The J&J Vaccine for COVID-19: What to Know

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woman with face mask getting vaccinated for covid-19 at a clinic with other people waiting their turn
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The U.S. Food and Drug Administration (FDA) authorized the single-shot Johnson and Johnson (J&J) COVID-19 vaccine February 27, 2021. More than 7 million of the tens of millions of people who have been fully vaccinated against COVID-19 in the United States received the J&J vaccine.

However, on April 13, 2021, the FDA and the Centers for Disease Control and Prevention (CDC) announced that six women between the ages of 18 and 48 had a serious reaction, likely tied to the J&J vaccine, involving blood clots in a vital area of the brain. The disorder is called CVST, or cerebral venous sinus thrombosis. Think of the cavernous sinus as a major crossroads inside the brain. If a blood clot forms there can be very serious neurologic consequences. The FDA and CDC announced a “pause” in administering the J&J COVID-19 vaccine while they research the cases.

The FDA and CDC are not prohibiting use of the J&J vaccine, leaving the decision between doctor and patient, though most people are vaccinated at locations other than their physician’s offices. Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, stated the main reason for the pause was to give public officials time to alert medical professionals on how to treat the condition, as it requires a different approach than other serious blood clots. Here’s what to know about the J&J vaccine.

How the J&J COVID-19 Vaccine Was Made

The J&J vaccine is a “viral vector vaccine.” It delivers a harmless version of a different virus—that’s the vector—containing a genetic code that makes part of a COVID-19 virus protein. When injected into your arm, the vaccine teaches your body to recognize and fight the virus if you are exposed to it later on. A COVID-19 vaccine made by AstraZeneca, which has been in use in other countries, uses a similar vector approach. The AstraZeneca vaccine is also linked to similar cases of blood clots, primarily in women under 60. Experts theorize the clots are a reaction to this particular form of vaccine.

The Moderna and Pfizer-BioNTech vaccines use a different vaccine technology known as mRNA. The vaccines contain the genetic code of a COVID-19 virus protein, but the code is in mRNA molecules instead of a viral vector. Your body makes the protein and, like with the viral vector, this triggers an immune response that protects you from getting COVID.

All vaccines help the body create cells with “memory” of how to fight a particular virus in the future, and none of the vaccines in the U.S. can give you COVID-19.

The Blood Clots That Are Causing Concern

Like all vaccines, the J&J version was investigated thoroughly for safety before emergency approval by the FDA. During the trials, experts studied the vaccine’s effects in a double-blind, placebo-controlled trial in some 40,000 people. The most common reactions were mild to moderate pain at the injection site, headache, fatigue, and muscle pain, most commonly in people under 60. There was one serious reaction of hypersensitivity, one case of CVST in a 25-year-old man, and one case of another kind of serious clotting disorder in a 59-year-old woman.

Since J&J vaccinations began in late February, six women who got the vaccine developed CVST in combination with a low platelet count, or thrombocytopenia. The women developed the symptoms 6 to 13 days after being vaccinated. One woman died, and one was in critical condition, as of April 13th.

Typically, about five people in a million develop CVST each year, not related to the vaccine. It is a rare form of stroke that occurs when a blood clot (thrombus) prevents blood from draining out of the brain. The blood cells can rupture, leaking blood into the brain tissue. Platelet cells are instrumental in helping blood clot when we cut ourselves or have an injury that bleeds; but, even with a low platelet count, clotting can still occur.

In the case of the AstraZeneca vaccine, researchers identified a protein, known as the platelet factor 4 (PF4) antibody, in patients who developed CVST and thrombocytopenia. The antibody was already known to cause an autoimmune clotting disorder in some people who were given the blood thinner heparin and developed a CVST. The symptoms can also occur in people who are not given heparin. The researchers suspect the PF4 antibody is linked to CVST and low platelet counts in the vaccine recipients.

Treating CVST and Thrombocytopenia vs. Blood Clots Alone

Heparin is a standard treatment for blood clots to thin the blood and help prevent new clots. However, an important note is that heparin is very dangerous and may be fatal when administered to patients with CVST combined with low platelet count.

Because CVST is so rare, public health officials are working to get the word to physicians and healthcare workers: If they have a patient who received the J&J vaccine and shows CVST or other blood clot symptoms, they should administer blood thinners other than heparin, as well as intravenous immune globulin.

The main symptoms of CVST are:

  • Severe headache

There are no confirmed risk factors for developing CVST to date, but experts hypothesize it may be an autoimmune response to the vaccine. If you received the J&J vaccine and develop these symptoms, which typically develop within three weeks after vaccination, you should contact your healthcare provider immediately or seek emergency care.

Weighing the Risks and Benefits of the J&J Vaccine

If you are scheduled to receive the J&J vaccine, consider talking with your doctor about the pros and cons specific to your situation. The J&J vaccine is highly effective at preventing COVID-19 and only involves one injection. Many public health experts believe these benefits of the J&J vaccine and its role in generating herd immunity outweigh the potential risk of CVST with thrombocytopenia.

Based on the number of people who received the J&J vaccine, CVST is extremely rare but it is possible. It is also possible that more cases may turn up upon additional investigations. The FDA and CDC have said they will move quickly to assess the J&J cases and keep the public informed. If you want to be vaccinated now, before J&J vaccinations resume, you can reschedule your appointment to receive one of the mRNA vaccines instead.

With virtually any medical treatment, there is some degree of risk of side effects. When the polio vaccine was introduced in the 1950’s, saving countless children’s lives, there were manufacturing complications that led to children contracting polio from the vaccine. The vaccination drive was paused. The problems were cleared up, the vaccine program continued, and polio was eradicated from the United States as of 1979.

The COVID-19 pandemic can be ended if enough people get vaccinated, protecting your health and the health of your family and community.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Apr 14
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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