The F.D.A. ended his recommended hiatus on the J. & J. vaccine, clearing the way for states to use it again.

About 10 million doses or more of the Johnson & Johnson vaccine, which is manufactured at the company's Dutch facility, are on shelves in the United States and could be used immediately. Several states, including Texas, Alabama, Utah, and Wisconsin, said they expected to follow the recommendations of the C.D.C. and F.D.A. once the decision has been made.

The vaccine has immense potential benefits. If vaccinations are resumed for all adults, 26 to 45 cases of the coagulation disorder are expected in the next six months, according to a model developed by Dr. Sara Oliver, a C.D.C. Scientists presented at the meeting on Friday. However, 600 to 1,400 fewer coronavirus-related deaths would be expected over the same period.

The vaccine, which is easy to store and only requires one shot, is also particularly suitable for hard-to-reach populations, including people living in their home country, homeless or incarcerated.

Other possible cases of the coagulation disorder, including some in men, are currently being investigated. Dr. Shimabukuro also mentioned a case that occurred in a 25-year-old man who was taking part in a clinical trial of the vaccine.

Twelve of the 15 women with confirmed cases developed blood clots in the brain. Many had blood clots elsewhere as well. Initial symptoms, which include a headache, usually begin six or more days after vaccination, said Dr. Shimabukuro. As the disorder develops, it can cause increased headaches, nausea and vomiting, abdominal pain, weakness in one side of the body, difficulty speaking, loss of consciousness, and seizures.

Dr. Shimabukuro found that seven of the women were obese, two had hypothyroidism, two had high blood pressure, and two were using oral contraceptives. It is not yet clear whether any of these factors could increase the risk of developing a coagulation disorder after vaccination.

Patients' symptoms are very similar to a rare syndrome that can be caused by heparin, a widely used blood thinner. This is shared by Dr. Michael Streiff, a hematologist at Johns Hopkins University, joined the panel. Heparin, which could typically be used to treat blood clots, shouldn't be used to treat these patients, he said.