April 14, 2021

Covering COVID-19 is a daily Poynter briefing of story ideas about the coronavirus and other timely topics for journalists, written by senior faculty Al Tompkins. Sign up here to have it delivered to your inbox every weekday morning.

Journalists should keep some key points high in their mind as the Centers for Disease Control and Prevention meets today to figure out how concerned we should be about six cases of patients who took Johnson & Johnson’s COVID-19 vaccine and developed serious blood clots. That is six cases out of 6.8 million doses administered to date. In other words, one in a million people. It’s rare.

But this is a serious concern. Of these six women, one has died and one is currently hospitalized.

Today, the CDC will convene a meeting of the Advisory Committee on Immunization Practices. Next, the FDA will review the CDC’s analysis. So the pause could last beyond today.

Johnson & Johnson also has delayed its rollout in Europe, which will have a more severe impact there because European countries are already facing a vaccine shortage.

A key now is to narrow the investigation to see which populations may be more at risk; for example, different demographics or people who have underlying conditions.

All six cases occurred among women between the ages of 18 and 48, and symptoms occurred six to 13 days after vaccination, according to a joint statement on Tuesday from Dr. Anne Schuchat, principal deputy director of the CDC, and Dr. Peter Marks, director of the Food and Drug Administration’s Center for Biologics Evaluation and Research.

The symptoms all occurred within three weeks with an average of nine days after vaccinations. A common symptom of patients who developed clots was headaches, which physicians said they feared will set off widespread concerns from every vaccinated person who has a headache. Dr. Marks said he would be more alert to patients who reported severe headaches, low platelet counts and sharp pains in their abdomens.

Dr. Marks says it “is possible we will learn of more cases.” He also said there is no known link yet between the clots and birth control since all of the cases involve women of childbearing age.

The CDC and FDA ordered a “pause” but not a “stoppage” to using the Johnson & Johnson vaccine. That means that physicians could still use the vaccine if they determine for whatever reason that it is best for a patient. Dr. Marks says “this temporary pause” will “hopefully not have any effect” on President Joe Biden’s goals for vaccinating the nation.

Dr. Janet Woodcock, acting commissioner of the FDA, says that the FDA is committed to vaccinations and to patient safety at the same time. “The message to the patients,” she said, “… would continue to be to get vaccines that are available to them because the risks from the pandemic are significant.”

What exactly is under investigation?

This image accompanied a call with the FDA after the CDC and the FDA said Tuesday, April 13, 2021, it was investigating clots and reduced platelet counts in six women, days after receiving the Johnson & Johnson vaccine. On the call were Dr. Peter Marks, director of the FDA Center for Biologics Evaluation and Research, acting FDA commissioner Dr. Janet Woodcock and deputy director of the CDC Dr. Anne Schuchat. (FDA via AP)

The very rare cases under review involve blood clots combined with low levels of blood platelets occurring within two weeks of vaccination.

Symptoms include:

  • shortness of breath
  • chest pain
  • leg swelling
  • persistent abdominal (belly) pain
  • neurological symptoms, including severe and persistent headaches or blurred vision
  • tiny blood spots under the skin beyond the site of injection

The medical words used to describe the blood clot condition are thrombosis, including cerebral venous sinus thrombosis, splanchnic vein thrombosis and arterial thrombosis.

It might be useful to remind yourself of your high school biology class lesson.

Veins carry blood from the body back into the heart. Arteries carry oxygen-rich blood away from the heart to the body. A venous thrombosis means a clot in blood heading back to the heart and an arterial thrombosis is a clot in blood going from the heart to other parts of the body, including major organs.

That said, here is what the CDC and FDA are worried about.

Thrombosis: This is local coagulation or clotting of the blood in a part of the circulatory system.

Cerebral venous sinus thrombosis: As you might imagine, it is related to your brain and sinuses. Johns Hopkins explains, “Cerebral venous sinus thrombosis (CVST) is the presence of a blood clot in the dural venous sinuses, which drain blood from the brain. Symptoms may include headache, abnormal vision, any of the symptoms of stroke such as weakness of the face and limbs on one side of the body, and seizures.”

Splanchnic vein thrombosis: This condition is more connected to abdomen pain. The mesenteric, splenic or portal veins supply blood to the liver. Researchers say you can expect to find this condition in about one to four cases per million people. That is important, because out of 7 million people vaccinated, you could easily expect to find more than the six cases that showed up with clotting problems having nothing to do with the vaccine.

Arterial thrombosis: This is just what it sounds like, a clot in an artery. This kind of clot causes blocked blood flow to the heart or brain and the symptoms include chest pain.

Did the clots show up in the drug trials?

A lab technician looks at a computer screen during research on COVID-19 at Johnson & Johnson subsidiary Janssen Pharmaceutical in Beerse, Belgium, Wednesday, June 17, 2020. (AP Photo/Virginia Mayo)

It may surprise you to know that Johnson & Johnson did get some data on embolic and thrombotic events during the drug trials. But that data didn’t prove much.

In the trials, which involved tens of thousands of volunteers (note this does not include the nearly 7 million who have gotten the vaccines since), 25 people experienced a clotting issue. But, and pay attention to this, 15 of the people who had the issue while participating in the trial got the actual vaccine while 10 got a placebo. This underscores the fact that clotting shows up in everyday life and these results did not establish a causal relationship. (Go to page 7 of this link to see the reference I just mentioned. You can go to pages 46-47 to get the demographic details from the people who suffered clotting issues during the trial. Very few of them fit the young female demographic in question now.)

The CDC is especially concerned about how to treat blood clots that might be associated with a vaccine. In other words, are these clots different in any way?

