Understanding Links Between COVID-19, Vaccines, and Thrombosis

This video was originally published on sister publication HCPLive.

Right now, the Advisory Committee on Immunization Practices (ACIP) is convening an emergency meeting to discuss adverse events that recently led to thrombotic events in 6 women administered the Johnson & Johnson COVID-19 vaccine in the US.

The committee, meeting following the federal pause of Johnson & Johnson vaccine distribution by the US Food and Drug Administration (FDA), is addressing the matter of cerebral venous thrombosis risk among women aged 18-49 vaccinated with the one-shot prophylaxis.

But what is this concerning side effect—and what is its link to both COVID-19 and adenovirus-based vaccines designed to prevent the pandemic virus?

In an interview with sister publication HCPLive, Maja Zaric, MD, interventional cardiologist and assistant professor at Zucker Medical School, discussed the risk of thrombotic events now observed in a pair of adenovirus-based COVID-19 vaccines: that from Johnson & Johnson, as well as AstraZeneca.

Per Zaric, the chimpanzee-based adenovirus vector is made inactive, made unable to replicate, and is therefore doses in “large amounts” to vaccinated persons.

“Each vaccine carries somewhere over 50 billion particles,” Zaric explained. “This is a massive amount of adenovirus that has to be injected because it doesn’t replicate in order to achieve the effectiveness.”

What’s being observed in affected patients is the development of PF4 factor antibodies, which inhibits platelet development—a pathology similar to heparin-induced thrombosis (HIT).

“What happens is there is an abrupt cascade of clotting activated in the venous system that is not typically seen in COVID patients, but broader in the vaccine reaction,” Zaric explained.

This commonly occurs in the patient’s brain or cut systems. Symptoms have occurred up to 2 weeks following vaccination—far beyond the standard local site and symptomatic reactions anticipated with COVID-19 vaccines—and include headache, blurry vision, swelling, high temperatures, and shortness of breath.”

Mortality risk with cerebral venous thrombosis is up to 25%, Zaric said.

“The condition rapidly develops and consumes large amounts of coagulation factors and platelets, therefore causing simultaneous clotting,” she explained. “It can be treated early on, when diagnosed."

“We’re just starting to pick and recognize these cases in the US,” Zaric added. “I would be alert on those folks who get the vaccination over the next 2-3 weeks.”