Thread by @ArmstrongDrew

What's causing the blood clots? FDA's Peter Marks says this is just a theory, but that it could be an immune response that occurs very rarely after vaccination, causing activation of blood platelets.

Presser available live here:

Woodcock says FDA/CDC have done an extensive review of the reported events and looked at the background rate of these clots.

Marks says these types of clots have a background rate of 2-14 per million people. BUT says there's a pattern of events similar to Europe events.

Marks: "We have to take the time to make sure we understand this complication."

FDA's Marks says one reason they're raising this is because the standard treatment for blood clots -- heparin -- can actually make THIS type of clot worse. So you need to pause + get the word out. Worst case would be people harmed b/c of erroneous treatment.

Keep in mind that w/ the mRNA shots, we saw cases of anaphylaxis. That's one reason why there's 15 mins of post-injection monitoring, and health workers are on the look out for those reactions.

Nothing's free from risk, it's how you manage it.

FDA's Peter Marks: "I hesitate to cause it a class effect."

BUT

"What we're seeing with the Janssen vaccines looks very similar to what we were seeing with the AstraZeneca vaccines."

Slightly different vectors, but they are "in the same general class."

More Marks: Says pay attention to J&J statement today on "voluntary action" with regard to pausing its two-dose trial.

Sure sounds like they'll be putting that on hold...

Marks: Says the side effects have been seen in a median of nine days after vaccination, in a window of 1-3 weeks.

This is different than the immediate post-vaccine side effects, which are headache + flu-like symptoms.

But there are gonna be a lot of calls to doctors...

Marks: Says what to really look for is people showing up at an ER with a "very severe headache", shortness of breath and pain in legs or abdomen, that's a sign to ask about vaccine history and check platelets.

Briefing over. That was a clear and useful discussion from FDA about the risks. Next up -- what J&J has to say, and tomorrow's adcomm + any FDA action.