Nearly 8 million doses of the Johnson & Johnson vaccine have now been administered. Among men and women who are 50 or over, there has been less than one case per million doses.
The clotting disorder is “rare but clinically serious,” Dr. Tom Shimabukuro, the deputy director of the C.D.C.’s immunization safety office, said at the meeting.
Roughly 10 million doses or more of the Johnson & Johnson vaccine, produced at the company’s factory in the Netherlands, are sitting on shelves across the United States and could be deployed immediately.
The vaccine has immense potential benefits for the population. If vaccinations resume for all adults, 26 to 45 cases of the clotting disorder would be expected over the next six months, according to a model presented by Dr. Sara Oliver, a C.D.C. scientist. However, 600 to 1,400 fewer Covid-19 related deaths would be expected over the same time period.
The vaccine, which is easy to store and requires just one shot, is also especially well-suited for use in hard-to-reach populations, including people who are homebound, homeless, or incarcerated.
Additional potential cases of the clotting disorder, including some in men, are currently being reviewed. The C.D.C. scientist also mentioned one case that developed in a 25-year-old man who participated in a clinical trial of the vaccine.
Twelve of the 15 women in the confirmed cases developed blood clots in the brain. Many also had clots elsewhere. Initial symptoms, which include headaches, typically begin six or more days after vaccination, Dr. Shimabukuro said. As the disorder develops, it can cause more severe headaches, nausea and vomiting, abdominal pain, weakness on one side of the body, speech difficulties, loss of consciousness and seizures.