Why You Shouldn't Compare Blood Clots After Johnson & Johnson Vaccine to Birth Control

This week, federal officials urged a pause in the administration of the Johnson & Johnson COVID-19 vaccine due to reports that some vaccine recipients developed severe blood clots. The clots, called cerebral venous sinus thrombosis (CVST), appeared in six people out of the 6.8 million people who have already received the vaccine.

Blood clots linked to the Johnson & Johnson vaccine were reported in six women, all between the ages of 18 and 48. Federal officials say they will investigate the cases before determining whether the vaccine is safe for continued distribution.

After the announcement, people took to social media to compare the risk of clotting from the vaccine to the risk posed by oral contraceptives. For some estrogen-based oral contraceptives, the chances of developing abnormal blood clots are 3 to 9 out of 10,000—a much higher rate than the 1 in one million risk of developing clots from the Johnson & Johnson vaccine.

Despite the relatively higher risk of clotting from contraceptives, experts say it’s inaccurate to compare the two.

What Are Blood Clots?

A blood clot is a clump of congealed blood. These commonly arise when someone is injured or cut. “Clotting is incredibly important in the body, because it stops us from bleeding out if we have an injury,” Adam Taylor, PhD, professor of anatomy at Lancaster University in the U.K., tells Verywell.

The women who reported clots linked to the vaccine also all exhibited a low platelet count. Platelets are cells that exist in large numbers in the blood. When we have a wound, they are key in helping the blood clot to avoid further damage or blood loss. People who don’t have a sufficient platelet count—about 150,000 per microliter of blood—may not clot properly.

Clotting From the Vaccine

It appears that the Johnson & Johnson vaccine can affect a person’s platelet count, but scientists aren’t yet sure how. The vaccine can also seemingly cause platelets to stick together to plug up key passageways.

Normally, after blood delivers oxygen and nutrients to the brain, it drains out channels called venous sinuses. These sinuses funnel the blood into jugular veins and down through the neck back to the heart.

It appears that in some people who received the Johnson & Johnson vaccine, platelets stick these small sinuses together, causing clots. The clots block the blood in the brain, putting pressure on the veins, sometimes causing them to break and leak blood back into the brain. This can damage the brain tissue and can sometimes affect vision, movement, and brain function.

If this condition isn’t treated quickly or thoroughly, it can lead to a stroke. Typically, CVST affects five in one million people each year.

Contraceptive Blood Clots

While oral contraceptives and the Johnson & Johnson vaccine can both cause abnormal blood clots, they do so through two different processes. Taylor, who wrote an article comparing the CVST clots caused by the AstraZeneca vaccine in the U.K. to oral contraceptive clots, says that blood clotting is a complex process, and clots can form in many different ways with different effects on the body.

Oral contraceptive pills increase the levels of certain proteins that help the body with the natural clotting process. Sometimes, when these so-called “clotting factors” are abundant in the blood, there are increased chances of blood clumping.

Unlike the vaccine-induced CVST, which mostly affects the brain, these clots usually occur in veins in the leg. Sometimes, the leg clots, called deep vein thrombosis, can break off and travel up to the lungs. When this happens, you may feel your legs swell or ache. Clots that form in the lungs, known as a pulmonary embolism, may cause you to experience shortness of breath or other respiratory symptoms.

Fortunately, these clots can be effectively treated with anticoagulants—medications like heparin that break down the clots. In the FDA statement, officials say it’s unclear whether the same treatments will be safe and effective against vaccine-induced clots, and whether the typical course of treatment may even be dangerous to a patient.

What This Means for People Who Use Oral Contraceptives

There is currently “no compounding risk” of using contraceptives and getting the Johnson & Johnson vaccine, Jen Villavicencio, MD, MPP, Darney/Landy Fellow at the American College of Obstetricians and Gynecologists, tells Verywell in an email.

“There is currently no evidence to support discontinuing or changing one’s birth control method,” Villavicencio says. “We know from decades of use and clinical data that hormonal birth control is safe and effective and that thanks to the variety of hormonal and non-hormonal options available, individuals are able to find the contraception that works best for them.” 

For some, the current attention on vaccine efficacy provides an opportunity to open the discussion about how to improve the safety of oral contraceptives.

“We keep saying, ‘oh well, the risk of vaccines is lower than it is for contraceptives,’” Taylor says. “That may be the case, but why have we been living with that risk for oral contraceptives to one large portion of the population for such a long period of time?”

Assessing the Risk

If you have already received the Johnson and Johnson or AstraZeneca vaccine it is very unlikely that you have or will develop a CVST blood clot.

But it’s still a good idea to remain vigilant. Look out for severe headache, blurred vision, fainting or unconsciousness, confusion, pinprick rash or bruising away from the vaccine injection site. If you experience any of these symptoms within the first three weeks of receiving the vaccine, contact your health provider to seek care, Johnson & Johnson said in a statement.

For the vast majority of people, the risk of developing dangerous blood clots from COVID-19 is far greater than the risk posed by the vaccines. In a preprint analysis published this week, researchers from the University of Oxford found a 39-in-a-million chance of developing CVST among people infected with COVID-19.

“Your likelihood of getting blood clots from COVID is hugely increased compared to the risk of clotting from oral contraceptives and certainly compared to any of the vaccines that are currently be being administered,” Taylor says. “If we want to get back to our way of normal life, vaccines are touted as a significant step in the right direction to doing that.”

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.