Click Here to learn about our most recent COVID-19 updates including vaccine information, visitor restrictions, testing, and more.

What can we help you find?

Sorry, we couldn't find any content for "{{results_term}}." Try searching again.

COVID-19 Resources

Johnson & Johnson Vaccine Pause: Things You Should Know

Apr. 13, 2021

On April 13, 2021, the U.S. Food & Drug Administration and the Centers for Disease Control and Prevention announced the agencies are reviewing data involving six reported cases of a rare and severe type of blood clot in individuals after receiving the Johnson & Johnson COVID-19 vaccine. More than 6.8 million people have received the vaccine in the U.S. to-date.


Out of an abundance of caution, the agencies recommended a pause in the distribution of the Johnson & Johnson vaccine until that review is complete.

Carl J. Fichtenbaum, MD, professor in the Division of Infectious Diseases in the Department of Internal Medicine at the University of Cincinnati College of Medicine and a UC Health physician, answers some questions about this new development:

1. Why did the FDA halt distribution of the Johnson & Johnson vaccine? 

The FDA recommended a “pause” while they are investigating six reported cases of blood clots that have occurred after vaccination. In these cases, a type of blood clot called cerebral venous sinus thrombosis (CVST) was seen in combination with low levels of blood platelets (thrombocytopenia). All six cases occurred among women between the ages of 18 and 48, and symptoms occurred between six and 13 days after vaccination.

2. Why would a vaccine cause blood clots?

This is what the FDA and CDC will review, but there may be an immune system response that is causing clotting to occur. This is known to happen with other products like heparin.

3. Should I be concerned if I got the Johnson & Johnson vaccine?

Most of the instances of clots occurred in the first few weeks after administration. If you had this vaccine a month ago, the risk is very small. These are very rare events, occurring in 1-in-100,000 to 1-in-250,000 vaccinations.

4. What should I do if I got the Johnson & Johnson vaccine recently? 

There is no need to change your activities or behavior. If you develop any symptoms that are new, contact your doctor.

5. What possible adverse effects should I watch out for?

Unexplained swelling in your leg, tenderness in the calf or thigh, unexplained abdominal pain, headache or mental confusion can all be signs of a blood clot.

6. When should I call a doctor or go to the hospital? 

IF you have a new problem that lasts more than 24 hours and you cannot explain it, that might be a time to contact your doctor. If you are having chest pain, shortness of breath, altered thinking or confusion or a severe headache that won’t go away, you should contact your doctor sooner.

7. What’s the difference between the Johnson & Johnson vaccine and others like Moderna and Pfizer? 

Each vaccine uses a different technology to produce the same result of having your immune system respond. J&J uses a chimpanzee adenovirus that does not cause disease in humans to produce the code needed to make the COVID-19 spike protein. The Moderna and Pfizer vaccines inject the mRNA code wrapped in a lipid envelop that then produces the COVID-19 spike protein.

8. How do we know these vaccines are safe?

Safety is based upon the risks that occur and the benefit gained. And the medical community uses its judgment of what side effects are manageable or not. For example, we know that people who get the vaccine have headaches more frequently in the 1-3 days following vaccination, but that it is usually manageable. 

Sometimes, after any vaccine is approved, there are rare side effects that can be detected. If they only happen with 1 in every 100,000 doses or more, typically it takes a while to discover and understand these issues. For example, if we gave 100 million doses of vaccine X and the rare occurrence of a problem was 1 in 100,000, there would be 1,000 people affected.

This must be balanced by asking: Is the problem manageable? And by giving vaccines, are we protecting people from a dangerous disease? In this case, the answer is yes. COVID-19 is dangerous. More than 562,000 Americans have died and many others hospitalized and very sick. And more still have chronic lingering problems.

The bottom line is that COVID-19 vaccines appear safe. There may be some rare side effects. We need to know more about who might get those and how do we treat them. No intervention is completely without risk. On balance, however, getting a COVID-19 vaccine is much safer than the alternative of getting and spreading COVID-19.