Doran Fink, an official of the Food and Drug Administration, proposed a different strategy to the panel, suggesting that the vaccine could go back into use while researchers continued to study the potential risk. Doctors and patients could be provided with information about the findings so that patients could consider whether to accept the vaccine. “Our current thinking is that this risk could be managed by inclusion of warning statements,” Dr. Fink said.
But some experts on the C.D.C. panel leaned in other directions, fearing that more patients could be harmed if vaccinations resumed without a full understanding of the potential risks. One warned that the rare condition could cause long-lasting neurological damage. Others reminded their colleagues of the risk from Covid itself, and the message the panel would send if it prolonged a suspension in the use of a one-and-done vaccine.
The Advisory Committee on Immunization Practices, or ACIP, is a panel of independent experts who advise the C.D.C. on its vaccine policies.
The clotting disorder of concern in the vaccine recipients is different — and much rarer — from typical blood clots, which develop in hundreds of thousands of people every year. The seven women experienced not only clotting in the brain but a notably low level of platelets, parts of the blood that help form normal clots in response to an injury.
None of the women had recently given birth, which can increase the risk of more common blood clots, and only one was known to be taking hormonal treatment. So far, there is no evidence that birth control pills, which can also raise the risk of blood clots, were involved.
Three of the women had large, dangerous clots in other parts of their body, not just in the brain.
The rare combination of severe clots and low platelets stood out to experts as a safety signal. Why it develops is not known, and so far there is no way to predict whether an individual is susceptible.
The condition is very similar to one linked to the AstraZeneca Covid vaccine, also affecting many relatively young women in Europe, where that vaccine was in wide use. Researchers in Germany and Norway found that patients there had developed antibodies that activated their platelets — an aberrant response to the vaccine — setting off a cascade of clotting and bleeding. Specialized blood tests can detect the antibodies to confirm the diagnosis, and some of the U.S. patients tested positive. Not all were tested.