The CDC Vaccine Advisory Panel will meet on Wednesday to review the blood clotting incidents. The FDA, which will hold a press conference Tuesday morning, will review the CDC analysis and conduct its own research.
“Until this process is completed, we cautionarily recommend taking a break from using this vaccine,” FDA Chief Vaccine Regulator Peter Marks and CDC Assistant Director Anne Schuchat said in a joint statement.
“Right now, these adverse events seem extremely rare. The safety of Covid-19 vaccines is a top priority for the federal government and we take all reports of health problems following a Covid-19 vaccination very seriously,” officials added.
Blood clot concerns first arose when the FDA reviewed the J&J vaccine for emergency approval. However, the agency’s vaccine advisory board recommended approving the shot 22-0 in late March noted a possible connection with rare coagulation cases. The FDA then said that the information available showed no link between the shot and the clotting reports, but that they would continue to monitor the frequency of blood clots in the broader population to understand a link to the vaccine.
The notice from federal health authorities comes just days after the European Medicines Agency investigated four reports of blood clotting in people who received the J&J vaccine. One of the cases occurred in a person participating in a clinical trial while the other three were reported in the US, the European regulator said on Friday.
The EMA said all four cases were so-called thromboembolic events – where a blood clot forms in one vessel, breaks off, and blocks another vessel – and that one person died. The agency added that it was not clear whether the clots were a side effect of the vaccine.
European regulators have also been investigating reports of blood clots related to a Covid-19 vaccine from AstraZeneca, which, like Johnson & Johnson, uses a weakened adenovirus as the basis for its shot. The EMA said last week that there is a “possible link” between the AstraZeneca shot and cases of clotting and low platelets, but supported continued use of the vaccine.