From the desk of Dr. Domenic Zambuto M.D.

Our understanding about COVID-19 infections continues to grow and evolve. The same is true about the vaccines available that help prevent COVID-19 infections. What we do know is that besides the respiratory issue that can be severe and life threatening COVID-19 infections are associated with a significant increase risk of developing blood clots. Patients with varicose veins already have a known increased risk for blood clots, adding a COVID infection to this further increases the risk for developing blood clots.

Why increased clots with COVID-19 infections?

It appears there are several factors that contribute to the increased risk of developing blood clots with COVID-19 infections. COVID-19 infections can cause a severe inflammatory response in some people. Severe inflammation can trigger the clotting system to activate. Inflammation is a normal part of our defense/healing mechanisms.

When we are injured or have a local infection, inflammation brings in numerous factors that help us heal. Certain injuries require clotting as part of the healing process. When there is severe inflammation clotting can get over activated and clots will form that are harmful. This is seen in some cases of severe COVID-19 infections.

From what we know now this is an important part of the increased clotting seen in COVID-19 infections. Other severe infection (with bacteria and viruses) also trigger increased clotting as a result of inflammation but severe COVID-19 infections are much more likely to have clotting which is why other additional factors are felt to be involved. The clotting is seen both in arteries and in veins. In veins blood flow is slower making clotting more likely in general.

Patients who are severely ill from COVID-19 infections tend to be less active and less mobile. Immobility also increases the risk of developing blood clots in our veins. While most of the increased clotting is seen in severe infections it is not completely limited to that group of patients alone.

The good news is that vaccines are reducing the occurrence of severe infections which reduces the risk of COVID-19 related blood clots. The other good news is that better early treatments of COVID infections is also reducing the worsening of COVID infections which leads to fewer severely ill patients and all the subsequent complications (including blood clots).

COVID-19 Vaccinations and Blood Clots

There has been recent news both from Europe and the United states that raises the concern of blood clots in people after receiving COVID-19 Vaccinations. The good news is that the two most common vaccines used in the United States (the Pfizer and the Moderna vaccines) have not been found to have a high risk of clots. So far hundreds of millions of doses of these two vaccines have already been given in the United States.

Blood clots have been reported in a small number of patients after receiving the AstraZeneca vaccine in Europe and the Johnson and Johnson vaccine in the United States.

Given the large number of vaccines it appears that the risk for these clots is very low.

Both of these vaccines work differently than the Pfizer and Moderna vaccines. The Pfizer and Moderna vaccines use messenger RNA delivered to the cell in a vaccinated person from a lipid(fatty) membrane. The cells then make a protein encoded by the messenger RNA and it is that specific protein that triggers an immune response that is protective for COVID-19 infections. The Astra Zeneca and the Johnson and Johnson vaccines work differently.

• Both vaccines are viral vector vaccines.

• Both use a modified cold (adeno) virus to carry genetic material to the cell in a vaccinated person. The cell then makes the encoded protein and this generates an immune response resulting in immunity to the COVID-19 virus. These viral vector vaccines are made from cell cultures.

One researcher in Germany, who is a blood expert, believes these viral vector vaccines cause an auto-immune response that leads to the blood clots.

Dr. Andreas Greinacher believes that the many (his lab has identified over 1000 in the Astra Zeneca vaccine) trace proteins in these viral vector vaccines perhaps in combination with a preservative used with the vaccine produce compounds that induce this problematic immune response that leads to the clotting disorder. More research is needed.

What is clear is that the abnormal clotting response related to these two vaccines is very rare and seems more likely to happen in younger women. Further study of this is ongoing. We do know that COVID-19 infection is far more dangerous than the rare chance of complications from these vaccines.

If you have any questions about the Covid-19 Vaccine please reach out to your primary care doctor or learn more by visiting The Centers for Disease Control and Prevention.