Dr. Marks said in the Tuesday news conference:

The issue here with these types of blood clots is that if one administers the standard treatments that we as doctors have learned to give for blood clots, one can actually cause tremendous harm or the outcome can be fatal.

One needs to make sure that providers are aware that if they see people who have low blood platelets, or if they see people who have blood clots, they need to inquire about the history of recent vaccination, and then act accordingly.

Let me drill down on that just a little. One reason for the pause, health officials emphasized, is to alert doctors that the usual way of treating blood clots may make things worse if the clot is caused by a vaccine. Usually, a doctor’s first treatment for clots is the drug heparin, but that might not be the best course of action for a vaccine-linked condition.

A second reason for the pause is to try to get an answer for why nearly all of the cases in the U.S. and Europe involve women under age 50. Do the patients with CVST have anything else in common, including an underlying health condition?

Is the Johnson & Johnson issue connected to concerns over the AstraZeneca vaccine?

A nurse holds vials of AstraZeneca vaccine against COVID-19 during a vaccination campaign at WiZink indoor arena in Madrid, Spain, Friday, April 9, 2021. (AP Photo/Manu Fernandez)

In the days ahead, you will hear medical experts talk about something called a “class effect.” By that, they mean a classification of vaccines that are produced in a similar way.

The Johnson & Johnson vaccine is an adenovirus vector vaccine — the same type as AstraZeneca’s vaccine, which also is under investigation for similar problems. At least 222 suspected clotting cases have been reported among the 34 million people who have received the vaccine, according to a report in the journal Science.

The AstraZeneca vaccine is not approved for use in the United States but it is widely used in Europe.

European researchers have been studying clotting reports for weeks. This is one of the detailed investigations from Norway that involved five health care workers, including four women, one of whom died. All received the AstraZeneca vaccine, but there is no direct proof that the vaccine caused the clotting problems.

In the Tuesday morning news conference, Dr. Marks would not address whether there is a “class effect” at play here but said what everybody was thinking: “I think it is plainly obvious to us already that what we’re seeing with the (Johnson & Johnson) vaccine looks very similar to what was being seen with the AstraZeneca vaccine.”

The CDC explains, “Viral vector vaccines use a modified version of a different virus (the vector) to deliver important instructions to our cells.”

The CDC explains the three-part process that vector vaccines go through to produce antibodies in your body:

  1. First, the vector (not the virus that causes COVID-19, but a different, harmless virus) will enter a cell in our body and then use the cell’s machinery to produce a harmless piece of the virus that causes COVID-19. This piece is known as a spike protein and it is only found on the surface of the virus that causes COVID-19.
  2. Next, the cell displays the spike protein on its surface, and our immune system recognizes it doesn’t belong there. This triggers our immune system to begin producing antibodies and activating other immune cells to fight off what it thinks is an infection.
  3. At the end of the process, our bodies have learned how to protect us against future infection with the virus that causes COVID-19. The benefit is that we get this protection from a vaccine, without ever having to risk the serious consequences of getting sick with COVID-19. Any temporary discomfort experienced after getting the vaccine is a natural part of the process and an indication that the vaccine is working.


There are two other important points. Vector vaccines do not inject the COVID-19 virus into your system and they do not affect a patient’s DNA, both of which have become widespread social media rumors.

The vaccines not affected by this pause are produced by Moderna and Pfizer and they involve mRNA technology, which is quite different. The Russian vaccine, Sputnik V, is also a vector vaccine. It will be worth watching to see if the Russian medical authorities take any precautionary steps.

What happens now?

Both Pfizer and Moderna announced Tuesday that they would step up their production and be able to meet America’s vaccine needs even without Johnson & Johnson, if it comes to that.

This afternoon, the CDC’s Advisory Committee on Immunization Practices will look over the data and could make a number of suggestions, including:

  • Stop using the Johnson & Johnson vaccine
  • Resume using the Johnson & Johnson vaccine but impose restrictions on who should get it, which is what several European countries have done
  • Resume unrestricted use of the Johnson & Johnson vaccine by declaring it to be safe

The Food and Drug Administration will take the panel’s recommendations under consideration and determine the next steps.

Will pausing the vaccine increase hesitancy?

I like what Dr. Carlos Del Rio told CNN:

So what it means to people at this point in time is I think you’re likely going to be OK. … Don’t freak out. I would be going on with my life, but I would be very attuned to my body. If I develop shortness of breath, if I develop leg pain, if I develop a headache, and I’m within two to three weeks of having had the Johnson & Johnson vaccine, I would immediately notify my healthcare provider.

Dr. Leana Wen, who you see on cable TV pretty often, says this pause could prove to be reassuring to the public if it is portrayed as transparent caution to be sure the vaccines are safe. Dr. Wen writes:

In the meantime, this is what I am telling my patients — and myself: The incidence of CVST is extremely low. People who are within three weeks of having received the Johnson & Johnson vaccine should call their doctor if they have a severe headache, shortness of breath, abdominal pain or one-sided leg or arm swelling.

Those who received the Pfizer or Moderna vaccines should not be concerned, and those who have not yet been inoculated should still sign up to be vaccinated as soon as possible. The most important takeaway remains that covid-19 is a major health threat that’s claiming hundreds of lives every day in the United States, and the carefully and thoroughly vetted vaccines we have remain our best and only way out of the pandemic.

We’ll be back tomorrow with a new edition of Covering COVID-19. Are you subscribed? Sign up here to get it delivered right to your inbox.

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Al Tompkins is one of America's most requested broadcast journalism and multimedia teachers and coaches. After nearly 30 years working as a reporter, photojournalist, producer,…
Al Tompkins

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