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The Johnson & Johnson vaccine, prized for being delivered in one dose, is undergoing investigation for the potential that it may — in very rare circumstances — cause blood clots. Here’s what you need to know:

1. Nearly 7 million Johnson & Johnson vaccines have been delivered in the United States.

2. Six women ages 18 — 48 experienced unusual blood clots originating in veins that drain blood from the brain. And, unfortunately, one has died.

3. As a result of this very serious finding, the government has halted use of this vaccine until more information is known.

4. In all six cases, the condition happened between 6 and 13 days after vaccination.

5. The condition is extraordinarily rare. Fewer than one in one million people are affected. SVMC has given about 2,000 Johnson & Johnson vaccines. Statistically speaking, we would likely need to give 500 times that many to encounter a blood clotting issue among one of our patients.

6. Those affected also had low platelet counts. Platelets are the part of the blood that helps blood clot and stops bleeding. This is counterintuitive, as you would expect someone with a clotting issue to have high platelet counts. Scientists are working intently to discover the issue.

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7. The AstraZeneca vaccine, which is not yet approved in the United States, was produced using the same technology and has also been connected to unusual clots in very rare cases in Europe. Patients were sometimes diagnosed with a similar condition (TTP or thrombotic thrombocytopenia purpura) associated with receiving Astra Zeneca vaccine.

8. Doctors are learning how to treat this unique clotting condition now. Treating this problem differs from treatment of other kinds of blood clots.

9. If you received the Johnson & Johnson vaccine, there are no recommendations at this time to stop certain medications or pursue any treatment.

10. If you experience severe headache often with visual changes, leg swelling or pain, chest pain, skin eruption of purpura, or shortness of breath within 2 weeks after receiving the shot, contact your healthcare provider.

11. As directed, neither SVMC nor the State of Vermont are giving Johnson & Johnson vaccines at this time. There are no Johnson & Johnson vaccines scheduled at SVMC clinics, and there is no need to reschedule. The state of Vermont is reaching out to residents scheduled to receive Johnson & Johnson vaccines this week and offering them Moderna vaccinations.

12. There is a potential that the use of Johnson & Johnson vaccines will resume once scientists have defined the risk factors. For instance, Johnson & Johnson may be used for older adults, where the risk of this type of clot is even lower than it is for younger people.

If you have questions not addressed here, please e-mail them to We will answer them directly or in an upcoming e-newsletter.

Marie George, MD, is an infectious disease specialist at Southwestern Vermont Medical Center in Bennington.


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