The Johnson & Johnson COVID-19 vaccine will continue in limbo for at least a few weeks because a federal vaccine advisory committee on Wednesday declined to make recommendations without more information about a possible link between the shot and an ultra-rare, life-threatening blood-clotting disorder.

The panel agreed to reconvene in a week or two to consider whether the vaccine should be continued, discontinued, or recommended only for certain groups of the population.

The Centers for Disease Control and Prevention and the Food and Drug Administration on Tuesday “paused” use of the single-shot vaccine pending investigation of six cases of the clotting disorder in women aged 18 to 48, one of whom died.

At Wednesday’s meeting, the CDC’s Advisory Committee on Immunization Practices learned that nine cases have been found among the 7.2 million U.S. recipients of J&J’s immunization, authorized in early March. Seven of those cases were reported to the government’s Vaccine Adverse Event Reporting System, and two additional cases — including a 25-year-old man — were identified by J&J in its clinical trial data.

“I do not want to vote on this issue today. I do not feel we have enough information to make an evidence-based decision,” said panel member Beth Bell, a professor of public health at the University of Washington.

Panel member Helen Talbot, a health-policy professor at Vanderbilt University, said strokes may be underreported in older adults who get the vaccine, “so I hesitate to say just use it in people over 50.”

“In this country, we have very good alternative vaccines that we are not seeing any safety signals in,” Talbot added, referring to the Pfizer-BioNTech and Moderna vaccines.

While Pfizer and Moderna use RNA-based vaccine technology, J&J and AstraZeneca (which is not approved in the United States) use adenoviruses to carry genetic instructions that prime the immune system. Experts theorize that, in extremely rare cases, the adenovirus triggers an autoimmune response that disrupts normal clotting ability.

In Europe, the AstraZeneca vaccine has been linked to the blood-clotting disorder, mostly but not exclusively among women under age 50. Britain has reported 79 cases, 19 of them fatal, among 20 million recipients of the shots. Other areas of Europe have had 86 cases, 18 fatal.

After halting use of AstraZeneca’s vaccine, European regulators concluded the benefits of slowing the pandemic outweigh the remote risk of the rare clotting reaction. Denmark this week announced it would shelve the vaccine, but many countries have opted to restrict use based on age and gender.

A few people at Wednesday’s meeting were dismayed by the lack of a recommendation because the J&J vaccine — a single dose that does not require special refrigeration — is much easier to deliver to elderly, poor, and homebound people than the Pfizer and Moderna two-shot regimens are.

“Not making a decision is tantamount to making a decision,” said Nirav Shah, director of the Association of State and Territorial Health Officials. “The people most at risk of COVID-19 will remain at risk. I would urge any pause be accompanied by consideration of the equity issues.”

Aaran Maree, chief medical officer of J&J’s Janssen division, told the panel, “While causality has not been fully established, we recognize these events do represent an important potential risk” of the vaccine.

CDC scientists presented data estimating that the annual incidence in the general population of dangerous clots in veins draining the brain, called cerebrospinal venous thrombosis, is less than one in a million people. But the vaccine-related disorder is even rarer; the clots are accompanied by depletion of platelets, the blood component essential to clotting. Basically, the increased clotting uses up the body’s store of platelets, so the platelet count gets dangerously low.

Vaccine-induced cases of the clotting disorder “appear to exceed what would be expected based on background rates,” said Tom Shimabukuru, deputy director of the CDC’s immunization safety office.

While recommendations are yet to come, federal health officials have sent an alert to health-care providers so they are better prepared to recognize and treat the disorder. The normal treatment for clots, the anticoagulant heparin, should not be used because it can worsen the cascade of complications. Instead, doctors should use non-heparin blood thinners and give an immune-boosting drug called immunoglobulins. The steroid prednisone may also be helpful.