How serious is the Johnson & Johnson blood clot risk compared to common medications?

A week ago, people across the U.S. woke up to news that the Food and Drug Administration and the Centers for Disease Control and Prevention are recommending a “pause” in the use of the Johnson & Johnson COVID-19 vaccine after it was linked to a rare form of blood clots.

There have been six reported cases of a condition called cerebral venous sinus thrombosis (CVST) — a type of blood clot in the brain that can lead to a stroke — out of the more than 6.8 million doses of the vaccine that have been administered in the U.S., according to a joint statement from the agencies. All six cases happened in women between the ages of 18 and 48, with symptoms developing six to 13 days after they were vaccinated.

The CDC plans to have a meeting of the Advisory Committee on Immunization Practices on Wednesday to review the cases, and the FDA will review that analysis. Until then, the agencies say that they are recommending “a pause in the use of this vaccine out of an abundance of caution.”  Several states, including New York, New Jersey, Florida and Michigan, are following the agencies’ recommendation. According to the CDC,  more than 74 million Americans are fully vaccinated, with the majority receiving either the Pfizer-BioNTech vaccine (36,194,022) or the Moderna vaccine (31,014,082).

Some people have taken to social media claiming that the risk of blood clots is much greater with other medications, including birth control. While experts say that there are valid concerns about a possible link between CVST and the Johnson & Johnson vaccine, they also agree that some other medications come with a chance of developing the disorder — and some with a higher risk than the possible 0.00009 percent risk presented by this particular vaccine.

“For many medications that we use commonly, the risk of serious side effects is much greater than one in a million,” says Dr. Martin J. Blaser, director of the Center for Advanced Biotechnology and Medicine at Rutgers University.

CVST is rare overall — it affects about 5 in 1 million people each year, according to Cedars-Sinai. In general, though, “drugs that can cause blood clots are all medications that can do this,” say Jamie Alan PhD, assistant professor of pharmacology at Michigan State University.

But what are those medications, exactly? Here’s a breakdown….they can include:

• Oral contraceptives.The exact risk varies by type, but “oral contraceptives containing estrogen, or any estrogen-containing product” can raise the risk of CVST, Alan says. One meta-analysis of 861 studies on CVST found that the risk of developing the condition is 7.59 times higher in women who are taking oral contraceptives than in those who are not taking the pills.
• Testosterone supplementation. Excess testosterone in the body is “converted to estrogen, so testosterone supplementation also carries a risk of CVST,” Alan says. This is a rare complication, but it can happen. A 2019 case report details the story of a 33-year-old man who experienced CVST after taking testosterone replacement therapy as prescribed by his doctor.
• Warfarin.This medication, which is commonly used to treat and prevent blood clots, comes with an increased risk of CVST within the first few days of its use, Alan says.
• Heparin.This medication is also used to prevent blood clots. One study found that up to 9 percent of patients who are treated with it had issues with brain bleeding afterward. “Heparin increases the risk of CVST, but we still use it,” says Dr. Thomas Russo, professor and chief of infectious disease at the University at Buffalo in New York. “All physicians have seen this syndrome.”
• Nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin and ibuprofen also come with an increased risk of blood clots and brain bleeding, and not just CVST either, Alan points out.

Overall, CVST “isn’t very common, but when this occurs, it can be traumatic,” Alan says.

Experts stress that the associated risk of CVST from the Johnson & Johnson vaccine is incredibly low.  “People have forgotten that COVID-19 is the clear and present danger,” says infectious disease expert Dr. Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security. “COVID-19 can cause blood clots and kill you. The world needs to get a lot better at risk-benefit calculation.”

Blaser stresses that CVST seems to be a “very, very rare complication” of the Johnson & Johnson vaccine — if the link is determined through more analysis. “It’s reasonable to pause and look at the data,” he says. Russo says that the news shouldn’t keep people from getting vaccinated against COVID-19. “There is not a 100 percent cause-and-effect situation with CVST and the Johnson & Johnson vaccine, but I’m concerned that this association will prove to be real,” he says. “In the meantime, there are two other very good vaccines in the mix.”

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