Johnson & Johnson's COVID-19 vaccine will remain in limbo for a while longer after government health advisers declared Wednesday that they need more evidence to decide if a handful of unusual blood clots were linked to the shot—and if so, how big the risk really is. The CDC expects its advisers to reconsider the evidence within two weeks, the AP reports. So far the clots have occurred between one and three weeks after people received the J&J vaccine, and officials cautioned that more reports could surface. The reports are exceedingly rare—six cases out of more than 7 million US inoculations with the one-dose vaccine. But the government recommended a pause in J&J vaccinations this week, not long after European regulators declared that such clots are a rare but possible risk with the AstraZeneca vaccine, a shot made in a similar way but not yet approved for use in the US.
These are not run-of-the-mill blood clots. They occurred in unusual places, in veins that drain blood from the brain, and in people with abnormally low levels of clot-forming platelets. The six cases raised an alarm bell because that number is at least three times more than experts would have expected to see even of more typical brain-drainage clots, said CDC's Dr. Tom Shimabukuro. “What we have here is a picture of clots forming in large vessels where we have low platelets,” Shimabukuro explained. “This usually doesn’t happen,” but it’s similar to European reports with the AstraZeneca vaccine. When the clots were spotted after AstraZeneca vaccinations, scientists in Norway and Germany raised the possibility that some people are experiencing an abnormal immune response, forming antibodies that disable their platelets. That’s the theory as the US now investigates the J&J reports. The good news: The government says there are no signs of similar clots after vaccination with the Pfizer and Moderna shots that are the mainstay of the COVID-19 fight in the US.
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