Dr. Aaron S. Weinberg
What are blood clots?
- “Common” blood clots are traditionally referred to as deep vein thrombosis (DVTs) and Pulmonary Embolism (PE). Typically, the blood clots form in the legs as DVTs and then break off and travel to the lungs where they are called PEs. When they reach the lungs, they plug up the blood vessels and can cause low oxygen levels, trouble breathing, and even heart failure, and death. There are many different conditions that can lead to the formation of these blood clots. This is a common condition with over 1 million cases per year in the US and over 100,000 deaths making it the 3rd leading cause of cardiovascular death behind heart attacks and strokes.
Does COVID-19 disease increase a person’s chances of “common” blood clots?
- Yes! Physicians have been alarmed by the rates of DVTs and PEs during the COVID-19 pandemic and the disease significantly increases a person’s chances of developing this condition. A patient has a 1 in 5 (1 in 3 if you end up in the ICU) chance of developing a blood clot when you are hospitalized with COVID-19 infection.
Do the current COVID-19 vaccines on the market increase a person’s chances of developing the traditional and common PEs/DVTs?
- No. Your chances of developing traditional blood clots does not seem to be increased by the vaccines and your true risk is due to whatever underlying factors you have regardless of a vaccine.
- In the phase 3 clinical trial data, there were 11 cases of blood clots in the vaccine group and 3 cases in the placebo group, which was on par with what would be expected in the general population and was too small of a number to determine whether the additional few cases in the vaccine group was due to a causal association with vaccination or due to chance alone. In fact, real-world data post-vaccination seems to indicate that there does not appear to be an association between the vaccine and traditional thromboembolic disorders (DVT and PE) in healthy patients overall, since the total rate of thromboembolic events following vaccination is lower right now than what is expected when we consider the usual rate of such blood clots in the general population.
- In summary, vaccines do not seem to increase your chances of having a traditional DVT or PE however, if you do develop covid-19 disease then your chances of developing such blood clots will increase significantly.
What kind of blood clots might be associated with the J&J and AstraZeneca vaccines?
- Interestingly the two vaccines receiving the attention and possible association between blood clots and vaccines are the two viral vector vaccines. We do not know whether this is a coincidence and whether we will see a similar issue with the mRNA vaccines or whether it is something specific to the viral vector technology or process that may increase such risk in certain rare individuals.
- What is catching the attention of authorities is not an increased risk of typical DVT or PE blood clots but rather a very rare clinical syndrome that may be occurring in a select few patients who may be genetically susceptible. This syndrome which has been coined “vaccine induced immune thrombotic thrombocytopenia (VITT)” results in blood clots in more unusual locations of the body, such as the veins in the brain (cerebral venous thrombosis), the veins of the abdomen, in addition to the legs and lungs. These patients also tend to have low levels of platelets, which are the cells that help the body form clots and are noticeably lower because they are being consumed by the clotting process.
What causes VITT (vaccine induced immune thrombotic thrombocytopenia)?
- Scientists believe it may be linked to a very rare autoimmune process in a minority of genetically susceptible individuals. The reason they think this is because they have discovered elevated levels of autoantibodies (antibodies are the body’s immune proteins that fight infection) which target platelet factor 4 (PF4) antigen which are on a person’s platelets or “clotting cells”. The vaccine in very rare cases may cause a person to develop these antibodies which attack ones-own clotting system causing the clotting cascade and clinical problems.
How is it treated?
- With early recognition and by seeking medical attention, the condition is potentially treatable with blood thinners and intravenous immune globulin therapy.
What are the signs and symptoms of VITT?
- People should be aware that if they experience unabating severe headaches, new neurologic symptoms, vision changes, seizures, abdominal pain, nausea/vomiting, petechial rash, new unusually easy bruising/bleeding, leg pain or swelling, chest/back pain, or shortness of breath, they should seek immediate medical attention.
What are some of the normal symptoms a person experiences after a covid vaccine?
- Fever/chills, fatigue, headache, or muscle/joint aches that occur 24 to 36 hours after getting the vaccine are normal and resolve quickly unlike with VITT which typically lasts much longer in duration and the onset is also later.
When does VITT typically occur?
- This condition typically appears within two weeks of receiving the vaccine. However, it can occur any time within 3 weeks after receiving the vaccine.
Have we seen a condition similar to VITT before in other areas of medicine?
- Yes. We have seen a similar process develop in response to a commonly used blood thinner called Heparin. In this condition patients also develop auto-antibodies in response to the medication in addition to clots in unusual places and low platelets. This condition is known as autoimmune heparin-induced thrombocytopenia (or “HIT”). This is also a rare condition, and we still use this medication regularly on a daily basis in every hospital around the world since the benefit outweighs the risk.
Who seems to be most susceptible?
- Again, this is very very rare! However, we have seen this mainly among females <50 years old within the first two weeks of vaccine receipt (can be any time within 3 weeks post-vaccine).
How many people have had VITT so far?
- Astrazeneca Vaccine: Among approximately 34 million vaccine recipients in the United Kingdom and European Economic Area, there were 169 cases of cerebral venous sinus clots and 53 cases of splanchnic vein clots reported.
- J&J Vaccine: Nearly 8 million doses have been administered in the United States to date with only 15 cases of clots at unusual sites in the setting of low platelets and three of these cases resulted in unfortunate death.
If I received a J&J vaccine should I do anything special?
- No. The risk of forming blood clots from a vaccine is extremely low. Just be aware of the symptoms of blood clots (see FAQ question “What are the signs and symptoms of VITT?) and if you do experience any of these within 3 weeks post-vaccination, please contact a medical professional right away.
What are the regulatory authorities saying about this condition?
- After investigating and extensively reviewing the data on these cases, medical licensing authorities in Europe and the United States have concluded that the benefits of these vaccines far outweigh this very rare risk. Unfortunately, with almost every therapy on the market there is that very rare serious side effect which can sometimes even result in death however the chances of experiencing that are extremely rare. The US CDC/FDA has recommended resuming the J&J vaccine and has placed a warning of the possible very rare blood clotting syndrome association. The regulatory bodies will continue to monitor the situation and provider any further recommendations as they become available.
Putting it in perspective:
- You have a 1 in 100 chance of being hospitalized from COVID-19 infection if you catch the virus
- If you are hospitalized with COVID you have a 1 in 5 (1 in 3 if you are in the ICU) chance of developing a blood clot (DVT or PE) when you are hospitalized with COVID from the infection and the body's response to the virus.
- You have less than a 1 in one million chance of developing vaccine induced immune thrombotic thrombocytopenia (VITT)
- According to the world health organization (WHO) the probability of getting a blood clot from the Janssen vaccine is 0.000088% (your risk of getting a blood clot from COVID-19 infection is on average 20-30% higher)
- J&J vaccines that have been given to date have likely according to statistical modeling resulted in saving 120,000 lives that may have been otherwise lost due to COVID-19 infection
- COVID-19 infection and its medical consequences are far riskier in terms of one’s safety and health than any risk posed by the vaccines. The medical community is recommending and encouraging patients to get vaccinated with any vaccine that is available.
- However, women <50 years of age should be aware of this rare risk and that there are other COVID-19 vaccine options available (Pfizer and Moderna) for which the risk has not been seen.
Link to blog article we published: