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Citing an “abundance of caution,” federal health officials called for a pause in the use of the Johnson & Johnson vaccine Tuesday, following concerns that the vaccine may be linked to a rare but severe type of blood clotting.

The concerns stem from six reported cases of the blood clot in the United States. All of the cases were reported in women under the age of 50. Nearly 7 million doses of the Johnson & Johnson vaccine have been administered in the United States. That means the blood clotting was reported in about 1 in 1.1 million vaccinations.

Some women quickly noted that those rates are far lower than that of some hormonal contraceptives, which also carry risks of blood clotting.

The comparisons were intended to highlight the fact that the risks of blood clotting with the vaccine were significantly lower than widely used birth control pills.

Jen Villavicencio, an obstetrician-gynecologist and family planning fellow at the American College of Obstetricians and Gynecologists, cautioned against drawing any kind of comparison between birth control medication and the Johnson & Johnson vaccine.

“It’s comparing apples and cashews,” said Villavicencio. She emphasized that the concern with the Johnson & Johnson vaccine is that it could be connected to a blood clot syndrome, rather than the singular blood-clotting episodes that can happen with other medications.

“We’re talking about a vaccine during a pandemic that’s being administered to millions of people under an emergency-use authorization, versus hormonal birth control, which has decades and decades and decades of science and safety data behind it, and very well-known risks associated with it that are known by all of the providers who would prescribe it,” she added.

Villavicencio noted that typically, a provider can screen patients for risk factors and determine the right birth control for them. Villavicencio placed the risk of getting a blood clot from hormonal birth control at “1 to 5 in 10,000,” adding that people typically weigh this risk against a far greater concern: an unintended pregnancy. A 2018 study from the Centers for Disease Control and Prevention found that 12.6 percent of all women ages 15 to 49 use oral contraceptives.

She understands why some people may be alarmed by the possible connection between the Johnson & Johnson vaccine and severe blood clotting. We are getting a “front row seat of the scientific method,” she said, which involves asking questions, recalibrating advice, dealing with unknowns and taking in new data. All of that can be distressing, she added.

It “feels like a whiplash sometimes: ‘Get the vaccine, but now we’re pulling the vaccine back,’ ” she said.

To Sarah Hill, a research professor and author of “This Is Your Brain on Birth Control,” the move to pause and review the vaccine highlights deeper issues with how the medical community treats women.

“We’re not calculating risk the same way with the vaccine as we are with birth control,” Hill said. “In some ways, I think that this is evidence of how cavalier we are about birth control and its impact on women’s health.”

The women who reported blood clots developed symptoms six to 13 days after getting vaccinated, according to the CDC and the Food and Drug Administration, though officials say there is not yet a definite explanation for the clots. Three additional cases of reported blood clotting that may be linked to the Johnson & Johnson vaccine are being investigated in Europe.

The reported clots are rare in their severity and because they may require different treatment from other kinds of blood clots. Federal officials said symptoms include severe headache, abdominal pain, leg pain or shortness of breath within three weeks of being vaccinated. The pause in reviewing the Johnson & Johnson vaccine is in part to “ensure that the health care 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,” the CDC said.

Peter Marks, a top vaccine official at the FDA, said there was no clear link between hormonal birth control and the six Johnson & Johnson blood clot cases, noting that the normal rate of brain blood clots in the general population was 2 to 14 per million people a year.

For now, Hill encourages women to think about any potential risk of the vaccine “holistically.”

While the blood clots themselves are more severe, the likelihood of getting one remains far lower than what has been “deemed to be acceptable” for other frequently used and prescribed medications, including hormonal birth control, she said.

The bottom line, she says, is that no matter the treatment, women deserve to have more information and attention on what their health risks are at difference phases of their lives. Part of the problem is that a substantial amount of medical research still treats women as though they’re “small men,” said Hill, noting that women’s bodies can go through “major physiological changes in response to our [menstrual] cycles alone.”

She pointed to other side effects that women have experienced after the vaccine, including worsening or irregular periods. And, as the Johns Hopkins School of Medicine notes, getting a coronavirus vaccine has also led to “false positives” on mammograms because of the way vaccinations can temporarily enlarge lymph nodes.

“It’s complicated because our bodies change a lot,” Hill said. “But that doesn’t mean that it’s not necessary to study them.”

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