What You Need to Know About COVID-19 Vaccines, Birth Control, and Blood Clots

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What You Need to Know About COVID-19 Vaccines, Birth Control, and Blood Clots

Martha Kempner

Comparisons of COVID-19 vaccines to the birth control pill, which carry a higher risk of blood clots, is not helpful nor entirely scientifically accurate.

On Tuesday, the Centers for Disease Control and Prevention (CDC) suggested temporarily pausing use of the Johnson & Johnson’s COVID-19 vaccine while researchers investigate a handful of reports of potentially dangerous blood clots.

This news, which came on the heels of similar incidents possibly related to the AstraZeneca vaccine, makes the already difficult job of encouraging vaccination among a somewhat reluctant public even harder.

Unfortunately, too many media outlets have taken it upon themselves to ease the public’s concerns by making quick comparisons to other medications, like the birth control pill, that carry a higher risk of blood clots. This is not helpful, nor is it entirely scientifically accurate. And it may end up encouraging young people using birth control to skip the vaccine and ditch their pills.

Around 7 million people in the United States have already gotten the J&J vaccine, and there have been six reported cases of blood clots. In Britain and the European Economic Area (which includes the countries of the European Union plus Iceland, Norway, and Lichtenstein), over 34 million people had gotten the AstraZeneca shot as of April 4, and health officials had received 222 reports of blood clots. By the numbers, this is a very rare condition and seems to happen more often in younger women.

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Perhaps that’s why so many news outlets thought to compare the risk of blood clots from the vaccine to the risks young women might face from hormonal birth control.

A recent Business Insider article, with the headline “Panic Over AstraZeneca’s Shot Is Overblown,” noted birth control’s clot numbers are scarier: “After a year of taking birth-control pills, about one in 1,000 women will develop blood clots. (The risk is about 1 in 10,000 for all young women, so it’s elevated nearly tenfold in birth-control takers.)” This is a bit of an overstatement; most experts agree that hormonal birth control increases the risk of blood clots by three- to four-fold among pill takers without underlying health issues.

Such comparisons may seem like an easy way to explain risk, but even when accurate they don’t tell the whole story and so risk stirring up unnecessary fears about hormonal contraception.

A more familiar kind of blood clot

The blood clots that might be linked to the new vaccines are part of a condition known as cerebral venous sinus thrombosis (CVST), and they have not been well studied. CVST occurs when a clot (a mass of coagulated blood) forms in the brain’s venous sinuses, preventing blood from draining out of the brain and potentially leading to hemorrhage or stroke. Symptoms of CVST in these cases seemed to appear within two weeks of receiving the vaccine and were accompanied by low platelet levels, making treatment more complicated. The pause on vaccine distribution is designed, in part, to give experts time to determine the best treatment options.

By contrast, we know a lot about deep vein thrombosis (DVT), the blood clot condition related to the pill. This type of clot usually forms in the lower legs, thigh, or pelvis. The biggest risk with DVT is that a portion of the clot breaks off and travels through the veins to the lung, causing a pulmonary embolism. Risk for DVT is increased when someone is on hormonal birth control that contains estrogen (most hormonal birth control contains both estrogen and progestin) but also after surgery, during pregnancy or right after childbirth, and after extended periods of air travel.

While researchers are racing to figure out whether any underlying conditions make one person more at risk of CVST after a vaccine than another, we already know what increases the risk of DVT: smoking, high blood pressure, family history of clots, and obesity, among other things. Providers often caution women in these categories against going on hormonal birth control in the first place. The other important distinction between the new complications and those associated with birth control pills is that we know how to treat both DVT and pulmonary embolism.

The danger of comparing the risks by the numbers is that pill users will conflate the two medical issues and draw inaccurate conclusions about their own risk.

We don’t need another “pill scare”

In 1995, the U.K. Committee on Safety of Medicines warned that certain newer formulations of birth control pills presented higher risk of blood clots. The news was widely reported in the media, even as family planning officials expressed fears that this would lead to people dropping birth control altogether, which would, in turn, lead to more unplanned pregnancies. Research proved them right—over the course of the following year, conception rates in the U.K. were 4 to 7 percent higher than expected, and abortion rates were between 3 and 13 percent higher than expected.

The women who were taking the pill in 1995 had likely already been told by their health-care provider that hormonal birth control carried some risk of blood clots, but the information had been delivered in a more personalized and less alarming way. Reading it in a headline must have been shocking if it led to many women to simply stop using contraception. Many of the women who made this decision were likely not even on the brands of the pill included in the announcement.

This came to be known as “the pill scare,” and it could easily happen again.

Risk comparisons won’t work

We are a society of headline readers who often skip the details in favor of fear. Comparisons may seem like an easy way to make abstract risk concepts relatable, but they aren’t particularly useful. Anyone who has ever expressed a fear of flying has undoubtedly been told that they are more likely to die in a car accident. But all it takes is one headline about a plane crash killing everybody on board, and statistical probability becomes meaningless.

The job of those promoting the vaccine has become exponentially harder this week, but those of us who have spent careers promoting correct and consistent contraception use must ask the media to stop trying to help by using the pill as a comparison measure. This can only cause confusion, and possibly unintended pregnancy.