So, what happens now if you’ve already received the single dose from Johnson & Johnson’s vaccine? We asked infectious disease doctors to explain what you should know.

First, what is cerebral venous sinus thrombosis?

Cerebral venous sinus thrombosis (CVST) is a blood clot that forms in the venous sinuses, a network of blood vessels in the brain, according to Cedars Sinai. This type of clot keeps blood from draining out of the brain, which may cause blood cells to break and leak into the brain tissues, causing a hemorrhage. This is the same type of blood clot that was reported in a small number of people who received the AstraZeneca vaccine, which was temporarily suspended in some European countries.

CVST is a rare form of stroke, impacting about five people in 1 million each year. Certain factors increase your risk of CVST, including pregnancy, cancer, obesity, and inflammatory bowel disease. Certain medications can also increase your risk, including birth control pills, says Dr. Adalja.

Because this type of blood clot is different from a standard blood clot, treatment is different, the FDA and CDC statement says, which is one main reason the agencies have suggested the pause. “Usually, an anticoagulant drug called heparin is used to treat blood clots,” the statement says. “In this setting, administration of heparin may be dangerous, and alternative treatments need to be given...This is important, in part, to ensure that the healthcare 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.”

Your blood clot risk is actually higher if you become ill with COVID-19.

Experts agree that the CDC and FDA’s move is clearly out of an abundance of caution. “It’s a very smart decision and it shows that our system of vaccine safety surveillance works,” says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine. “The risk of having a CVST from the Johnson & Johnson vaccine based on what we know so far is a rate of about one per million doses,” he says. “That’s like finding a needle in a haystack.”

“There’s a risk-benefit ratio to consider,” Dr. Adalja adds. “Even if those six cases were related to the vaccine, the risk-benefit ratio still favors getting the Johnson & Johnson vaccine greatly.”

Dr. Schaffner calls this a “possible causal association” and notes that the same is being investigated with the AstraZeneca vaccine, which uses similar technology to the Johnson & Johnson vaccine.

But there are other possible explanations to keep in mind, too. Richard Watkins, M.D., an infectious disease specialist and a professor of internal medicine at the Northeast Ohio Medical University says he “wouldn’t be surprised” if the women impacted had other risk factors for CVST, like taking birth control pills or having an underlying condition.

In the case of birth control pills, research has found that the risk of developing CVST is 7.59 times higher in women who are taking oral contraceptives compared to those who are not. Based on the data available right now, the risk of developing a CVST from the Johnson & Johnson vaccine is lower than the risk to the general population.

Then, there’s the actual side effects of the coronavirus to keep in mind. “You know what else causes a much higher risk of blood clots than the vaccine? COVID-19,” Dr. Watkins says. According to a meta-analysis published in the journal Thorax, 7.8% of people with COVID-19 are at risk of developing a pulmonary embolism (a blood clot in the lungs) and 11.2% are at risk of deep vein thrombosis, a blood clot in a deep vein (usually in the legs).

What should you do if you’ve received the Johnson & Johnson vaccine or have been scheduled to receive one?

Dr. Adalja is concerned about the lasting effects of the FDA and CDC’s statement. “Even if the committee finds the cases are unrelated, the damage will have been done to the Johnson & Johnson vaccine,” he says. “It will be irreparable, because we already have vaccine hesitancy. This is going to be hard to come back from and it will delay control of the pandemic. It could have been handled a lot better.”

Until an investigation into the six cases of clots has been done, keep in mind that there’s a lot that still needs to be answered. Experts agree that the preliminary data is potentially concerning, but Dr. Adalja stresses that it’s “far from conclusive.” That means it’s hard to even know for sure if these cases of CVTS are related to the vaccine—but experts should know more soon.

If you have a vaccine appointment scheduled for the Johnson & Johnson vaccine, contact your vaccine provider. Some states, like New York, are already swapping in either the Pfizer or Moderna vaccines for people who have Johnson & Johnson appointments scheduled.

And if you have already received the Johnson & Johnson vaccine, the CDC and FDA recommend looking out for any unusual symptoms within three weeks of receiving the Johnson & Johnson vaccine, including a severe headache, abdominal pain, leg pain, or shortness of breath.

If you happen to experience any of these symptoms, contact your healthcare provider to ensure a proper diagnosis. But rest assured that “this is an extremely small risk,” Dr. Schaffner says. “Let’s not panic.”

This article is accurate as of press time. However, as the COVID-19 pandemic rapidly evolves and the scientific community’s understanding of the novel coronavirus develops, some of the information may have changed since it was last updated. While we aim to keep all of our stories up to date, please visit online resources provided by the CDC, WHO, and your local public health department to stay informed on the latest news. Always talk to your doctor for professional medical advice.

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