The U.S. CDC and the U.S. FDA have identified six cases in the U.S. of a “rare and severe” type of blood clot, which seems to be linked to the COVID-19 vaccine by Johnson & Johnson.
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The U.S. Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA) have identified six cases in the U.S. of a “rare and severe” type of blood clot, which seems to be linked to the COVID-19 vaccine by Johnson & Johnson.
That is six cases out of more than 6.8 million doses that have been given in the U.S., according to a joint statement from Anne Schuchat, principal deputy director of the CDC and Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research.
The blood clots are cerebral venous sinus thrombosis (CVST), which were observed in combination with low levels of blood platelets (thrombocytopenia). All cases were in women between 18 and 48 years of age. The symptoms occurred six to 13 days after vaccination.
The joint statement notes that treatment for CVST is different than for a typical blood clot. A typical blood clot would be treated with heparin, an anticoagulant, but in this setting, “heparin may be dangerous, and alternative treatments need to be given.”
This follows an ongoing controversy over the AstraZeneca-Oxford vaccine, for rare blood clots. In mid-March, more than a dozen countries suspended deployment of the AstraZeneca-Oxford University vaccine after incidences of blood clots were reported.
Per data received as of March 8, 17 million people in the European Union and United Kingdom had received the vaccine and there had been 15 cases of deep vein thrombosis and 22 cases of pulmonary embolism. Incidences were first reported in Denmark and Norway, who halted distribution, followed by Germany and France and other countries.
Germany’s Health Minister Jens Spahn admitted it was a “very low risk” but would be above average if it were actually linked to the vaccine. The more recent data suggests 222 suspected cases in Europe among 34 million vaccination, with more than 30 deaths.
On March 14, AstraZeneca issued a statement, noting, “A careful review of all available safety data of more than 17 million people vaccinated in the European Union (EU) and UK with COVID-19 Vaccine AstraZeneca has shown no evidence of an increased risk of pulmonary embolism, deep vein thrombosis (DVT) or thrombocytopenia, in any defined age group, gender, batch or in any particular country.” In fact, the company pointed out, “This is much lower than would be expected to occur naturally in a general population of this size and is similar across other licensed COVID-19 vaccines.”
The CDC indicated it will hold a meeting of the Advisory Committee on Immunization Practices (ACIP) tomorrow to review the cases and evaluate their significance.
“Until that process is complete,” the statement said, “we are recommending a pause in the use of this vaccine out of an abundance of caution. This is important, 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.”
They also note that this is “extremely rare.”
European regulators say there have been “four serious cases of unusual blood clots” in Europe, and they are still investigating, although they say that “it is currently not clear” if there is a link between the vaccine and the clots.
Johnson & Johnson said in a statement that in its tracking of side effects identified “a small number of very rare events following vaccination. At present, no clear causal relationship has been established between these rare events and the [J&J] COVID-19 vaccine.”
The CDC and the FDA also recommend that anyone who has received the J&J vaccine who is experiencing severe headache, abdominal pain, leg pain or shortness of breath within three weeks of receiving the shot should contact their health care provider.
The European Medicines Agency (EMA) has reinforced that the benefits of the vaccine outweigh the risks for most people.
“These are very rare side effects,” said Emer Cook, executive director of EMA stated last week. “The risk of mortality from COVID is much greater than the risk of mortality from these side effects.”
Both the J&J and AstraZeneca vaccines use the same technology. They use an adenovirus, a common cold virus, to carry the gene for the COVID-19 virus’s spike protein into the body, where it produces the protein, and the immune system is trained to recognize it. The J&J vaccine utilizes a human adenovirus while the AstraZeneca vaccine uses a chimpanzee version.
At this time, an actual link between the vaccines and the blood clots has not been proven. Nor has a reason for why the vaccines would cause the clots understood, if there is a link.
Behnood Bikdeli, a cardiologist at Brigham and Women’s Hospital in Boston, told Scientific American, “Somebody who gets the vaccine could have a stroke or a heart attack a week later because they were already going to have a stroke or a heart attack. It’s good to be vigilant about these things as we move forward and collect the data, but the absolute number of events and the event rate are so remarkably low.”
At this time, there is not much data defining these types of blood clots in unvaccinated populations, which makes it difficult to know if there’s an actual connection between these rare types of clots and the vaccines, or if it’s merely that there’s an increased awareness of illnesses and unusual symptoms in light of the vaccine rollout.
Scientists are trying to determine what aspect of the vaccine could be causing the clots, and they have theories, but no solid leads. Sabine Eichinger, a hematologist at the Medical University of Vienna, said, “Of course, there are hypotheses: maybe it’s something with the vector, maybe it’s an additive in the vaccine, maybe it’s something in the production process … I don’t know. It could be any of these things.”
The leading theory appears to be an unusual and rare immune response similar to what is called heparin-induced thrombocytopenia (HIT), where the immune system makes antibodies to a complex of heparin and a protein known as platelet factor 4 (PF4). This causes platelets to form dangerous clots throughout the body. Some research has identified that patients with the clots had antibodies to PF4.
The research team out of University of Griefswald was initially calling the reaction in the AstraZeneca cases vaccine-induced prothrombotic immune thrombocytopenia, but have modified it to vaccine-induced immune thrombotic thrombocytopenia (VITT). Their theory is that in each dose of the vaccine, there are about 50 billion virus particles, and some might break apart and release their DNA.
DNA has a negative charge, just like heparin, which might help bind it to PF4, which has a positive charge. That bound complex might trigger the production of antibodies, which could signal the body to increase blood coagulation.
But they also theorize that these patients may have antibodies already present and the vaccines just boost them. More data and analysis will be necessary.
