"I think this is an unusual occurrence of a serious adverse event that you want to make sure before you go forward you investigate it thoroughly," chief medical advisor Dr. Anthony Fauci said while taking the podium at the White House Press briefing Tuesday.
Out of nearly seven million shots given, six people developed a serious blood clot condition. One person died and one is still in critical condition. The six were all women between the ages of 18 to 48 and symptoms started within two weeks after vaccination.
Many experts are saying that while this is a very small number of incidents, it's still good to pause and investigate.
Doctor Pascal Jabbour is a vascular neuro-surgeon at Jefferson Health. He says it is too soon to tell if the vaccine is to blame, but explains the type of clot reported is unusual. It's called a cerebral venous sinus thrombosis, or CVST.
It's different than a clot associated with a stroke. That's in an artery of the brain; this is in a vein.
"So there is a problem with the blood leaving the brain and what happens is this can cause some brain swelling, it can cause blurry vision, it can cause seizures," said Dr. Jabbour.
In the reported cases, it was combined with low platelets. Platelets help to stop bleeding.
Dr. Jabbour says this combination makes treating the condition challenging.
"It puts the patient at the opposite spectrum which is bleeding and forming clots," he said.
He says traditional treatment of a blood clot would be blood thinners, but giving a blood thinner in this case could be very dangerous.
That is why the CDC is working to get the message out to healthcare providers so they know how to treat this condition if detected.
In the meantime, patients who recently received the shot should watch for severe headache, abdominal pain, leg pain or shortness of breath and reach out to your healthcare provider if you experience these symptoms.
And for more perspective, these cases, although serious, are less than one in a million.
But for patients hospitalized with COVID-19, 16% experienced some sort of blood clot. No similar incidents have been reported with the Pfizer or Moderna vaccines.