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Do COVID-19 Vaccines Cause Blood Clots?

Why do some people think that COVID-19 vaccines cause blood clots?

In addition to rare reports of patients developing blood clots after receiving the AstraZeneca/Oxford COVID-19 vaccine, there are now some reports of similar clots after the Johnson & Johnson vaccine.

Do COVID-19 Vaccines Cause Blood Clots?

The reports of six cases of blood clots following the Johnson & Johnson vaccine, including one that was fatal, has led the CDC and FDA to recommend a pause in giving this vaccine. That’s after seven million doses of this vaccine have been administered in the United States.

An emergency ACIP meeting will review safety data about the Johnson & Johnson vaccine.
The pause allows ACIP to review all of the safety data about these blood clots. And time to update educational materials, as the treatment for these types of blood clots is different than other blood clots.

There is also a report from the European Medicines Agency safety committee (PRAC) which concluded that “unusual blood clots with low blood platelets should be listed as very rare side effects of” the AstraZeneca/Oxford COVID-19 vaccine, a vaccine that is not yet approved in the United States.

So does that mean that COVID-19 vaccines cause blood clots?

Well, no.

First, understand that only these two COVID-19 vaccines which use similar technology are being investigated. No extra risk of blood clots has been found with the mRNA COVID-19 vaccines from Pfizer and Moderna.

Also, experts still aren’t exactly sure if the vaccines are causing the blood clots, although the pattern of low platelet counts and clots in patients receiving either vaccine is suspicious enough to be considered a signal for further investigation.

“The Committee carried out an in-depth review of 62 cases of cerebral venous sinus thrombosis and 24 cases of splanchnic vein thrombosis reported in the EU drug safety database (EudraVigilance) as of 22 March 2021, 18 of which were fatal. The cases came mainly from spontaneous reporting systems of the EEA and the UK, where around 25 million people had received the vaccine.”

AstraZeneca’s COVID-19 vaccine: EMA finds possible link to very rare cases of unusual blood clots with low blood platelets

And even if they do, it appears to be a very rare reaction.

“A key consideration will be whether there have been more cases of adverse events than would have been expected without vaccination.”

Does the AstraZeneca COVID-19 vaccine really cause blood clots?

Overall, there have not even been more cases of blood clots in folks getting one of these COVID-19 vaccines.

“Overall, the number of cases of embolic and thrombotic events after vaccination reported to EudraVigilance (see section 3) in relation to the number of people vaccinated was lower than the rate of such events in the general population.”

COVID-19 vaccine safety update

But there is an increase in people under age 55.

“In the reported cases, including some that resulted in death, these events occurred within 14 days after vaccination. They occurred mostly in people under 55 years of age, the majority of whom were women. However, these patient characteristics could reflect the higher proportion of such individuals offered Vaxzevria in vaccination campaigns. As part of the preliminary assessment, the number of cases reported were compared to rates for these events applicable to the general EU population before the SARS-Cov-2 pandemic. This comparison showed increased numbers in vaccinated people. Such imbalances in numbers of cases between the general and vaccinated populations were not visible for the older age groups.”

COVID-19 vaccine safety update

One of the most important things to understand about all of this?

“This is a recommendation and it’s not a mandate. It’s out of an abundance of caution. We’re recommending that the vaccine be paused in terms of its administration. However, if an individual health care provider has a conversation with an individual patient and they determined that the benefit-risk for that individual patient is appropriate, we’re not going to stop that provider from administering the vaccine, because it could be right in many cases, that benefit-risk will be beneficial overall to that individual in the large majority of cases.”

Peter Marks, MD, PhD

The risk of getting one of these blood clots is extremely low and you typically have a much greater risk of blood clots if you get COVID-19!

And fortunately, at least in the United States, there are plenty of mRNA vaccines that folks can get while the Johnson & Johnson vaccine is under this pause.

More on COVID-19 and Blood Clots

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