Since the CDC lifted its pause on the Johnson & Johnson vaccine over cases of rare but potentially deadly blood clots linked to the shots, two more cases have been reported, including the first in a male patient.
The agency’s panel of experts investigated 15 cases of blood clots, all in women aged 18-48, and concluded that "there is likely an association but the risk is very low,” according to CDC Director Rochelle Walensky.
While experts believe there may be a link, it is not clear yet what might be causing it.
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“We have a small signal that it seems to be more in the young, more in females,” said Dr. Panagis Galiatsatos, Director of the Tobacco Treatment Clinic and Assistant Professor of Medicine at the Johns Hopkins School of Medicine. “But we have to keep in mind it’s a small sample - 15 cases - it’s hard to create a generalization based off of that.”
AstraZeneca’s COVID-19 vaccine has also been linked to cases of blood clots, and Galiatsatos says there may be some connection.
Both AstraZeneca and Johnson & Johnson’s vaccines use a similar technology known as a “viral vector.”
“So then it does take us a moment to take a step back and try to understand: what is unique about that vaccine that can result in this? Even though it is rare, we can at least try to figure out what part of the vaccine can cause it.”
Galiatsatos says this viral vector technology has been around for many years and used in other treatments before the COVID-19 pandemic without these issues, but all connections between the clots and the vaccines should be explored.